No abstract

Nitrogen use efficiency (NUE) of tef, a major staple crop in Ethiopia, is very low, either caused by untimely use of nitrogen (N) fertilizers or lack of other essential nutrients like sulphur (S). The average grain yield of this crop is low, averaging < 0.8 Mg ha -1 in farmer's fields of the semiarid conditions. Therefore, the present study was conducted to see the effect of the timing of combined N and S fertilization on the yield, yield components, and N and S concentration in the plant parts of the crop. A factorial combination of three rates of N (0, 70, and 105 kg ha -1 ) with four rates of S (0, 16, 32, and 48 kg ha -1 ) was applied in randomized complete blocks in three replications. The experiment was carried out in the 2004 and 2005 cropping seasons in the Cambisols of the semi-arid area of Ethiopia. The crop responded significantly (P < 0.05) to both split (one-third at planting and two-thirds at late tillering) and whole (all at planting) N and S applications and years. Combined N and S fertilization increased the dry matter (DM) and grain yields on average by 1.7 and

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 15 N 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 barleywheat 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.