Yield Decline of Major Crops Induced by Erosion On the Ultisols of Owerri, Southeastern Nigeria: Maize Response to Natural Erosion.

Few studies have been made to quantify the yield decline trends of major stable crops induced by erosion (natural and artificial) on the ultisols of Southeastern Nigeria, even though it is known that erosion’s impact on soil productivity is crop, environment and soil specific. This paper reports an aspect of a larger body of research work conducted between 1996 and 2002 to document erosion-induced productivity decline in ultisols of Southeastern Nigeria. The specific objective of the study was to quantify the impact of various levels of in situ erosion on maize yield and yield attributes. Field studies were conducted on non eroded (NE), slightly (S), moderately (M) and severely (Sv) eroded phases of a fine, loamy, kaolinitic isohyperthermic Typic Tropohymult, which included two croppings of maize in 1998 and 1999. Statistical design was a Completely Randomized Design (CRD) with four replications. Maize yields and yield attributes declined significantly with increasing severity of erosion at both croppings and the blanket application of NPK fertilizer and improved management practices boosted yields of the second crop without masking the effects of erosion. The relative yields of maize grain in 1998 were 100:23:16:10 for NE:S:M:Sv eroded sites, and the corresponding yield values were 3.8, 0.86, 0.59 and 0.39 Mg ha-1 respectively. The best-fit regression equations, with six soil variables explained 47.3% of variability in maize grain yield and soil organic matter content (SOC) was the most important indicator. Mean linear yield decline rates per centimeter of soil lost was 0.290mg for Slight, 0.159 for moderate and 0.113 Mg ha-1 for severely eroded. The calculated half-life of the soils under current management systems is 18 to 25 years.