Monday, 7 February 2022

New tool to measure soil mineralisable nitrogen


The Potential Mineralisable Nitrogen (PMN) test and N mineralisation calculator are new tools to help farmers to reduce nitrogen (N) losses, save on fertiliser costs and maintain productivity.

There is increasing pressure for farmers to reduce their N inputs and outputs; and matching your soil N supply and N fertiliser with your crop N demand is more important than ever.

Your soil supplies N through two main forms: mineral N (nitrate and ammonium) and mineralisable N (N released from organic matter throughout the season). We’re already very good at measuring mineral N and we use that knowledge when developing N fertiliser recommendations. However, the soil can also supply significant amounts (40–300kgN/ha) of mineralisable N.

Until recently, our ability to accurately measure and predict how much mineralisable N the soil will supply has been limited. The old Anaerobic Mineralisable Nitrogen (AMN) test was less accurate and the results were hard to interpret. For these reasons, Ravensdown partnered with Plant and Food Research (PFR) to develop a new method to measure mineralisable N and to interpret these results into the real world.

PFR has done some great work, identifying the Potentially Mineralisable Nitrogen (PMN) test as a faster and more accurate method of measuring N mineralisation. This test is a significant improvement on the old AMN test.

PFR has also conducted a series of in-field mineralisation trials around the country, allowing the development of the N mineralisation calculator.

The N mineralisation calculator allows the PMN value to be more accurately interpreted into the real world. The N mineralisation calculator uses the PMN value and inputs ‘reality’ (local climate data and soil order) to provide a farm-specific month by month release of mineralisable N.

The calculator is available for the main soil orders in the cropping areas: Canterbury, Tasman/Marlborough, Manawatū-Whanganui, Hawke’s Bay, Gisborne, Waikato and Auckland.

Outside of the calculator-available areas PFR has also developed general guidelines that allow interpretation of the PMN test. Your local agri manager can provide expert advice and guidance on the PMN test and N mineralisable calculator.

Through having a more accurate soil mineralisable N test and better interpretation of the results, we can more accurately match soil N supply + fertiliser N with crop N demand. This is improving N fertiliser recommendations, ensuring optimal:

  • Productivity – there is adequate N to meet your crop demand
  • Profitability – you get the most bang for your fertiliser buck
  • Environmental outcomes – avoid over applying N, reducing N losses.

If you’re growing a crop and you want to improve your N fertiliser recommendations (improving profitability and environmental outcomes, while maintaining productivity) talk to your local agri manager about the PMN test and the N mineralisation calculator today.