Soil cation exchange capacity dynamics under bush fallow in South-Western Nigeria

The trend of change in the cation exchange capacity of ferrallitic soils under bush fallow in south-western Nigeria was examined during the first 10 years following the cessation of cropping. The general trend is that the soil cation exchange capacity increases over time but this increase is largely restricted to the 0–10 cm layer of the soils. Three years of fallowing in the study area was generally inadequate to maintain soil cation exchange capacity at a level that would ensure continued high fertility. It is suggested that a short fallow of 3 years should be accompanied by the application of organic manures and inorganic fertilizers to increase the supply of plant nutrients. Soil percentage base saturation decreased with increasing length of the fallow period, presumably due to nutrient uptake from the soil by fallow vegetation. It is suggested that soils should be limed after a long fallow of >10 years in order to increase soil percentage base saturation and nutrient availability. Organic matter appears to be the main factor influencing the cation exchange capacity of soils under bush fallow in the study area. The effects of fallow vegetation on organic build-up in fallow soil and their implications for managing soil fertility during cropping are discussed.