A METHODOLOGICAL APPROACH FOR IRRIGATION SCHEDULING IN A RUSTIC GREENHOUSE BY USING A STRESS THERMAL INDEX

Abstract

The use of sensors and actuators allows the precise application of irrigation through automated and feedback systems; however, its high cost makes it difficult to adopt in medium to low-technology greenhouses. The aim of this study was to evaluate an indicator based on thermal stress to schedule the daily irrigation in tomato (Solanum lycopersicum) grown under a greenhouse. A thermal stress index (TSI) was estimated from the differences between the optimum temperature for tomato photosynthesis and the air and foliage temperature. With the TSI, the schedule in which the irrigation sheet is applied, calculated from a type B mini-evaporimeter and the tomato crop coefficient (Kc) were estimated. Results indicate that five to eight irrigations per day should be applied with irrigation times no longer than 12 min (2 to 4 mm d^-1). The applied volume was 1.8 L/plant, similar to that estimated in studies employing sap flow sensors. This methodology allows estimating the irrigation calendar and simplifying its management. The use of type B mini-evaporimeter allowed the estimating of the daily irrigation sheet from the air and crop temperature to identify thermal stress and thereby infer the time of irrigation during the day.