Fertilizer nitrogen recommendations for silage corn in high-fertility environment based on pre-sidedress soil nitrate test

The purpose of this study was to measure corn response to nitrogen (N), to evaluate the feasibility of using the pre-sidedress soil nitrate test (PSNT ) for making fertilizer N recommendations for silage com, and to evaluate t he environmental and economic implications of adopting fertilizer N recomme ndations based on the PSNT in south coastal British Columbia, Canada, a reg ion of high soil N fertility. Eighty-seven trials were conducted from 1994- 1996 with corn or forage grass as a preceding crop on fields having a histo ry of manure application. Non-manured trials received no spring manure appl ication whereas manured trials received a spring application typical of tha t farm field. In 1994, treatments included sidedress N rates of 0, 30, 60, 90, 120. and 150 kg N ha(-1) replicated twice. In 1995 and 1996, trials wit h less than 30mg NO3-N kg(-1) soil to 30cm depth prior to sidedress receive d the same treatments as in 1994, whereas trials with concentrations above this value received two treatments, 0 and 150 kg N ha(-1), replicated four times. Trials received less than 50 kg N ha(-1) at planting. Yield response to sidedress N was limited, with 71, 87, and 55% of trials with 90% or hig her relative yield (yield at 0 kg N ha(-1) divided by yield at 150 kg N ha( -1)) in 1994 1995 and 1996, respectively. The limited yield response was at tributed to high soil N mineralization, which averaged 166 and 146 kg N ha( -1) for non-manured trials in 1995 and 1996, respectively. The critical PSN T value (above which no yield response to sidedress N is expected) was pred icted to be 19 and 23 mg NO3-N kg(-1) soil using the Cate-Nelson procedure and a linear-plateau regression procedure, respectively. A critical PSNT te st value of 32 mg NO3-N kg(-1) soil was predicted using a linear-plateau re gression of the estimated N rate which would maximize economic return (N-ME R) against PSNT test value. In addition, a model designed to minimize the r isk of yield loss was developed with a critical PSNT test value of 30mg NO3 -N kg(-1) soil. Average soil N03 content at harvest was slightly higher for sidedress N rates based on the minimum risk model (70 kg N ha(-1)) than at N-MER (64 kg N ha(-1)). Based on a survey of farm fields, the potential to reduce fertilizer N application in south coastal BC was estimated to be ab out 90 kg N ha(-1) yr(-1).