A critical review of soil phosphorus dynamics and biogeochemical processes for unlocking soil phosphorus reserves

This chapter provides an overview of the relative contributions of organic and inorganic sources to soil phosphorus (P) accumulation, its dynamics, and the use of amendments in unlocking soil P reserves. Phosphorus availability for plants is limited due to insoluble compound formation with aluminum, iron, and calcium in the soil. Despite continuous replenishment through physicochemical and biological processes, about two-thirds of agricultural land globally suffers from P deficiency. Inorganic fertilizers, organic manure, and waste products are commonly used to address this deficiency. However, the resulting P input exceeds crop removal, resulting in environmental challenges. Excessive P application and inadequate consideration of crop demand have led to a significant buildup of residual P in global soils. Residual soil P can be transformed into bioavailable forms through geological, chemical, and biological processes. Geological processes, accelerated by factors like vegetation and climate, enhance P solubilization from soil minerals. Soil acidification, influenced by root activity and rainfall, further promotes P release. Chemical processes like desorption and dissolution also contribute to P availability, influenced by soil properties. Biological mechanisms facilitated by microorganisms play a vital role in unlocking soil P reserves. Understanding these processes is crucial for global food security. Efficient P use involves practices like simultaneous nitrogen and P application, organic matter addition, zero tillage, cover crops, strategic P placement, and specific crops that mobilize P. Inorganic and organic soil amendments, by influencing gene expression, soil acidification, and organic acid production, enhance P bioavailability.