Response of Starter Nitrogen and Phosphorus Fertilizer Rates to Nodulation, Nitrogen Fixation, and Net Nitrogen Balance on Groundnut (Arachis hypogaea L.) in the Semi-arid Tigray Region of Ethiopia

For small-scale farmers in developing countries, biological nitrogen fixation through legumes is an affordable method of reducing reliance on nitrogen fertilizer. The study aimed to look at how groundnut nodulation, biological nitrogen fixation, atmospheric nitrogen, and the net nitrogen balance were affected by starter nitrogen and phosphorus fertilizer dosages. The three times replicated treatments of three nitrogen levels (0, 15 and 30 kg N ha-1) and four phosphorus levels (0, 23, 46 and 69 kg P2O5 ha-1) were arranged in a factorial combination using a randomized complete block design (RCBD). The results of the analysis demonstrated that, in comparison to plots without nitrogen fertilizer, the number of nodules per plant was significantly increased by the single application of nitrogen alone at a dose of 15 kg ha-1. Compared to 69 kg P2O5 ha-1, biological nitrogen fixation rose by 88.41% at 46 kg P2O5 ha-1; nonetheless, it was significantly similar to zero and 23 kg P2O5 ha-1. The nitrogen derived from the atmosphere (50.9%) was significantly higher in the control treatments. The interactive application of 15 kg of nitrogen ha-1 and zero phosphorus resulted in a significantly greater net nitrogen balance (-4 kg ha-1), whereas the co-application of 30 kg ha-1 of nitrogen and zero phosphorus resulted in the lowest measurement of net nitrogen balance. Therefore, large nitrogen fertilizer application rates are not necessary to promote BNF in groundnuts.