The present work was planned to study the influence of bio – organic additives ( i.e. compost (CM) and farmyard manure (FYM), as organic fertilizers and Bacillus megaterium (Bm) and Bacillus polymyxa (Bp), as biofertilizers) on calcium solubilization from rock phosphate in sandy and alluvial clayey soils. Pot experiment was conducted in a greenhouse of the Environmental Studies and Research Institute (ESRI), University of Sadat, Menoufia Governorate, Egypt during summer season of 2014.
The experiment was laid out in a complete randomized design (CRD) arrangement with three replications. Each soil bulk was divided into portions, each was assigned to one treatment, and each treatment replicated 3 times. Rock phosphate, as insoluble calcium source was added at a rate of 4 gm kg-1. Compost or FYM was added at a rate of 2% organic carbon (OC) to each soil. Each pot was contained 500 g of the soil mixed with rock phosphate and organic fertilizer. Bm or Bp was added to each potted soil at a level of 2 ml of culture suspension. Different parameters were determined along the periods of incubation (120 days).
Results showed that, all added amendments increased calcium solubilization in both soils with time of incubation. Soil pH values were decreased with incubation time up to 60 days. EC dSm-1 and soil CO2 release rate significantly increased in both soil as an indicator of increasing the bio activity and calcium solubilization in the soil solution by increasing the incubation time. The highest increasing rate of soil EC and CO2 release were obtained with added bio-organic fertilizer mixture than each one alone. Soluble calcium in the soil solution raised with the individual additions of organic or biological with prolonging the incubation time, according to the descending order CM > FYM, Bm > Bp. The order for the effect of the common treatments was followed: CM + Bm > CM + Bp, FYM + Bm > FYM + Bp. Overall total comparison, the descending order was followed: CM + Bm > CM + Bp > FYM + Bm > FYM + Bp > CM > FYM > Bm > BP. The single application of each bio-and organic fertilizers showed the following increases mean values of calcium solubilization compared to the control (W.B.O.): CM (88.89 & 98.26%), FYM (57.78 & 68.70%), Bm (20.00 & 26.09%) and Bp (4.44 & 9.57%), for the sandy and alluvial clayey soils, respectively. Incorporation of CM or FYM plus each of the biofertilizers greatly augmented calcium solubilization, as compared with the single additive of each of the bio-organics. The highest increases rates induced by using any of CM or FYM each with Bm, reached 166.67 & 128.89% and 197.39 & 147.83% above their control (W.B.O.) treatment in the sandy and alluvial clayey soils, respectively.