Wheat responses in semiarid Northern Ethiopia to N2 fixation by Pisum sativum treated with phosphorous fertilizers and inoculant

Nitrogen fixation (N-2) by leguminous crops is a relatively low-cost alternative to N fertilizers for smallholder farmers in Africa. Nitrogen fixation in pea (Pisum sativum L. cv. Markos) as affected by phosphorus (P) fertilization (0, 30 kg P ha(-1)) and inoculation (uninoculated and inoculated) in the semiarid conditions of Northern Ethiopia was studied using the 15N isotope dilution method and locally adapted barley (Hordeum vulgare L. cv. Bureguda) as reference crop, The effect of pea fixed nitrogen (N-2) on yield of the subsequent wheat crop (Triticum aestivum L.) was also assessed. Phosphorus and inoculation significantly influenced nodulation at the late flowering stage and also significantly increased P and N concentrations in shoots, and P concentration in roots, while P and N concentrations in nodules were not affected. Biomass, pods m(-2) and grain yield responded positively to P and inoculation, while seeds pod(-1) and seed weights were not significantly affected by these treatments. Phosphorus and inoculation enhanced the percentage of N derived from the atmosphere in the whole plant ranging from 53 to 70%, corresponding to the total amount of N-2 fixed varying from 55 to 141 kg N ha(-1). Soil N balance after pea ranged from -9.2 to 19.3 kg N ha(-1) relative to following barley, where barley extracted N on the average of 6.9 and 62.0 kg N ha(-1) derived from fertilizer and soil, respectively. Beneficial effects of pea fixed N-2 on yield of the following cereal crop were obtained, increasing the average grain and N yields of this crop by 1.06 Mg ha(-1) and 33 kg ha(-1), respectively, relative to the barley-wheat monocrop rotation. It can be concluded that pea can be grown as an alternative crop to fallow, benefiting farmers economically and increasing the soil fertility.