Net Plant Available Phosphorus Release from Organic Composts in Clay Loam Soil Varies with Temperature in Subtropical Agroecosystems

Purpose Phosphorus (P) deficiency is a widespread constraint in subtropical agroecosystems, particularly in clay loam soils with high P-fixation potential. Although organic composts are increasingly promoted for sustainable nutrient management, the temperature-mediated kinetics of P release from different compost types remain poorly understood. This study aimed to quantify the temporal dynamics of net plant-available P release from contrasting organic composts under different temperature regimes. Methods A 330-day laboratory incubation experiment was conducted using a P-deficient clay loam soil amended with six commonly used organic composts: poultry manure (PM), vermicompost (VC), bio-slurry (BS), cow dung (CD), water hyacinth compost (WHC), and rice straw compost (RSC). Incubations were carried out at 15, 25, and 35°C. Available P was measured at 13 sampling intervals using standard colorimetric methods. A first-order kinetic model was applied to estimate the apparent easily releasable P pool ( Pa , %) and the apparent P release rate constant ( k , day ^− 1 ). Results Temperature significantly influenced both the rate and magnitude of P release. PM consistently exhibited the highest and most rapid net P availability across all temperature regimes, with peak release at 35°C. VC and BS also showed relatively rapid P release, whereas WHC and RSC displayed pronounced slow-release behaviour, with peak availability occurring after 60–120 days. Model-derived Pa and k values increased with temperature (15–35°C) for all composts, indicating enhanced apparent P release under warmer conditions. Differences among composts were closely associated with their biochemical properties, particularly C:P ratio and organic matter recalcitrance. Conclusions Compost type and temperature interact strongly to regulate P availability in subtropical clay loam soils. These findings highlight the importance of compost selection and thermal conditions for optimising nutrient synchronisation with crop demand and support the development of compost-based P management strategies under climatic variability.