Phosphorus use efficiency of Indian mustard (Brassica juncea) under semi arid conditions in relation to phosphorus solubilizing and mobilizing microorganisms and P fertilization

Efficient use of soil and applied phosphorus is key to sustainable production of Indian mustard (Brassica juncea) in calcareous semi-arid tracks of Indian sub-continent. And suitable P application strategy and use of phosphorus solubilizing and mobilizing micro-organism (PSMM) could enhance the P use efficiency and thereby productivity of Indian mustard. Thus, an experiment was conducted during 2008-2009 and 2009-2010 to test some of these measures under irrigated fallow-mustard system. The seed yield of Indian mustard was increased by 5.5 % due to PSB inoculation and 10.8 % due to PSB + VAM over noninoculation. However, the incorporation of VAM alone showed antagonistic results. Similarly the basal application of 17.6 kg P/ha significantly increased the yield by 14.0 % over no-P fertilizer. The splitting of P levels to 15.4 kg P/ha basal + 2.2 kg P/ha foliar spray at 35 DAS further improved the seed yield by 26.9 % over basal application of P and 44.7 % over no-P. The interaction effect between PSMM and P application strategies was additive. The combined use of PSB + VAM and 15.4 kg P/ha basal + 2.2 kg P/ha foliar spray at 35 DAS increased the seed yield by 61.9 % over absolute control. These variations in yields were attributed to corresponding variation in primary and secondary branches, siliquae per plant, siliqua length, seeds per siliqua and 1000-seed weight. The total P uptake in Indian mustard varied from 6.1 at absolute control to 15.9 kgP/hawhen PSB + VAM and split P fertilizer were put together. But irrespective of the quantum of total uptake the share of P in seed varied a narrow range of 80.3-86.0 %. It was further confirmed by decreasing P harvest index with improvement in treatment, indicating accumulation of excess P in straw. The agronomic P efficiency (AE_P) of applied P ranged between 14.5 kg seed/kg P fertilizer at 17.6 kg P/ha basal application to 37.7 kg seed/kg P at 15.4 kg P/ha basal + 2.2 kg P/ha foliar spray at 35 DAS. The corresponding increase in apparent recovery efficiency (RE_P) was 21.9-45.7 %. A synergistic effect of PSB and PSB + VAM and antagonistic effect of VAM was observed in AE_P and RE _P at both P fertilization levels.