| Summary: | Influence of starter nitrogen (N) and phosphorus (P) applications on mycorrhizal colonization and nodulation of soybean (Glycine max (L.) Merill) was investigated at two sites of humid forest margins of Cameroon. Four soybean varieties, TGX 1838-5E (var1), TGX 1879-7E (var2), TGX 1828-4E (var5) and TGX 1805-13F (var6), were grown for four months in fields from different fallow ages, in a factorial combination of 30 kg N.ha-1 and 30 kg P.ha-1, with five replicates, in a randomized complete block design. Soil acidity varied strongly with site, being 5.9 and 4.5, at Nkometou and Mengomo, respectively. Fractional mycorrhizal colonization (FMC) was not affected by soil pH. FMC significantly varied among fields between 20% and 40%, was significantly reduced by P fertilization while effect of N amendment was contrasted. Nodulation was strongly influenced by soil pH: high nodulation in Nkometou but extremely low in Mengomo. In Nkometou, early maturing soybean varieties (var2 and var5) yielded higher nodule number and mass than late-maturing ones (var1 and var6). Var2 exported the highest biological N and var6 the lowest. Plant P uptake only differed among fields. Nodulation and grain yield did not respond to the fertilizer rates. Negative, highly significant correlations were established between nodule number and mass (r= - 0.726; p< 0.0001; n= 68), between nodule number and FMC (r= - 0.682; p< 0.0001; n= 68). However, a positive and highly significant correlation was obtained between FMC and nodule mass (r= 0.976; p< 0.0001; n= 68). Such biological reactions to fertilization could be attributed to effective indigenous arbuscular mycorrhizal fungi and bradyrhizobia.
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