Crop resilience patiently built on soil health
GroundCover™ Issue: 121 | Author: Janet Paterson
“Over a 10-year period I’ll back my low-input system any day, but if you want to pick out an individual season over the past decade then, sure, we could have made more money with a higher-input approach,” he says.
Stuart says on-farm trials over the past eight years show that inputs costs equate to one tonne of a two tonne per hectare crop but 2t of a 3t/ha crop.
“But I’m happy to take the 2t because it would cost me twice as much to chase the 3t, which could result in reduced profit, especially in low decile years.”
Stuart is convinced soil health is central to the resilience of farming systems and over the past decade has implemented technical and biological practices to foster soil biology and structure on his 5000-hectare property.
These include reduced tillage, a move towards controlled-traffic, deep-tillage, strategies to improve soil pH, the use of soil bio-stimulants and encouraging biology to boost soil organic carbon.
“We’ve seen gradual improvements to our soil organic carbon levels over time,” Stuart says.
“Organic carbon in the upper 10 centimetres of the soil profile has risen from 0.6 to 0.8 per cent to about 0.8 to 1 per cent, and some parts of the farm have even reached 1.5 per cent.”
Even larger percentage changes in organic carbon have been measured at the 10 to 20cm and 20 to 30cm depths.
In response, Stuart has reduced his fertiliser rates by as much as 50 to 90 per cent, depending on soil test results, and only rarely uses fungicides and insecticides.
“A healthier soil seems to make the plants more resilient to many pests and diseases and we’ve seen the response curve to nutrient application flatten quite considerably."
Stuart helped establish the Liebe Group soil biology trial site to investigate how soil biology influences soil carbon, water and nutrient efficiency, and crop productivity.
While the amount of added organic matter in the long-term trial (now in its 12th year) is not economical on a large scale, the trial is quantifying the relationships between soil organic carbon, soil biology, nutrient availability and crop yield.
“The results show more nitrogen, phosphorus and potassium are available when organic matter is introduced, and that there is more stored water in the top 10cm and no limit to the number of microbes, provided there is sufficient organic carbon,” Stuart says.