With soil nitrogen stocks on the decline due to intensive agricultural production, focusing on future productivity rather than short-term gains is of utmost importance, according to CSIRO research scientist Jeff Baldock.
Speaking at the GRDC Grains Research Update in Adelaide last week, Dr Baldock said increasing rates of N fertiliser application loses efficacy quickly, due to high application quantities increasing the potential for N loss.
Dr Baldock said a more effective long-term solution needed to be focused on maintaining soil organic matter, where 95 per cent of naturally existing N was contained.
While preventing soil organic matter decomposition seems a plausible way to maintain stocks, Dr Baldock said the process was essential to reap the positive benefits provided by the material.
“Increasing organic matter amounts is more effective than preventing decomposition, because decomposition and natural cycling is essential for various soil properties and functions,” he said.
Management practices for organic matter addition are slow, and a greater focus should be placed on assisting the natural flow of organic carbon into the soil.
We need to know we're mining soil and be prepared to rebuild it. If not, we run into trouble.
“The manner of maintaining a carbon-friendly management practice can vary across crops and soils, with residue retainment a possibility for achieving better organic carbon stock,” he said.
N requirements surpass what is naturally available in the soil, yet Dr Baldock stressed the importance of ensuring soils weren’t overloaded with synthetic fertilisers to the point where their value was obsolete.
“If synthetic N is added to the extent that availability exceeds requirements, the slow-release synchronous behaviour of N mineralisation from soil organic matter is lost,” he said.
The key to balancing availability with demand comes in the form of an N calculation, which Dr Baldock developed.
“Calculations need to involve direct inputs and outputs, as well as natural processes which indicate the agronomic efficiencies of systems,” he said.
Moving forward, Dr Baldock believes valuing the natural capital of soil, and quantifying soil value was important to prevent irreversible soil degradation.
“We need to know we're mining soil and be prepared to rebuild it. If not, we run into trouble,” he said.
While altering management practices may be associated with increased costs, Dr Baldock said cost offset should become possible if soil value is acknowledged.
"Lessening opportunity costs can be achieved by entering into markets that value maintenance of the soil resource base, in turn attracting higher returns," he said.