ABSTRACT

Field experiments were conducted at the Teaching and Research Farm of Michael Okpara University of Agriculture, Umudike (MOUAU) and the Research Farm of the National Root Crop Research Institute, (NRCRI) both in Umudike, Ikwuano Local Government Area of Abia State in the 2012 and 2014 respectively on the effects of percentage leaf defoliation and NPK 15:15:15 fertilizer application on the growth and yield parameters of cassava (Manihot esculenta (L.) Crantz) TMS 419 sourced from the National Root Crop Research Institute, (NRCRI). The experiments were laid out in a factorial experiment fitted into a randomized complete block design (RCBD). The first experiment was laid out as a 4 by 3 factorial scheme with three (3) replications and twelve (12) treatment combinations, that gave a sum total of thirty-six (36) plots in all while the repeat experiment was laid out as a 2 by 3 factorial scheme with three (3) replications and six (6) treatment combinations, that gave a sum total of eighteen (18) plots. Two months after planting (2MAP), defoliation and the application of NPK 15:15:15 fertilizer were carried out simultaneously using the different rates of treatments which were 0%, 25%, 50%, 75% and 100% for defoliation and 0kg/ha, 150kg/ha, 200kg/ha, 300kg/ha and 400kg/ha for fertilizer applied. The results showed that significant defoliation effect was observed on plant height (5%) in both experiments at 50%, 75% and 100%, fertilizer applied was only significant in the second experiment with 400kg/ha fertilizer applied being more significant. Also, significant defoliation effect (5%) were observed in the number of leaves, number of branches, and likewise significant fertilizer effect (5%) were observed in the number of branches at 300kg/ha, number of leaves at 150kg/ha to 300kg/ha with interaction, leaf area, fresh stem weights at 300kg/ha to 400kg/ha, and the stem dry weights at 200kg/ha to 300kg/ha, these significant effects shown by the fertilizer applied, implied that the fertilizer at the different rates of treatments compensated for the effects of defoliation which were as a result of the distortion of the photosynthetic capacity of the leaves being defoliated. Although with defoliation, NPK fertilizer applied and the interaction showed no significant effect on the yield parameters, but there were some reasonable percentage yield from the results obtained with 200kg/ha to 400kg/ha fertilizer applied, while the plots with all levels of defoliation and zero NPK applied yielded lowly, which implied that the NPK applied was effective, although not significant but showed that, there existed a source-sink relationship. It therefore showed that farmers can still achieve reasonable yield regardless of the degree of defoliation considering the fact that there must be an alternate source of nutrients such as the NPK 15:15:15 fertilizer used in the experiment ranging from 200kg/ha to 400kg/ha, and for the farmers with livestock farming inclusive. This is of great importance to them, owing to the fact that they can defoliate cassava leaves at 25% and 50% level of defoliation for their animal’s feed production and yet have some reasonable yield available for consumption at harvest.