Evaluation of soil structural quality and soil fertility indicators of dryland and fadama milieus using soil profile pits

Abstract Soil profile pits between 0 and 20 cm for eighteen different soil pedons in the dryland and fadama areas of Kebbi State, Nigeria, were used to evaluate the soil structural quality and soil fertility indicators for soil management suggestions. There were significant differences between the dryland and fadama sites for chemical indicators (P<0.001), and also variations existed between the sites for NPK ratios and soil reaction (pH). Nitrogen and phosphorus were evaluated at very low and low levels, whereas potassium appeared to be moderate. The common ratios for NPK compounds in the fadama site were 1:1:2, 1:1:3, 1:1:4 and 1:2:5; however, in the dryland site, there were diverse ratios, which appeared to differ from one site to another. Three classes of CEC were evaluated for the dryland (very-low, low, and moderate) and fadama (low, moderate, and high) sites. Soil pedons 1, 2, 5, 7, and 8 were extremely acidic, while soil pedons 10 and 18 were strongly acidic; soil pedons 9, 12, 15, and 17 were moderately acidic; soil pedons 3, 4, 11, 13, and 14 were slightly acidic; and soil pedons 6 and 16 were neutral and slightly alkaline, respectively. The soil structural quality at the dryland and fadama sites was classified into seven (7) classes, five of which were related to dryland sites (weak, very weak, moderate, strong, and good); however, the other two classes were related to fadama sites (well and good structures). It is suggested that the management of dryland and fadama sites in the study area can be achieved through four different applications: (a) the use of abundant organic manure to improve soil fertility, (b) the use of chemical fertilizer with high amounts of nitrogen and phosphorus but very low potassium and (c) the improvement of organic carbon and organic matter content by the return of organic residues (plant and animal materials) to the soils after crop harvest to enhance the rapid development of soil organic carbon and organic matter.