Phosphorus Management in Maize-Onion Cropping Sequence under Rainfed Temperate Conditions of Inceptisol

A field experiment was conducted during 2003–04 and 2004–05 to evaluate the direct effect of phosphorus (P) levels and their solubilizers on maize and residual effect on succeeding onion under rainfed temperate conditions of Kashmir valley. Yield and P uptake of maize were significantly increased with increasing levels of P up to 13.1 kg ha⁻¹ whereas post-harvest soil available P increased significantly up to 19.7 kg P ha⁻¹. Significantly higher root colonization, vesicular arbuscular mycorrhizal (VAM) spore density and viable counts of Pseudomonas striata were recorded with the application of 6.6 kg P ha¹³ over rest of the treatments but significantly decreased with increasing levels of P from 6.6 to 19.7 kg ha⁻¹. Co-inoculation of VAM+ phosphate solubilizing bacteria (PSB) significantly enhanced the maize yield, P uptake by grains and stover, root colonization, VAM spore density and Pseudomonas striata population over sole inoculation of VAM and PSB. Interaction P₆₆ x (VAM+PSB) was superior to all the combinations in respect of colonization, VAM spores and Pseudomonas striata counts whereas P₁₃₁ x VAM+PSB recorded maximum increase in yield and P uptake of maize. Highest residual effect on bulb yield of onion and available P after onion was recorded under 19.7 kg P ha⁻¹ followed by 13.1 kg P ha⁻¹ which increased the onion yield by 15.7 and 17.3% and available P by 21.9 and 39.8% over no-P during 2003–04 and 2004–05, respectively. Application of 13.1 kg P ha⁻¹ along with VAM+PSB was adequate for sustaining crop productivity and maintaining soil health in maize-onion cropping sequence under temperate rainfed Inceptisol.