Effect of nitrogen on nodulation and yield of soya beans under two systems of production in Sudan

SummaryTwo experiments were run over a 3-year period in the central rainlands of Sudan under two systems of production, rainfed and irrigated, to assess the effects of system of production, inoculation and nitrogen fertilizers on plant and nodule development and grain yield of soya beans. Nodulated plants could fix more than 80 kg N/ha under irrigation whereas under rainfed conditions nodulation was neither effective nor efficient. Soya bean was responsive to nitrogen fertilizers under both systems of production giving significant increments in grain yields. Non-nodulating plants with added nitrogen fertilizers produced more total dry matter than nodulating plants during the vegetative phase until flowering time. At 2 weeks after flowering total dry-matter production for both types was equal and from then on to maturity nodulating plants outyielded non-nodulating ones in total dry-matter production. In 1979 and 1980 yield of irrigated nodulating soya-bean grain was 0·53 and 1·54 t/ha higher than rainfed yields whereas the difference in grain yields of the non-nodulating soya beans was 0·21 t/ha and zero during the same two seasons, respectively. There was a contrasting inverse relation between the number of nodules and dry weights under the two systems of production. Fewer and heavier nodules were produced under irrigation whereas under rainfed conditions nodulation was profuse and nodules were light. On the evidence available 1–4 g/m length of the granular form of soil implant inoculant (Nitragin), i.e. 16·6·66.4 kg/ha, is to be recommended for irrigated soya-bean production in Sudan.