Computational Modelling of Soil-Water-Plant Dynamics Under Subsurface Drip Irrigation in Semi-Arid Nigeria

This study develops and validates a comprehensive computational model of soil-water-plant dynamics under subsurface drip irrigation in semi-arid Nigerian conditions, advancing theoretical understanding of the coupled physical-biological processes governing water use efficiency in precision irrigation systems. Subsurface drip irrigation is the most water-efficient irrigation technology available, yet its adoption in Nigeria is negligible partly due to the absence of design tools and management guidelines calibrated for Nigerian soil and crop conditions. A theoretically grounded simulation model is essential for generating the scientific basis for system design and optimisation recommendations. This study develops a three-dimensional variably saturated flow model using the Richards equation, coupled with solute transport, root water uptake, and evapotranspiration partitioning models, implemented in HYDRUS-3D. The model is parameterised for five major Nigerian soil series representing contrasting textures from north to south, using soil hydraulic properties measured from field samples at sites in Sokoto, Kano, Benue, Ogun, and Anambra States. Crop root development is modelled dynamically using the RLD model calibrated for maize and tomato. Model validation uses soil moisture sensor array data from three subsurface drip experimental plots. Long-term simulation experiments test the effect of emitter spacing, depth, irrigation frequency, and deficit irrigation on water use efficiency and yield across soil types. Findings reveal strong interactions between soil texture and optimal drip design parameters that previous studies based on single soil types could not capture. Sandy soils in the North West require shorter emitter spacing and higher frequency irrigation than clayey soils in the South East for equivalent water distribution. The study recommends soil-specific design guidelines.

Keywords: subsurface drip irrigation, soil-water-plant modelling, HYDRUS, semi-arid Nigeria, Richards equation.