When carbon moves around a grazing paddock, above and below ground, nitrogen goes for the ride. The amount of nitrogen partnering carbon at any point in time is known as the carbon:nitrogen ratio. The issue for producers is that nitrogen sometimes chooses to part company with carbon before it moves into sheep and cattle. This happens as grass matures and dries out.
However, this is not a problem with edible shrubs such as old man saltbush or fodder trees like leucaena. Their nitrogen (protein) content over summer is much more constant because they have the ability to remain green. In the case of saltbush, it grows in both summer and winter and is not affected by frosts, so maintains its nitrogen/protein year round.
Edible shrubs and fodder trees have the ability to draw on deep moisture not available to the grasses.
INCREASING THE PATHWAYS BY WHICH CARBON CAN FLOW INTO THE PADDOCK
There are different pathways by which carbon enters the paddock.
At one extreme, we have the fast growing annuals with shallow roots that utilise the surface moisture.
At the other extreme, are perennial edible shrubs and fodder trees that transfer the use of rain further into the future. They can grow under adverse conditions. They maintain carbon flows over time because of their deep roots sourcing moisture deeper in the landscape.
Leucaena has the added advantage of directly introducing some nitrogen into the surrounding soil.
THE IMPORTANCE OF “GREEN PICK” (GREEN LEAF)
The graph above demonstrates how wool production increases from one to three kilogram per head with a very small increase in “average supply of green leaf”. At first glance, the production curve appears to go straight up then to the right. In fact, it is leaning a little to the right as it rises quickly. This indicates that production is increasing quickly while supply of green leaf is only increasing marginally.
Perennial edible shrubs and fodder trees are both important sources of “green pick” which is critical for production in dry times.
SHEEP AND CATTLE SELECT TO MAXIMISE “GREEN PICK”
In the graph, the consumption of shrubs (shown at the top of the graph) is going up and down depending on the availability of green grass.
When cattle couldn’t source “green pick” from green grasses, they sourced it from shrubs.
Note how the shrub consumption decreases briefly in April when there is a short-term increase in green grasses.
In dry times, the rumen microbes in sheep and cattle rely on shrubs and fodder trees to supply protein/nitrogen for them to build their little bodies. Then they can break down poor quality (low protein/nitrogen) grass and empty the rumen quicker.
USING OLD MAN SALTBUSH PLANTATIONS FOR RESTING PASTURES AFTER RAIN
In the mid 1990’s, the Federal Department of Agriculture became aware that I was suggesting that old man saltbush (OMSB) plantations could be used as somewhere to put livestock, to allow resting of pastures for a short period after rain – the time when the bulk of the carbon flows into the paddock. I was subsequently funded to conduct a $272,000 Drought Regional Initiative project to perfect the use of OMSB for this role.
The drought resistance of OMSB means it is always available for this role, especially important when an isolated fall of rain arrives during dry times or when rain arrives at the end of a drought, when pastures are bare.
Seeing OMSB plantations as a management tool for resting pastures after rain is a paradigm shift for those who see it solely as a drought reserve. A case of using it in the mud and not the dust.
Nitrogen content drives digestibility and unless the digestibility of the feed can be maintained above about 50%, then methane emissions skyrocket.
Edible shrubs and fodder trees speed up the flow rate of pasture (carbon) through the rumen of livestock in dry times, when the nitrogen content of standing grass is low. They increase the flow rate by changing the carbon:nitrogen of the total diet, which lowers methane emissions per kg of production.
With the cattle at Alice Springs, if the shrubs had not been available during the times when they were eating them, methane emissions per kg of production would have really risen.
Australia has the most variable climate in the world which appears to be becoming even more variable. Reducing the effect of this variability is the best way to reduce methane emissions. This is where edible shrubs and fodder trees fit in.
Resting pastures after rain, increases pasture resilience. Resilient pastures are greener over time, which is another way to reduce the effect of a variable climate.
Edible shrubs and fodder trees hold nitrogen with carbon longer.If present, they are the only spot where adequate nitrogen is held in the pasture when grass has lost its nitrogen.
They also transfer the use of rain further into the future i.e. they generate carbon flows when it is not raining.
This discussion is a bit like the relay runner passing the baton i.e. passing the baton to the next species responsible for running nitrogen through your sheep and cattle. Your race is over if there is nowhere to pass the baton.
The blog will start again at the end of January 2018.
Short term carbon is the fast moving carbon and long term carbon is the slow moving carbon. To put fast and slow moving carbon into a commercial analogy, think of cash flows versus capital.
Cash flows keep you in business, just like the fast moving carbon that keeps you in business too. Think of the slow moving carbon as really part of your capital base, just like cattle yards and buildings.
THE CASH FLOW ASPECT
The fast moving short term carbon makes money for you because it feeds all the life in the soil that keeps the soil productive AND feeds sheep and cattle. Remember cattle are 18% carbon, with all this carbon coming from the fast moving carbon. It is the faster moving carbon that builds larger root systems in plants so that they can access more moisture and nutrients to grow. It is central to plant energy reserves that determine how well plants can come out of dormancy. The ability to respond to isolated small falls of rain is especially important in dry years when getting something to grow is critical.
Ground cover is fast moving carbon as is organic matter that supplies nutrients to plants.
THE CAPITAL ASPECT
Humus in the soil is long term carbon which is the by-product of microbial activity (consumption).
This slow moving long term carbon is important for a different reason. It provides long term resilience by holding resources. It is essential for increasing the “storage” of both water and nutrients in the soil for plant growth.
A lot of literature uses the terms “organic matter” and “humus” very loosely, as if they were the same thing, which they aren’t. Organic matter is the raw material for humus.
Humus helps hold water in the root zone. Because humus is smaller in particle size than clay, it has a greater water holding capacity than clay. Smaller particles have a higher surface area to volume, which increases holding capacity. This also explains why sand, which has large particles, has a poor water holding capacity.
Because humus is highly charged, it will aggregate many particles into stable aggregates. This leads to better soil structure and it is resultant pores that hold extra water containing the soluble nutrients like nitrate nitrogen.
Also, humus is the habitat for long-term populations of microbes.
The cation exchange capacity (CEC) is a measure of soil fertility and quantifies the volume of mineral elements that the soil can hold and make available for plants to use. Humus has a higher CEC than clay particles, so is better at keeping nutrients in the paddock.
HOW TO REDUCE CARBON FLOWS & CASH FLOWS
Management that leads to a reduction in carbon flows from any rain that falls, also reduces cash flows.
The above photo was taken after 30mm of rain. This is a grazing operation that will be out of production soon. The question has to be asked, when should carbon flows be harvested? When possible, pastures should be rested for a short period after rain to maximise carbon flows into the paddock, like in the foreground. In other words, graziers need to let sheep and cattle only harvest the surplus, not the means by which a usable surplus is generated.
Letting animals over consume plants when they are trying to grow is one way to reduce carbon flows, however, when perennial grasses are not exposed to grazing, they become moribund. Moribund grass introduces a lot less carbon than grass correctly grazed.
CAPITALISING SHORT TERM CARBON
It is very hard to establish a figure, but it would appear that about 2% of long term soil carbon leaves the system each year i.e. flows back to the atmosphere. It also appears that about 2% of carbon flows find their way into the long term pool.
All businesses have to maintain capital infrastructure. Think of carbon flows as maintaining the pool of long term soil carbon. If carbon flows are really well managed, this can lead to a capital gain if more carbon moves into the long term pool than moves out. Of course, there is a limit to how much long term carbon the soil can store.
When I ran the “financial analogy” past Ruaridh Petre, he responded by broadening it further,“Life on earth is an economy that runs on carbon. The more busily plants and microbes trade carbon molecules, the more prosperous the ecological economy becomes. Also, you’ve got to use carbon to store carbon.”
Erosion is an immediate reduction in earning capacity, because it removes both short term and long term carbon.
ENTERPRISE: Cattle. Contract rearing of dairy heifers
PROPERTY SIZE: 100 hectares
AVERAGE ANNUAL RAINFALL: 700 mm
ELEVATION: 56 m
MOTIVATION FOR CHANGE
Rising production costs and animal health concerns
Introducing biologically-based soil conditioners to balance the mineral and microbial status of the soil
Strategic use of foliar fertilisers
Ceasing chemical inputs
Innovations commenced: 1995
Stock output increased by 33%
25% reduction in irrigation used per animal weight produced
Infertile sand converted into fertile dark soils showing organic matter down to 60cm
Thriving pastures with fewer weeds
Faced with rising production costs and animal health concerns, David Clayfield made the link that improving soil health – physically, chemically and biologically – could address the cause of animal health and low productivity problems.
David eliminated the use of chemical and acid-based fertilisers, replacing them with biologically-based soil conditioners tailored to rectify deficiencies identified through soil tests.
Fifteen years on, yellow sands have turned into dark, healthy soils with a substantial increase in soil organic matter. Irrigation requirements have reduced from the region’s typical seven to eight megalitres per hectare each year to five to six, subsequently reducing the energy used for pumping and distribution.
Pastures are thriving, animal health has improved and productivity has increased, while the veterinary bills have plummeted – positive results, all round.
David’s grandfather came to Clover Estate in the mid 1930s to manage a large grazing estate. He bought a portion of it when the estate was subdivided for soldier settlement blocks after World War II. David’s father grew up on the farm and has now retired, leaving David to run the property.
The typical soil in the region is five metres of sand overlying limestone. Native vegetation is low open forest dominated commonly by manna gum (Eucalyptus viminalis), brown stringybark (Eucalyptus baxteri) and blackwood (Acacia melanoxylon). Most of the native vegetation in south-east South Australia has been cleared to make way for farming and plantation forestry, but there is a small remnant left on the Clover Estate property.
There are no surface streams in the limestone plains area of south-east South Australia – rainfall infiltrates into the limestone, which forms an extensive shallow aquifer system. Dairying and cropping in the region depend on pumping irrigation water from this aquifer system.
David’s grandfather and father operated Clover Estate as a dairy farm for many years, irrigating the pastures using water pumped from the shallow limestone aquifer underlying the property. After the dairy industry was deregulated the property proved to be too small to run viably as a milk producing dairy farm. Since 2000, the farm has been used to raise dairy heifers that are bred elsewhere in the district.
Heifers are reared on contract on a ‘pay for weight gain’ basis. The calves are brought to the property at four to five months age and within one year they have gained about 200 kg, i.e. a young dairy cow. The farm has the capacity to ‘turn off’ 600 to 700 heifers a year.
The current market for these young cows is the Republic of China. The heifers are shipped to China where they are mated upon arrival and begin producing milk before they are two years old.
A total of about 62 hectares of Clover Estate is irrigated and the rest is used for unirrigated grazing and cutting hay to provide feed
during winter. A highly modified landscape, almost all native flora on Clover Estate has been replaced with introduced pasture species.
DEFICIENT SANDY SOILS
South-east South Australia is made up of distinct land systems. The main underlying geological formation comprises limestone layers that have produced fertile soil, including the famous ‘terra rossa’ (red earth) soils of the Coonawarra wine region. Scattered in bands across the plains are low wide sand ridges, running roughly parallel to the present coastline. These sand ridges formed along ancient coastlines in the past few million years as the sea level rose and fell and the land surface was uplifted during ice ages. These sandy soils have low natural fertility.
When the large grazing properties were ‘broken up’ for farming and closer settlement, these sandy soil plots were not in demand. The sandy areas in private ownership were used for grazing, rather than cropping.
Clover Estate and many other properties in the area have been used for dairying, irrigated with groundwater pumped from the limestone aquifer, for many years. This groundwater is rich in calcium, which increases pH from natural levels of around 5, that is, slightly acidic, up to 7 to 8, which is slightly alkaline. This change causes nutrient imbalances and encourages growth of Yorkshire fog or velvet grass (Holcus lanatus), a perennial grass. Holcus lanatus is generally considered in Australia to be a weed of saline and waterlogging-prone sites and has little grazing value. The traditional way to redress the nutrient imbalances in the area is to use superphosphate and potash – potassium-rich fertiliser.
In 1992, a soil test showed organic carbon at 2.1%, total cation exchange capacity 3.5, and deficient levels of 17 macro and micro soil nutrients at Clover Estate. Prevailing advice was to continue to apply higher amounts of chemical fertiliser to maintain production. But high chemical and fertiliser inputs and high water use were proving to be financially unsustainable. Furthermore, excessive weed competition had been developing despite regular use of knock-down and selective herbicides. Insecticides were used regularly for red-legged earth mite and other pests.
These problems, high levels of irrigation per animal production unit, on top of recurring animal health issues – mastitis, prolapse, sore feet – and concern about personal exposure to chemicals, led David to investigate more sustainable ways to improve soil and forage quality.
“The aim was to start with the soil health, by balancing the mineral and microbial status of soil, and the subsequent benefits in forage quality and animal health would follow.”
David had realised that management of animal health with medicines was only addressing the symptoms of animal health and performance, rather than the causes. Equally, chemical management was only creating recurring problems at extra cost. Conversely, improving soil health and mineral balance and availability in pasture would address the cause of animal health and low productivity problems.
David found that experimentation and mineral supplementation redressed some animal health problems. Success with this process indicated the strong link between animal nutrition and health. This prompted David to undertake further investigation to address animal health problems through the soil and fodder.
David’s aim was to stop using chemical or acid-based fertilisers and pesticides. He wanted to improve soil fertility and water-holding capacity by adding biologically-based stimulants that increase soil organic matter.
He encountered challenges with adopting new methods, the initial impediment being a lack of information about alternatives to the ’single super’ use way of farming. He was required to perform ongoing research, education and trial and error to identify his options and learn more about the links between soil and animal health.
David initially drew on information from Pat Coleby, a practitioner of animal health through soil health, which provided a useful guide. He also attended short courses in different approaches to fertiliser management, increasing his understanding and confidence in soil mineral and microbial management. David notes, “I have utilised interactions with agronomists and soil scientists from biological product supply companies to assist in fertiliser program management and planning”.
David also read widely to supplement the courses and consultation. His collection of reference books include Charles Walters and C.J. Fenzau’s Eco-farm; Arden Andersen’s Science in Agriculture: Advanced Methods for Sustainable Farming; and Pat Coleby’s Healthy Land for Healthy Cattle.
An equally significant challenge was the lack of interest from other farmers, extending even to ridicule of some of the changes made and methods tried.
egardless, David advises, “Work it out, stick to it, no matter what everyone thinks. With the experience and knowledge now available, you could build carbon and fertility in your soil in much less time than it took us to learn how by trial and error”.
TURNING SAND INTO SOIL
Understanding the physical, chemical, and biological aspects of soil through applied soils science and putting this knowledge into practice over time, has been the fundamental innovative practice applied at Clover Estate.
“Testing the soil and observing the plants and animals, it became obvious that use of chemicals and acidic fertiliser were not a long-term solution”, David says. He stopped using chemical fertilisers in the mid 1990s, five years before the switch from milking to raising heifers.
“The aim was to start with the soil health, by balancing the mineral and microbial status of soil, and the subsequent benefits in forage quality and animal health would follow.”
The process began with soil testing to assess the situation. Soil treatments were applied with the objective of addressing mineral balance, improve soil biological processes and overall soil fertility specific to paddock soil test results. The key ingredients are residue-digesting fungi and nitrogen-fixing bacteria, including strains of Azotobacter, Bacilus, Pseudomonas, and Trichoderma1LawrieCo (2009) Sustainable update Winter 2009, LawrieCo Sustainable Farming, Wingfield, South Australia. Nutrients, carbohydrate and minerals are added to enable the bacteria and fungi to multiply in temperature-controlled 5000 litre aquaculture tanks. The minerals included a carbon, humic base to stimulate soil biological processes and organic matter building activity. The resulting brew is applied to the paddocks yearly at 50 litres a hectare.
In addition to soil building programs, a range of bio-fertilisers, such as foliar and fertigated (application through an irrigation system) mineral, microbial, kelp, fish, humic and fulvic fertilisers have been applied over the past 15 years. Leaf tests are taken to identify lacking nutrition, enabling application of nutrients to address imbalance in plants.
Animals’ performance and grazing preference, along with observing the plant species that are growing, are used as an additional guide as to excess and deficit minerals in the soil.
To target these treatments accurately, David has equipped himself with a refractometer, to measure the sugar concentration in plant sap, and other measurement devices and has soil tested by an agricultural laboratory in Adelaide.
In David’s words, the three rules for the soil remediation techniques he has developed and applied are “balance, balance and balance – carbon to nitrogen ratio, calcium to magnesium ratio, etc. … look at the whole picture from soil to human health”.
The results are evident in the soil profiles of remnant and treated soils. Soil carbon has increased by 45% in the top 150mm, and potentially substantially more at depth. Organic carbon measurements show an increase from 2.07% in 1992 to 2.92% in 2011.
David estimates that, since the mid 1990s, stock output has increased by 33% while he is using 25% less irrigation water per animal weight produced.
As is usual in the region, centre pivot systems are used at Clover Estate to irrigate with water pumped from the shallow limestone aquifer. Centre pivot irrigation uses sprays fitted on a boom that travels in a circle around the centre pivot point. Electric motors are used to drive the wheels that carry the boom. Two such systems operate at Clover Estate, one of about 300 metres radius, covering about 28 hectares, and the other a 330 metres radius, covering 34 hectares. A neutron probe is used to measure soil moisture levels and determine when watering is needed.
Due to the improved structure of the soils, David has found that his total water use is now around 5-6 Ml/ha/year compared with the 7-8 Ml/ha/year commonly used on sandy soils in the region. This is particularly noteworthy in relation to rainfall, with eight of the last ten years receiving below-average annual falls. As well as using less water, David’s energy costs from pumping and driving the boom have halved.
Cessation of chemical weed control and David’s soil management has ensured vigorous growth of preferred pasture species, combined with rotational grazing. The property is fenced into 50 paddocks, ranging from two to six hectares. The rotational grazing cycle also aims to break the life cycle of intestinal gut parasites.
David highlights, “Pasture plants grow better and there are now a lot fewer weeds. Lucerne varieties that had been abandoned due to poor performance by most typical, chemically managed properties perform exceptionally well on our property. Lucerne, rye grass, clovers, are the predominant species, along with a variety of herbs for balanced pasture. Animal health issues are primarily averted, due to the density and balance of the minerals in our pasture”.
“Strategic use of selected foliar fertilisers… reduces or eliminates sap sucking insects attacking the pasture. We have found also that foliar fertilisers strengthen our desirable forage species, making them more competitive over weeds.”
David believes that “Holistic management includes an appreciation of natural processes and an understanding of applied soil science. If soil biology functions to its best ability, the availability of minerals to plants will be at its best. If animals and people have access to adequate mineral diversity in diet, then disease is less … and performance is better. Our farm enterprise is more profitable, and more enjoyable. We will leave an improved legacy.”
“Our example has inspired other farmers, particularly dairy and graziers, to adopt aspects of soil management as we have. Looking at our soil profile, black to the depth that it is, speaks for itself. Most farmers appreciate that something is different and improved on our property. We are happy to share our journey, as it appears to give confidence to other food producers to take on similar management. Less chemicals affecting the environment, with improved quality of food for consumers is a better outcome than prior to adopting biological farming system.”