Assessment of the productivity of sweet potato varieties grown on soil amended with prunings of agro-forestry tree species in south eastern Nigeria
The agronomic effectiveness and economic viability of soil amendment with prunings of agro-forestry tree species in sweet potato production on a highly weathered soil of South Eastern Nigeria were assessed in a field study conducted in 2010 and 2011 at the research farm of the National Root Crops Research Institute, Umudike, Abia State, Nigeria. Treatment comprised prunings of three agro-forestry tree species (Dactyladenia barterii, Gliricidia sepium and Chloropenthra microphylla) in factorial combinations with three sweet potato varieties (Ex-Igbariam, TIS 87/0087 and TIS 2532.OP.113) arranged in a randomized complete block design with three replications. Optimum NPK fertilizer recommendation for sweet potato production in South Eastern Nigeria and a plot having neither the agro-forestry tree pruning nor inorganic NPK fertilizer amendment were included as checks. Results showed that Soil amendment with prunings of agro-forestry trees resulted in variable increases in such soil chemical properties as total N, total organic carbon, exchangeable K, available P and pH relative to absolute control. Such increases in soil chemical properties following application of the treatment were highest in optimum NPK fertilizer control treatment. Also, total root yield production potentials of sweet potato were enhanced following soil amendment with either agro-forestry tree prunings or optimum NPK fertilizer treatment compared to when there was no amendment. Similarly, application of the treatments resulted in the production of higher number of saleable roots and lower number of un-saleable roots relative to the un-amended control. Amending the soil with prunings of G. sepium gave the highest return per Naira invested followed by C. microphylla and optimum NPK fertilizer. With the exception of D. barterii pruning, soil amendment with G. sepium, C. microphylla prunings or optimum NPK fertilizer proved to be more economically beneficial for sweet potato production on the highly weathered soil of South Eastern Nigeria than the absolute control.
Keywords: Productivity, agro-forestry tree pruning, sweet potato and soil amendment