Soil organic matter plays a key role in ensuring healthy soils and sustainable agriculture production, but Australian soils are generally lower in organic matter compared to the rest of the world according to Grains Research and Development Corporation funded research.
Queensland Department of Agriculture and Fisheries senior development extension officer Jayne Gentry said organic matter was key to the physical, chemical and biological functions of the soil.
‘‘In the northern grain region, soil organic matter’s major role through its mineralisation is providing nitrogen and other nutrients in a form available to crops and pastures,’’ she said.
Ms Gentry said levels of soil organic matter were measured by testing soil for soil organic carbon, which composes about 60 per cent of soil organic matter.
GRDC research reveals that at current fertiliser prices every one per cent of soil organic carbon measured in the top 10cm equates to about $1500 to $2000 in nutrients.
Ms Gentry said the answer to increasing soil organic carbon was maximising biomass production through good agronomy.
‘‘Research showed us that returning cropping country to pasture will increase soil organic matter levels, but there were large variations indicating not all soil types or pastures will perform the same,’’ she said.
‘‘Soil type influences the speed by which carbon levels change, with sandy soils losing carbon faster than clays which are best for storing carbon as they coat and protect the carbon from microbial breakdown.’’
Due to the effect declining soil organic matter levels have on the soil’s capacity to mineralise nitrogen, the research also explored the results of applying synthetic fertilisers or organic sources.
‘‘The most promising practice to date to rebuild soil organic carbon stocks in the shortest time appears to be the establishment of a highly productive pasture rotation with annual applications of nitrogen fertiliser,’’ Ms Gentry said.
She said it was critical that growers tested soil organic carbon correctly to track changes in soil organic matter and ensure results could be interpreted accurately.