Abstract:
The physical and chemical responses of a degraded sandy clay loam Ultisol to two leguminous and four grass cover crops in southern Nigeria were studied after five years to assess the rejuvenative effects of the covers. There were relative increases of 26% and 112% in soil organic carbon and phosphorus levels and also appreciable improvements in the CEC and Ca levels under vegetative covers compared with the initial conditions. The improvements were more pronounced with legume covers than with grass covers. Furthermore, the vegetative covers improved mean organic carbon level by 28% and appreciably improved mean CEC, Ca, and Mg levels over the values for the bare soils. The percentage of water-stable aggregates >1.0 mm was significantly reduced under bare fallow (x = 27.7%) compared with soils under vegetative cover x = 79.3%). The correlation between water- stable aggregates >1.0 mm and exchangeable aluminum was negative and significant (r = -0.705°) at p = 0.05. There were highly significant treatment effects (P = 0.01) for penetrometer resistance, pore size distribution, water infiltration, water retention and saturated hydraulic conductivity. Grass and legume fallows which protect the soil and guarantee regular additions of organic materials are ecologically sound and socially acceptable components of sustainable agricultural production. Indications, however, are that this degraded tropical Ultisol would require a period exceeding five years under vegetative covers for restoration of its fertility to acceptable productive status
