Dairy effluent used on cropping farms is an excellent fertiliser, but its action is quite different to chemical fertilisers, farmers were told at the Foundation for Arable Research (FAR) field day at Chertsey in Mid Canterbury.
FAR has been managing research on the use of dairy shed effluent on arable farms since 2007.
FAR farm systems research manager Diana Mathers illustrated the potential by saying that when long term, high fertility dairy pasture was taken out of pasture and put into a maize crop, there were enough nutrients in the soil for two seasons of maize.
"What happens when dairy farmers run out of ground for effluent? Can we use it on cropping ground?"
Applying dairy effluent to low fertility cropping farms offered a win-win for both farming types. It would reduce the nutrient loading on dairy pastures, decreasing the risk of production issues such as grass staggers and nutrient losses to the environment, while providing macro and trace elements for crop production and reduce fertiliser costs.
She said the supply of effluent would increase, but there were a number of challenges in applying it to arable farms.
These included the volume that had to be transported and difficulty applying it, when and how to put it on, and how the nutrients were released to the crop.
Plant and Food Research scientist Craig Tregurtha said effluent came as liquid slurry or in a solid form.
While dairy effluent was applied in a liquid solution on dairy farms, the solid form was likely to be used on cropping farms because transportation was easier.
He said the release of nutrients from effluent was typically slower than from commercial fertilisers because many nutrients contained in effluent were present in organic forms that had to be released by soil processes before they were available to plants.
Understanding the rate of release was critical because that influenced the amount of extra fertiliser that might be required to reach crop yield targets.
Likely application times were spring or autumn.
Spring application worked in well with crop establishment, with the opportunity for more nutrients to be available for the crop, but it could delay planting in a wet season, or it could reduce crop emergence if it was applied too close to planting.
Autumn application usually coincided with fewer field applications, but could increase the risk of winter leaching.
To ensure the appropriate amount of effluent was applied, the nutrient composition had to be assessed as close to application as possible. A guide to the depth of effluent required to achieve application rates of 100 and 200kg/ N/ha has been produced.
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