Dig deeper if you really want to know about Nitrogen

Rain encourages soil microbes to mineralise soil organic nitrogen (N) into plant available mineral forms. Some mineral N can leach, moving down in the soil profile with subsequent rain.

Deep N soil testing can better estimate the amount of N available in the soil for the crop to make use of, compared to a 0 – 10cm soil test. A more accurate view of nitrogen available in the soil improves the capacity to match nitrogen fertiliser rates to crop demand.

Considerations for deep N soil testing

  • Nitrogen is more likely to be found deeper in the soil following significant rain events.

  • Soil sample close to or just after sowing.

  • Crop root depth is a good guide for how deep it’s worth sampling.

  • Break soil samples into increments e.g., 0-10, 10-60 or 10-90cm.

  • Ensure correct sampling technique to avoid any fertilizer bands if sampling after sowing.

 

Charlie Walker is the Head of Agronomy at Incitec Pivot.

 

Further information

eXtensionAUS An N-rich-strip shows if your crop needs a boost this season,

GRDC Get the right advice on soil test results, Dig deep for nitrogen picture

Back Paddock Soil testing for deep nitrogen – use and misuse

Acknowledgements

Charlie Walker, Incitec Pivot, Chris Dowling, Back Paddock Co, Therese McBeath, CSIRO

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