During the 2022/23 "Summer" in the North Island, Leftfield Innovation conducted research for Wairarapa, Waikato and Ohakune regions to investigate the potential of using spring-sown wheat crops to 'scavenge' nitrogen as part of different farm systems.
Our field trials were severely tested by extreme rainfall over this period, with the Wairarapa experiencing 180mm and Ohakune 390mm above their long-term average rainfall during the growing period. The rainfall did impact the trials with reduced crop establishment, yield and grain quality, but despite this, the trials showed measurable success in achieving N uptake at targeted soil depths and allowed conservative financial modelling to be undertaken.
The wheat crops did not add to the amount of nitrogen leaching, and demonstrated an uptake of N at depths below that of pasture zone root systems, reducing the risk of N leaching into waterways, while also allowing for N availability for pasture or crops at shallow depths as part of a farm system. At the harvest of the field trials, the total nitrogen was highest in the top 30cm of the soil.
Using wheat as part of a dairy farm system also showed significant benefits in reduction of greenhouse-gas emissions (though insignificant in the Ohakune pastoral-vegetable farm system trial).
Financially, there was a negligible cost for the Waikato and Wairarapa dairy farms ($232/ha and $166/ha respectively), whereas there was a higher return for the Ohakune pastoral / vegetable operation ($268/ha).
While the trials were conducted under adverse growing conditions, they have demonstrated that wheat can be introduced into a farm system at negligible total cost to reduce nitrogen leaching and greenhouse gas emission. Given the opportunity this presents for non-traditional wheat regions in the North Island, with better growing conditions in a more typical season this offers an exciting prospect for improving overall farm and environmental performance, while increasing New Zealand's grain supply and food security.
LFI's detailed report has been submitted to Our Land and Water. LFI also thanks the farmers involved, The Agribusiness Group and Champion Flourmills for their assistance with the project.