Long-term manuring and fertilization influence soil inorganic phosphorus transformation vis-a-vis rice yield in a rice-wheat cropping system

A study on the rice-wheat cropping system was conducted at Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India, to assess the effects of long-term manuring and fertilization on transformation of the inorganic phosphorus (P) fraction in soil after 22years of the crop cycle. Soil samples were collected after Kharif from seven treated plots having different types of organic amendments like farm yard manure, paddy straw and green manuring with 50% substitution of nitrogen levels in rice crop only. The result showed that the yield trend of rice was maintained due to the buildup of P from various organic inputs. Although cultivation for 22years without adding any fertilizer caused a significant decrease in almost all the forms of P viz. avail-P, saloid P, iron phosphorus fraction (Fe-P), aluminum phosphorus fraction (Al-P), calcium phosphorus fraction (Ca-P) and total P in control. Partial substitution of inorganic fertilizer N (50%) with organics, however, caused a significant increase in almost all the P fractions in soil over the control. The relative abundance of all the fractions of inorganic P irrespective of treatments was as follows: Fe-P > reductant soluble P fraction > occluded P > Al-P > Ca-P > saloid P. Saloid and Fe-P were the dominating fractions responsible for 92% variation of available P and total P levels, respectively.