Symbiotic N2-Fixation Estimated by the15N Tracer Technique and Growth ofPueraria phaseoloides(Roxb.) Benth. Inoculated withBradyrhizobiumStrain in Field Conditions

Abstract

This field experiment was established in Eastern Cameroon to examine the effect of selected rhizobial inoculation on N2-fixation and growth ofPueraria phaseoloides. Treatments consisted of noninoculated andBradyrhizobium yuanmingenseS3-4-inoculatedPuerariawith three replications each.Ipomoea batatasas a non-N2-fixing reference was interspersed in eachPuerariaplot. All the twelve plots received 2 gN/m2of15N ammonium sulfate 10% atom excess. At harvest, dry matter yields and the nitrogen derived from atmospheric N2-fixation (%Ndfa) of inoculatedPuerariawere significantly (P<0.05) higher (81% and 10.83%, resp.) than those of noninoculatedPueraria. The inoculation enhanced nodule dry weight 2.44-fold. Consequently, the harvested N significantly (P<0.05) increased by 83% in inoculatedPueraria, resulting from the increase in N2-fixation and soil N uptake. A loss of 55 to 60% of the N fertilizer was reported, and 36 to 40% of it was immobilized in soil. Here, we demonstrated that both N2-fixing potential ofP. phaseoloidesand soil N uptake are improved through field inoculations using efficient bradyrhizobial species. In practice, the inoculation contributes to maximize N input in soils by the cover crop’s biomass and represent a good strategy to improve soil fertility for subsequent cultivation.