Effects of Cropping Frequency on Soil Physical Properties in Southwestern Nigeria

Abstract

ABSTRACT The effects of fallow management systems on soil physical properties and intercropped maize (Zea mays L.) grain were studied in Ibadan, southwestern Nigeria between 1994 and 1995. The A-horizon of the Alfisol at the site had a coarse texture which was rapidly degraded by continuous cropping. A split-plot experiment with 4 replications, which was established in 1989, was used for the study. The fallow systems comprising natural fallow, Pueraria phaseoloides and Leucaena leucocephala were mainplots whereas 25, 33, 50 and 100% cropping intensities were subplots. During the continuous cropping or 1-year cropping after 1-year to 3-year fallow periods, intercrops of maize (cv. DMR-SR-W TZ8843) and cassava (Manihot esculenta Crantz, cv. TMS 30572) were cultivated. Surface (0-15 cm depth) soil bulk density, soil strength, aggregate stability, and water retention were measured. Also, intercropped maize root density, and grain yields were evaluated. Surface soil bulk density ranged from 1.18 g cm″3 (25% cropping intensity) to 1.31 g cm−3 (100% cropping intensity), with significant differences between the 100% and 25% and between the 100% and 33% cropping intensities. Soil aggregate stability and soil strength followed a similar trend of low to high rating as cropping intensities increased. Although soil water retention was generally similar, the fractal dimensions of soil pore, D, between 2.92 and 2.93 indicated high irregularities of the pores. This irregularity was attributed to low stability of soil of the aggregates of the coarse-textured soil. The effects of fallow were obscured by the coarse-textured surface soil, and might not be noticed at all if the topmost layer (0-5 cm) of soil was not sampled. Intercropped maize grain yields ranging from 2.6 to 3.8 t ha−1 with 25% cropping intensity, between 1.7 and 2.0 t ha−1 with 33% cropping intensity and from 0.6 to 1.3 t ha−1 with continuous cropping were observed. Crop growth and yield were enhanced by low cropping intensities (25 and 33%) of any of the fallow management systems.