Evaluation of Phosphorus Availability Indices in Relation to Inorganic Fractions of Phosphorus under Acid Alfisols Growing Tea in Himachal Pradesh

Phosphorus values/indices using the extractants, viz. Mehlich 1, Mehlich 3, Bray 1, Bray 2 and Olsen were evaluated in relation to inorganic phosphorus fractions in tea growing soils of Himachal Pradesh. The mean relative abundance of inorganic phosphorus fractions followed the order of RSP (reductant soluble P) > Fe-P > Ca-P > Al-P > Saloid-P in both depths. However, RSP content was higher in sub-surface soil than in the surfacesoil. Stepwise regression analyses show that Al-P and Ca-P are the predominant fractions contributing towards availability of phosphorus. Evaluation of these extractants under unpruned crop situation of mature China hybrid tea, fertilized with graded doses. of phosphorus revealed that phosphorus uptake by the crop and extractable phosphorus of the four extractants were correlated significantly, except Bray 2 phosphorus. The suitability of Mehlich 3 extractant as an index of phosphorus availability is discussed in detail. Regression equations were calculated between Mehlich 3 extractable phosphorus and phosphorus extracted by other extractants.