Diagnosing P status and P requirement of tea (Camellia sinensis L.) by leaf and soil analysis

In this paper we present a new method for evaluating soil and plant tests for phosphate (P). We apply it to field experiments conducted over 2 years in four widely separated tea gardens of the Terai and the Dooars regions at the Himalayan foothills of India. We applied 5 levels of P to each site and measured yield, P concentration in the leaves, and Bray P values through time. Leaf P concentrations were closely described by a 3-dimensional Mitscherlich equation in which one of the independent variables was the amount of P applied and the other was the initial Bray P value. From this, we calculated the relative effectiveness of the applied P and the Bray P. The effectiveness of the applied P relative to that measured by Bray P, ranged from 0.87 down to 0.55. We added values for applied P and Bray P, with appropriate weighting for relative effectiveness, to calculate an effective level of P for each treatment. The relation between yield and effective P was then closely described by a Mitscherlich equation modified to permit a different maximum for each site. These relationships were used to show that P requirement was greatest on the most productive sites and in the middle of the growing season when growth rates were largest. We also tested the relation between leaf P concentration and yield. Yield was linearly related to leaf P over a concentration range of about 3 to about 4 g P kg−1. The regression lines for different yield levels were close to parallel but with different intercepts. We propose that leaf P analysis could be used to monitor P status and that soil tests plus the values for relative effectiveness of applied P be used to estimate fertilizer requirement.