Interaction Effects of Soil Texture and Water Table Soil Scienceh on Nitrogen Mineralisation in Fadama Soils of Borno State, North East Nigeria

This study investigates the interaction effects of soil texture and water table Soil Scienceh on nitrogen mineralisation dynamics in fadama soils of Borno State, located in Nigeria's North East geopolitical zone. Fadama soil nitrogen supply is central to the productivity of dry-season irrigated crops in the North East, but the simultaneous influence of texture (controlling aeration and substrate availability) and water table fluctuation (controlling redox conditions) on nitrogen mineralisation has not been studied in Borno State fadama soils, creating a gap in understanding the nitrogen economy of these systems. Using a controlled laboratory incubation design with structured treatments, five fadama soil textures (from sandy loam to heavy clay) were incubated at three simulated water table positions (free-draining, 30 cm below surface, and saturated) at 25 degrees Celsius for 60 days. Mineralised ammonium and nitrate were measured at 7-day intervals by KCl extraction and colorimetric determination. Enzyme activities (urease and protease) were measured at three time points. Findings revealed significant texture-water table interaction effects on mineral nitrogen release. Sandy loam soils under free-draining conditions released 2.3 times more nitrate than under saturated conditions, while clay soils showed smaller water table effects but slower overall mineralisation rates. Ammonification consistently exceeded nitrification under saturated conditions across all textures. Urease activity was highest in clay soils regardless of water table treatment, attributed to clay surface enzyme stabilisation. The study provides texture-specific and water regime-specific nitrogen mineralisation parameters applicable to fadama fertiliser recommendation models for Borno State. Keywords: nitrogen mineralisation, fadama soils, water table, soil texture, Borno State.