Index based fertility evaluation of some basement complex soils for citrus production in Nigeria
Soil fertility is a major factor influencing its productivity and the eventual yield of citrus in Nigeria. Fertilizer application to citrus trees is often carried out without recourse to appropriate soil information. Therefore, a study was carried out to assess and classify the fertility status of some basement complex soils supporting citrus production in southern and northern Nigeria. Soil samples were taken from representative soil profile pits and analysed for soil physical and chemical properties. Soil fertility classification was done using the Fertility Classification System while fertility assessment was based on soil samples collected from 0 – 50cm soil depth and rated on Soil Fertility Index (SFI) of 0 -100. The basement complex soils of southern Nigeria were characterized by low nutrient reserves, low organic matter content, waterlogging/poor drainage and high degree of leaching. The coarse nature and high gravel content of the soils are the main factors limiting soil productivity for citrus production. The range of actual SFI was 14.45 – 39.34 while the range of potential SFI was 72 – 100. Fertility constraints in the Northern basement complex soils include texture, strong dry season and low organic matter. Actual SFI ranged from 21.16 – 28.21. The soils are low in exchangeable potassium (0.34 cmol -1.74cmol//kg) and low to marginal for available phosphorus (3.17 mg/kg – 5.92 mg/kg). The values of both exchangeable K and available P are below the required values of 15 – 80 mg/kg (available P) and 100 cmol/kg – 200 cmol/kg (exchangeable K) required for citrus production. The soils are low to medium in fertility and should be improved through appropriate fertilizer application in order to attain optimum citrus production.