EVALUATION OF NITROGEN USE EFFICIENCY OF VEGETABLES GROWN UNDER AGRI-PHOTOVOLTAIC SYSTEMS IN NORTH-CENTRAL NAMIBIA

Agriculture in arid and semiarid regions encounters substantial challenges attributable to climatic variability, limited water resources, and nutrient-deficient soils. Nitrogen (N) is essential for tomato (Solanum lycopersicum) growth and affects yield, water efficiency, and fruit quality. Agri-photovoltaic (Agri-PV) systems offer a promising and sustainable solution to land-use competition by concurrently facilitating solar energy generation and horticultural production. This study examined the combined effects of nitrogen application rate and Agri-PV-induced shading on the physiological performance and yield characteristics of tomatoes. The experiments were carried out with tomato seeds planted in an Agrovoltaics experimental field at the School of Agriculture, University of Namibia, Namibia. The split–split plot experimental design featured two nitrogen levels: the recommended rate (150 kg N ha⁻¹) and an adaptive rate (120 kg N ha⁻¹), combined with three shading conditions: 60% shade (chequered boards), 40% shade (opaque boards), and full sunlight (control). Phosphorus (P) and potassium (K) were applied at the recommended rates of 90 kg P ha⁻¹ and 75 kg K ha⁻¹. Growth and yield parameters were analysed using SAS 9.4. There were no statistically significant differences in yield between the nitrogen levels; however, shading treatments significantly influenced fruit weight yield, with intermediate shading enhancing production. At harvest, the 40% chequered shade treatment showed the highest values of fresh fruit yield (kg/m²) compared to opaque and with similar values of fruit numbers. These outcomes indicate that Agri-PV systems can control microclimatic conditions, reducing excessive heat and light stress while sustaining or enhancing crop productivity. The integration of Agri-PV with optimised nitrogen management supports both renewable energy generation and sustainable agriculture, offering a viable strategy for climate-smart food production systems.