| Summary: | A study was carried out to determine the effect of P fertilizer and maturity class (days to maturity) on nodulation and N2 fixation by soybean in the Nigerian moist savanna (NMS). One early (TGx1485-1D), one medium (TGx536-02D), and two late (TGx923-2E and TGx1670-1F) soybean varieties were sown at four sites in NMS with P application rates of 0, 30 and 60 kg. ha-1. Nodulation increased with days to maturity and P rate. In late varieties, application of P substantially increased number of nodules.plant-1 by 84-134%, and nodule dry weight.plant-1 by 20-50%. Increasing P rate significantly increased specific nodulation (number of nodules per root dry weight) by 24-39% for all varieties but depressed nodule mass to whole plant mass ratio in medium and late varieties. Weight nodule-1 significantly reduced with increasing P rate and days to maturity class. Although nodule efficiency (g N fixed/nodule g weight) increased with P rate and days to maturity, only in medium (TGx536-02D) and late (TGx1670-1F) varieties was it significantly increased with P application. Over all varieties, P application significantly increased nodule efficiency by 6-10%. At harvest, N derived from the atmosphere was 61- 83 kg.ha-1 in early and medium varieties, and 78- 109 kg.ha-1 in late varieties. It increased significantly by 100-148% when P was applied. With an initial available soil P content < 7 mg.kg-1 at most sites, N2 fixation increased in soybean with application of P and days to maturity.
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