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

Abstract

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 corn, and to evaluate the environmental and economic implications of adopting fertilizer N recommendations based on the PSNT in south coastal British Columbia, Canada, a region 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 history of manure application. Non-manured trials received no spring manure application whereas manured trials received a spring application typical of that 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 with less than 30 mg NO3-N kg−1 soil to 30 cm depth prior to sidedress received 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 higher 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 attributed 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 PSNT value (above which no yield response to sidedress N is expected) was predicted 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 test value of 32 mg NO3-N kg−1 soil was predicted using a linear-plateau regression of the estimated N rate which would maximize economic return (NMER) against PSNT test value. In addition, a model designed to minimize the risk of yield loss was developed with a critical PSNT test value of 30 mg NO3-N kg−1 soil. Average soil NO3 content at harvest was slightly higher for sidedress N rates based on the minimum risk model (70 kg N ha−1) than at NMER (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 about 90 kg N ha−1 yr−1.