ABSTRACT

Cassava nutrition and population are some of the factors that affect the yield of cassava. Some farmers prefer to plant more than one stake per stand in order to increase yield of roots without regard to the fertility status of the soils. This research was designed to determine the best source and rate of compound fertilizer (NPK) for NR 8082 variety, the optimum rates of NPK fertilizer (15:15:15) and agrolyser for NR 8082 variety and the number of stem cuttings per stand and NPK fertilizer rates for optimum stem and root production of TME 419 cassava variety in Southeastern Nigeria in 2017/2018 and 2018/2019 late cropping seasons. The experiments were factorial arrangement and fitted into a randomized complete block design (RCBD) with three replications. The first experiment involved three NPK fertilizer sources (NPK 15:15:15, NPK 20:10:10 and NPKMg 12:12:17:2) and four application rates (0, 200, 400, and 600 Kg/ha) laid out in a 3 x 4 factorial arrangement fitted into RCBD. The second experiment involved four rates of NPK 15:15:15 fertilizer (0, 200, 400 and 600 Kg/ha) and four rates of agrolyser (0, 0.8, 1.6 and 2.4 Kg/ha) in a 4 x 4 factorial arrangement laid out in RCBD. The third experiment involved four number of stem cuttings per stand (1, 2, 3 and 4) and five rates of NPK 15:15:15 fertilizer (0, 200, 400, 600 and 800 Kg/ha). The results indicated that application of NPK fertilizer (15:15:15) significantly increased dry matter content and reduced moisture content of the root tubers compared to other fertilizer sources. In 2017/2018 cropping season, application of 400 Kg/ha NPK (15:15:15) fertilizer significantly increased starch content and reduced moisture content of the storage roots. In 2018/2019 cropping season, however, NPK fertilizer application at 600 Kg/ha produced significantly higher root yield than 0 Kg/ha, although the lower rate of 200 Kg/ha gave similar results as 600 Kg/ha. Agrolyser application did not influence stem and root yields but it decreased significantly dry matter and starch contents of the tuberous roots. Increasing the number of cutting to 4 cuttings per stand significantly increased leaf area index across sampling dates in 2017/2018 and stem yields in both cropping seasons compared to 1 or 2 cuttings per stand. The use of 4 cuttings per stand in 2018/2019 also significantly increased storage root yield compared to fewer number of cuttings per stand while dry matter and starch contents of the root tubers were markedly higher at 2 or 3 cuttings than at 1 or 4 cuttings per stand in 2017/2018 cropping season. NPK fertilizer (15:15:15) application at 800 Kg/ha in 2018/2019 produced significantly higher storage root yield than the control, but not over the lower rates of 400 to 600 Kg/ha. Application of NPK fertilizer at 600 Kg/ha significantly increased dry matter content of the root relative to other fertilizer rates in 2017/2018 cropping season. Based on the findings, it is recommended that under a droughty situation in a relatively fertile soil, NPKMg 12:12:17:2 fertilizer be applied at low rate of 200 to 400 Kg/ha or fertilizer application discouraged for high dry matter and starch yields, of NR 8082 cassava variety. For TME 419 variety with little or no branching single erect stem, the use of 4 cutings per stand is recommended for high root yields and 3 and 2 number of cuttings for high dry matter and starch contents, while NPK fertilizer at 400 to 600 Kg/ha is recommended for high root yields and high dry matter and starch contents of root tubers.