Phosphorus Critical Level and Optimum Nitrogen Rate Determination on Bread Wheat for Sustainable Soil Fertility Management and Economical Production at Lume Area of Oromia Region, Ethiopia

Abstract

Nutrient management is indispensable for crop production and productivity increments on different soil types.  Therefore soil nutrient calibration study is pertinent to increase efficiency use of inorganic fertilizer like DAP and Urea. Based on this understanding site specific soil test based crop response studies for P on bread wheat was made from year 2010-2012 at Lume district. The objective of the experiment was to determine economically optimum N, Phosphorus critical (Pc) and Phosphorus requirement factor. The experimental treatments was  developed by factorial combination of four  levels of N (0, 46, 92 and 138 Kg ha-1) and P (0, 23, 46 and 92 Kg ha-1) chemical fertilizer that laid out in randomized complete block design with two replications and 40m² plot area for each. After 21 days, intensive composite soil samples were collected from each plot for the determination of available P in ppm.  Plant height, biomass and grain yield data were collected from 9m². The collected data were subjected to two way factorial analysis of variance (ANOVA) using the General Linear Model (GLM) procedures of SAS (SAS, 2001). Comparison of treatment means was performed using Fisher’s Least Significant Difference test at P < 0.05 probability level.  The application of N indicated that significant difference between plant height, biomass and grain yield of bread wheat. However the application of P was not significant on plant height, straw yield and grain yield at Lume whereas the interaction effect of N and P application on grain yield, plant height and straw yield correlation was significant.  Furthermore, the study was revealed that phosphorus critical (Pc) point for bread wheat was 19, and phosphorus requirement factor were also 4.92. In addition, a partial budget analysis made using the annual average bread wheat grains prices showed 46 kg N ha^-1 gave a marginal rate of return of 187%, which is above acceptable minimum rate of return.

Keywords: P- critical, P- requirement factor, partial budget, Acceptable minimum rate of return