Fluids beat granular in soil trials

Data indicate that fluid fertilizers are superior to granular for delivery of phosphorus (P) for crop nutrition in calcareous soils. Field and glasshouse experiments have demonstrated in southern Australian soils the benefits of fluid formulations for crop nutrition. Experiments were performed using similar fertilizer products delivered either in fluid or granular form to calcareous soils. Isotopic and spectroscopic techniques were used to characterize reactions. Granular fertilizers were found to be inferior to fluids (even with the same formulations) due to the precipitation of insoluble Ca/Al phosphates similar to crandallite in the fertilization zone (i.e., in and around the granule). As determined by isotopic dilution studies, P diffusion from the incorporation zone was inhibited with granular applications and the ability of P in the fertilized zone was also reduced when P was applied in granular form. Fixation of applied P is minimized when fertilizers are supplied in fluid form. Some formulations may have the added advantage of liberating fixed P in the soil-to-plant available forms