Rehabilitation of degraded lands by means of fallowing in a semi-arid area of northern Nigeria

Land degradation in semi-arid regions of Nigeria is a very serious problem and therefore rehabilitation of degraded lands is essential. This article reports the results of an investigation which was carried out to assess the extent to which fallowing rehabilitates degraded lands in a semi-arid area in northern Nigeria. An inferential approach was used which involved side-by-side comparison of plots located within an area of uniform climatic, geologic and geomorphic characteristics, but which have been under fallow for different periods of time (2, 5, 10 or 15 years). Using a systematic sampling procedure, topsoil and subsoil samples were collected from each of the fallow plots and also from a plot under a plant community of well over 80 years of age which was chosen to serve as the control (fairly natural vegetation). The extent to which the land of each fallow plot had been rehabilitated could be assessed by comparison with the condition of the control plot. The samples were analysed for texture, bulk density, water-stable aggregates greater than 0.50 mm, moisture content, organic matter, pH, cation exchange capacity (CEC), total nitrogen, available phosphorus and exchangeable bases. An analysis of variance (ANOVA) technique was used to test for significant differences amongst the fallow plots, while Student's t-test was used to compare the mean values of the soil properties of the control with the same properties under each of the fallow plots. The results obtained varied considerably, but in general it was observed that there were decreases in the coarsening of soil texture and bulk density, but increases in other soil properties with increases in the length of the fallow period. However, the changes were generally found to be more significant under the older fallows (10 and 15 years) than under the newer fallows (2 and 5 years). The causes of these trends and their implication for sustainable land development in the area are discussed. It is concluded that for land rehabilitation to be effective in this area, either fallow times must be quite long, or ways of improving the soil's recuperative capacities under short-term fallow should be sought.