Preliminary compositional nutrient diagnosis for rubber tree in the humid forest zone of Cameroon

The main source of natural rubber is the rubber tree (Hevea brasiliensis), an important crop to the Cameroonian economy. In order to improve yields while maintaining tree sustainability, nutrient norms must be derived for proper nutrient and sustainable soil fertility management. The aim of this study therefore, was to derive compositional nutrient diagnosis (CND) norms for Hevea brasiliensis grown under the ecological conditions of Cameroon. A survey of 130 Hevea brasiliensis fields was carried out to collect leaf samples and yield data. The leaf samples sampled were under shade of canopy and at least 100 days old and the yield data was measured as kg/ha per year of dry rubber. The leaves were analysed for N, P, K, Ca, Mg, S, Fe, Mn, Mo, Na and Zn. Using the yield data, the sampled population was divided into high- and low–yielding sub-populations. The CND norms were derived from a high-yielding sub-population (fields yielding >1,667 kg/ha) following standard procedures. The CND indices were calculated and used for the assessment of the nutrient status of a low- yielding sub-population of Hevea. The preliminary CND norms obtained for the different elements were as follows: V*N = 3.61±0.14, V*P = 0.94 ±0.16, V*K = 2.53±0.23, V*Ca = 2.47±0.24, V*Mg = 1.43 ±0.18, V*S = 1.1 ±0.10, V*Ca = 2.47±0.24, V*Na = -2.38 ±0.15, V*B = -3.63±0.27, V*Cu = -4.04±0.18, V*Fe = -1.41±0.39, V*Mn = -0.96±0.50, V*Mo = -8.18±0.35, V*Zn = -2.73 ± 0.15 and V*R = 11.25 ±0.10. Where V*R represents the norm for nutrients not analysed. The results showed that the micro nutrients except for Cu, Zn and Mo were deficient. The obtained nutrient norms are recommended for nutrient assessment in H. brasiliensis plantations in Cameroon.