Macro and Micro Nutrients Status of Selected Soils Based on Land Use in Southwest, Nigeria

In Africa, production of food per capita had suffered a decline in the past decade despite the enormous increase in population. To sustain the growing dependence on agricultural production the use of fertilizers became paramount and more fertilizers are now applied than before. Ironically, agricultural production problem persisted. This could be attributed to improper use of fertilizers due to lack of proper methods of soil analysis that should give a true picture of the soil status. This study therefore assessed the macro and micronutrient status of selected soil in Ibadan (South western, Nigeria) based on four different land uses Twenty-four (24) bulk surface soil samples (0 -2 0 cm depth) were collected from the four different land use types within the University of Ibadan Campus. Particle size analysis, soil pH, total N, available P, organic C, CEC, exchangeable K, Ca and Mg, Mn, Fe, Cu and Zn were determined. Available phosphorus was extracted with Bray P-1 method. . Total nitrogen was determined using macro Kjeldahl digestion. Exchangeable Bases (Mg2+, Na+ , K+ , and Ca2+) were extracted using NH4 OAc. Ca2+ and Mg2+ were determined using Atomic Absorption Spectrophotometer, while K+ and Na+ were determined by flame photometer. Micronutrients (Cu, Zn, Mn and Fe) were extracted using 0.1N HCl. The results indicated that the soils ranged from near neutral to slightly alkaline. Soil samples were predominantly sandy. All the soils were very high in Organic matter content. The values for cultivated soil indicated that Total nitrogen was low for cultivated soils (1.05 ± 0.15 g/kg) while that of fallow and forest (1.69 ± 0.11 g/kg ) and (1.74 ± 0.09 g/kg) soil were moderate and high in dumpsite soils (5.47 ± 0.22 g/ kg). Available phosphorus in the soils ranged from moderate to extremely high with a mean of 8.87 ± 0.40 mg/kg for cultivated land use and 10.95 ± 0.66 mg/kg and 55.49 ± 1.12 mg/kg for forest and dumpsite soils respectively. Exchangeable K+, Ca2+, Mg 2+ were above the critical values in the studied soils and followed the order Cultivated > fallow > forest > dumpsite. Micronutrients in the soil were observed to follow this order: Mn > Fe > Ni > Zn >Cu with cultivated, having the lowest concentration and dumpsite soils having the highest concentrations of micronutrient. Available manganese and zinc were above the critical levels of 5.0 and 1.0 mg/kg for Mn and Zn respectively. Organic carbon, Zn, NH4 OAc, CH3 COOH, HCl and EDTA had significant (P≤ 0.05) positive correlation with pH (r =0.91***, 0.95***, 0.83**.0.96***, 0.76 ***and 0.83*** respectively). Mn also correlated positively with Cu (r=0.79***) but negatively with Zn (r=-0.84***) at P ≤ 0.05 and the other extractants. Zinc correlated significantly with all the extractants positively. All the extractants correlated positively with each other significantly at (P ≤0.05). The low Nitrogen content in the cultivated soils can be boosted by the addition of N-based fertilizers.