Symbiotic N₂-Fixation Estimated by the ¹⁵N Tracer Technique and Growth of Pueraria phaseoloides (Roxb.) Benth. Inoculated with Bradyrhizobium Strain in Field Conditions

Figure 1

Experimental design. IP = inoculated Pueraria, NIP = noninoculated Pueraria, and IpB = Ipomoea batatas. IP and NIP treatments were each replicated 3 times, giving a total of 6 Pueraria plots. Ipomoea plots (six) were interspersed in each Pueraria plot as non-N₂-fixing references. Plot’s size was 4 m². In each plot, plant spacing was 50 cm corresponding to 9 hills per 1.5 m 1.5 m for both Pueraria and Ipomoea. For Pueraria, seeds were sown but thinned to 3 plants per hill after the seedlings were well established while, for Ipomoea, uniform seedlings of 10 cm length were transplanted two weeks after the sowing of Pueraria seeds. Pueraria inoculation was performed using the effective strain B. yuanmingense S3-4 (2.094 10⁸ cells per hill) three weeks after seed’s sowing. All plots received 2 gN/m² of ¹⁵N labelled ammonium sulfate 10% atom excess applied at 1 and a half months after Pueraria seeds were sown. Plots were regularly weeded throughout the rain-fed prone experiment that lasted 4 months.