Using the presidedress soil nitrate test and organic nitrogen crediting to improve corn nitrogen recommendations
2002
Andraski, T.W. | Bundy, L.G.
The PSNT and N crediting for organic N inputs can improve the accuracy of corn (Zea mays L.) N recommendations, but are often not used due to producer concerns about their reliability. This study compared the use of these techniques for identifying optimum N rates and quantifying economic returns in 101 N response field experiments with corn conducted during 1989-1999. The accuracy of PSNT recommendations was highest for sites with average or above average May-June air temperatures and high soil yield potential. The frequency of excess N recommendations from the PSNT increased from 16 to 59% when May-June temperatures were >0.56 degrees C below average likely due to slower organic N mineralization. Use of N recommendations based on the PSNT or book value N credits (BVNC) lowered N rates by 90 to 102 kg ha(-1) in systems with recent manure or legume N inputs and increased average economic returns for all cropping systems by $19 ha(-1) compared with unadjusted N recommendations (i.e., economic gain). Economic gains using PSNT- or BVNC-based recommendations were generally highest in the first year following organic N inputs with an average gain of $34 ha(-1) for both methods. Conversely, economic gains were higher using the PSNT ($40 ha(-1)) than the BVNC ($2 ha(-1)) 1 to 3 yr after the organic N additions on high yield potential soils where May-June air temperatures were average or above. Results from this work confirm that adjusting N application rates for corn using the PSNT or BVNC is more profitable than not making these adjustments.
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