PhD

Three field experiments were conducted in three locations representing the major rubber growing regions in South India to study the response to nutrient applications on growth characters, yield and latex flow characteristics and to study the inter-relationship between soil and plant nutrients on yield. It was also envisaged to assess the relative response in the different locations and to make economic analysis of the benefit of manuring. Three levels of 0, 40 and 80 N ha-1, 0, 30 and 60 kg P2O5 ha-1 and 0, 40 and 80 kg k2O ha-1 and two levels of 0 and 10 kg MgO ha-1 were used. A 33 x 2 partially confounded factorial split plot experiment in randomised block design with two replications was followed.
The 80 kg level of N and 30 and 40 kg levels respectively of P and K were optimum for girth increment in all the locations. Application of Mg was also beneficial. For virgin bark thickness the 40, 30 and 40 kg levels of N, P and K respectively were sufficient in all the locations and application of Mg was not beneficial. For bark renewal 80 kg N was optimum at Thodupuzha whereas the 40 kg level was sufficient in the other locations. The 60 kg level of P was useful at Kulasekharam and Thodupuzha while 30 kg was sufficient at Balussery. The 40 kg level of K was optimum in all the locations and application of Mg was not beneficial. The 80 kg level of N gave the maximum weight of leaf litter in all places while for P and K the 30 and 40 kg levels respectively were sufficient. Magnesium was beneficial only at Balussery in one year.
The 40, 30 and 40 kg levels respectively of N, P and K gave the highest total volume of latex in all the locations except at Balussery where 80 kg K was superior to 40 kg. Application of Mg was beneficial at Balussery while it had a reducing effect at Kulasekharam and no effect at Thodupuzha. Application of N and K reduced the plugging index and that of P and Mg increased it in all the locations. For dry rubber content, the 80 kg level of N was optimum at Kulasekharam while the 40 kg level was sufficient in the other locations. With regard to P and K the 30 and 40 kg levels respectively were sufficient. Application of Mg was beneficial only at Thodupuzha.
In the case of yield of rubber 40 kg N and 30 kg P2O5 were found to be optimum in all locations. The 40 kg level of K2O was sufficient at Kulasekharam and Thodupuzha while the 80 kg gave the highest yield at Balussery. At Thodupuzha and Balussery application of Mg was beneficial while at kulasekharam it reduced the yield.
Application of N increased the organic carbon content of soil. The available P, K and Mg contents of soil were increased by the application of the respective nutrients. The N, P, K and Mg contents of leaf and latex were increased by application of the respective nutrients. Application of P as rock phosphorus also increased the available Ca content of soil and Ca contents of leaf and latex.
The yield of rubber was positively correlated with girth increment, rate of bark renewal, initial flow rate, total volume and dry rubber content of latex and negatively with plugging index. Yield was also positively correlated with the available N, P, K and Ca contents of soil N, K and Ca contents of leaf and P and K contents of latex and negatively correlated with Mg contents of soil and leaf. The strongest correlations with yield were given by soil N, latex P and K and leaf Ca.
Total volume of latex was positively correlated with the available N, P, K and Ca contents of soil, N, K and Ca contents of leaf and P and K contents of latex. The dry rubber content of latex was positively correlated with the available N, P and Ca contents of soil, N, K and Ca contents of leaf and N, P, K and Ca contents of latex. The plugging index was positively correlated with the P and Ca contents and negatively with the N and K contents of soil, leaf and latex. Positive correlations, were obtained between soil and leaf nutrients, soil and latex nutrients and leaf and latex nutrients in the case of N, P, K and Ca.
In the case of yield of rubber 40 kg N and 30 kg P were found to be optimum in all the locations. The 40 kg level of K was sufficient at Kulasekharam and Thodupuzha while the 80 kg level gave the highest yield at Balussery. Application of Mg was beneficial at Thodupuzha and Balussery while at Kulasekharam it reduced the yield.
An overall evaluation of the economic analysis indicated that 40 kg N, 30 kg P2O5 and 40 kg K2O were the optimum doses in all the three locations. Application of Mg was profitable only at Thodupuzha.