Effect of Poultry Manure, Defatted Palm Kernel Cake and Their Combinations on the Yield Performance of Sweet Potato (Ipomoea batatas (L.) Lam) and Chemical Characteristics of a Sandy Loam Ultisol of South-Eastern Nigerian

A two- year (2010 and 2011 cropping seasons) field trial was carried out on a Sandy loam Ultisol in south-eastern Nigeria to evaluate the effect of Poultry manure (PM), Defatted palm kernel cake (DPKC) and their combinations (PM + DPKC) on the yield of sweet potato and soil chemical properties. The experiment was laid-out in a randomised complete block design with the treatments consisting of PM, DPKC, PM + DPKC (1-1 by weight) applied at the rates of 5 and 10 t ha-1 each and a control (no soil amendment).The treatments were replicated four times. A significantly (P ≤ 0.05) higher sweet potato yield performances and improved soil chemical characteristics were recorded from plots that received any of the soil amendments compared to the un- amended (control plots). Apart from the combined application of PM and DPKC at the rate of 5 t ha-1 which gave a significantly higher yield values relative to single application of either PM or DPKC at similar rate; the effect of the other treatments at the same rate of application on the crop yield and yield related parameters did not differ significantly. However, plots that had either DPKC alone or in combination with PM gave a significantly higher root-vine yield ratio and commercial harvest index, irrespective of the rate of application. Similarly, combined application of PM and DPKC resulted in a significantly higher soil org. C, available P and exchangeable bases. The crop yield values and soil properties recorded from plots treated with PM + DPKC at the rates of 5 and 10 t ha-1 did not differ significantly, hence combined application of PM and DPKC at the rate of 5 t ha-1 could be considered suitable for sweet potato yield and soil nutrient conservation for sandy loam ultisol of south-eastern Nigeria.