RELATIONSHIP BETWEEN LATE SPRING SOIL NITRATE CONCENTRATIONS AND CORN YIELDS IN NEW-YORK

Proper N management is important to optimizing profit and minimizing N loss. The efficiency of N use may be improved in humid regions with a reliable soil test to guide fertilizer N recommendations. Recently, a presidedress nitrate soil test (PSNT) has shown promise as a means of quantifying the size of the potential mineralizable organic N pool in soil. This study was conducted to determine if the PSNT could be used for corn (Zea mays L.) production to identify N responsive and nonresponsive sites, predict the economic optimum fertilizer N rate, and improve the current fertilizer N recommendation procedure. The PSNT gave a useful and defined critical level of 21 ppm nitrate-N, delineating N responsive from nonresponsive sites. The success rate for making the correct decision about N responsiveness was 84%, indicating a good relationship between the PSNT and the ability of the soil to supply N. The PSNT was less precise in determining the economic optimum fertilizer N requirement (R2 = 0.50) for sites below the critical level. This probably was due to the inability of the PSNT to quantify organic N mineralization. The standard N recommendation, based on estimates of N availability from organic sources, was a slightly better predictor of the fertilizer N requirement (R2 = 0.67) than the PSNT. There is a need to further improve the methodology used for formulating fertilizer N recommendations.