Development And Evaluation Of A Continuous Leaf Monitoring System for Measurement Of Plant Water Status

In this study, an inexpensive leaf monitoring system was developed for monitoring plant water status, and the system was evaluated for remote data collection and precision irrigation management. This system, named the "Leaf Monitor", monitored plant water status by continuously measuring leaf temperature and other microclimatic parameters in the vicinity of the leaf. It consisted of a thermal infra-red sensor to measure leaf temperature, and sensors to measure environmental conditions such as air temperature and relative humidity, photosynthetically active radiation (PAR) and wind speed. The sensor system also consisted of a leaf holder, a solar radiation diffuser dome, and a wind barrier for improved performance of the unit. Each leaf monitor system was incorporated into a mesh network of wireless nodes, allowing data collection and transmission at 16 minute intervals over the web. Experiments were conducted during the growing seasons of 2013 and 2014 in commercial walnut and almond orchards. The wireless nodes were found to be a reliable source for providing power and transmitting data.;The wireless mesh network consisted of leaf monitors, soil moisture sensors, line pressure sensors, and an actuator that could control timing and duration of water application. The network was tested in field conditions for its ability to continuously monitor the leaf by logging leaf temperature, air temperature, relative humidity, wind speed, PAR, and implement precision irrigation management over two growing seasons. The system was found to work well and we were able to visualize all data as well as manage irrigation with minimal technical problems.;A Crop Water Stress Index (CWSI) and Modified Crop Water Stress Index (MCWSI) for quantifying water stress levels were developed using the Leaf Monitor data. To account for spatial variability in plant water stress level, three different management zones were developed. Tree-specific/zone-specific stress indices were calculated using a method developed for the Leaf Monitor data. Temporal variability in stress index was accounted for by adjusting the stress calculation algorithm after every irrigation over the season. We found that adjusting the stress index calculation temporally (i.e., irrigation specific) tends to improve sensitivity for detecting changes in plant water stress.;MCWSI values were found to be highly correlated with measured plant water stress. Relationships between Deficit Stem Water Potential (DSWP) and MCWSI were developed for both crops based on data collected in two seasons. A linear relationship was found for the walnut crop, with R2 = 0.67. A quadratic relationship was found for the almond crop with R2 = 0.76. The relationships showed almond trees to be more tolerant to water stress compared with walnut trees. The relationship between MCWSI and DSWP was used to implement variable rate irrigation. Pre-irrigation, MCWSI was used to calculate the irrigation prescription for low frequency irrigation in walnuts. Preliminary analysis showed 92% accuracy in making effective irrigation management decisions. On an average, 40% less water was used for variable rate irrigation (compared with 100% evapotranspiration replacement). (Abstract shortened by UMI.).