ABSTRACT

A 3-year field research work was conducted in 2015, 2016 and 2017 cropping seasons at the Forestry Research Institute of Nigeria, Eastern Research Station, Umuahia in Abia State to study on plant spacing, integrated nutrient management and its residual effects on the soil, growth, yield and quality of cocoyam in Umudike with the aim of identifying optimum spacing and assessing the effects of integrated nutrient management on the soil, growth yield and quality of two cocoyam species. This study involved two field and one laboratory experiments. Experiment one examined the effect of plant spacing, organic manure sources and residue of organics on the soil, growth and yield of Xanthosoma sagittfolium (NXs 001). This experiment was laid out in a 3 x 3 factorial arrangement in randomized complete block design (RCBD) in which Factor A consisted of three organic manure sources- control, poultry and goat manures. Poultry and goat manures were applied at 5 t ha-i. Factor B comprised three different plant spacings — 0.30 x 1.0 m, 0.40 x 1.0 m and 0.5 x 1.0 m. There were a total of 9 treatment combinations with three replicates. Experiment two examined the effect of poultry manure, NPK and residue of integrated nutrient management on the soil, growth and yield of Colocasia esculenta var. edeofe purple (NCe 003). This experiment was laid out in a 3 x 3 factorial in randomized complete block design (RCBD) in which poultry manure formed Factor A with three levels - 0, 5, 10 t ha-' while NPK 20:10:10 fertilizer formed Factor B with three levels - 0, 300, 600 kg ha'. There were a total of 9 treatment combinations with three replicates. Treatments were applied in 2015 and repeated in 2017 in both experiments while residual effect of the soil amendments was observed in 2016 with the same crops. Experiment three was to determine the effect of integrated plant nutrient management on chemical composition of tannia and taro. At the end of 2017 harvest, one cocoyam plant was uprooted from fertilized and unfertilized plots and partitioned into leaf, stem and corm fractions. Field data were taken on the following crop attributes: plant height, plant girth, number of leaves/plant, number of suckers/plant, leaf area/plant, leaf area index/plant, number of cormels/plant, corm girth/plant, corm yield/ha, cormels' yield/ha, average yield of cormels/ha, total yield/ha, dry matter yield/plant, harvest index and disease assessment. The samples were analyzed for chemical composition using 3 x 2 factorial arrangements fitted into randomized complete block design in which plant part samples formed Factor A with 3 levels while integrated plant nutrient management formed Factor B comprising two levels. Fisher's least significant difference (F-LSD) was applied to detect significant difference between two means at 0.05 % probability. The results showed that significant yield and yield components were obtained from the application of 600 kg ha-' NPK fertilizer in 2017 cropping season. These results also showed that a combination of NPK fertilizer and poultry manure significantly increased percent concentration of mineral elements under study in relation to the control.