CORN YIELD, NITROGEN UPTAKE AND NITROGEN USE EFFICIENCY AS INFLUENCEDBY NITROGEN-FERTILIZATION

Improving efficient use of applied nutrients in crop production is a d esirable agronomic, economic, and environmental goal. Field experiment s with com (Zea mays L.) were carried out at two sites with contrastin g soil textures in southwestern Quebec from 1988 to 1990. Objectives w ere 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 fa vourable heat units and rainfall, yields of grain com were quadratic f unctions 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 ap plication. 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 o n the Ste. Rosalie site in 1990, and 286 and 179 kg N ha-1 for 1989 an d 1990, respectively, on the Chicot site. A normal fertilizer rate (17 0-44-141 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. Gr ain 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.