A Leaf Monitoring System for Continuous Measurement of Plant Water Status to Assist in Precision Irrigation in Grape and Almond crops

Measurement of plant water status (PWS) provides the key information necessary to implement efficient irrigation management schemes in almond orchards and vineyards. A continuous leaf monitoring system based on leaf temperature and relevant microclimatic variables is currently available to obtain PWS. These systems can be installed after careful analysis of how soil and plant characteristics are distributed throughout the field to implement site-specific irrigation. Crop water stress index (CWSI) or modified water stress index (MCWSI) values are usually computed with leaf monitor data, which requires a knowledge of well-watered and fully stressed conditions. Although these values can be estimated by assuming that trees reach saturation after each irrigation event, this is not the case when deficit irrigation is implemented. We proposed a new methodology to compute CWSI and MCWSI using the continuous leaf monitor data, where the well-watered and dry conditions were measured using a well-watered tree and a simulated dry leaf. The objectives of this work were: (1) to implement a plant water stress based site-specific irrigation management scheme in an almond orchard and (2) to assess PWS of grapes and almond trees by comparing MCWSI and CWSI with deficit stem water potential (DSWP). A wireless network was used in each study site to interface the leaf monitors, soil and pressure sensors, as well as latching solenoid valves. Two management zones were created using unsupervised fuzzy classification based on soil and plant characteristics in the almond orchard. In each management zone two treatments were implemented: grower and stress based. Leaf monitors were tested in grapes by measuring PWS in eight vines, where four of them corresponded to vines that were not being watered following full irrigation to experience increasing amount of stress and four other vines corresponded to vines that were watered daily after a long period of stress to recover from stress. In grapes, MCWSI and DSWP were found to be linearly related with a coefficient of determination value of 0.70. In almonds, CWSI and DSWP were found to be strongly correlated with a second order relationship and a coefficient of determination value of 0.78. Additionally, preliminary results indicated that the management zones #1 and #2 of the almond orchard required approximately 70% and 90%, respectively, of the water used in grower based irrigation.