An Original Theoretical Investigation of the Soil-Plant-Atmosphere Continuum in Drip-Irrigated Vegetable Production Systems of the Nigerian Dry Season

Drip irrigation in Nigerian dry season vegetable production creates a distinct soil-plant-atmosphere continuum characterised by localised moisture fronts, concentrated nutrient supply zones, and evaporative demand driven by high temperatures and low humidity, and an original theoretical framework for this continuum under Nigerian conditions would improve irrigation design and scheduling models. This study developed an original theoretical framework for the soil-plant-atmosphere continuum (SPAC) in drip-irrigated vegetable production under Nigerian dry season conditions. A multi-disciplinary methodology was employed, combining physical measurement experiments, crop physiology investigations, and model development. Field experiments were conducted with tomato and pepper at Sokoto and Kano research stations during the 2022-2023 and 2023-2024 dry seasons. Measurements included soil matric potential at 10, 20, and 30 cm radial distance from drip emitters, plant stem xylem pressure potential, stomatal conductance, transpiration using sap flow sensors, and atmospheric evaporative demand (reference ET0 from Penman-Monteith calculation). The original SPAC-DryNigeria model was constructed by adapting the van Genuchten soil water retention model for Kano calcareous and Sokoto sandy soils and parameterising a root water uptake function for the concentrated wet bulb geometry of drip emitter zones. The model successfully predicted within-day plant water status variation with a RMSE of 0.08 MPa. Optimal drip irrigation scheduling algorithms derived from the model reduced water use by 32 percent compared to calendar-based farmer practice while maintaining 98 percent of potential yield. Expert review confirmed significant original contribution to SPAC modelling for tropical drip irrigation systems.

Keywords: soil-plant-atmosphere continuum, drip irrigation, dry season vegetables, SPAC model, Nigeria