Soil Phosphorus Distribution and Enzyme Activities as Influenced by Phosphorus Application and Microbial Inoculation under Maize-Wheat Cropping System in a Typic Haplustept

Abstract

Low phosphorus (P) availability in Indian soils limits crop production. A study was undertaken to evaluate the effect of P fertilization (No P, 33% P, 50% P, 100% P and 100% P of recommended P in 3-splits as main-plots) and microbial inoculants [control, arbuscular mycorrhiza (AM), phosphate solubilizing bacteria (PSB), and AM+PSB as sub-plots] on P availability, P fractions and soil enzymes related to P cycle in a maize-wheat system. The study revealed that compared to no P, application of 100% P increased soluble P, Al-P, Fe-P and reductant-P by 63.3, 14.6, 31.5 and 18.3%, respectively, but no significant change in Ca-P status was recorded. Inorganic and total P stocks increased significantly after receiving 100% P for a period of two years, although organic P remained unaffected. Available P was highest in plots receiving 100% P. Highest alkaline (ALP) and acid phosphatase activity (ACP) was with 50% P application. Inoculation with AM+PSB effectively improve soluble P but reduce Al-P, Fe-P and Ca-P content by 20.8, 18.3 and 23.3%, respectively over control. Co-inoculation also resulted in higher ALP and ACP compared with individual inoculants and control. These enzymes correlate well with Olsen and soluble P fraction. Soluble P is positively correlated with Olsen-P (r =0.899*), Fe-P (r=0.384**) and red-P (r=0.418**). Percent contribution of different fractions to the total P was in the order of organic P (49.01%) > Ca-P (26.04%) > reductant P (15.64%) > Fe-P (4.37%) > Al-P (3.57%) >loosely bound-P (1.37%).