Improving Nitrogen Use Efficiency
Mid-row banding to boost irrigated cropping productivity
Capacity to Deliver - LP021-002
The issue
Irrigated winter crops in the Western Murray Valley require often require more than 150 kgN.ha-1 of fertiliser nitrogen to achieve high yield targets. Generally, not all of this fertiliser can be supplied at seeding, as it can cause seedling damage, excessive growth and consequently lower yields. Hence, most growers topdress high rates of nitrogen during the growing season to supply nitrogen in the high demand period. However, topdressed nitrogen can be inefficient, with losses up to 40% from from volatilization or up to 95% from denitrification in waterlogged soils.
The solution
Mid-row banding (MRB) places high rates of nitrogen between plant rows at seeding. Placing the fertiliser below the soil surface negates volatilisation losses and the high concentration of fertiliser is toxic to nitrification microbes; slowing the conversion of urea to nitrate, which is susceptible to denitrification. In addition, the increased distance from the plant row to the band delays crop access to the nitrogen and reduces the risk of seedling damage and excessive growth. To test the feasibility of this method we conducted two trials in 2017-18 and measured nitrogen concentration before and after an induced waterlogging event (10 days of inundation) and yield in comparison with topdressing at stem elongation.
The impact
Our trials validated that the majority of the mid-row banded nitrogen withstood waterlogging conditions, even after 10 days of inundation. We also observed that mid-row banding 120-135kg N/ha at sowing increased grain yield by 1.25-1.8 t/ha, compared with the control. Topdressing resulted in a similar yield response. This resulted in an Apparent Nitrogen Recovery Efficiency (ANRE) of 19-31% for MRB compared with a topdressing efficiency of 28-30%.
Learnings
Mid-row banding resulted in a similar nitrogen use efficiency to topdressed nitrogen in our experiments and appears to be a valid method for irrigated cropping in the Western Murray Valley. It is likely to have an ideal fit in soils prone to waterlogging where topdressing can be inefficient. Considerations for adoption include a lower operating speed required at sowing to apply the high rates of fertiliser, a lack of available seeders capable of mid-row banding without modification and an inability to alter nitrogen inputs in response to seasonal conditions.
Key facts
- Placing fertiliser into a concentrated mid-row band at sowing can reduce losses via volatilisation and denitrification.
- The majority of the mid-row banded nitrogen was preserved during waterlogging.
- Mid-row banded nitrogen achieved similar grain yield and nitrogen efficiency as topdressing.