Effects of Fertilizer application on N and P uptake, recovery and use efficiency of bread wheat grown on two soil types in central Ethiopia.

Nutrient deficiency is a major constraint wheat (Triticum spp.) production in Ethiopia. To improve nutrient management strategies for wheat production, information is required on the effects of applied fertilizer on crop N and P uptake, recovery and use efficiency, and on the level of post-harvest soil mineral residues in the major soil types. Therefore, a recently released, high-yielding bread wheat (T.aestivum) cultivar "Kubsa" was grown in a multi-location on-farm N by P fertilizer response trial during the 1995 and 1996 cropping seasons in two soil zones of the central highland of Ethiopia: a poorly-drained Vertisol zone, using an improved drainage technique, and a highly-weathered reddish-brown Nitisol zone. The results from the combined analyses for each zone indicated that wheat N and P content, uptake, recovery and use efficiency were significantly affected by fertilizer application. Application of N fertilizer increased g rain and straw N content in both soil zones, increased grain and straw P content in the Vertisol zone, but decreased grain P content in the Nitisol zone. Application of P fertilizer increased grain P content in both zones, increased straw P content in the Vertisol zone, and had no effect on either grain or straw N content in either zone. All whet N and P uptake parameters exhibited a significant response to both applied N and P in each soil zone. The physiological efficiency of N and P showed relatively little response to the r ate of applied N and P, while the apparent recovery (AR) and agronomic efficiency (AE) of both nutrients exhibited a consistent response to N and P application rates in each soil zone: higher application rates of each nutrient significantly decreased the AR and AE of that nutrient, while increasing the AR and AE of the other nutrient. The enhancement of the AR and AE of P by applied N and vice versa emphasizes the importance of balanced crop nutrition: by ensuring that wheat crops are adequately supplied with both N and P, Ethiopian producers will optimize the biological and, hence, the economic efficiency of applied fertilizer. In this study, applied N and P fertilizers had few discernible effects on the post-harvest soil chemistry parameters studied in each zone.