Continuous, Proximal Leaf Monitoring System to Assist with Precision Irrigation Implementation Using a Wireless Mesh Network of Sensors and Controllers in Almonds

Abstract. Precision irrigation techniques can help ensure the necessary amount of water reaches plant roots at the right time in the drought-prone climate of California‘s Central Valley. To achieve this goal, a leaf monitor was developed which measures leaf temperature and other microclimatic variables (air temperature, relative humidity, light, and wind speed) necessary to calculate a crop water stress index (CWSI). This leaf monitor can be connected to a wireless mesh network for remote data reporting and irrigation control. Fourteen leaf monitors were interconnected in a 4-acre almond orchard through a wireless network. Irrigation was scheduled independently in two management zones, which were created from evaluation of soil and plant characteristics. CWSI values were calculated using a saturated reference tree that received 150% water and a dry reference, simulated by a leaf with broken stem. CWSI values were continuously used to guide irrigation decisions in each zone to achieve a targeted stress level which varied based on fruit development stage. Midday measurements of stem water potential were obtained to validate all irrigation decisions. When the average stress of a managed zone exceeded allowable levels, irrigation was implemented at a defined percentage of estimated evapotranspiration. This percentage was adjusted until the desired stress level was achieved at regular time intervals. Zone 1 required 75% and Zone 2 required 86% of the water applied by the grower. Water productivity was significantly higher and applied water was significantly lower in stress-based management zones compared to grower treatment. Yield and quality parameters were not significantly different between the zones and treatments. These results suggest this method of precision irrigation may be a useful tool for irrigation scheduling and increased water savings in almonds.