Australian soil organic matter levels are declining under continuous cropping cycles, but there is hope for improvement as a new $3.5 million project gets underway.
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The five-year investment by the GRDC, in partnership with CSIRO and industry partners Kalyx Australia and Delta Agribusiness, is expected to generate international interest with its focus on improving soil organic matter through effective nutrient management using a whole-of-system approach to increase soil microbes.
This CSIRO-led project will identify the most effective ways to increase soil organic matter from crop residues in a dryland cropping systems and detail the cost-benefit analysis of a range of nutrient and residue management strategies for grain growers.
The project will also conduct a lifecycle assessment of inputs for carbon accounting purposes.
Soil organic matter contributes to a range of biological, chemical and physical properties of soil and is essential for supplying nutrients to crops, preserving soil structure and maintaining water infiltration.
Although plant residues are very high in carbon, nutrients such as nitrogen, phosphorus and sulphur are required to break it down to build healthy soils with high levels of humus.
GRDC sustainable cropping systems manager north John Rochecouste said an approach to nutrient management that took into account soil biota function and nutrient requirements could avoid the continued long-term rundown of soil organic matter.
"Retaining carbon via stubble on the ground through no-till farming practices does not always lead to an increase in soil organic matter in the ground," Mr Rochecouste said.
"Additions of nutrients, such as nitrogen, phosphorus and sulphur, beyond that used by the crop, are needed to support the soil biota to 'break down' the stubble carbon into humus.
"This research is necessary because it offers a way to increase soil organic matter and will provide quantitative measures of the carbon benefits and the costs of achieving changes in soil carbon."
This research will test the cost and yield benefits of 10 different nutrient supply strategies at eight sites across Australia.
CSIRO chief research scientist Dr John Kirkegaard said the research showed a holistic approach was needed which followed a new paradigm to 'fertilise the system, not just the crop'.
"We're discovering that providing carbon via no-till and stubble retention practices is only part of the process and what we actually need to do is provide the microbes with the nutrients they need to grow their populations while they use the crop residue as the energy source," Dr Kirkegaard said.
The project will look at a number of factors such as nutrient types, timing and rates, positioning, and even whether a nutrient supply option can be created that targets and uses existing nutrients in soil and residue to reduce costs.
"No commercial fertilisers currently target these nutrient ratios to build soil organic matter from residue, so there's potential for fertiliser companies to innovate in product development too," Dr Kirkegaard said.
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