Integrated Soil-Water-plant Modeling to Optimize Fertilizer and Irrigation Use Efficiency in Smallholder Farming Systems: A Mechanistic Narrative Review
Samuel Abiodun Youngoke
*
Department of Agricultural Engineering, Federal University of Technology Akure, Ondo, Nigeria.
Chisom Esther Ejezie
Plant and Soil Science Department, Oklahoma State University, Stillwater, Oklahoma, United States.
Michael Mba Kusibu
Department of Environmental Science, University of Technology and Applied Sciences, Navrongo, Ghana.
Victor Chidera Owuala
Department of Soil Science and Technology, Federal University of Technology Owerri, Owerri, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Smallholder farming systems in sub-Saharan Africa, South Asia and Mediterranean environments often operate under simultaneous water limitation and soil nutrient constraints, reducing crop productivity and resource-use efficiency. This review examines how integrated soil-water-plant modelling can support coordinated management of irrigation and fertiliser inputs in low-resource agricultural systems. It focuses on the mechanistic links among soil water movement, nutrient transport, root uptake, crop physiological response and nutrient loss pathways. Process-based modelling frameworks, including DSSAT, APSIM, AquaCrop, CropSyst, STICS and HYDRUS, are considered in relation to their capacity to represent these interactions and inform management decisions. The review indicates that soil moisture status directly affects nutrient dissolution, mass flow, diffusion, microbial nitrogen transformations, root hydraulic conductance and transpiration-driven nutrient delivery. Therefore, irrigation and fertilisation should not be treated as independent management operations. Model-guided scheduling can help identify periods when crop nutrient demand, root-zone water availability and fertiliser mobility are better aligned. Reported studies in smallholder-relevant systems suggest potential improvements in nutrient-use efficiency and reductions in irrigation demand under calibrated modelling conditions, although outcomes vary with soil type, crop, rainfall regime, irrigation infrastructure and model parameterisation. Important constraints include limited soil and weather data, insufficient local calibration, structural uncertainty, weak representation of heterogeneous fields and limited extension capacity. Overall, integrated modelling offers a scientifically grounded pathway for improving water and nutrient management, but its practical value depends on careful validation and context-specific implementation.
Keywords: Integrated soil-water-plant modelling, smallholder farming, irrigation scheduling, fertiliser-use efficiency, nutrient-use efficiency, crop simulation, water productivity, resource optimisation, DSSAT, APSIM, AquaCrop, HYDRUS