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Category: Soil carbon types & carbon flows

Placing more emphasis on “carbon flows” for profitable farming

By Alan Lauder

Farmers, advisors and scientists have become too preoccupied with carbon stocks and measuring carbon and not paying enough attention to carbon flows. Just talking about carbon stocks is far too narrow. If you want to understand how your paddocks function, how to make more money, how to produce better greenhouse outcomes, how to reduce the impact of dry times, then all of these things will be clearer if you understand the concept of carbon flows.

The most important thing that happens in your paddocks is that carbon comes down from the atmosphere and flows through the paddock above and below ground, then returns to the atmosphere. In the process of doing this, carbon keeps your paddocks productive and healthy.

To understand the difference between the concept of carbon flows and carbon stocks, any carbon that is flowing through the paddock at the time of measurement, is recorded as a stock. Carbon flows are ongoing while carbon stocks are a measurement at one point in time. Carbon stocks at the time of measurement are called short term (labile), medium term and long term (non-labile).

Thinking carbon flows is to be aware of how much activity is occurring in your paddock. This is because products that follows carbon, energy, nutrients and water are central to production. The better you manage carbon flows, the more of these three you have access to.

Figure 1 shows carbon flows in action in the real world. Increasing carbon flows by planting saltbush have led to a long term degraded claypan turning into productive country.

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Figure 1: Carbon flows in action. Left: Old Man Saltbush planted into a barren salt pan. Right: Three years later pasture has invaded the pan. Source: Alan Lauder and Rory & Kathy Frost

In the right hand image you can see carbon is now flowing in the area around the shrubs. In other words, the landscape is becoming more resilient. It is the carbon flows introduced by the planted saltbush, which has improved the soil. As the soil improved, grass was able to germinate and further expand the area that carbon is flowing through.

All this happened over a two year period at Yelarbon Qld, when rainfall was well below average. This highlights that with good management, dry times do not have to ruin the health of your landscape. The critical thing in dry times, is that you allow what rain does arrive, to produce some inflow of carbon. How well you let plants grow after rain determines how much carbon flows into your paddocks. This will be one of the themes of today’s talk.

After carbon flows started again, energy, nutrients and water all followed. Plants are now growing, which is introducing energy. The build up of organic matter is increasing nutrient supply. Looking at the prolific grass, water is obviously getting in.

Carbon management not explained

I spent 30 years running a grazing business in Western Queensland before leaving the land in 2000. Not once in that time was it ever explained to me that my success relied on how well I managed carbon in the paddocks. Discussing land management in terms of carbon management simply wasn’t part of extension.

It is ironic that carbon trading has introduced carbon into extension, when discussing carbon and what it does, should have always been central to discussing land management. It will probably take many years to see adequate attention paid to the “carbon flows” aspect of land management given past uptake of new approaches by institutions.

It is the ongoing flow of carbon that makes it possible for all the life on this planet to exist above and below ground. We are 18% carbon and I assume cows are similar. Grass is about 45% carbon when dried. All the life that lives in the soil and is responsible for keeping it well structured and fertile, also need carbon to build their little bodies, regardless of how small they are.

To help you understand the concept of carbon flows, carbon keeps moving out of its existing structure into new structures. The carbon atoms are always moving. Carbon is joined to just oxygen when it is carbon dioxide, then after photosynthesis it is in the more complicated carbohydrate structure in plants, then another form in cows and so on. The same process of carbon compound change is occurring in the soil – it keeps changing its structure as it keeps moving.

Each farmers day job is recycling carbon and in the process turning some of the carbon that is flowing through the paddock, into saleable carbon products, like grain, meat, fibre or hay. Selling cattle is harvesting carbon when it has entered the cattle part of the food chain.

A rural producer sells something that has lived and all life relies on the ongoing flow of carbon through the landscape. Nitrogen is just one thing that joins carbon in building life. You know this combination as the carbon:nitrogen ratio of life. When people get their head around the flows way of thinking, they quickly discover that the bulk of the carbon movement in the paddock, involves short term carbon compounds, not long term carbon compounds.

Above ground carbon important too

We are too focused on just soil carbon in extension. Extension does talk about ground cover, but we never talk about it in terms of carbon. Carbon flows only seem to be discussed as carbon when they are below ground. Institutional extension services focus on stocking rate, pasture utilisation rates and maintaining a minimum level of ground cover. This is 1980’s science as a government employee explained to me and is a disservice to farmers and export income. What sets the level of ground cover is how much carbon a particular form of management allows to come in after rain.

How much of the ground cover is then consumed is important, but it is the second decision you make. If you are just thinking stocking rate, then carbon flows are not part of your thinking. The only time we seem to think about carbon being above ground is in trees, but this is only because it is seen as long term carbon. Grass is short term carbon. This highlight the misplaced preoccupation with long term carbon when management changes are reflected mainly in short term carbon.

Figure 2 demonstrates the importance of short term carbon. In the figure the red section is the faster moving short term carbon and the black section is the very slow moving long term carbon.

 

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Figure 2: How ratios of short and long term carbon vary as soil organic carbon is increased. Source: Derived from Chan et al 2010

When soil organic carbon went from 1.5% to 2.5%, the change was driven by increases in the short term carbon called labile carbon. Look closely at the size of the black section, which is non labile carbon (long term carbon), and there is virtually no change. The percentage of long term carbon has changed on the left hand diagram, but this is because of the increase in the labile carbon (red section) has changed the total.

Two paddocks can have equal long term carbon stocks but it is the one that has the most carbon flowing through it that will have the highest level of production

It would be clearer for farmers if we discussed the different types of carbon in the landscape in terms of how quickly or slowly it moves. Some of the carbon moves very quickly through the paddock on its way back to the atmosphere. Some stays a bit longer and some of the carbon is moving very slowly. The faster moving carbon has a different role to the slower moving carbon. The energy is sitting in the red pool.

I am not suggesting that long term carbon is not important, because it is. The better soils have higher long term carbon levels, which is why you pay more money for them. What I am saying is that long term carbon is the carbon you have far less control over.

Figure 3 highlights that carbon flows have to be maintained because carbon keeps leaving the system. The arrows on the CO2 sections represent the loss of introduced carbon via consumption. Apart from fire oxidising carbon compounds, the oxidisation process relies on one life form consuming another. The diagram highlights that the outcome of photosynthesis is being reversed with every consumption event. You can see some of the original flow heading towards longer term carbon as it becomes less and less digestible.

 

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Figure 3: Decomposition of organic material and conversion to soil organic carbon. Source: Stevenson 1986

 

The carbon that flows in after rain initially goes into the fast moving carbon pool. Then some finds it way into the medium term pool and finally a little into the long term pool.

As a general comment, 75-80% of carbon that enters the soil will be gone within twelve months. The actual amount is determined by moisture levels and temperature. This highlights that if your management is not focused on carbon flows, then you run the risk of running short of this commodity.

You can be confident with the long term carbon measurement as it is measuring slow moving carbon. However with the faster moving carbon, you have to be careful of the circumstances under which you measure. It is very easy to catch a spike that is not representative.

Now coming back to the Carbon Farming Initiative (CFI). Any carbon that is in the stable long term pool has to start the journey as fast moving carbon, so soil carbon trading relies on the same management as making more money. You have to increase carbon flows. In fact this is the first example of the broader rule – “The greenhouse outcomes of the grazing industry are a reflection of economic efficiency”.

There is a reason why a paddock is more productive when carbon moves faster. It is simply because everything that is joined to carbon as it moves through the soil becomes available to plants sooner. Think energy and nutrients.

It is important to remember that the long term soil carbon is also flowing, but at a slower rate. For those interested in soil carbon trading, it is important to be aware that there is always a little bit flowing out of the long term carbon pool, that’s why all soils have a total carbon equilibrium. Carbon flows are going both ways, in and out.

Photosynthesis and energy storage

When photosynthesis occurs in plants when they grow after rain energy is stored. That is, the carbon in carbon dioxide, now forms more complex carbon bonds in carbohydrates. This is what scientists refer to as construction of energy.

How all life sources energy during consumption, is to break these complex bonds and release the energy. It is a case of reversing photosynthesis and converting the carbohydrates back to carbon dioxide. We breathe in oxygen to oxidise the carbon compounds and then breathe out carbon dioxide.

It is short term carbon and not long term carbon that is responsible for energy availability.

In Figure 1 there is a lot more energy residing in the soil with the higher short term carbon levels created by higher carbon flows in the recent past. Just as more nutrients are available.

Carbon flows different to the carbon cycle

Those in extension not thinking carbon flows the way I am presenting it, think that the discussion is simply along the lines of the typical carbon cycle diagram. The carbon cycle diagram is a one dimensional discussion explaining that carbon cycles, whereas the carbon flows discussion is about what carbon is achieving as it moves. It also focuses on how you can increase the flows of carbon. It explains why current carbon flows are influenced by all the feedback loops that come into play, depending on their previous management.

The resilience of your paddocks and their ability to respond to falls of rain, especially in dry periods, is determined by your previous management of carbon flows. Now for an example.

The right hand (RH) side of the fence in Figure 4 is a pasture paddock, not a farming paddock. Notice the water right to the fence line, then nothing on the surface over the fence.

 

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Figure 4: How grazing management impacts carbon flows. Left: stock route intermittently grazed. Right: paddock set stocked. Source: Patrick Francis, Jerilderie, February 2003

 

The figure highlights what can happen, when animals are allowed to eat grass every time it tries to grow after rain and so greatly reduce carbon flows into the paddock.. Energy reserves are short term carbon. Resting after rain, to allow plants let energy in, is like keeping some charge in the battery.

To understand the failure on the right hand side of the fence, think of the soil as a construction site. What lives in the soil, keeps it well structured and fertile.  If plants are not allowed to grow and feed carbon compounds to all the workers in the soil, then they die.

These images highlight that resilience relies on carbon flows.  Think of resilience as having two components, plant resilience and soil resilience. Plant resilience fails first, then soil resilience declines. This highlights that your animal management affects the soil, by effecting plants first.

Figure 5 gets back to your day job, which is converting water molecules into carbon molecules. This is a practical example of the linkage between water use efficiency (WUE) and carbon flows.

 

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Figure 5: When rainfall is adequate and carbon flows have been managed plant water use efficiency and productivity is prolific. Left: Stock route. Right: 10m away on the other side of a fence. Source: Patrick Francis Jerilderie October 2010.

Figure 5 taken at the same spot as Figure 4 but during a high rainfall spring highlights that WUE relies on plant resilience and soil resilience. It also highlights that present carbon flows, rely on past carbon flows. Just as money makes money, so carbon makes carbon. Figure 5 explains what is behind disappointment when a paddock does not respond to rain very well.

Taking water use efficiency further, perennials bring down more carbon over time than annuals do. I wouldn’t like to be trading soil carbon on the RH side of the fence.

Short and long term resilience

The fast moving carbon supplies short term resilience. On the other hand, the slow moving carbon supplies resilience over time. It protects the long term survival of the system.

Management that increases fast moving carbon maintains larger root systems in plants which allows them to access more moisture and nutrients to grow, figure 6. This increases short term resilience.

 

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Figure 6: Management that increases carbon flows maintains larger root system and boosts plant resilience. Source: WA Department of Food and Agriculture.

 

One way water gets into the soil is by running down beside roots. The level of water infiltration and to what depth, is influenced by the volume of roots and their depth. This is called the wick effect.

The fast moving carbon is part of energy reserves central to short term resilience. It is ground cover that increases water use efficiency by lifting wind and keeping the sun off the soil.

Root exudates are soluble carbon released into the soil by root tips and this supports soil microbes to make nutrients available to plants. Root exudates are some of the fastest moving carbon in the system.

Organic matter that supplies nutrients is short term carbon.

It is short term carbon that maintains soil biology responsible for creating macro-pores in the soil. These macro-pores will still be there after this fast moving carbon that facilitated their construction is back up in the atmosphere. Compaction occurs in a lot of soils when carbon flows fall.

The slow moving carbon (the long term carbon also called humus) is the other half of the resilience story. It supplies the long term resilience of your paddock. It greatly increases the nitrogen storage capacity of the soil. It provides better soil structure which provides spaces for water. It changes the pH of the soil and helps buffer against any toxic elements present. Because it is more stable, it is much less affected by management.

The Carbon Grazing principle

The size of carbon flows following rain is influenced by your management. The only way that carbon can move from the atmosphere to your paddock, is via photosynthesis. Given that it is moisture that promotes photosynthesis, then it is moisture that promotes the introduction of carbon. Nature has designed the system, so that water activates the storage of carbon in the landscape.

If you think about it logically, the bulk of the carbon enters the landscape in the short period following rain. This highlights the need, to focus management around this point in time. Letting animals eat plants when they are trying to grow after rain, reduces photosynthesis and in some cases, completely shuts it down.

There are some subtle realities that underpin the Carbon Grazing principle. Remember, it is a principle, and not a new land management system. It applies to all successful land management.

Because there is no pattern to when rain arrives, in other words, when carbon arrives, the message is that pasture rest is TIMING and not TIME. Basing resting decisions on a certain period of TIME, is no guarantee that carbon will arrive.

This is not an attack on cell grazing, where cells may be locked up for 120 days. Cell grazing implements the Carbon Grazing principle, because when rain arrives, the bulk of the cells do not have animals in them. Stating the obvious, continuous grazing never implements the Carbon Grazing phase of rest after rainfall.

Carbon Grazing is 4 – 6 weeks rest after rain. The period does not commence until the plants actually start growing. Also, it is important to not get caught up on the exact time, as factors like temperature influence the necessary time. Carbon Grazing is about maximising carbon flows. It is the window of opportunity too many people miss.

Figure 7,8 and 9 provide a summary of carbon flows principles. I am grateful to Patrick Francis, Moffitts Farm and the former editor of the Australian Farm Journal, for constructing the slides.

The three slides have the same format. They all rely on pictures and graphs to demonstrate the above ground and below ground outcomes, depending on how well carbon flows are managed.

Figure 7 demonstrates the outcome of applying the Carbon Grazing principle which  maximises carbon flows each time it is applied.

 

 

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Figure 7: Impact of pasture rest after rain when Carbon Grazing principle is practiced. Source: Patrick Francis www.moffittsfarm.com.au

 

The first point to note in Figure 7 is the positive effect on ground cover as the photos show. The wording on the photos makes an important point that is often overlooked – ground cover is labile carbon. It was discussed earlier that the carbon flows debate extends past what happens in the soil to also include what happens above ground.

The pie chart is a reproduction of Figure 2 where Chan et al showed that the increase of soil organic carbon from 1.5% to 2.5% was just about solely due to the increase in labile carbon. This makes sense, because the increased carbon level would be a reflection of the increased amount of carbon flowing through the paddock.

The green graph line reflects carbon flows over time. You will notice that water use efficiency (WUE) and resilience parallels carbon flows. This is consistent with WUE relying on resilience and resilience relying on carbon flows. The green line charts your success in converting water molecules into carbon molecules – which is your day job.

There is a reason for the slight increase in labile carbon in the second pie chart. Current carbon flows rely on past carbon flows. It is the slightly increased short term resilience provided by the previous rest after rain that has influenced current carbon flows. In well managed paddocks only marginal changes are likely – it is more a case of maintaining what has already been achieved. It is poorly managed paddocks that supply the greatest opportunities for increases.

Putting management aside, the labile carbon stocks are set by seasonal conditions, and will fall in dry years. It is available water that influences carbon flows. Sometimes water does not arrive and sometimes your management is responsible for it escaping before being able to generate carbon flows.

The red and black graph lines represent labile carbon stocks and non-labile carbon stocks. The pie charts are representative of the direction these lines take.

Figure 8 shows set stocking. It represents a system that is operating at a lower carbon equilibrium above ground and below ground. The first thing you notice is that the pie graphs are smaller than the previous slide. The labile carbon is a much lower percentage of total soil carbon simply because carbon flows are smaller.

 

 

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Figure 8: Impact of set stocking on carbon flows. Source: Patrick Francis www.moffittsfarm.com.au

There is only a marginal increase in the green line after more rain, which highlights that carbon flows are not meeting their potential. Bare pastures have lower WUE. They do not respond as well to rain and revert to the non growth phase quicker. This is reflected in the lower percentage of labile carbon.

Figure 9 brings in the impact of a dry season or drought followed by heavy rain. It  shows the risks with set stocking. The green line drops and is consistent with lower carbon flows in a dry season.

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Figure 9: Impact drought on carbon flows when set stocking or short –term rotational grazing is practiced. Source: Patrick Francis www.moffittsfarm.com.au

 

The telling message is the extent of the drop in the labile carbon and non labile carbon from wind erosion and soil erosion. This would not have occurred if the paddock had started with better ground cover and higher labile carbon levels in the soil.

The wind and water erosion that has occurred has removed labile and non labile carbon and this is reflected in the smaller second pie graph. Not only is the second pie graph smaller, but it also has a lower percentage of labile carbon. The assumption is that labile carbon resides more in the surface soil.

The future earning capacity of this paddock has reduced. With the removal of labile carbon there is a removal of stored energy and nutrients. With the removal of non labile carbon goes long term resilience.

Take home message

It is not until we pay more attention to the carbon flows aspect of carbon, that more attention will be paid in extension to promoting when the bulk of the carbon enters the paddock. This broader focus will lead to higher production.

I would like to finish by saying that the only time you can prepare for drought is when it rains. This is the only time you can increase your stock of above ground labile carbon.

Find out more:

For more details about Alan Lauder’s Carbon Grazing principles visit www.carbongrazing.com.au  ; Patrick Francis has a series of articles on carbon flows and soil health on www.moffittsfarm.com.au . Source: This is an edited version of a presentation Alan Lauder gave at the Mareeba Rotary Field Days, May 2013. Rory and Kathy Frost saltpan reclamation – see article this web site in “Soil carbon types & carbon flows”.

Glomalin: hiding place for soil carbon

By Don Comis

A sticky protein seems to be the unsung hero of soil carbon storage. Until its discovery in 1996 by United States Department of Agriculture’s, Agricultural Research Service (ARS) soil scientist Sara F. Wright, this soil “super glue” was mistaken for an unidentifiable constituent of soil organic matter. Rather, it permeates organic matter, binding it to silt, sand, and clay particles.

 

A microscopic view of an arbuscular mycorrhizal fungus growing on a corn root. The round bodies are spores, and the threadlike filaments are hyphae. The substance coating them is glomalin, revealed by a green dye tagged to an antibody against glomalin. Photo: Sara Wright.

A microscopic view of an arbuscular mycorrhizal fungus growing on a corn root. The round bodies are spores, and the threadlike filaments are hyphae. The substance coating them is glomalin, revealed by a green dye tagged to an antibody against glomalin. Photo: Sara Wright.

 

Not only does glomalin contain 30 to 40 percent carbon, but it also forms clumps of soil granules called aggregates. These add structure to soil and keep other stored soil carbon from escaping. As a glycoprotein, glomalin stores carbon in both its protein and carbohydrate (glucose or sugar) subunits. Wright thinks the glomalin molecule is a clump of small glycoproteins with iron and other ions attached. She found that glomalin contains from 1 to 9 percent tightly bound iron.

Glomalin is causing a complete reexamination of what makes up soil organic matter. It is increasingly being included in studies of carbon storage and soil quality. In fact, the U.S. Department of Energy, as part of its interest in carbon storage as an offset to rising atmospheric carbon dioxide (CO2) levels, partially funded a study by lab technician Kristine A. Nichols, a colleague of Wright’s. Nichols reported on the study as part of her doctoral dissertation in soil science at the University of Maryland.

That study showed that glomalin accounts for 27 percent of the carbon in soil and is a major component of soil organic matter. Nichols, Wright, and E. Kudjo Dzantor, a soil scientist at the University of Maryland-College Park, found that glomalin weighs 2 to 24 times more than humic acid, a product of decaying plants that up to now was thought to be the main contributor to soil carbon. But humic acid contributes only about 8 percent of the carbon. Another team recently used carbon dating to estimate that glomalin lasts 7 to 42 years, depending on conditions.

For the study, the scientists compared different chemical extraction techniques using eight different soils from Colorado, Georgia, Maryland, and Nebraska. They found that current assays greatly underestimate the amount of glomalin present in soils. By comparing weights of extracted organic matter fractions (glomalin, humic acid, fulvic acid, and particulate organic matter), Nichols found four times more glomalin than humic acid. She also found that the extraction method she and Wright use underestimates glomalin in certain soils where it is more tightly bound than usual.

In a companion study, Nichols, Wright, and Dzantor teamed up with ARS chemist Walter F. Schmidt to examine organic matter extracted from the same soils under a nuclear magnetic resonance (NMR) imager. They found that glomalin’s structure differs from that of humic acid—or any other organic matter component—and has unique structural units.

In a current study in Costa Rica, partly funded by the National Science Foundation, Wright is using glomalin levels and root growth to measure the amount of carbon stored in soils beneath tropical forests. She is finding lower levels of glomalin than expected and a much shorter lifespan. “We think it’s because of the higher temperatures and moisture in tropical soils,” she explains. These factors break down glomalin.

Forests, croplands, and grasslands around the world are thought to be valuable for offsetting carbon dioxide emissions from industry and vehicles. In fact, some private markets have already started offering carbon credits for sale by owners of such land. Industry could buy the credits as offsets for their emissions. The expectation is that these credits would be traded just as pollution credits are currently traded worldwide.

How glomalin works

It is glomalin that gives soil its tilth—a subtle texture that enables experienced farmers and gardeners to judge great soil by feeling the smooth granules as they flow through their fingers.

Glomalin, extracted from undisturbed Nebraska soil and then freeze-dried. Photo: Keith Weller.

Glomalin, extracted from undisturbed Nebraska soil and then freeze-dried. Photo: Keith Weller.

Arbuscular mycorrhizal fungi, found living on plant roots around the world, appear to be the only producers of glomalin. Wright named glomalin after Glomales, the taxonomic order that arbuscular mycorrhizal fungi belong to. The fungi use carbon from the plant to grow and make glomalin. In return, the fungi’s hairlike filaments, called hyphae, extend the reach of plant roots. Hyphae function as pipes to funnel more water and nutrients—particularly phosphorus—to the plants.

“We’ve seen glomalin on the outside of the hyphae, and we believe this is how the hyphae seal themselves so they can carry water and nutrients. It may also be what gives them the rigidity they need to span the air spaces between soil particles,” says Wright.

As a plant grows, the fungi move down the root and form new hyphae to colonize the growing roots. When hyphae higher up on the roots stop transporting nutrients, their protective glomalin sloughs off into the soil. There it attaches to particles of minerals (sand, silt, and clay) and organic matter, forming clumps. This type of soil structure is stable enough to resist wind and water erosion, but porous enough to let air, water, and roots move through it. It also harbors more beneficial microbes, holds more water, and helps the soil surface resist crusting.

Scientists think hyphae have a lifespan of days to weeks. The much longer lifespan of glomalin suggests that the current technique of weighing hyphae samples to estimate fungal carbon storage grossly underestimates the amount of soil carbon stored. In fact, Wright and colleagues found that glomalin contributes much more nitrogen and carbon to the soil than do hyphae or other soil microbes.

Rising CO2 Boosts Glomalin

In an earlier study, Wright and scientists from the University of California at Riverside and Stanford University showed that higher CO2 levels in the atmosphere stimulate the fungi to produce more glomalin. They did a 3-year study on semiarid shrub land and a 6-year study on grasslands in San Diego County, California, using outdoor chambers with controlled CO2 levels. When CO2 reached 670 parts per million (ppm)—the level predicted by mid to late century—hyphae grew three times as long and produced five times as much glomalin as fungi on plants growing with today’s ambient level of 370 ppm.

Longer hyphae help plants reach more water and nutrients, which could help plants face drought in a warmer climate. The increase in glomalin production helps soil build defenses against degradation and erosion and boosts its productivity. Wright says all these benefits can also come from good tillage and soil management techniques, instead of from higher atmospheric CO2.

“You’re in the driver’s seat when you use techniques proven to do the same thing as the higher CO2 that might be causing global warming. You can still raise glomalin levels, improve soil structure, and increase carbon storage without the risks of the unknowns in global climate change,” she says.

Putting glomalin to work

Wright found that glomalin is very manageable. She is studying glomalin levels under different farming and ranching practices. Levels were maintained or raised by no-till, cover crops, reduced phosphorus inputs, and the sparing use of crops that don’t have arbuscular mycorrhizal fungi on their roots. Those include members of the Brassicaceae family, like cabbage and cauliflower, and the mustard family, like canola.

“When you grow those crops, it’s like a fallow period, because glomalin production stops,” says Wright. “You need to rotate them with crops that have glomalin-producing fungi.”

In a 4-year study at the Henry A. Wallace Beltsville (Maryland) Agricultural Research Center, Wright found that glomalin levels rose each year after no-till was started. No-till refers to a modern conservation practice that uses equipment to plant seeds with no prior plowing. This practice was developed to protect soil from erosion by keeping fields covered with crop residue.

Glomalin went from 1.3 milligrams per gram of soil (mg/g) after the first year to 1.7 mg/g after the third. A nearby field that was plowed and planted each year had only 0.7 mg/g. In comparison, the soil under a 15-year-old buffer strip of grass had 2.7 mg/g. Wright found glomalin levels up to 15 mg/g elsewhere in the Mid-Atlantic region. But she found the highest levels—more than 100 mg/g—in Hawaiian soils, with Japanese soils a close second.

“We don’t know why we found the highest levels in Hawaii’s tropical soils. We usually find lower levels in other tropical areas, because it breaks down faster at higher temperature and moisture levels,” Wright says. “We can only guess that the Hawaiian soils lack some organism that is breaking down glomalin in other tropical soils—or that high soil levels of iron are protecting glomalin.”

It’s persistent and it’s everywhere!

The toughness of the molecule was one of the things that struck Wright most in her discovery of glomalin. She says it’s the reason glomalin eluded scientific detection for so long.

“It requires an unusual effort to dislodge glomalin for study: a bath in citrate combined with heating at 250 °F for at least an hour. No other soil glue found to date required anything as drastic as this. We’ve learned that the sodium hydroxide used to separate out humic acid in soil misses most of the glomalin. So, most of it was thrown away with the insoluble humus and minerals in soil. The little bit of glomalin left in the humic acid was thought to be nothing more than unknown foreign substances that contaminated the experiments.”

Once Wright found a way to capture glomalin, her next big surprise was how much of it there was in some soils and how widespread it was. She tested samples of soils from around the world and found glomalin in all.

“Anything present in these amounts has to be considered in any studies of plant-soil interactions,” Wright says. “There may be implications beyond the carbon storage and soil quality issues—such as whether the large amounts of iron in glomalin mean that it could be protecting plants from pathogens.”

Her  work with Nichols has shown that glomalin levels are even higher in some soils than previously estimated.

“Glomalin is unique among soil components for its strength and stability. Other soil components that contain carbon and nitrogen, as glomalin does, don’t last very long. Microbes quickly break them down into byproducts. And proteins from plants are degraded very quickly in soil.

“We need to learn a lot more about this molecule, though, if we are to manage glomalin wisely. Our next step is to identify the chemical makeup of each of its parts, including the protein core, the sugar carbohydrates, and the attached iron and other possible ions.

“Researchers have studied organic matter for a long time and know its benefits to soil. But we’re just starting to learn which components of organic matter are responsible for these benefits. That’s the exciting part of glomalin research. We’ve found a major component that we think definitely has a strong role in the benefits attributed to organic matter—things like soil stability, nutrient accessibility, and nutrient cycling.”

As carbon gets assigned a dollar value in a carbon commodity market, it may give literal meaning to the expression that good soil is black gold. And glomalin could be viewed as its golden seal.

Find out more:

This research is part of Soil Resource Management, an Agricultural Research Service  National Program described on the web at < http://www.nps.ars.usda.gov >.At the time  Sara F. Wright and Kristine A. Nichols are with the USDA-ARS Sustainable Agricultural Systems Laboratory in Beltsville, Maryland. Source ARS  Agricultural Research magazine, September  2002.

Dried samples of undisturbed soil (top row) and material left after extractable organic matter has been removed (bottom row). Although minerals are the most abundant components of soil, organic matter gives it life and health. Photo: Keith Weller.

Dried samples of undisturbed soil (top row) and material left after extractable organic matter has been removed (bottom row). Although minerals are the most abundant components of soil, organic matter gives it life and health. Photo: Keith Weller.

 

 

 

 

Carbon flows in action

 

By James Nason

Southern Queensland landholders Rory and Kathy Frost have turned a long-term claypan into productive land that is now growing cattle feed with a complete cover of grass. The Frosts run a mixed cattle and sheep farming enterprise near Yelarbon on the Queensland/New South Wales border.

Over the past five years they have used their understanding of carbon flows to regenerate a claypan that used to be bare, even in normal years, into country that is now carrying total groundcover of grass. While the changes have coincided with a recent run of wet years, they cannot be explained away simply by seasonal factors. Were that the case, similar outcomes would have been achieved in wet years of the past. A longer run of high rainfall years in the 1970s produced no such changes in the same claypan.

According to Alan Lauder the author of “Carbon Grazing”, the story of how the Frosts have regenerated a long-term degraded area offers not only thought-provoking practical messages for other landholders, but interesting insights into the basics of how landscapes function and potentially valuable implications for ongoing extension programs.

Go with the carbon flow

Pictures taken over a five year period on the Frost’s property document the step-by-step process of regeneration that has occurred across their claypan. Rory says the changes were achieved by focusing on work to initiate “carbon flows” in the area, to activate the processes upon which healthy and productive paddocks rely. He likened the process of repairing a claypan to rehabilitating a former mine site. In each case the starting point is a near lifeless landscape which is slowly brought back to life below and above the ground by managing the flow of carbon.

“The natural world can’t function without carbon flows,” he explains. “Soil life, grasses and herbages all rely on carbon flows to exist. Energy, nutrients and water all follow carbon – this is the fundamental basis of all life on the planet.”

To repair the claypan, Rory and Kathy said they had to work out how to get carbon flowing into the degraded area again. That was something of a catch 22 situation. The claypan badly needed plants to ensure short-term carbon flowed in from the atmosphere via the plants to feed soil life and supply it with energy. The soil life would then restructure the soil and make it healthy and fertile again.

However, no perennial plants could establish from seed on the claypan to kick-start the ongoing carbon flows required for a healthy and productive landscape. Water was not getting into the soil to let plants establish. Water was shedding on the claypan after just 1mm of rain.

Kathy recalls that when they bought the property, they were not sure what they could do with the claypan. It was a daunting task, given it had been there for at least the 30 years that their next-door neighbour had lived in the area.

Native perennial kick-starts carbon cycle

Then they learned about the role that old man saltbush, a perennial deep-rooted shrub capable of establishing in harsh, claypan-like conditions, could play in regenerating such areas if planted as seedlings. They purchased and planted bare-rooted saltbush seedlings in 2007. These seedlings effectively started the regeneration process by cycling carbon in their immediate vicinity.

The carbon compounds deposited by the saltbush on the soil surface in the form of litter, and all of the different carbon compounds introduced below ground by the shrubs, supplied energy and a food source to allow soil life to return.

Kathy and Rory could see that the soil life was changing their soil structure for the better when they noticed the soil cracking near the saltbush about two years after it was planted. The cracking was a sign that the soil structure of the claypan was starting to change dramatically.

As water entry increased, the carbon flows also increased because other plants were able to germinate in the improved soil near the saltbush. The claypan continued to repair progressively further away from the saltbush as other plants kept entering on the edge of repaired areas. By this stage, other plants had taken over from the saltbush as the repair agent.

It is the same principle at play when normal paddocks remain productive, when management allows plants to grow after rain and maintain the flow of carbon compounds cycling through the paddock. By year five, all of the soil had improved to the extent that perennial grasses now had an environment suitable for their establishment. In year two couch was the only grass present. At year three the bulk of the claypan was still not favourable for perennial grass establishment.

Grass roots change

Another anecdote illustrates the changes that have occurred. In the first year, not long after the saltbush was planted, Rory attempted to conduct a soil test on the claypan using a vehicle mounted soil sampling unit. It could not be done because the soil was so hard it bent the sampling rod. Five years later, the roots of perennial grasses are now able to penetrate the same soil. This serves as testament to how nature utilises carbon flows to keep soil soft and to maintain productivity. The claypan between the saltbush rows was not ripped at any stage.

Kathy Frost says the decision to plant the saltbush has provided further benefits, because, without that intervention, more of the claypan would have blown and washed away, and the erosion would have ended up in the nearby Dumaresq river. She said dysfunctional landscapes became increasingly infertile with time, because they had a low potential for capturing new resources.

In support of this point, Rory said that animal manure dropped on the claypan had helped the regeneration process, as it washed across the claypan and penetrated the soil in the areas where vegetation was establishing. No applications of fertiliser have been provided during the five year period. Following the reintroduction of carbon flows, the landscape has effectively been able to capture the resources it requires. The prolific clover which has followed the improvement in water penetration has also played a role in increasing the soil fertility, which in turn has helped the perennial grasses to establish.

The claypan drops slightly towards the west. The general pattern was initially for regeneration to spread east, towards the direction from which the water came. As water ran across the claypan, it entered the soil when it reached the first of the vegetation.

The first two years saw well below average rainfall. In effect, on most occasions when rain fell, there was not enough water to get to the downside of the saltbush rows. Rory said the claypan had previously been in a continual state of drought, regardless of how much rain fell.

This highlighted the correlation between water use efficiency (WUE) and prior carbon flows. WUE is a measure of how successfully a production system converts water molecules into carbon molecules (ie the level of plant growth from supplied water). Improved WUE is a recognised driver of profit in the grazing industry. For the Frosts, the regenerated claypan is now contributing to profit as it is now able to convert rainwater into groundcover for livestock to eat.

“Wick effect” enables water penetration

As part of the regeneration process, the saltbush roots supplied a “wick effect” by allowing rain to go deeper into the soil by running down beside the roots. As other plants entered, their roots continued the wick effect across the claypan. The depth that grass roots penetrate the soil is determined by the flow of carbon available to build the roots (roots are about 45 percent carbon when dried).

Rory said he developed his current understanding of the importance of carbon flows five years ago from Alan Lauder, the founder of the Carbon Grazing principle. The Carbon Grazing principle focuses on the role of carbon flows and how to maximise them.

“It was after discussions with Alan that I came to understand how carbon flows organised so many important processes that occur in the paddock. Given that cattle are about 18pc carbon and rely on the energy transported by carbon to grow, it is easy to see the linkage between my bottom line and how successfully carbon flows are managed. Soil life utilises carbon flows to release phosphorus and make it available to plants,” he said.

Source: James Nason is a senior journalist with the on-line publication Beef Central, www.beefcentral.com

 

Rory Frost inspecting planted saltbush. It was the catalyst for a long term claypan turning into thick grass instead of shedding water after one millimetre of rain.

Rory Frost inspecting planted saltbush. It was the catalyst for a long term claypan turning into thick grass instead of shedding water after one millimetre of rain.

 

 

 

 

 

 

 

 

 

 

After two years: The missing saltbush leaves eaten by livestock allow the pattern of regeneration around the saltbush to be clearly seen.

After two years: The missing saltbush leaves eaten by livestock allow the pattern of regeneration around the saltbush to be clearly seen.

After three years: Less of the claypan is visable as other plants expand the regeneration process.

After three years: Less of the claypan is visable as other plants expand the regeneration process.

 

 

 

 

 

 

 

 

After five years: The once-bare claypan is now covered in dense grass. Picture taken in mid-June 2012.

After five years: The once-bare claypan is now covered in dense grass. Picture taken in mid-June 2012.

 

 

 

 

 

 

 

 

 

Carbon stocks versus carbon flows

Carbon stocks are a measure of the different carbon compounds present at a particular point in time. In the case of carbon trading, the amount of carbon atoms present is measured, so carbon can be traded as a commodity. In the case of organic matter, soil tests measure the stock of this carbon compound to quantify the health of the soil.

Carbon flows on the other hand are an indication of how much activity is actually occurring in the system. It could be the amount of carbon flowing into a paddock over one year or after a rainfall event. Plants allocate some of the carbon flows to below ground and the remainder goes into plant parts above ground.

The higher the flows, the higher the level of plant production. Plants release some of the carbon flows directly to soil life as part of getting the resources they require. The percentage of carbon flows released above ground for livestock to consume, is influenced by previous management and environmental conditions.

Alan Lauder suggests that the way soil samples are taken means they do not include all of the short term carbon that those focused on carbon flows would consider relevant. He believes this is because the focus generally is not on carbon flows – it is on carbon stocks, especially long-term carbon.

Long term carbon stocks do not generally change much over time and are often a reflection of what type of soil you have and where you are in Australia in terms of temperature and rainfall. It is the short term carbon stocks that are highly variable. A small percentage of the new carbon coming in each year can potentially end up in long-term carbon stocks.

On Rory and Kathy Frost’s cattle property, the claypan is likely to substantially build long-term carbon stocks over time because it is coming off a low base. Short-term carbon stocks (labile carbon) are a measure of what has happened in the recent past in terms of carbon flows. This is where the discussion on stocks and flows overlap.

The amount of labile carbon present is also an indication of the resources that will become available to plants in the near future, assuming there is adequate moisture to see them released. There are some who feel that to be able to manage and understand soil organic carbon, it is important to monitor and measure only labile carbon levels.

Carbon flows are much more influenced by management than long term carbon stocks. One reason grazing country and cropping country has a different level of soil organic carbon is because properly managed pasture has higher carbon flows over the year. Two paddocks can have equal long term carbon stocks but it is the one that has the most carbon flowing through which will have the highest level of production – a bit like capital versus cash flows.

The change in the Frost’s claypan shows all the good that carbon leaves behind as it flows through a paddock. Just as money makes money, so carbon makes carbon as the regenerated claypan demonstrates.

Implications for extension

As a producer, Kathy Frost said that it was when she understood the concept of carbon flows that current extension information became easier to understand. She said that producers had to try to pull information together, whereas scientists tended to pull in the opposite direction as they are forced to become experts in a particular field, and concentrate on just part of the overall system.

She believes this “reductionist science” has held back the connection between “carbon flows” and how the system works, and this is reflected in a lot of current extension programs. As soon as she understood the concept of carbon flows, the separate issues that extension officers talked about fitted together.

“It joined up all the dots,” she said. “I could see the big picture of how the landscape really functioned by following the path of carbon. Everything suddenly became simpler and obvious.

“Getting ground cover into perspective is a good example. Maintaining ground cover is at the forefront of current extension. Putting aside letting animals eat too much pasture after it has grown, it is carbon flows that determine the level of ground cover. This is simply because grass is about 45pc carbon when dry, so ground cover will not exist without carbon flows.

“Traditional extension would observe that the ground cover on the claypan is increasing, however modern thinkers would note that carbon flows have increased over the five years.”

Carbon flows ‘natural entry point of the debate’

Alan Lauder’s book “Carbon Grazing” is used by learning institutions including the Colorado State University in America and his approach to discussing carbon flows is set to be introduced into the curriculum of a leading Australian university in 2014. Associate Professor Allan Dale of the Cairns Institute at James Cook University says Lauder’s clear ideas about the central role of carbon stocks and flows “cut through several complex cross-cutting debates between soil scientists, carbon traders and agronomists in ways that can make practical sense to cattle producers”.

“Alan understands that securing profitability is the key to good grazing management, and that the management of carbon stocks and flows in the paddock over time drives enterprise profitability. From this, pasture and soil health, animal health, erosion management, water retention and tradeable greenhouse gas emission avoidance and sequestration all follow. Alan takes some very complex system principles and turns those into the pragmatic actions needed for producers to stay in the grazing business for the long term.”

Despite this level of support Lauder’s concepts are yet to be adopted into ongoing extension programs. He says there is a view that his work on carbon flows simply fine tunes existing extension programs, or tells the same story in a slightly different way, but he rejects these contentions. He sees carbon flows as a “natural entry point of the debate”, and believes that adding carbon flows does not discredit current extension work, and nor would it require existing extension work to change.

“It is more like adding an introductory module that helps producers and students see how all the current topics discussed fit together. It also focuses producers on something their management has some control over. We may not have any control over how much rain arrives but we do have some control over how effective it is.”

He also believes that incorporating carbon flows into extension work in Queensland would help to reduce the flow sediment and nutrients onto the Great Barrier Reef. A soon to be released report will discuss the particle size of sediment going onto the Great Barrier Reef, as a result of different land management. It would appear that better management of carbon flows will result in a lower percentage of the particle size that can kill coral. – James Nason

 

Claypan carbon flow restoration has historical link

By Patrick Francis

Cathy and Rory Frost’s claypan carbon flow restoration using saltbush is not a new technique, but their understanding of why it works is. The same technique was highlighted in the booklet “Your Asset – The Soil, conservation for permanent agriculture” published in 1957 by the Bank of New South Wales.

This booklet published in 1957 demonstrated that planting saltbush in a grid on a claypan can eventually lead to full revegetation. It was a message that went missing for another 40 years.

This booklet published in 1957 demonstrated that planting saltbush in a grid on a claypan can eventually lead to full revegetation. It was a message that went missing for another 40 years.

It is remarkable that a bank would consider publishing on a such a topic but it highlights an level of understanding still missing in some parts of extension and agribusiness today, that the natural resource farming relies on is its most precious asset. Much of contemporary agribusiness, extension and research is fixated on productivity increases using costly inputs that try to substitutes for soil health, soil quality and carbon flows.

The booklet’s coverage of repairing claypans, caused in the first place by persistent overgrazing particularly in dry years, describes scald reclamation experiments conducted in the Bourke (NSW) district during the early 1950’s.

“There ploughing and contour furrowing gave poor results. Best results were obtained with checker-board furrowing in half-chain squares and sowing with such species as the annuals, flat-topped saltbush (A. inflate), annual saltbush (A. muelleri), and pop saltbush (A.spongiosa), and the perennial bladder saltbush (A. vesicaria). Plants gradually spread across the open spaces when grazing is carefully controlled.”

Why the lessons from this successful research were not generally adopted across the pastoral zones particularly where soil erosion was so prevalent (Western Division of NSW and Murchison Gascoyne district WA) is difficult to understand. History suggests that despite dedicated work by soil conservation service officers in state departments of agriculture, erosion continued to worsen through the 1960s, 70s and 80s. Soil erosion in central Victoria was the catalyst for a different approach to land management with farmer initiated trials to find new solutions – the landcare movement started. It became a national program in 1990.

Landcare farming initiated a revival in approach and a method of funding trials to develop novel solutions as well as a greater understanding amongst participating farmers of causes so that true solutions rather than band-aid works were introduced.

Soil carbon is not all the same

By Alan Lauder

Given that the bulk of the “improvement” in production comes from increasing labile (short term) soil carbon versus long term soil carbon, it is unlikely that the importance of this reality is going to resonate with many farmers while the focus in so many processes remains mainly on long term carbon.

This is not to suggest that long term soil carbon is not important, just that with better management it is still slow to increase and this is why it’s contribution to improvements in production are marginal in the short term. Some soils naturally have higher long term carbon levels than others but this is a separate issue.

Figure 1: Soil organic matter components. Source: USDA NRCS

Figure 1: Soil organic matter components. Source: USDA NRCS

The term “soil organic carbon” (SOC) is used very loosely at times, especially by some focused only on the long term tradable carbon. SOC can be analysed and quantified in total or in its components as figure 1 shows. It is important for farmers to understand the differences involved if they are to make a positive impact on the levels of the different types in their paddock soil. One particular scientist was probably referring to increasing non-labile (long term) soil carbon when he wrote, “Remember that you need to grow a hell of a lot of EXTRA crop/pasture OM to raise the OC levels”. His interest in carbon flows only related to what percentage of the carbon flows ended up in long term carbon (stabilised organic matter), not how ongoing carbon flows influenced the labile (active fraction organic matter) pool so important for production.

Recently Jeff Baldock of the CSIRO was quoted in the media as saying,So far, he said, little work has been done that allows scientists to predict how improving soil carbon levels will affect productivity”. Has he made this comment simply because the main focus has been on long term carbon stocks due to carbon trading and National Carbon Accounts?

For those interested in a better understanding the influence of labile carbon on production, an area worth investigating is water extractable organic carbon (WOEC) in conjunction with water extractable organic nitrogen (WEON). It would appear that these two combined is a better measure of nitrogen mineralization or immobilization than soil organic carbon (SOC) and total organic nitrogen (TON).

Understanding the past’s influence on the current debate

Before the opening of the debate on climate change, carbon was not given the priority it is now when discussing land management. I know from personal experience that the word carbon was not mentioned to me once by extension processes during the thirty years I operated a rural operation prior to leaving in 2000. Organic matter was discussed but it was not explained in the context of being carbon.

Reductionist science is probably the reason for landscape carbon processes never being given the priority they should be, especially in the past. This is why educational processes are still adapting. Knowing the background explains why a lot of people still struggle with carbon and what to associate it with, for example plant absorption of carbon dioxide (CO2) in photosynthesis. So it is no surprise that exactly what carbon does in the soil, how it does what it, and the number of different forms it takes, is still not clear to many farmers.

A farmer’s day job is managing carbon flows i.e. recycling carbon dioxide and in the process turning a percentage of the flows into saleable carbon products like grain, meat, fibre or hay. All else being equal, the higher the level of carbon flows the higher the level of production and the better the soil is maintained to support future production.

A farmer sells something that has lived and all life relies on the “ongoing” flow of carbon through the landscape. Without the ongoing flow of carbon and all the compounds it forms as it moves, the landscape would become bare and lifeless. Without carbon flows there would be no available energy or the main building block of life, which is carbon (soil carbon supplies both for what lives in the soil).

While it is critical to discuss and understand the soil carbon component of the carbon recycling process, it is important that we do not limit the discussion of carbon flows to just the soil. Carbon also flows above ground. It is above ground that carbon is initially captured through photosynthesis, with some flowing below ground immediately and more getting into the soil later via litter.

In the case of grazing, this is why animal management is central to soil carbon outcomes. Remembering that grass is about 45% carbon when dried,  how livestock grazing is managed is critical for carbon flows.  The percentage of ground cover consumed by animals influences the amount of litter joining the soil carbon flows. While the need to maintain ground cover has long been promoted with animal management, discussion usually focuses more on a safe consumption level with inadequate emphasis given to the carbon flows aspect which sets the level of ground cover prior to consumption.

Water use efficiency (WUE) is a measure of how successfully pastures or crops convert available water into carbon compounds i.e. the level of carbon flows achieved from a given amount of water. While it is a measure of above ground production, it is also a reflection of how much carbon flows into the soil.

There is a strong case for shifting emphasis onto “carbon flows”, rather than concentrating on increasing non-labile soil carbon. Here are some of the reasons why:

  • The natural world can’t function without carbon flows
  • All else being equal, the paddock with the highest carbon flows through it will be the most productive. The term “through it” is used because introduced carbon keeps leaving the paddock and returning to the atmosphere as CO2 through respiration.
  • Two paddocks can have equal long term carbon stocks but it is the one that has the most carbon flowing through it that will have the highest level of production – a bit like capital versus cash flows
  • The importance of carbon flows is that they organise so many important processes that occur in the paddock
  • Understanding carbon flows integrates knowledge across all disciplines i.e. overcomes reductionist science
  • Forms the link between science and productivity i.e. explains why production is not as high as it could be in many cases
  • The foundation of healthy, productive and resilient paddocks is ensuring that there are adequate carbon flows over time. Given that 75 – 80% of labile carbon introduced into the soil can be gone within twelve months ( the actual time depends on moisture and temperature), some within a day, it is easy to run short of this commodity that is setting the level of life above and below ground. Marginal years supply fewer opportunities for carbon to flow in, which is why producers not focused on the importance of carbon flows, always suffer a much higher reduction in production in marginal years than they should. Observing what happens above ground, they have much lower water use efficiency (WUE) with what water does arrive
  • Improving carbon flows reduces the effect of drought (landscape resilience relies on adequate carbon flows over time, not just long term carbon)
  • Improving carbon flows increases water infiltration (especially important in marginal years)
  • It focuses the debate on causes instead of symptoms e.g. puts the discussion on ground cover into better perspective. Ground cover is 45% carbon (on a dry basis) so the level of groundcover is initially determined by the level of carbon flows. The level of consumption of ground cover by livestock is the secondary management decision. Stocking rate is not the only consideration
  • It is when producers understand the concept of carbon flows that current extension becomes easier to understand i.e. it is following the path of carbon that makes it easier to understand how the landscape functions
  • The level of carbon flows is an indication of how much activity is actually occurring in the system
  • It is important to understand that carbon keeps changing to different compounds as it keeps moving through the soil food web.
  • The percentage of current carbon flows released above ground for livestock to consume is influenced by previous management of carbon flows
  • To better understand carbon in the big picture, it is useful to consider carbon stocks and carbon flows as related, but separate debates. It is the emphasis on the Kyoto process that has kept the emphasis on long term carbon stocks instead of carbon flows which are short term carbon stocks
  • Carbon flows are much more influenced by management than long term carbon stocks
  • It is only when producers are made aware of the importance of better managing carbon flows for higher production and better environmental outcomes, that they consider changing away from the management practices that reduce the flow of carbon in i.e. implement management practices that maximise carbon flows. Spreading knowledge is the key to changing attitudes because people need to understand and see the logic before they are prepared to change
  • Better management of carbon flows reduces methane emissions per kg of production by ruminant animals
  • Better management of carbon flows improves water quality in rivers, estuaries and finally the Great Barrier Reef
  • Carbon flows in are part of a feedback system. Carbon flows over the previous 12 months influences the level of photosynthesis when rain arrives, especially in marginal years
  • The system functions in such a way that the bulk of the carbon flows in after rain. It is water/moisture that activates photosynthesis which is responsible for introducing carbon from the atmosphere to the paddock/landscape to form all the important carbon compounds that a healthy and productive landscape relies on
  • Removing animals from pastures for 4-6 weeks after rain will greatly increase the flow of carbon in, especially after dry spells. This is the Carbon Grazing principle which is about maximising carbon flows by allowing plants to photosynthesize to their maximum in the short period after rain. Research suggests that ground cover can be increased by up to 80% from short term pasture rest versus leaving animals in the paddock after rain
  • Locking up paddocks for long periods of time is no guarantee that carbon will flow in (it may not rain over the period). Removing animals after rain to increase carbon flows in, highlights why true pasture rest is TIMING and NOT TIME. Pasture rest should be seen as an exercise to increase SHORT TERM (labile) carbon stocks in the paddock, both above and below ground. The focus should be on adding labile carbon to the system with the understanding that a very small percentage of this labile carbon could become long term carbon to both increase these long term stocks and replace some of the long term carbon that is oxidising
  • Calling pasture rest TIMING and NOT TIME is not an attack on cell grazers who lock up cells for up to 120 days. They are applying the Carbon Grazing principle because when the rain does arrive, most of the cells do not have animals in them to restrict the flow of carbon in. We should not focus on what is the best management system as everybody’s circumstances are different. It is not important how the application of the Carbon Grazing principle is achieved, the point is that it should be applied at least once every year. Obviously the more times the better. In low rainfall areas, a higher price is paid for missing opportunities to rest pastures after rain.
  • The practical aspect of seeing pasture rest as TIMING instead of TIME, is that an alternative home for the animals only has to be found for a short period of time. There are ways of resting pastures without selling animals
  • When comparisons are made between different management systems, it is probably not investigating the management of carbon flows in marginal years that has led to unexpected results. Plants and soil life interact differently in marginal years and this influences carbon balances.
  • What follows carbon? Energy, nutrients and water – the basis of all life and rural production
  • Soil tests are only reliable for long term carbon. They do not measure some of the labile carbon present that is critical to future carbon flows
  • Maybe for pure scientists, we should call ground cover what it is – above ground organic matter. It is labile carbon. It is part of the total carbon pool in the paddock. It is short term carbon which is why we run short of it when it has not rained for a while. Not only is the carbon debate in many cases being limited to long term carbon but it is also being limited to discussing below ground carbon (soil carbon). It is carbon flows that supply the above and below ground carbon pools. This suggests that there should be more focus on discussing when the bulk of the carbon arrives for the purpose of improving land management.
  • Carbon flows are the cornerstone of profit, landscape resilience (critical for reducing the effect of drought and floods) and better environmental outcomes including the atmosphere. Better managing carbon flows is critical to dealing with our very variable climate which seems to be getting even more variable.

To view pictures of how a degraded and completely unproductive paddock returned to full production following management changes to reintroduce carbon flows, go to http://www.beefcentral.com/p/news/article/2306 then go to http://www.beefcentral.com/p/news/article/2308 for further discussion on carbon stocks and carbon flows. I gave Rory and Kathy Frost free seedlings and free use of a planting machine to conduct this project after they were refused funding because it was felt there would be no positive environmental outcomes.  

 

 

Alan Lauder is the author of "Carbon Grazing".

Alan Lauder is the author of “Carbon Grazing”.

 

 

 

Plant liquid carbon pathway works against grain yield in low organic matter soils

By Patrick Francis

An interesting scenario for many cropping paddocks as a result of two years of above average rainfall is being forecast by a farm consultant. Ken Sharpe was until recently employed by a commercial company as a cropping agronomist. He now has his own consultancy. Sharpe was finding an increasing divide between what his former employer was advocating for crop productivity and his personal knowledge surrounding the importance of increasing the labile (short term or available to microbes with the growing season) soil organic carbon (SOC) levels.

Low organic matter soils result in more plant liquid carbon released into soil resulting in lower grain yield.

Low organic matter soils result in more plant liquid carbon released into soil resulting in lower grain yield.

As an employee Sharpe was engaged not only to advise farmers but also sell fertilisers. His experience with farmer client Bill Smits Rochester Victoria  demonstrated that on this particular farm applying more fertilisers was not the answer to lifting crop yields while maintaining soil health.

“Crop responses to fertiliser are stagnant and declining in many paddocks and increased fertiliser inputs are required just to maintain current yields.  This is especially the case where organic carbon levels have dropped.    It is becoming more apparent  that labile soil organic carbon levels are the critical factor in achieving higher yields and improving fertiliser efficiency,” Sharpe says.

He is concerned that in many cropping paddocks with already lowSOC(less than 1% carbon or less than 2% organic matter) the extended wet period of 2010-11 has resulted in the total mineralisation of what organic matter is left.

“This will be seen in following years as soils with reduced water holding capacity and soils with a poor and cloddy structure and a higher requirement for chemical fertiliser. With current farming practices it will take many years to rebuildSOCto adequate levels and this will have serious consequences for crop yield.”

Sharpe contends that increasedSOClevels are needed to improve crop yields. The benefits ofSOCare accepted to be:

  1. Improved soil structure for root growth and water infiltration
  2. Increased water holding capacity
  3. More available nutrients from recycled organic matter.

But Sharpe believes there is a fourth benefit generated from liquid carbon compounds exuded by plants into the rhizosphere (the few mm of soil surrounding fine roots).

“Microbes feed on this carbon energy source which results in a localised acidic zone. This acidification acts to solubilise nutrients from the soil for plant growth. Interestingly, plants respond to low soil carbon situations by exuding more plant synthesised carbon, this is sometimes referred to as liquid carbon.

“We have all seen the extraordinary growth in sections of paddocks where organic matteris higher and wish for the whole paddock to be the same.     Understanding howSOC improves plant production will help to raise its importance in managing crop nutrition,” he says.

Plant dry matter composition

Sharpe says conventional inorganic fertiliser is important to supply the basic and limiting nutrients required by our food crops. The focus  on them should not be exclusive however and must be put into some perspective.

“The elemental nutrients NPKS we apply are only 4% of dry matter composition. They are important for the plant synthesis of hydrogen (6%) and the oxygen (48%) fraction of plant dry matter (DM) which are synthesised from both the atmosphere and from water. Water will continue to be a major limitation to yield”.

The carbon content of cereal crops (42%) is a primary building block of plant structure and yield and this element must be sourced almost totally from the atmosphere, that is from photosynthesis.

The low carbon composition of the atmosphere (~0.0094% C or 0.035% CO2) means that carbon is an expensive element for the plant to synthesise. The process of photosynthesis and respiration is inefficient and any management that can improve carbon allocation to plant growth must be considered.

Plant carbon must be synthesised from the atmosphere to build plant dry matter (DM). The next greatest source of carbon is in the soil from recycled plant material that is, SOC. This is the resource Sharpe says farmers can manage.  It is important to understand that plant growth continues to improve as SOCincreases towards 2-2.5%.

Most farmers recognise thatSOCresults from dead plant residue and root material returning to the soil each season but don’t know about it coming from plant root exudation, that is the liquid carbon source. The importance of this factor is totally overlooked in understanding crop nutrition.

Plant research papers quote the plant carbon allocation to the rhizosphere is between 5 – 50% of total synthesised carbon.

“This carbon is a loss to potential yield. No other factor offers farmers the chance to improve productivity by this amount.    It represents a potential loss of productivity  because what goes into liquid carbon could have been allocated to the plant itself, especially for above ground growth and grain  and is an overlooked factor in raising crop water use efficiency and fertiliser efficiency.”

Two questions immediately arise about root exudation of soluble carbon:

  1. Why does the plant allocate carbon through roots?
  2. Why does the amount of this carbon allocation vary so much?

At the growing tip of each root is an area where the plant interacts with the soil. Plant carbon is exuded through this tip as the root grows through the soil profile. Microbes feed on this liquid carbon and the populations of microbes quickly increase to consume it.

The result of this biological activity is (generally) an area of increased acidification (~pH3.7 from carbonic acid). This acidification of the soil zone solubilises and releases nutrients in the elemental form.  Sharpe says these nutrients are over and above the nutrients released through biological decomposition of organic matter.

New nutrient source

“These are new nutrients to the crop nutrition equation and the basis of plant production on earth for millions of years.   Farmers should request a Total P measurement on their next soil test to determine accessible background levels of phosphorus. This total soil phosphorus is accessible when labile SOC levels are at 2-2.5%.

“Fertiliser is applied to supply a source of nutrients for non-limiting plant growth. As the roots explore soil away from this concentrated fertiliser band the rhizosphere must still continue to allocate liquid carbon away from plant growth and productivity. Farmer trials should compare sites with different SOC levels to establish crop productivity and fertiliser efficiency.

“From many years of personal observation of commercial production and of plant and fertiliser response trials a correlation between SOC and plant productivity is clear and evident. Crops grown with lower SOC (<2%) levels tend to require more fertiliser and more growing season water than adjoining crops grown on “healthier” soil,” he says.

Artificial fertiliser increases the availability of elemental nutrients for crop production and supplies the soil bank with nutrients that can be deficient. Plant uptake of these fertiliser applied nutrients, such as phosphorus, is only partial in the year of application.

Where high levels of labile (biologically digestible) SOC exists; the action of soil biological feeding is to release soil bound nutrients so they are available for plant uptake. This occurs in all production systems as roots explore the soil zone away from the concentrated fertiliser band.

Where SOC is very low (<1%) the plant must compensate with significantly increased exudation of liquid carbon to feed the soil biology; to then solubilise soil bound nutrients for plant uptake.

Quantifying the production effect of SOC

Sharpe says his review of plant physiology research suggests that liquid carbon exudation can be 5-30% of plant synthesised carbon for 3-5T/ha crops (equivalent to 8-12T/ha total DM production above ground).  Higher yielding crops can exude 30-50% liquid carbon (25T/ha total DM production above ground). This greater amount is probably a function of a faster growth rate and a longer growing season.

“ My communication with researchers such as Dr P. Syltie (USA) suggests that while these enormous levels of exudation have been measured the association with SOC levels has not been made,” he says.

“Canadian research quoted in GRDC literature has found fertiliser inputs compared to crop production has poor efficiency (kgs elemental nutrient applied compared to kgs of elemental nutrient exported) in soils with less than 2-2.5% SOC. Soil with less than 1% SOC has extremely poor fertiliser and production efficiency.  A level of 2% SOC also seems to be the figure used by international researchers to designate a soil as ‘healthy’”.

Combing this information begins to put meaningful numbers on crop production and SOC, figure 1.

Figure 1: Proposed relationship between soil organic carbon percent and liquid carbon exudates. Source Ken Sharpe

Figure 1: Proposed relationship between soil organic carbon percent and liquid carbon exudates. Source Ken Sharpe

 

 

Sharpe says as labile soil carbon increases from 0 to 2% the soil microbes have an increasing carbon feed source that will release soil nutrients that are adequate for crop production. Where SOC is less than 2% the plant must allocate more liquid carbon to the rhizosphere. This allocation of carbon, on the y axis, is a loss to dry matter production in that year. In the second year of growth the soil carbon is increased and yields will be higher.

“From the scientific literature it appears 3-5T/ha grain crops allocate up to 30% liquid carbon in a low SOC situation and high yielding cereals(10T/ha+)  can exude up to 50% of plant synthesised liquid carbon.”

He says farmers should use these trend lines in figure 1 to quantify the potential reduction in productivity between two sites with differing SOC. It allows farmers to start putting a yield response onto SOC versus applying more fertiliser or water.

Where low SOC (<2%) exists plants must exude more liquid carbon to grow and yield. To achieve similar production levels to a higher SOC site there appears to be a requirement for using higher rates of phosphorus to speed plant growth rates.

Higher phosphorus availability increases the speed of plant functioning. A crop on a low SOC must grow faster and requires more phosphorus to achieve an equivalent yield to a high SOC crop paddock.  The export of phosphorus in the grain remains the same for both situations although higher inputs are needed on the low SOC site.

“To maximise P availability to growing crops and pastures the farmer should focus on raising soil pH to around 6 (in CaCl2) and the SOC (above 2%),” Sharpe says.

But there is another important point about the type of carbon in the soil.

“The standard soil tests for SOC can give a total carbon number which includes unavailable char. To be able to manage and understand SOC it is important to monitor and measure only labile carbon levels.”

Labile carbon is the short term carbon formed from current crops or pasture dry matter that is readily decomposed by soil microorganisms, it is distinctly different from long-term carbon such as biochar which depending on its source can survive in the soil for decades or even centuries.

New tests based on potassium permanganate will allow farmers to sample and test for labile carbon only. This  test is a good indicator of climate resilience, that ise. the ability to respond to rainfall. It might even show that two landscapes with an identical SOC test are not similar.  The test is currently $20+gst and offers an alternative to more frequent measuring of SOC without the higher cost of the usual full nutrient test kit.

Microbes will use excess nitrogen to digest organic matter and SOC before it becomes available for plant use. This will create a situation of high fertility and plant response in the immediate term but will also burn up and lower SOC levels in the longer term.  This means when using nitrogen it should be applied to match crop demand to minimise excess burn up of SOC.

“The expense of building SOC levels will be wasted where nitrogen rates in excess of crop demand are applied and microbial digestion increases,” Sharpe says.

Take home message

Liquid carbon is exuded by the plant roots to access soil bound nutrients. Higher labile SOC results in increased microbial feeding to also release soil bound nutrients.

Where 2-2.5% labile SOC exists, enough microbial feeding occurs to solubilise soil bound nutrients so that plants will exude less liquid carbon to the soil to access these same nutrients. This plant carbon can then be used for significantly increased plant growth and function.

Find out more

Ken Sharpe 0427 466 955, kenpcspakistan@hotmail.com

 

Key points to managing soil organic carbon

  • Target a minimum 2% SOC (labile).
  • As a rule of thumb this is 20T/ha in the top 100mm.
  • Plant material has about 42% carbon content
  • Animal manures have about 18% carbon content.
  • Residue left on the soil surface contributes little to SOC
  • Incorporation of crop residue, green and brown manure crops should be used strategically when SOC drops below the planned level.
  • Less than 1% SOC will yield poorly.
  • Cultivation with no organic matter destroys soil structure however cultivation to incorporate organic matter will improve soil structure.
  • Incorporated organic matter must be decomposed before seeding a new crop.
  • Livestock grazing in the rotation can improve SOC.

 

 

 

Grazing boosts soil carbon – US

Decades of ploughing throughout the Piedmont region of the United States have degraded the soil, allowing much of it to be washed away and robbing what is left of nutrients and organic matter. Sorghum, cotton, soybean, and wheat are still widely grown in the region, which stretches all the way from Alabama to New Jersey. But because the soil is so degraded, growers have allowed much of the land to revert to forests and pastures.

“Growers need guidance on whether keeping the land unused is the best way to restore degraded soils or whether allowing cattle to graze on it is a viable option,” says Alan Franzluebbers, an Agricultural Research Service ecologist at the J.Phil Campbell, Natural Resource Conservation Center in Watkinsville, Georgia.

The center was started in 1937 to look for ways of improving soil quality for farmers in the southeasternUnited States. Franzluebbers led a project where researchers planted grasses on 15ha of rolling, eroded land in northeasternGeorgiaand allowed Angus weaners (average 212 kg liveweight) to graze there to assess the effects on soil quality.

Coastal bermudagrass was planted initially, and after five years, tall fescue was drilled into it, when the bermudagrass was in a dormant winter stage, to extend the grazing season from 5 months to 10 months of the year. The research team, varied the number of cattle per hectare, and over 12 years they assessed how the soils would respond to four different scenarios: moderate grazing (average of 5.8 steers per hectare maintaining a target 3t/ha pasture cover), intensive or heavy grazing (8.7 steers per ha, to maintain 1.5t/ha pasture cover), no grazing and letting the grass grow, and no grazing but cutting the grass for hay.

Fig 1: Soil organic C content at a depth of 0 to 6 cm as affected by forage utilization regime and years of management

Under each scenario they looked at the amount of soil compaction that occurred, the amounts of soil organic carbon and nitrogen found in the soils, and the amounts of surface plant residues, which help prevent erosion.

They also looked at the effects on the soil of three different fertilizer treatments (inorganic fertilizer alone, organic broiler litter alone, and a mix of inorganic fertilizer and organic broiler litter). The team found that fertilizer type made little difference, but different grazing scenarios produced dramatically different effects.

Land that was grazed produced more grass than ungrazed land, and grazing led to the most carbon and nitrogen being sequestered in soil. Sequestering carbon and nitrogen in the soil has become a major goal for agriculture because it reduces greenhouse gas emissions. Whether grass was grazed moderately or intensely made little difference on sequestration rates.

Cutting grass for hay reduced the amount of surface residue and increased soil compaction but didn’t change the amounts of organic carbon and nitrogen in the soil. Land left unused had the highest surface residue and least soil compaction and  was better at sequestering carbon in the soil than haying.

From an environmental standpoint, grazing has traditionally been viewed as less desirable than leaving the land unused. But the results, published in the Soil Science Society of America Journal, demonstrate that if growers manage cattle so that pastures are grazed moderately, they’re restoring soil quality and cutting greenhouse gases by keeping carbon in the soil as organic matter rather than releasing it into the atmosphere as carbon dioxide.

Find out more: Alan Franzluebbers is with the J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, Georgia , Alan.Franzluebbers@ars.usda.gov  or visit  www.nps.ars.usda.gov