Field experiments were conducted in 2000 through 2001 to assess yield trends of maize and cassava in a rotational cropping sequence under integrated use of manure (poultry manure, M) and fertilizer (NPK 20:10:10, F) on a degraded Ultisol of southeastern Nigeria. The experiment was a 4 x 4 factorial in a randomized complete block design (RCBD) with three replications. The results showed no direct significant M x F interaction effect on maize grain yield. However, increasing levels of manure and fertilizer, increased maize grain yield significantly. The highest grain yields of 4.45 and 3.95 t ha-1 obtained at the highest manure and fertilizer rates of 30 t ha-1 and 500 kg ha-1 , which were similar to the yields obtained with 10 t ha-1 manure and 250 kg ha-1 fertilizer, out-yielded the control by 2.9 and 1.2 times (191.6 and 21.1%), respectively. Residual effect of the treatments on cassava root yield showed no significant fertilizer effect while there were significant manure and M x F interaction effects on cassava fresh root yield. Application of manure alone at 20 t ha-1 (M2) and in combination with 125 kg ha-1 fertilizer (M2F1) gave the highest root yields of 46.34 t ha-1 and 49.76 t ha-1, representing 31 and 70.7% increase over the control, respectively. These yield figures were similar to that obtained with the application of manure at 10 t ha-1 (M1 and M1F0), It was concluded that poultry manure agro waste induced superior maize and cassava yield performances to NPK fertilizer and that while higher rates of the application of manure alone or in combination with fertilizer may be the technical optimum, 10 t ha-1 poultry manure rate could be recommended as an economic optimum for sustainable crop production on the degraded Ultisol at Umudike, Southeastern Nigeria. Keywords: Maize and cassava yields, direct and residual effects, double rotational cropping system, manure and inorganic fertilizers, degraded Ultisols.

Keywords: Maize and cassava yield responses, double rotational cropping system, manure and inorganic fertilizers, degraded Ultisols