Equations for Estimating Nitrogen Fertilizer Requirements from Soil Analysis for Maize (Zea Mays L.) Grown on Alfisols of Northwestern Ethiopia

Abstract

                With the prime objective of developing equations for estimating nitrogen fertilizer requirements of maize on Alfisols of Northwestern Ethiopia, field experiments were conducted at 20 sites. At each site, the treatments (five rates of N fertilizer) were arranged in a randomized complete block design with four replications. After maturity, yields and yield components data were collected. Soil parameters determined for indexing availability of nitrogen were organic matter content, total N, NH₄-N, NO₃-N, inorganic N (NH₄+NO₃-N), inorganic N production on aerobic incubation, and ammonium-N released on autoclaving with dilute calcium chloride. Reliable methods were identified by fitting relative grain, relative dry biomass and N yields in a double log curvilinear regression model and those availability indices giving superior correlation were selected. Consequently, nitrogen availability indices that were found most reliable and grain yield data were fitted into the Mitscherlich-Bray model.

                 Results of the experiment revealed that organic matter, total N, and NO₃-N were the most reliable N availability indices. The equations developed for estimating N fertilizer requirements of maize were: (a) log (100 - y) = 2 - 0.1103b - 0.006411x; (b) log (100 - y ) = 2 - 2.0566b - 0.006481x; and (c) log (100 - y) = 2 - 0.0220b - 0.006414x for organic matter, total N and NO₃-N, respectively, where y was relative yield goal, b was N availability index expressed as % for the former two indices and mg kg^-1 for the later, and x was the N fertilizer requirement. The three equations were statistically proven to give equally reliable estimates of N fertilizer requirement of maize on Alfisols of Northwestern Ethiopia. Nevertheless, in seasons where rainfall is heavy, high probability of nitrate leaching may make the later method less effective.