Inorganic pPhosphorus fractions and phosphorus availability in long term fertilizer cum manurial trails under coconut cultivation

Abstract

Phosphorus is one of the major nutrients required for coconut production. The information about the fate of native and applied phosphorus in soil is essential for better management of the nutrient. To study the changes occurred in soil inorganic P fractions and P availability in soil after 43 years of coconut cultivation were studied from a long term fertilizer cum manurial experiment at CPCRI, Kasaragod during 2017-18. There were 6 treatments viz., tillage with organic and inorganic fertilizer, tillage with inorganic fertilizer, tillage with basin forking, tillage alone, herbicide application without tillage and fertilizer and control and three replications. Soil samples were taken from two depths from coconut basin and interspaces for analysis. Phosphorus was fractionated into Easily Soluble P (ES-P), Aluminium P (AI-P), Iron P (Fe-P), Calcium P (Ca-P) and Reductant Soluble P (RS-P) at two depths (0-30 cm and 30-60 cm) through sequential extraction. The dominant phosphorus fraction in the coconut basin at 0-30 cm depth was Ca-P and the trend was as follows: Ca-P>Fe-P>RS-P>A1-P>ES-P. But at 30-60 cm depth, RS-P became the dominant fraction and the trend was Fe-P>Ca-P >RS-P>> Al-P>ES-P. Long-term phosphorus fertilization would facilitate the accumulation of soil Ca-P, and thus improve soil P availability. In the interspaces, Fe-P was the dominating fraction in both the depths followed by Ca-P and RS-P. The difference in P fractions in manured and nonmanured plots clearly showed that the manured plots have high content of all the inorganic phosphorus fractions in both the depths.