Abstract:
This study assessed the soil nutrient contents in nine forests and adjacent grasslands and the effect of acidulated rainwater in nutrient leaching in those soils in Nsukka areas, Nigeria. A total of 36 disturbed, 36 undisturbed (monolith) soil samples from 0-20 cm depth and 36 rainwater samples were collected. The rainwater collected were acidulated with nitric acid rates of 0.6 ml, 0.4 ml, and 0.2 ml to reduce pH to 3.2, 4.2 and 5.2 respectively, and used to leach the soil samples in monolith boxes. The samples were analyzed for physicochemical properties and factorial in randomized completely block design (RCBD) was employed to partition the data for statistical analysis. From the particle size distribution, the soil textures ranged from loamy sand through sandy loam to clay loam. The textural class predominant in the forest was loamy sand while that in grassland was sandy loam. The pH of the soils studied was generally acidic ranging from 3.9 (extremely acidic) to 5.4 (strongly acidic), organic matter (OM) content (0.65 to 2.97 g/kg) and total nitrogen (0.02 to 0.032 g/kg) were generally low. Exchangeable bases were also low (0.04 to 2.25 cmol/kg). The CEC ranged from 6.85 to 22.9 cmol/kg, base saturation from 8.25 to 31.25 %, and available phosphorus from 0.46 to 7.69 mg/kg. The respective effects of three different acidulated rainwater rates (0.6, 0.4, 0.2 ml) with pH values of 3.2, 4.2 and 5.2 on selected soil chemical properties of the leachates of forest land showed that pH (4.22, 4.05 and 5.2) ranged from extremely acidic to very strongly acidic, Ca2+ (37.5, 15.5 and 52 mg/l) was generally high while K+ (4.88, 2.86 and 3.81 mg/l), Mg2+ (10.8, 12.6 and 21.6 mg/l) and Na+ (1.43, 1.19 and 1.5 mg/l) were generally very high, Av.P (0.14, 0.186 and 0.05 mg/l) was generally low while OM (6.6, 0 and 6.6 mg/l) was generally medium. For grassland leachates, pH (3.77, 4.27 and 5.7) ranged from extremely acidic to moderatly acidic, Ca2+ (26, 14.5 and 29 mg/l) ranged from high to very high while K+ (2.5, 1.79 and 3.45 mg/l), Mg2+ (20.2, 12.6 and 14.4 mg/l) and Na+ (1.13, 1.06 and 1.81 mg/l) were generally high, Av.P (0.14, 0.186 and 0.186 mg/l) was generally very low while OM showed trace in all. Significantly higher pH, Ca2+, K+, OM and significantly lower Mg2+, Av.P, and Na+ were recorded in the leachates of forest soils when compared to those of grassland soils in acidulated rainwater rates. Both land uses showed similar nutrient contents, hence the acidulated rainwater showed significant (P<0.05) different in Ca2+, K+, OM, and Av.P of the leachates while Mg2+ and N+ were not significantly (P<0.05) affected by the acidulated rainwater. The high content of soil chemical properties in most of the leachets from acidulated rainwater implies that acid rain increases the rate of soil nutrients leaching thereby lowering soil fertility.
