Characterization of particulate organic matter in soils of selected districts in agro-climatic zones of Tamil Nadu, India

Cropping practices and agro-climatic conditions at specific sites have a direct impact on the processes involved in organic matter accumulation in cultivated soils. Soil particulate organic matter (POM) contributes significantly to soil fertility by improving nutrient status and availability. A study on delineation of soils in selected districts of Tamil Nadu was carried out by collecting surface soil samples from continuously cropped lands. Surface soil samples were taken at 15 cm depth from 37 villages across 16 major districts represents the 7 agro-climatic zones of Tamil Nadu. A series of tests were carried out to record POM parameters linked to soil fertility in continuous cropping. POM levels were found high (> 5 g kg-1) in 16 locations, with the majority of those in the hilly, high-altitude, high-rainfall and Cauvery delta zones. In the western zone, the soils from the long-term fertilizer experiment (LTFE) and the permanent manurial experiment (PME) also had high POM concentrations. Within the total POM component, coarse POM (0.5 - 2.0 mm) constituted to 94.5 %, fine POM (< 0.5 mm - floating) constituted to 77.2 % and bound POM (< 0.5 mm - particle bound) constituted to 60.0 % in soils. In correlation analysis, POM exhibited a strong negative relationship with soil pH and CaCO3 whereas a strong positive relationship with SOC.