IMPACTS OF P AND N FERTILIZERS ON COMMON BEANS (PHASEOLUS-VULGARIS, L) GROWTH, NODULATION AND P AND N UPTAKE IN A POT EXPERIMENT

A pot experiment was conducted with a Nicaraguan volcanic soil to study the response of common bean (Phaseolus vulgaris L.) to applications of single superphosphate (P) and triple superphosphate (TSP), in amounts equivalent to 60 kg P2O5/ha and of urea (N), 20 kg N/ha. The P and N were placed singly or together on the surface (P(s), N(s), P(s)N(s)), or 6 cm below the surface (P6, N6, P6N6), or one was placed on the surface and the other 6 cm below it. In addition, TSP and N were placed together on the surface or 6 cm below it. All treatments, including the control, were triplicated. Shoot and root dry weights (DW) of the flowering plants and their P and N contents were recorded. P and N, applied singly or together, significantly (p less-than-or-equal-to 5 %) and consistently increased shoot DW, regardless of the application method used. Root DW was also increased significantly, but with less consistency. Dry matter production was highest in the P(s)N(s) treatment. Nodulation was three times higher in the P(s) treatment than in the control, and markedly higher than in the P6, P(s)N(s), P6N(s), P6N(s) and P6N6 treatments. By contrast, the N(s) and N6 treatments decreased nodulation 8 and 35 times respectively. Whereas fertilization did not significantly affect the tissue concentration of P and its transport indices, in most cases it increased tissue concentrations of N and N transport indices. Single superphosphate was more effective than triple superphosphate at increasing bean DW.