PO 21. Recognize factors that influence the results of the pre-sidedress nitrogen test.

  1. Rotation
  2. Manure type and history
  3. Timing of sampling relative to weather patterns
  4. Depth of sampling
  5. Field variability
  6. Sample processing

Most universities in the Northeast do not use a soil nitrogen test, because nitrate is very mobile and soil nitrate tests do not correlate well with actual N supply from the soil.  Rather, nitrogen requirements are based on yield potential, N supply from the soil, and other organic N sources (composts, animal and green manures) and N uptake efficiency.  The exception to this is the Pre Sidedress Nitrogen Test (PSNT).

The PSNT is an in-season nitrate test for corn that predicts organic N to be mineralized.  It is designed to:

  1. Estimate the soil's nitrate supplying potential
  2. Decide if that is enough N to meet crop needs

Vermont determines application rates based on PSNT results.  Other states (e.g. NY) use the PSNT as an indicator only.  By avoiding the unnecessary application of N, producers save money and reduce the risk of nitrate leaching.

Testing is done at sidedressing time, just before the period of major N demand.  It is most useful for fields with a history of manure and/or sod incorporation.  However, it cannot be used if broadcast or pre-plant N has been applied (over 40 lb N/acre), as "leftover" nitrate will be detected and will overestimate soil supply.

 

 


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