Arun C Kanagalabavi, Sanketh GD, Khaja Mohinuddin D and Dayanand Patil
Phosphorus (P) is the second most limiting nutrient for crop production, with 43% of global arable soils deficient in P, significantly restricting crop growth. In India, the rising demand for P-fertilizers is challenged by reliance on imported high-grade rock phosphate (RP) and sulphur. Low-grade RP, suitable for acid soils, offers potential for alternative applications through methods such as mixing with elemental sulphur, partial acidulation and dry compaction with soluble P-fertilizers. RP has been a fundamental raw material for producing phosphatic fertilizers like single super phosphate, diammonium phosphate and nitro phosphates. Despite large reserves of total P in soils, only a small fraction is available to plants, necessitating the continuous application of phosphatic fertilizers to enhance crop yield. The efficiency of water-soluble P fertilizers is low (15–20%) under acidic and neutral to alkaline conditions. Various factors influence the effectiveness of RP as a direct P-fertilizer, including soil properties, plant species and fertilizer management. Efforts to enhance RP's immediate availability include partial acidulation, dry granulation, phospho-composts, microbial solubilization, earthworm casts, calcination and transgenic approaches, offering promising pathways to improve P availability for sustainable agriculture.
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