Application of Nuclear Magnetic Resonance Relaxometry for Soil Water Characterisation in Kogi State

Nuclear magnetic resonance relaxometry of hydrogen protons provides non-destructive characterisation of pore size distribution and water mobility in soil, offering complementary information to conventional moisture content measurements for irrigation management and geotechnical assessment. This study applies low-field NMR relaxometry to characterise soil water in samples from agricultural and riverine terrain in Kogi State, North Central Nigeria. Soil cores from four sites in the Lokoja floodplain and three upland sites in Okene LGA are collected at field moisture content and measured using a 2 MHz NMR relaxometer. T2 relaxation time distributions are inverted using regularised multi-exponential fitting to distinguish bound water in micropores from free water in macropores. Results indicate bimodal T2 distributions for all samples, with fast-relaxing components (T2 below 3 ms) associated with clay-bound water and slow-relaxing components (T2 greater than 10 ms) representing capillary and free water. Riverine floodplain soils show significantly higher macropore water fractions consistent with their higher hydraulic conductivity. NMR-derived porosity estimates agree with gravimetric measurements to within 4 percent. The study demonstrates NMR relaxometry as a practical soil water characterisation tool for research institutions and irrigation agencies in North Central Nigeria. Keywords: NMR relaxometry, soil water, pore size distribution, Kogi State, irrigation