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Apr 30, 2022Keywords:
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Main Article Content
Influence of Nitrogen and Phosphorus Fertilizers on Nitrogen Fixation, Nitrobacteria and Yield of Soybean under Irrigation in Sudan Savanna of Nigeria
Abstract
Irrigation farming has boosted grain legume production especially in non-salt affected areas. A field study was undertaken with Soybean (TGX 1904-6F) at the Irrigation Research Farm of Institute for Agricultural Research (IAR), Kadawa, Kano in the Sudan savanna to assess the effect of nitrogen and phosphorus fertilization on biological nitrogen fixation (BNF), nitrifying bacteria population and grain yield. A non-salt affected soil was cultivated. The treatments consist of two levels of nitrogen (0 and 20 kg N ha-1) applied as urea and four levels of phosphorus fertilizers (0, 6.6, 13.2, 26.4 kg P ha-1) applied as single super phosphate, while maize (Zea mays) variety SAMMAZ 14 was used as reference crop for estimating biological nitrogen fixation. The treatments were laid out in a randomized complete block design with levels of N and P in a factorial combination and replicated three times. Application of N fertilizer at 6WAP and 8WAP increased N2 fixed by 21.49% and 12.68% respectively, while % Ndfa was 6.53% and 8.40% respectively. Phosphorus at the rate of 26.4 kg P ha-1 at 8WAP increased N2 fixed (151.17 kg N ha-1) and % Ndfa (75.49%) by 21.84% and 7.47% respectively. Nitrogen fertilizer decreased grain yield by 15%, while Phosphorus at 26.4kg P ha-1 increased grain yield by 18.27% over the control. Nitrogen fertilizer increased Nitrosomonas spp by 43.64% and Nitrobacter spp by 174%, indicating the dominance of nitrite oxidizing bacteria (Nitrobacter spp), while phosphorus (26.4 kg P h-1) increased both populations by 8.51% and 51% respectively, indicating the importance of sufficient P in nitrification process. In conclusion, from the present study it shows that increasing levels of nitrogen negatively affected nitrogen fixation, grain yield of soybean, but enhanced nitrobacteria activity; suggesting that the soil N was adequate for the native strains of rhizobia to initiate nodule production on plant roots growing where no N was applied. Whereas, phosphorus at the rate of 26.4 kg P ha-1 at 8WAP enhanced N2 fixation, grain yield and nitrifying activity; indicating the importance of phosphorus in soybean growth and development.
