Variable Rate Nitrogen On Wheat.

An algorithm for the use of the Greenseeker to make variable rate nitrogen applications on wheat has been developed and tested for Kentucky.  Nitrogen was applied at different rates at the break of winter dormancy in February (Feekes 3).  At Feekes 5 and 6 Normalized Difference Vegetative Index (NDVI) readings were made on all treatments.  This resulted in a large NDVI range.  Within each of the Feekes 3 N treatments, different rates of N were applied at Feekes 6 to determine the rate of N needed for maximum yields with each Feekes 3 N treatment.  This resulted in an algorithm that gave the N rates needed at Feekes 6 or any NDVI reading.  To reduce problems associated with different varieties, weather, etc., a differential NDVI was used in the algorithm which compared any reading to 150 lb/ac N applied at Feekes 3.  The algorithm was developed over a 5 year period on two different soil types.

The algorithm was field tested on three different fields over a two year period.  Each field test was replicated at least four times.  The standard farmer flat rate application as recommended by professional wheat consultants was compared with the variable rate nitrogen application as determined by the algorithm.  In each case, the yields were higher (4 bu/ac average) and the economic returns were greater ($20/ac average) with the use of variable rate nitrogen treatment.  The variable rate nitrogen treatment resulted in a lower field average nitrogen rate on two fields and was higher on one field.