Irrigation volume and placement determine physiological responses and yield of tomato in Ghana

Tomato (Solanum lycopersicum L.) is an important horticultural crop in Ghana, but increased incidence of drought has limited irrigation water resources. Thus we evaluated the effects of different deficit irrigation techniques including conventional deficit irrigation (DI) that irrigated every furrow, and fixed partial rootzone drying (FPRD) that watered every second furrow throughout the season. Both treatments applied half as much water as full irrigation (FI). Full irrigation increased tomato fruit yield by 25%, but DI and FPRD produced similar yields. Nevertheless, the deficit irrigation treatments increased water use efficiency (WUE) by 59% compared with FI. Full irrigation increased leaf relative water content and stomatal conductance (by 18-23%) compared to the other treatments. To investigate whether alternating the wet and dry rootzones affected physiological responses to PRD, plants were grown in pots with their roots split between two compartments. PRD plants received half as much water as full irrigation, but the wet and dry sides of the pot were maintained throughout the experiment (fixed PRD) or alternated at each irrigation event (Alternate PRD). While alternating the wet and dry sides of the pot had few physiological effects, fixed PRD plants produced 26% higher fruit yield than plants receiving full irrigation. Although alternate PRD plants produced 15% less shoot biomass than the other treatments, fruit yield was maintained (relative to full irrigation) by increasing the harvest index. While treatment differences in plant biomass and yield could not always be attributed to variation in leaf-level physiology, increased harvest index of plants exposed to PRD suggests it may be a viable irrigation technique in Ghana. Adoption of PRD in Ghana likely depends on farmers’ perceptions of its ease of application and occurrence of local water scarcity.