IMPROVING THE PRODUCTIVITY OF A DEGRADED ULTISOL IN NIGERIA USING ORGANIC AND INORGANIC AMENDMENTS .1. CHEMICAL-PROPERTIES AND MAIZE YIELD

The comparative effectiveness of rice shavings, poultry manure and inorganic fertilizers in restoring the productivity of an eroded, low-fertility Ultisol in southeastern Nigeria was investigated over three cropping seasons. The treatments evaluated were: complete fertilizer (N, P, K and Mg) at the locally recommended rates (F1), complete fertilizer at one-and-half times the locally recommended rates (F2), rice shavings (RS), rice shavings + fertilizer at the locally recommended rate (RS + F1) and poultry manure (PM). A control (C) was also used. All treatments were applied in 1986 and their residual effects on maize and soil chemical properties evaluated in growing seasons 1987 and 1988. Rice shavings and poultry manure significantly increased the soil organic carbon, total nitrogen, exchangeable bases and cation exchange capacity during the first cropping season. By the third cropping season differences in these chemical properties were less apparent. Between 1986 and 1988 organic carbon decreased by 20, 21, 24, 50, 54 and 60% on the control (C), F1, F2, RS, RS + F1 and PM treatments, respectively. This was a reflection of the mineralization rates of organic carbon in these treatments. As a result of increased soil nutrients following applications, all amendments increased maize grain-yield over the controls through all three cropping seasons. The magnitude of increase was greater on organic waste-treated than on inorganic fertilizer-treated plots. The residual effect of RS was higher than that of PM because of the higher C:N ratio and slower decomposition rate of RS than PM. On all treatments only short-term ameliorative effects were obtained.