Nitrogen Concentration in Grain Size Fractions of Soils of Contrasting Land Units in the Humid Rainforest, Southeastern Nigeria (Published)
Nitrogen is critical for ecosystem functioning and environmental health. Its concentration in grain size fraction provides useful information about the activities in soils. Nitrogen (total, organic, nitrate and ammonium) contents in grain size fraction of soils of contrasting units (back swamp, levee and upland) in Egbema, southeastern, Nigeria were evaluated. Also nitrogen contents were correlated with selected soil properties (sand, silt, clay, bd, pH, available P, OC and ECEC). Equally bulk soil N contents were related with were the grain size fractions using regression analysis. Mean total, organic, nitrate and ammonium N contents ranged between 0.60-0.65, 0.82-0.84, 0.77-0.87 and 0.78-1.35 g kg-1, 0.57-0.66, 0.84-1.56, 0.50-1.08 and 0.77-0.84 g kg-1, 5.96-6.91, 4.50-7.00, 5.04-7.20 and 6.90-8.30 mg kg-1and 0.23-1.33, 0.84-1.56, 0.50-1.08 and 0.80-1.52 mg kg-1 in bulk soil, sand, silt and clay grain size fractions respectively. Also averaged over land units, mean total, organic, nitrate and ammonium nitrogen in top and sub soils varied as 0.65 and 0.62, 0.86 and 0.79, 0.86 and 0.78 and 1.21and 0.77 g kg-1 , 0.64 and 0.61, 1.13 and 1.43, 0.50 and 1.24 and 1.20 and 0.76 g kg-1, 6.71 and 6.28, 5.27 and 6.27, 6.33 and 6.49 and 8.71 and 6.53 mg kg-1 and 0.94 and 0.92, 1.13 and 1.43, 0.50 and 1.24 and 1.39 and 1.12 mg kg-1 in bulk soil, sand, silt and clay fractions respectively. Bulk soil N forms were higher in levee except being nitrate in upland while those in particle size fractions varied amongst land units. Concentrations of all N forms in bulk and grain size fractions were were better in top than sub soils. Total, organic, nitrate and ammonium N enrichment of sand, silt and clay grain size fractions varied with soil depth and land units with clay fraction more enriched than other size fractions. Nitrogen contents correlated with selected soil properties, with the magnitude varying. Furthermore, N content of bulk soil was related with concentrations of the grain size fraction. In general, N content of grain size fractions will seriously influence N activity in soils of different land units.