THE INFLUENCE OF LEVELS AND MODES OF NPK FERTILIZER APPLICATION ON GROWTH AND YIELD OF SOME IMPROVED CASSAVA VARIETIES IN NSUKKA, SOUTH EASTERN NIGERIA
A study was carried out at the Department of Crop Science, Faculty of Agriculture Experimental Farm, University of Nigeria, Nsukka to: (i) evaluate the growth and yield of four improved cassava varieties, (ii) determine optimum NPK fertilizer rate for increased productivity and (iii) determine the best mode of fertilizer application for increased productivity. The experiment was laid out in a randomized complete block design with three replications. Four varieties of cassava; TMS 01-1368 (yellow root), TME 419, TMS 98 05 05 and TMS 05 10, four levels of NPK fertilizer 0, 200, 400 and 600 and three modes of fertilizer application; single at 4 weeks after planting (WAP), split at 4 and 8 WAP and split-split at 4, 8 and 12 WAP were used for the study. Data were collected on the following agronomic and yield parameters: survival count, number of branches, number of leaves, plant height, stem girth, canopy diameter, tubers and garri yields (tonnes/ha). The variety TME 419 under the early establishment gave significantly (p<0.05) higher percentage survival count of 91 % although it was statistically similar to TMS 01 1368 (yellow root) with 90.8 %. The variety TMS 98 05 05 gave significantly (p<0.05) lower survival count and was statistically similar to variety TMS 05 10.The variety TMS 98 05 05 gave significantly (p< 0.05) higher number of leaves. TME 419 variety had significantly (p< 0.05) lower number of leaves in the second and fourth month after pplanting. Fertilizer application rate of 200 kg/ha gave significantly higher number of leaves at the second month after planting while 600 kg/ha gave significantly (p<0.05) higher number of leaves in the fourth month. The control gave the lowest number of leaves in both months and the single application of fertilizer gave significantly (p<0.05) higher number of leaves of 67 at the fourth month of crop growth. The variety TMS 98 05 05 at the early season planting gave significantly higher tuber and garri yields of 39.8 and 9.68 t/ha, respectively, at 12 months of crop growth although it was statistically similar to TMS 01 05. The rate of 200 kg/ha of NPK gave significantly (p < 0.05) higher tuber and garri yields of 24.69 t/ha and 5.15 t/ha, respectively at 6 months of growth. However, the rate of 400 kg/ha of NPK gave significantly (p < 0.05) higher tuber and garri yields of 39.4 and 10.12 t/ha at 12 months of growth. The 400 kg/ha rate of fertilizer gave similar growth and yield results when compared with 600 kg/ha rate and should be adopted because of lower production cost. Split application of fertilizer is statistically similar to split – split application and should be adopted for cassava production since it is more economical to farmers because it minimizes cost of labour for fertilizer application and reduction in total cost of cassava production. TMS 98 05 05 that showed significantly highest growth and yield measures could be adopted for production in Nsukka in order to boost cassava production.