Effects of sources of phosphorus and biofertilizers on productivity and profitability of soybean (Glycine max)—wheat (Triticum aestivum) system

A field experiment was carried out during 2005–06 and 2006–07 at New Delhi to study the effect of different sources of phosphorus [single superphosphate (SP) and rock phosphate (RP)] and biofertilizers (phosphate-solubilizing bacteria and vesicular-arbuscular mycorrhiza) on productivity, nutrient uptake, P balance in the soil, phosphorus-use efficiency and economics of soybean [Glycine max (L.) Merr.]—wheat (Triticum aestivum L. emend. Fiori & Paol.) cropping system. Application of 50% recommended dose of P as SP + PSB + VAM recorded the highest yield during the first year in soybean (2.0 t/ha) and during both the years in wheat (4.4 and 4.6 t/ha in the first and second years respectively), but that of 50% RD Pas RP + PSB + VAM registered the highest grain yield (2.2 t/ha) during the second year in soybean. P uptake and utilization efficiencies increased on application of both PSB and VAM under both the sources of P. In addition, the available P status of the soil improved by addition of both bio-fertilizers through both the sources. RP performed very poorly, but when inoculated with both the bio-fertilizers, it was comparable to SP. Although the highest net returns per rupee invested was observed in 0.5 RP+PSB+VAM, but 0.5 SP+PSB+VAM provided highest net returns of 34.4 and 41.3 thousand rupees in first and second years respectively, it gave benefit: cost ratio (B:C) very close to that of the previous treatment in the soybean-wheat cropping system. Thus half the dose of P could be saved through inoculation with both P-solubilizing and mobilizing micro-organisms to obtain higher productivity and profitability.