Central Coffee Research Institute, Coffee Research Station, Chikmagalur, Karnataka
*Present address: Indian Institute of Horticultural Research, 255, Upper Palace Orchards, Bangalore, Karnataka
Transformation and availability of applied P was studied in a long-term fertilizer trial on coffee in South India in which 0 to 370 kg P2O5/ha per annum had been added as ground rock phosphate for 18 years. There was a build-up of total as well as available P (extracted by five soil test procedures) in all the P treated plots. Its accumulation was largely in the Fe-P and reductant soluble fractions which appeared to be the major source of P uptake by coffee. Some residual effect of applied P was evident in pot culture experiment with coffee grown for one year. In another pot experiment with maize followed by bajra (Pennisetum typhoides), significant residual effect was observed on dry matter production and P uptake.
Of the five soil test methods for P, Bray II and North Carolina tests gave the highest correlation coefficients with uptake of P by coffee. These two procedures appeared to extract mainly Fe-P, Ca-P and reductant soluble fractions of inorganic P in the soil.
Residual availability of P, inorganic P fractions, long-term/effect, transformation of P
