EFFECTS OF NITROGEN AND PHOSPHORUS FERTILIZER RATES ON WHEAT (Tiriticum aestivum L.) YIELD AND SELECTED SOIL PROPERTIES IN KERSA DISTRICT, EAST HARARGHE ZONE, ETHIOPIA

Abstract

Low soil fertility resulting from land degradation, crop residue removal, low soil OM content and poor management practices is major constraint to crop production. Nitrogen (N) and phosphorus (P) are the most deficient nutrients of Ethiopia soil that limit the yield potential of cereal crops, particularly wheat. Determining the optimum rates of fertilizers, especially that of N and P, is the key to maximize the economic yield and maintain soil health in a sustainable way. The present study was conducted during the 2024 cropping season in Kersa district of east Hararghe zone, with the main objective to evaluate effects of nitrogen and phosphorus fertilizer rates on wheat yield, yield components and selected soil physical and chemical properties and thereby identifying the economically feasible nitrogen and phosphorus fertilizer rates. The experiment encompassed factorial treatment combinations of four levels of N (urea) and P(TSP) fertilizers plus control (0:0) laid out in randomized complete block design (RCBD). Composite and core soil samples were collected from the experimental site and experimental plots, and analyzed following standard laboratory procedures. Genstat 18th edition software version was used for the data analysis. Mean comparisons were done by Duncan’s multiple range test at the 5% level of significance. Results indicated that total nitrogen was in the low range; whereas available P was very low in the study site. The pH of the soil decreased as the level of nitrogen increased; which may be attributed to the acidifying ability of nitrogen fertilizer. Phenological and growth parameters like days to heading, days to maturity, plant height and spike length were highly significantly (p<0.001) influenced by the main effects of N and P. Number of productive tillers, number of seed per spike, thousand seed weight, above ground biomass and grain yield were significantly (p<0.05) affected by the interaction effects of N and P. The highest gran yield (4563 kg/ha) was obtained from the interaction of N and P at the rates of 184 kg/ha N and 92 kg/ha of P2O5. Agronomic efficiencies of applied fertilizers increased as the N and P rates became more balanced with the highest agronomic efficiency (5.51) was observed at the combination of 46 kg/ha N and 46 kg/ha P2O5. The economic analysis revealed that, the highest marginal rate of return (1595%) was obtained from the application of 184 kg/ha N and 46 kg/ha P2O5, followed by 92 kg/ha N and 92 kg/ha P2O5 (1129.79%) and 46 kg/ha N and 46 kg/ha P2O5 (980 %).It could be concluded that, low and middle income farmers may benefit from the 46:46 and 92:92 N and P combinations respectively; while high income farmers or investors could opt for184:46 combinations. However further research over several seasons and across wider production site is essential for more sound recommendations.