Prediction of Nitrogen Responses of Corn by Soil Nitrogen Mineralization Indicators

Abstract

Soil nitrogen mineralization potential (N_min) has to be spatially quantified to enable farmers to vary N fertilizer rates, optimize crop yields, and minimize N transfer from soils to the environment. The study objectives were to assess the spatial variability in soil N_min potential based on clay and organic matter (OM) contents and the impact of grouping soils using these criteria on corn grain (Zea mays L.) yield, N uptake response curves to N fertilizer, and soil residual N. Four indicators were used: OM content and three equations involving OM and clay content. The study was conducted on a 15-ha field near Montreal, Quebec, Canada. In the spring 2000, soil samples (n = 150) were collected on a 30- x 30-m grid and six rates of N fertilizer (0 to 250 kg N ha^-1) were applied. Kriged maps of particle size showed areas of clay, clay loam, and fine sandy loam soils. The N_min indicators were spatially structured but soil nitrate (NO3^–) was not. The N fertilizer rate to reach maximum grain yield (N_max), as estimated by a quadratic model, varied among textural classes and N_min indicators, and ranged from 159 to 250 kg N ha^-1. The proportion of variability (R²) and the standard error of the estimate (SE) varied among textural groups and N_min indicators. The R² ranged from 0.53 to 0.91 and the SE from 0.13 to 1.62. Corn grain N uptake was significantly affected by N fertilizer and the pattern of response differed with soil texture. For the 50 kg N ha^-1 rate, the apparent N_min potential (ANM) was significantly larger in the clay loam (122 kg ha^-1) than in the fine sandy loam (80 kg ha^-1) or clay (64 kg ha^-1) soils. The fall soil residual N was not affected by N fertlizer inputs. Textural classes can be used to predict N_max. The N_min indicators may also assist the variable rate N fertilizer inputs for corn production.