Continuous, proximal leaf monitoring system to assist with precision irrigation implementation using a wireless mesh network of sensors and controllers in almonds

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.