Dolomite Phosphate Rock–Based Slow-Release Fertilizers and Their Agronomic Effectiveness for Corn in Acidic Sandy Soils.

Phosphorus is one of the essential macro-nutrients required for plant growth. There is increasing concern regarding use of water soluble P fertilizers due to depletion of high-grade phosphate rock (PR) and leakage of P from agricultural production systems. Developing slow release P fertilizers may provide potential solution to sustainable agriculture. In this study, three dolomite phosphate rock (DPR) samples representing high-, medium-, and low-grade PR (DPR5, DPR1 and DPR7) were collected from central Florida. The samples were ground to < 100 mesh and subjected to activating with organic agents (HA or LSS). Greenhouse experiments were conducted to evaluate agronomic effectiveness of the activated DPRs on two typical agricultural soils (Alfisol and Spodosol) with corn as indicator crop, as compared with water soluble fertilizers. The results indicated that compared with three original DPRs, both HA- and LSS-activated DPRs significantly enhanced corn growth and increased shoot and root biomass in Spodosol except for HA-DPR7. In Alfisol, HA- and LSS-activated DPR had similar effect on shoot and root biomass of corn as original DPRs, whereas the diammonium phosphate (DAP) and DPR derived superphosphates (SPs) reduced root biomass, and there are no differences between DAP and SPs. HA- and LSS-activated DPR increased root and shoot Ca and Mg concentration but had minimal effect on plant P concentration as compared with original DPRs. Uptake of Ca, Mg and P by corn had a similar trend with shoot and root biomass for both Spodosol and Alfisol. In both soils, HA- and LSS-activated DPR increased pH and EC. All activated DPRs increased EC of both soils markedly compared with CK, whereas SP treatments decreased pH in both soils. The results demonstrated that DPR can be used as cost-effective fertilizers to improve crop growth on Spodosol and Alfisol in South Florida, but the activated DPR is more effective