Abstract:
The literature on infiltration and factors affecting it was reviewed. Special emphasis was given to the effects of different cultivation techniques. As infiltration is one of the key factors affecting soil erosion by water the literature review opened with a brief survey of erosion problems in Nigeria. The effects of different cultivation techniques on soil physical properties were assessed by measuring infiltration with double ring infiltrometers. The cultivation techniquee included a manual system, a bullock-powered system, a system of zero tillage and a variety of tractor-powered systems. An aggregate stability test was also carried out for selected treatments. The infiltration measurements were carried out on four occasions spaced over the growing season. Each infiltration run lasted four hours and the differences in cumulative infiltration between the third and the fourth hours were taken as the equilibrium infiltration rates. „ Infiltration was also measured in a 6-year old zero tillage experiment in which zero tillage was contrasted with continuous cultivation. In another experiment, infiltration in a field under grass fallow was compared with that in a 30 year old continuously cultivated field. The results of infiltration measurements showed that infiltration and cultivation technique were closely related. Cumulative infiltration under the manual system was superior to either the zero tillage or the bullock-powered system and greatly superior to the mechanised system. Statistical analysis of equilibrium infiltration rates confirmed this. The manual system was significantly superior to the bullockpowered and tractor-powered systems at 5% level of significance. The statistical analysis also showed that zero tillage was significantly superior to all the mechanised treatments while there was no significant difference among the mechanised treatments. The grass fallow was greatly superior to the continuously cultivated soil. The lowest infiltration rates were obtained in the mid-season when rainfall was at its peak suggesting that infiltration and initial soil moisture content were related. The aggregate stability test showed that the surface soil under zero tillage was much more stable than surface soil under any other treatment; the significance level was 0.1%. At the same level of significance, surface soil under manual and bullockpowered systems were more stable than surface soil under any of the mechanised treatments. In view of the importance of infiltration rate with respect to surface runoff and soil erosion, the conclusions about the effect of different cultivation techniques on infiltration should be tested for all the major soil types in Nigeria. In addition, further studies are needed to find out the exact causes of reduced infiltration in particular cases.
EFFECT OP DIFFERENT CULTIVATION TECHNIQUES ON INFILTRATION
