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

Abstract

                Field and laboratory experiments were conducted to develop equations for estimating phosphorus fertilizer requirements of maize on Alfisols of Northwestern Ethiopia. The field experiment on 20 sites was arranged in randomized complete block design with five fertilizer rates and four replications. At maturity, three central rows were harvested and yield and yield components data were collected. Laboratory analysis of soil samples was conducted following chemical soil analysis methods: Bray-1, Bray-2, Olsen, Mehlich-1, anion exchange resin and extraction with 0.01N CaCl₂. Parameters of the Quantity/Intensity relationships were also determined. Reliable methods were identified by fitting relative grain, relative dry biomass and P yields in a double log curvilinear regression model and those availability indices giving superior correlation were selected. Consequently, grain yield data and phosphorus availability indices were fitted into the Mitscherlich-Bray model to develop fertilizer recommendation equations.

                Results of the experiment revealed that among the methods giving quantity of available P, Bray-2 and Olsen methods gave the most reliable indices. Moreover, the intensity parameters in combination with the quantity parameters gave slightly superior correlation coefficient with yield parameters compared with their individual effects. The equations developed for estimating P fertilizer requirements of maize from soil analysis were: (a) log (100 - y) = 2 - 0.1468b - 0.007546x and (b) log (100 - y) = 2 - 0.1167b- 0.007546x for Olsen and Bray-2 methods, respectively, where y was desired relative grain yield (%); b was soil P availability index (mg kg^-1); and x was P fertilizer requirement (kg ha^-1). The two equations were statistically proven to provide equally reliable estimates of P fertilizer requirement of maize on Alfisols of Northwestern Ethiopia.