Field Evaluation of a Presidedress Soil Nitrate Test and Quicktest for Corn in Pennsylvania

Use of a presidedress soil NO3− test (PSNT) for corn (Zeu mays L.) could help to minimize uncertainties associated with managing N contributions from manure and legume crop residues. Understanding the performance and impact of this test under a wide range of conditions is necessary to target its use. A proposed quicktest method could improve the utilization of this test. This study was established to evaluate: (i) soil NO3− levels at sidedressing and the impact of the PSNT on fertilizer use under a range of field history classifications and (ii) the accuracy of the quicktest performed by persons with minimal laboratory experience. Quicktest kits were developed and distributed to extension agents and crop consultants. These cooperators offered free soil testing to farmers and collected field history information on each sample they analyzed (2725 samples). A subset (610 samples) was sent to a soil testing laboratory to compare quicktest and standard laboratory results. Quicktest accuracy was less than the laboratory method but adequate to ensure recommendations within 25 lb of the laboratory recommendation in 82% of the cases. Soil NO3− levels in manured fields were 3.3 ppm higher than nonmanured fields. Soil NO3− levels from fields following alfalfa (Medicago sativa L.) without a manure history were not different than fields with no legume and no manure, indicating the PSNT did not account for the increased N availability from alfalfa residues. Based on this research, the PSNT is effective to reduce unnecessary N applications to corn, particularly where high soil NO3− levels result from manure applications.