LAUSR

ABSTRACT This study was conducted in order to determine the status of different pools of inorganic phosphorus in surface and sub-surface soils, changed over 3 years of intensive cropping with Rice-Maize-Green gram (residual) under site-specific nutrient management and work out the correlation among different pools of P. Postharvest soil properties indicated that soil pH was increasing gradually due to lime addition as one input, in spite of the removal of basic cations. There was small but a positive build up of organic carbon, available N and P. There was a drastic reduction in available K status in postharvest soil with available S were found. Phosphorus was fractionated broadly in two groups (a) Inorganic-P and (b) Organic-P. The inorganic P fractions constituted 71.9–86.0% of total P, whereas organic-P constituted 14.0–28.1% in surface soil and 75.9–81% and 18.1–24.1% in subsoil, respectively. The sequence of different pools in order of Fe-P > RS-P > Al-P > Ca-P > occluded-P > saloid-P (surface soil 0–15 cm) and RS-P > Fe-P > Ca-P > Occluded-P > Al-P > saloid-P (Subsurface soil 15–30 cm). Bray’s extracted-P is positively correlated with Fe (r = 0.71*) and Al-P (r = 0.67*) indicating the major contribution of both fractions toward available P pool in surface soil, whereas, Al-P majorly contribute in sub-surface soil. Among the inorganic fractions of Phosphorus, Fe-P (r = 0.72*) are showing positive and significant relationship with total uptake of P, in surface soil and Al-P (0.70*) in sub-surface soil. Thus, understanding the use of both inorganic and organic fertilizer under intensive cropping for 3 years must be planned carefully because the interaction of different forms of P, in acidic soil and various other factors influencing P availability to plants.