COMPARISON OF EFFECTS OF SOME TILLAGE METHODS ON SOIL PHYSICAL-PROPERTIES AND YIELD OF MAIZE AND STYLO IN A DEGRADED FERRUGINOUS TROPICAL SOIL

In the predominantly ferruginous soils (Alfisols) at the Kurmin Biri grazing reserve in the subhumid zone of Nigeria, the profile is shallow because of the occurrence of a hardpan within or just below the plough layer. In addition, large-scale sheet erosion has removed most of the fertile top soil. In this paper, some of the effects on the soil and yields of maize (Zea mays L.) and a forage legume (Stylosanthes hamata (L.) Taub.) of ridging and subsoiling are compared with disc harrowing. Subsoiling significantly lowered the bulk density of the 0-10 cm soil layer by 0.04-0.09 g cm-3 and that of the 10-30 cm layer by 0.19-0.32 g cm-3. Bulk density values for the ridging and subsoiling treatments were statistically similar. Profile moisture storage to a depth of 45 cm was increased 15-30% by subsoiling. Water storage under the ridging and disc-harrowing treatments did not differ. Maize grain yield was increased 6% by ridging and 24% by subsoiling in comparison to disc harrowing. Compared with disc harrowing, dry matter yield of stylo was about 10% less with ridging but was improved 25% by subsoiling. Examination of the root distribution of both crops supports the hypothesis that the shallow hardpan seriously restricted root development. Yield increases with ridging and subsoiling were attributed to improved nutrient and moisture utilization as a result of increased rooting volume. Other possible constraints on crop growth imposed by the hardpan are discussed. © 1990.