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손상목,마크엠알리 한국국제농업개발학회 1996 韓國國際農業開發學會誌 Vol.8 No.1
A dependable soil nitrate test can be a valuable tool for improving profit margins for farmers while reducing potential nitrate enrichment of surface and ground waters. The objective of this report is so review the principles and methods of two different soil nitrate tests, the Preplant Nitrate Test (PPNT) and the Pre-sidedness Soil Nitrate Test (PSNT) that have been recently developed and implemented in the U.S.A. for corn production. Corn is the largest user of N fertilizer in the U.S.A. and these tests were developed to improve the efficiency of N fertilizer use. The PPNT and PSNT tests determine the same chemical species, NO₃^(-)-N. However, the tests evaluate fundamentally different entities of the soil N cycle. The PSNT measures soil NO₃^(-)-N content in the surface 30cm of soil when the corn is 15 to 30 cm tall, whereas the PPNT typically samples 60-120 cm of soil in the early spring prior to corn planting. The PSNT is based on a timely monitoring of the in situ mineralization process and NO₃^(-)-N measured in the procedure is primarily an index of mineralization intensity. This procedure is particularly well suited for corn production systems that involves the use of manures or other organic sources. The PSNT has been shown to be more accurate than stalk nitrate tests in predicting corn response to N fertilizer. The PPNT is a capacity measure of the size of the available soil N before planting, which is mainly residual NO₃^(-)-N from previous fertilizer applications and/or organic matter mineralization the previous summer. This test is more widely applicable in regions where leaching is limited during the winter due to frozen soils and/or low rainfall. Use of soil nitrate tests has decreased the use of $quot;insurance N$quot; on thousands of hectares in the U.S.A. These soil nitrate tests are an effective way to adjust N fertilization rates for site-specific factors, but the tests do have certain limitations that must be considered when making recommendations. However, significant N fertilizer reductions (an average of 33-56 ㎏ N/㏊), in conjunction with no decrease in yields, have been documented when these tests are properly utilized. These reductions in unnecessary N fertilizer applications increase grower profitability and reduce the potential for nitrate contamination of ground and surface waters.
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