CORN YIELD, NITROGEN UPTAKE AND NITROGEN USE EFFICIENCY AS INFLUENCED BY NITROGEN-FERTILIZATION

Improving efficient use of applied nutrients in crop production is a desirable agronomic, economic, and environmental goal. Field experiments with com (Zea mays L.) were carried out at two sites with contrasting soil textures in southwestern Quebec from 1988 to 1990. Objectives were to establish an optimum N fertilization rate for grain production, and to study fertilizer N use efficiency on a Chicot sandy clay loam (Grey Brown Luvisol) and a Ste. Rosalie clay (Humic Gleysol). Under favourable heat units and rainfall, yields of grain com were quadratic functions of fertilizer N rates on both soils. Maximum grain yields of com were calculated to require from 300 to 350 kg N ha-1 fertilizer application. However, large amounts of N fertilizer at both 285 kg ha-1 and 400 kg ha-1 were not recovered by the crop. Optimum economic grain yields at a price ratio of 10:1 N:grain were found at 273 kg N ha-1 on the Ste. Rosalie site in 1990, and 286 and 179 kg N ha-1 for 1989 and 1990, respectively, on the Chicot site. A normal fertilizer rate (170-44-141 kg N-P-K ha-1) and a high fertilizer rate (400-132-332 kg N-P-K ha-1) were used in 1989 and 1990 for N-15 microplot experiments. Grain and stover fertilizer N recovery (FNR) varied with N rate and year from 9 to 58%. Favourable climatic conditions substantially increased crop yield, and thus crop FNR. Residual FNR the second year was less than 5% of the initial applied N.