Using zeolite, molasses, and PGP microorganisms to improve apatite solubility and increase phosphorus uptake by Sorghum bicolor L. (Speedfed cultivar).

This study investigated the effect of the application of apatite (Ap), some amendments (zeolite and molasses), and some microbial inoculations (plant-growth-promoting microorganisms; including Claroideoglomus etunicatum, Serendipita indica, Enterobacter cloacae, and Brevundimonas sp) on P in organic (Po) and P in inorganic (Pi) fractions, alkaline phosphatase activity, and Sorghum bicolor L. (Speedfed cultivar) growth in sandy soil with pH 7.8. A factorial pot experiment in a completely randomized design was performed with three replications, using microbial inoculants (non-inoculated, Claroideoglomus etunicatum, Serendipita indica, Enterobacter cloacae, and Brevundimonas sp) and four amendments levels (control, Ap, Ap-Z (Ap-zeolite), and Ap-M (Ap-molasses)). Ap application increased all mineral fractions of P as follows: Ca10-P > Ca8-P > Ca2-P > Olsen P. Application of Ap-Z led to the increase of Olsen-P and Ca2-P to 1.21 and 1.67 fold as compared to Ap. Po was very low in soil, which was increased significantly with the application of amendments. In Ap-M treatments, the moderately labile Po and moderately non-labile Po increased significantly as compared to Ap treatments. Application of Ap-Z reduced pH more than Ap and Ap-M treatments. Furthermore, the largest amount of alkaline phosphatase was observed in Ap-M treatments. These findings show various mechanisms of microorganisms for using Ap in their metabolism in the presence of different amendments. Microbial inoculation (especially C. etunicatum) resulted in a decrease in pH and an increase in alkaline phosphatase. Application of amendments (Ap-Z and then Ap-M) resulted in better growth of Sorghum compared to control and Ap treatments. Application of Ap with zeolite and then molasses along with inoculation with plant-growth-promoting microorganisms were two useful solutions to improve the productivity of sandy soils.