Regulated deficit irrigation in green bean and watermelon greenhouse crops

Abstract

Mediterranean greenhouse growers of watermelon and green bean crops tend to reduce slightly the soil water availability during the flowering phase to enhance the fruit number and yield, but without measuring the soil or the plant water status. This deficit irrigation strategy (RDI) was studied on two representative growth cycles of green bean and one of watermelon. In each case, a well-watered crop acted as control. In the three well-watered vegetable crops, soil water matric potential (SMP) values were between −20 and −30 kPa throughout most of the respective growth cycles. These values avoid water deficits in Mediterranean greenhouse vegetable crops. The watermelon under RDI presented similar SMP to the well-watered crop, except during the flowering period when it reached values of −50 to −60 kPa, which are similar to, or slightly lower than, those recommended to prevent water deficits for cucurbitaceae crops. The autumn–winter and spring cycles of green bean under RDI presented progressively lower SMP values from the vegetative phase to the first fruit setting than the well-watered crops, reaching minimum SMP values of around −55 kPa for the autumn–winter cycle and of −75 kPa for the spring one. These minimum SMP values are similar for the autumn–winter cycle and lower for the spring cycle than those recommended to avoid water deficits in green bean crops grown in medium-fine textured soils. Overall, mild water deficits during flowering of watermelon and green bean crops grown in Mediterranean greenhouses did not improve the final fruit number or yield. In the two spring cycles (watermelon and green bean) the RDI strategy reduced the aboveground biomass and yield, whereas in the autumn–winter green bean cycle the RDI strategy reduced the vegetative biomass but did not affect yield. SMP threshold values can, however, be used by growers as a tool for controlling the equilibrium between the vegetative and reproductive growth of greenhouse soil-grown crops.