Influence of phosphorus or phosphorus-potassium fertilization on biomass and dinitrogen fixation of the stem-nodulating green-manure legumeSesbania rostratain different marginally productive wetland rice soils

摘要

The performance ofSesbania rostratavaries widely from site to site. This makes it difficult to predict the N yield and biomass of this plant in marginally productive soils, and to arouse the interest of farmers in green manure technology. Three consecutive pot experiments were conducted in a greenhouse at the International Rice Research Institute (IRRI) to evaluate growth, nodulation, N2fixation (C2H2reduction assay and15N dilution method), and N yield of 6-week-oldS. rostrataon 13 physicochemically different wetland rice soils of the Philippines and on three artificial substrates. The performance ofS. rostrataon the unfertilized controls was compared with two fertilizer treatments containing either P (100 mg P kg-1dry soil) or P+K (100 mg P kg-1and 200 mg K kg-1dry soil). In the control soils and substrates, the N yield ofS. rostratavaried between 20 and 470 mg N per pot, with the N rate from N2fixation ranging between 0 and 95. In three of the nutritionally poor soils even Mn toxicity symptoms apparently occurred withS. rostrata. P application alleviated these symptoms and increased the overall N yield considerably, mainly through increased biological N2fixation. An additional increase in N yield was obtained by the PK treatment. Multiple regression analysis between soil characteristics and the N yield ofS. rostratashowed that the original level of P (Olsen-extracted) and Mn in the soil accounted for 73 of the variance in biomass production byS. rostrataamong the unfertilized soils and substrates.