Subsoil phosphorus deficiencies identified in long-term research across the northern grain-growing region have spurred a new approach to fertiliser application for the Black family at Brookstead in south-east Queensland.
The Blacks – brothers Laurie and Jim, along with Jim’s son Peter – have invested in an Orthman (1tRIPr) strip tillage machine designed to cultivate the seedbed and place fertiliser down to a depth of 20 centimetres in the soil.
The aim is to address phosphorus deficiency in the subsoil, as opposed to the topsoil, which research has revealed is limiting yields by between 10 and 20 per cent on their 1618-hectare cotton and grain property.
GRDC-funded research, ongoing since 2006, has found that the constraint is reducing yields by up to 20 per cent on 25 farms, from Gunnedah, New South Wales, to Capella, Queensland, including the Blacks’ farm.
Leader of the collaborative research from the Queensland Alliance for Agriculture and Food Innovation Dr Mike Bell says deep fertiliser applications involving strategic tillage are the key to eliminating the phosphorus deficiency as a production constraint.
This is because phosphorus is an immobile nutrient that tends to remain in the top 10cm of the soil profile where it is placed using conventional practices for applying fertilisers. This contrasts with mobile nutrients, such as nitrogen and sulfur, that move with moisture into the deeper soil layers where plant roots are the most active in removing nutrients.
Dr Bell says potassium is another immobile nutrient likely to result in cropping losses in the future, particularly since the Blacks introduced cotton to their cropping program last year.
“Cotton has a higher potassium requirement than grain crops, so it’s like a canary in a coalmine that warns when reserves of the nutrient are close to running out.”
Peter Black says the potassium deficiency has already shown itself in the cotton crop they harvested in April. The new machine is expected to help redress the issue and avoid further productivity losses.
Although the Orthman 1tRIPr is set to “compromise” their zero-till practices, Peter says the minimal soil disturbance in its wake is expected to improve water infiltration and reduce compaction in the seedbed.
He says other benefits of the investment include the residual effects of deep-banding fertiliser over several years and the ability to apply a mix of nutrients deep and shallow in a single pass.
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