IS PASTURE REST TIME OR TIMING

The question has to be asked, what are we really trying to achieve with pasture rest?

The answer: Achieving the flow of carbon to all the parts of the paddock that it needs to flow into, above and below ground. Animals will reduce the flow of carbon if not managed properly. 

Some see pasture rest as an exercise in growing more pasture for sheep and cattle to eat. While this is an important outcome, there is more to it than this.

WHAT PASTURE REST SETS OUT TO ACHIEVE

There is an element of the present and the future with pasture rest.

The present is growing more feed for sheep and cattle to eat, remembering that pasture (ground cover) is 45% carbon. Creating ground cover also protects the soil and soil life in the short term.

The future is building paddock resilience. Paddock resilience relies on plant resilience and soil resilience. When paddocks are resilient, they have the capacity to produce to their maximum each time it rains, i.e. to generate max flows of carbon.

To remain resilient, plants need carbon flowing into them to maintain energy reserves and build extensive root systems, necessary for sourcing water and nutrients out of the soil.

Pasture rest is also about maintaining the health of the soil in which plants grow. To be productive, plants require a healthy soil that supplies them with water and nutrients. For the soil to remain healthy (resilient), plants need to be allowed to provide carbon compounds to feed all the soil life responsible for keeping the soil well structured and fertile.

RAINFALL/MOISTURE ACTIVATES SOIL MICROBES AS WELL AS PLANTS

If pasture rest is seen in terms of generating carbon flows, then we have to consider all the processes that contribute to generating flows.

It is so easy to give all the credit to plants for generating carbon flows and overlook the important role soil microbes play in helping plants grow (photosynthesise) after rain.

It is moisture that activates the soil microbes to consume organic matter and start the process of releasing the nutrients in organic matter into forms suitable for plant uptake.

I was told recently that the bulk of the action with soil microbes consuming organic matter occurs in the first 48 hours after rain. Another person conceptualised it for me by saying there is a puff of carbon coming out of the soil after rain, i.e. microbes are like us in that they release carbon dioxide as they consume carbon compounds.   

Growing plants support soil microbes directly by releasing energy directly to them through root exudates (liquid carbon). Plants also make soluble carbon available to mycorrhizal fungi which are located on their roots. This allows the fungi to extend out into the soil and source extra nutrients for the plants. This is a case of carbon bargained for nutrients.

It is after rain that soil microbes produce growth promotants for plants. Some of the activated soil microbes are also bringing in nitrogen from the atmosphere.

Livestock should be feeding on pastures’ excess growth, not the first flush after rain. Otherwise, they are hindering all the processes just discussed.

THE LOGIC BEHIND WHY PASTURE REST IS TIMING AND NOT TIME

Hang in there “cell grazers”, what you stand for is not being challenged here.

Nature has designed the system so that water activates the flow of carbon into the landscape via photosynthesis.

The bulk of the carbon arrives from the atmosphere in the short period following rain.

Straight after rain is when plants and microbes are working together. This is the time when plants have most in their favour to grow and produce carbon flows.

Straight after rain is when plants and microbes are working together. This is the time when plants have most in their favour to grow and produce carbon flows. 

Nature does not have a predictable pattern. Stated simply, we must allow nature to transfer carbon from the atmosphere to the landscape according to its time frame. This is why pasture rest is TIMING, i.e. “strategic rest” after rain.

Basing resting decisions on a certain period of TIME is no guarantee that carbon will come into the paddock because there is no guarantee that it will rain.   

I first raised TIMING versus TIME in a report in 1998. It was included in a paper I wrote with CSIRO for the proceedings of the 1999 International Rangelands Congress. The title of my poster, judged the best, at the 2008 Australian Rangelands Conference was, “Is pasture rest time or timing?”

WHEN IS PASTURE REST ACHIEVED?

Pasture rest is long enough when enough carbon has flowed to all of the areas in the landscape, above and below ground, that it needs to.This explains why paddocks lacking resilience require a longer rest period. 

After talking to a cross section of scientists and producers, it would appear that the required rest period after rain is about 4-6 weeks, remembering that temperature influences plant growth.

WHY SOME ARE THINKING TIME

It may be a misunderstanding of the cell grazing concept that is responsible for some land managers taking the position that pasture rest is about time. Cell grazing is often referred to as “time controlled grazing”.

I asked one of Australia’s leading cell grazers if he had a problem with me saying pasture rest is timing and not time, given that he locks up his cells for 120 days on average, which is time. He said he did not. He said the bulk of the outcomes he achieved over the 120 days was achieved in the short period after rain. He made the point that most of the cells did not have livestock in them after rain, so produced maximum flows. He also commented that he could achieve full recovery in four weeks. 

Cell grazing is just one of many methods producers use to increase carbon flows.

TIME RELATES TO CONSUMPTION

It is important not to confuse management of flows with consumption of existing stocks.

Resting for set periods of time when it is not raining, is a consumption issue (maintaining ground cover), and should not be confused with strategic / tactical rest after rain. The exception is when a regeneration event has occurred and freshly germinated perennial seedlings need to be protected to allow them to establish.

How much ground cover is consumed is important, but it is the second decision a producer makes, not the first. What sets the level of ground cover in the first place is the amount of carbon a particular form of management allows to enter the paddock after rain.

Provided it is not excessive, grazing is beneficial as it removes rank pasture that can inhibit pasture growth next time it rains.

COMMERCIAL PRACTICALITIES OF SEEING PASTURE REST AS TIMING

The practical aspect of seeing pasture rest as a short, but strategic, period of time, is that an alternative home for livestock only has to be found for a short time.

If pasture rest is seen as time, then animals have to be sold or agisted.

CONCLUSION

The people who achieve the most in land regeneration are not the ones who lock up country for the longest time. Instead, it is the ones who act when something can be achieved.

A rest at the right time is the basic catalyst for maintaining paddock resilience.

The only time you can prepare for drought is when it rains.


ALAN LAUDER

THE TWO DIFFERENT PROCESSES PLANTS USE TO GENERATE CARBON FLOWS

Did you know that there are two different systems of photosynthesis used by plants? One is called the C3 pathway and the other is called the C4 pathway. The main difference between these two systems is the compounds used in turning carbon dioxide into starch and sugar.

Plants using the C3 pathway rely on the enzyme, rubisco, to fix carbon atoms from carbon dioxide in the air. The first stable product in this process is based on three carbon atoms, hence it’s called the C3 pathway. 

Plants using the C4 pathway use the enzyme, PEP carboxylase, to fix carbon from atmospheric carbon dioxide during photosynthesis. The first stable product of this process is a four carbon molecule, hence it’s called the C4 pathway.

The photosynthetic pathway that a plant uses will determine the conditions under which the plant will grow. The chart below is a guide to their likely requirements and performance under differing conditions.

The difference between the C3 and C4 photosynthetic pathways

THE CONDITIONS EACH GROWS BEST UNDER

Generally, C3 plants are more “temperate” plants, growing best in cool, moist conditions. They take up CO2 through open leaf pores or “stomates” and convert this to carbohydrates (leaves, stems, roots and seeds). In cool, moist conditions, this process is three times more efficient in C3s than in C4s. Unfortunately, for C3s, as the temperature increases, rubisco combines with oxygen instead of CO2. This wasteful process is called photorespiration. It produces photoglycolate, a useless product to the plant, and breaks down carbon compounds to release CO2. In warmer, drier conditions, C3 plants will photorespire more than they photosynthesize. In effect, they begin to die. In contrast to this, C4 plants hardly photorespire at all, even as the temperature rises.

C4 plants grow best in warmer, drier conditions. The C4 photosynthetic pathway needs more sunlight energy than the C3 pathway to convert CO2 to carbohydrates. In hot, dry climates, very low levels of photorespiration balance this higher energy requirement. Most of the CO2 absorbed by C4 plants is permanently converted to plant material in warmer conditions. But in cooler conditions, C3 plants are more efficient converters of water and CO2 to plant matter than C4 plants. In fact, below 15° C, many C4 species begin to hay off as the energy necessary for the C4 photosynthetic process becomes increasingly limited. C4 plants grow best when energy from sunlight is plentiful.

SOME EXAMPLES OF C3 AND C4 PLANTS

C4 plants include the main grasses of the tropical savannahs, including black spear grass, kangaroo grass and golden beard grass, as well as crops like sugar cane, sorghum and corn. C3s crops include winter cereals, legumes, temperate pasture plants and all trees. C4 pasture plants are already more efficient than the C3s growing beside them and are thought not to gain as much from increased carbon dioxide levels in the atmosphere.

QUALITY VERSUS QUANTITY

The leaves of C3 plants are generally higher in nitrogen (protein) than those of C4 plants under the same conditions. This is because C3 plants have a higher concentration of rubisco (a protein) in their leaves. This explains why animals seek out C3 plants in preference to C4 plants putting them at more risk of being eaten out.

Annual grasses are C3s which is consistent with them being highly sought after by animals.

While C3 plants may produce higher quality feed, C4 plants nearly always produce more feed than C3 plants over a 12 month period. C4 plants are more water efficient, producing twice as much organic matter per litre of water to what C3 plants produce. A CSIRO scientist explained to me that on average, C4 plants require ¼ litre of water to produce 1 gram of pasture and C3 plants require ½ litre of water to produce 1 gram of pasture.

When paddocks degrade, the soil has a lower nutrient level. This reduces their ability to supply the nutrient requirements of C3 plants.

COMPLEXITY INCREASES CARBON FLOWS

The key thing a farmer or grazier wants to achieve, is to create an ecosystem that harvests carbon/energy efficiently. This requires multiple options to capture carbon. Having both perennials and annuals and C3 and C4 plants, where climate allows, is the best option. Almost all “natural” systems configure themselves to do this, but human intervention disrupts this process. We always seem to want to simplify the system by reducing the number of pathways, and thus the total efficiency of the system. 

CONCLUSION

Diverse grasslands are more capable of supplying ongoing “green feed” because they make the most efficient use of water and nitrogen when it is available. They are also more successful at maintaining the health of the landscape and making it more profitable, because carbon is being introduced and cycled more often.

If the climate changes, as predicted, then this will change the balance between C3s and C4s in some pastoral regions.

While C3 plants are seen in a better light because of their higher nitrogen content, we should never lose sight of the fact that C4 plants can photosynthesise at higher temperatures, when the C3s shut down and achieve nothing. It is better to have inferior carbon compounds, that can be supplemented for livestock performance, than having no carbon in the paddock for livestock to consume.

There is a need for more emphasis on how different these two plant groups are in their manipulation of carbon.


ALAN LAUDER

PLANTS DON’T JUST SIT THERE AND TAKE IT

Plants may not be able to move around but that doesn’t mean they have no control over their destiny. They have an amazing array of strategies for surviving and improving their environment.

We need a feed and a drink and so do plants. Apart from the carbon in the atmosphere being a food source for them, plants get the other things they need from the soil.

Plants are the ultimate networkers. They send chemical instructions via root exudates to soil microbes, to get them to do what they need done. 

ROOT EXUDATES: WHAT THEY ARE & WHAT THEY DO

Not all the carbon from photosynthesis is used in the construction of leaves, stems and new roots. Some is released as organic substances by the roots of plants. The energy is released by plant roots in the form of root exudates. This energy is released to the organisms living on or near their roots while plants are growing (photosynthesising). Because of the direct energy contribution from plants, the population of microbes in the rhizosphere around root tips can be 5-50 times greater than in the rest of the soil.

Root exudates are a direct energy transfer from plants to soil microbes, while organic matter is an indirect transfer.

THE COMPLEXITY OF PLANT INTERACTIONS WITH SOIL MICROBES

Carolyn Ditchfield generously wrote this for me some years ago. This explanation by Carolyn explains everything much better than I could do.

“Perhaps not consciously, there is a pervasive impression that plants are at the mercy of their environment. This is reinforced by conventional agricultural practices that focus on feeding the plant and protecting them with various chemical concoctions.

It is true that plants are not mobile so cannot physically escape their location, but they have an amazing array of strategies for surviving and even manipulating their environment. 

Often overlooked is their ability to modify the root zone. Up to 30% of the photosynthetic energy accumulated by a plant is dumped into the root zone as sugars, proteins and carbohydrates. Apart from the fact that combined, all these exudates contain carbon, they also act as a food source for soil biology. 

Much like the food web above ground, different soil microbes respond to different food sources below ground, i.e. different exudates attract/stimulate different microbial populations; and these soil microbes are a remarkably powerful workforce with individual species able to solubilise minerals (plant nutrients), fight ‘disease’, fix nitrogen, decompose organic materials, restructure soils, hold water, etc. 

Maybe coincidently, different plants produce different exudates. But even more interesting, individual plants change the composition of their exudates with environment, season, climate or phase of growth.

Although the research is yet to formalise the link, the clues are accumulating. A plant’s ‘decision’ to release a particular type of exudate from its roots has an active effect on which microbes get ‘nurtured’ in the root zone, and hence an active influence over its own maintenance and survival.”

SOME FIGURES PUT ON PLANT DECISION MAKING

Research has shown that P-stressed lupin plants secrete about 20- fold more acid phosphatases from roots compared to P-sufficient plants.

The graph below shows the percentage of photosynthesis that cropping plants allocated to exudates (liquid carbon) depending on the abundance of labile carbon (short term carbon) in the soil. Perennial grasses display similar behaviour.

Source: Ken Sharpe

MIS-MANAGE CARBON FLOWS AND LIVESTOCK GET LESS OF FUTURE INCOMING CARBON

It is well known that plants allocate more carbon from photosynthesis below ground when soils are less fertile. This means less of the production from photosynthesis becomes ground cover for sheep and cattle to eat. All else being equal, soil fertility reduces if carbon flows into the paddock reduce.

Below is a paddock where plants are now allocating plenty of carbon above ground.

This is an area where plants have been allowed to improve their own environment. This photo was taken in the Traprock country in South East Queensland which is known for its low fertility. 

CONCLUSION

As soil organic carbon gets lower, plants must exude more liquid carbon from their roots to grow.

Root exudates from grasses are the fastest moving/flowing carbon. This carbon will be back up in the atmosphere within 24 hours of entering the plant.

If the top half of a plant is hardly photosynthesising because of poor animal management, then the roots will be exuding little energy to the soil microbes.

Shortage of plant available phosphorus is known to be a production issue in some pastures. The availability of phosphorus to plants is influenced by how much soluble carbon plants are able to release to soil microbes.


ALAN LAUDER

WHAT REALLY IS PADDOCK RESILIENCE

The traditional definition of resilience is a paddock that is functional and able to withstand adverse conditions.

For those seeking tangible evidence of when resilience exists, it is the ability of a paddock to generate carbon flows from rain i.e. how well the pasture responds to rain. Perhaps the best test of resilience is the ability of paddocks to respond to isolated small falls of rain during a dry period.

A paddock that has the capacity to successfully produce carbon flows is one that is also well equipped to better withstand extreme events, be they drought, heat or heavy rain. 

LINKING RESILIENCE TO DIFFERENT PADDOCK RESPONSES TO RAIN

The fence line comparison above is a good starting point for discussing what underpins resilience.

The right hand side of the fence is a grazing paddock, not a farming paddock. Look at the surface water right up to the fence and nothing on the other side. This outcome is more than just different soil structure, as will be discussed.

Add some slope and the right hand side of the fence is at risk to erosion.

These two pictures show the productive capacity of each side of the fence at a later date i.e. the paddock’s inherent ability to produce carbon flows. The top photo is the left hand side of the fence and the bottom one the right hand side of the fence. The resilience of each side of the fence is very different. Stating the obvious, resilience and water use efficiency go hand in hand.

THE TWO COMPONENTS OF PADDOCK RESILIENCE

Paddock resilience has two components, plant resilience and soil resilience, and both rely on carbon flows.

PLANT RESILIENCE

Maintaining plant resilience relies on good animal management. Animal management that does not let plants grow to their potential after rain, reduces the flow of carbon into them.

Allowing carbon to flow into plants increases their resilience by increasing internal energy reserves for them to call upon and increases their root volume. 

The perennial grass plant above is what a plant lacking resilience looks like. It is struggling to come out of dormancy after good rain because it is short of stored energy. Energy reserves in plants are short term carbon brought in by carbon flows. In perennial grasses they are stored in the roots and also in the crown. These reserves are the energy source prior to green leaves collecting energy.This plant is generating no carbon flows to feed soil life, which is responsible for restructuring the soil and making it more fertile.

It is also not going to produce any ground cover. Ground cover increases water use efficiency by reducing evaporation in two ways, lifting the wind off the soil and keeping the sun off the soil. 

Increasing carbon flows into plants produces a more extensive and deeper root system to allow them to source more water and nutrients i.e. become more resilient. Roots are 45% carbon.

Roots act as wicks to take water down through the soil profile, especially important with harder soils. The water travels down beside the roots. The pooling in the fence line photo was not just due to poor soil structure, it was also due to a lack of roots in the paddock.

SOIL RESILIENCE

One aspect of soil resilience is how well water enters and how well the soil is able to retain moisture over time to promote plant growth.

Think of the soil as a construction site. If plants do not supply carbon compounds to all the life in the soil that are responsible for keeping it well structured and fertile, then they die.

Carbon flows into plants are the true source of soil organic matter which is about 58% carbon (short term carbon). Organic matter is the raw material for humus which is long term soil carbon. Humus is the undigested portions of organic matter.  

Because humus is highly charged, it will aggregate many soil particles into stable aggregates. This leads to better soil structure and it is the resultant pores that hold extra water containing the soluble nutrients like nitrate nitrogen.

Humus changes the pH of the soil and so buffers against any toxic elements present. 

Humus is smaller than clay particles, which is why it has a higher water holding capacity than clay i.e. it has a higher surface area to volume than clay.

Organic matter changes the bulk density of soil, which adds to water storage capacity.It also stores nutrients ready for soil life to mineralise them into the inorganic form which is plant available.

Flowing short term carbon also feeds the soil biology responsible for creating macro-pores in the soil. Macro-pores enhance air and water movement. These macro-pores will still be there after this fast moving carbon is back up in the atmosphere.

For every 1% increase in organic carbon, to a depth of 30 cm (12 inches), the soil is able to store an extra 144,000 litres of water per hectare. This is in addition to the water holding capacity of the soil itself.

With poor management, plant resilience reduces first, then soil resilience reduces. This highlights that your animal management affects the soil, by affecting plants first.

SHORT AND LONG TERM RESILIENCE

The fast moving short term carbon (plant energy reserves, root volume, organic matter and ground cover) supplies short term resilience. On the other hand, the slow moving long term carbon (humus) supplies long term resilience. It protects the long term survival of the system. Humus will slowly decline without good management of carbon flows.

Maintaining short term resilience helps maintain long term resilience.  

Long term carbon being lost from the paddock because of little short term carbon to help protect it.

INCREASING THE PATHWAYS FOR CARBON INFLOW

Because resilience relies on carbon flows, there is a need to increase the pathways for carbon to enter the paddock i.e. increase the mix of plants to cover all circumstances.

A production system based on perennials is more resilient than one based on annuals, simply because perennials generate more carbon flows over time, especially in marginal years.

FEEDBACK LOOP WITH CARBON FLOWS

The discussion to this point, highlights that current carbon flows are influenced by previous management of carbon flows. This is why water use efficiency over time is linked to management of carbon flows.

Just as money makes money, carbon also makes carbon i.e. carbon flows lead to more carbon flows.

CONCLUSION

Both plant resilience and soil resilience rely on carbon flows.  

With a resilient paddock, more water leaves the paddock via transpiration (creating carbon flows) instead of as run off or evaporation.

Resilient paddocks are more profitable and looking at the bigger picture, they supply better environmental outcomes for the rest of society.

The only time you can build paddock resilience is in the short period after rain.


ALAN LAUDER