ELUCIDATING THE PROCESSES THAT REGULATE THE MOBILIZATION OF HEAVY METALS FROM SOIL-APPLIED PHOSPHATE ROCKS AND DEVELOPING RHIZOBIOME-BASED STRATEGIES TO SEQUESTER THESE CONTAMINANTS.

With < 20% phosphorus (P) use efficiency, current crop production practices rely on a constant supply of P-fertilizers. However, the production of P-fertilizers is directly tied to the consumption of non-renewable phosphate rock (PR), which will be depleted within the next 50-80 years. This would result in widespread utilization of low-grade PR that has high amount of toxic trace elements. As the current fertilizer production technologies pass on 90% of contaminants in PR to the P-fertilizer, low-grade PR as raw-material would result in an unprecedented level of trace elements entering the agroecosystems, the fate of which is currently unknown.Here, using PR from five major P-mines in the U.S., coupled with a series of lab, greenhouse, and field experiments, and geochemical modeling, we propose to elucidate the factors that would influence the fate of contaminants in PR, and devise novel strategies to sequester the contaminants in stable forms while improving P utilization. The main objectives of the project are i) to identify P acquisition strategies of crop plants that result in high uptake of P and trace elements, ii) to identify the mineral composition of PR that are more vulnerable to leaching of trace elements, iii) to employ plant-microbiome association that can sequester the trace metals in chemically stable forms in soils, while efficiently utilizing the P from low-grade PR.