Demonstration of Improved Citrus Irrigation Using Soil Balance Model and Soil Moisture Sensors

The Citrus Water Management System (CWMS) is a computer software package that allows the user to store information required to simulate a water balance for each individual zone. Daily ET data can be manually entered by the user or automatically downloaded from the Florida Automated Weather Network (FAWN) once an appropriate station location is entered for each irrigation zone. The CWMS was demonstrated from 2012 to 2014 on a citrus grove that is irrigated in 178 irrigation zones controlled by the Motorola system. Rainfall and irrigation application for each irrigation zone are provided daily using two files generated by the irrigation control system and read by CWMS. Soil moisture data was collected using a series of multi-level capacitance sensors installed at selected locations in blocks irrigated by one of three irrigation scheduling methods. The three methods are: 1) control with irrigation practices following University of Florida Institute of Food and Agricultural Sciences (IFAS) recommended seasonal schedules; 2) manually adjusted irrigation schedules using soil moisture sensors; and 3) manually adjusted irrigation schedules using the CWMS model. Soil moisture data was automatically collected daily by a proprietary program supplied by the sensor manufacture. Average soil moisture for the 10-, 20-, 30-, and 50-cm depths ranged from 0.08 to 0.13 cm³/cm³ with the lowest values during the dry months and the highest values during the rainy season. The measured soil moisture was not significantly different than the simulated soil moisture for either 2012/2013 or 2013/2014 growing seasons. Average monthly water use in the IFAS recommended blocks decreased in 2013/2014 but were in the same range as average monthly water use reported by neighboring groves on a grove area basis Significant differences in water use were found in 2012/2013 and 2013/2014, when blocks irrigated with conventional irrigation scheduling was compared with blocks irrigated using soil moisture sensor data or model simulations on both a grove area basis and a per tree basis. Likewise, comparable reductions in irrigation system run time were found for sensor and model irrigation schedules. Water use savings of approximately 18% for blocks irrigated using sensors and 11% compared with the IFAS recommended schedule Fruit yields for all three irrigation schedules were not significantly different in 2012/2013 or 2013/2014 and were similar to the initial year. Thus yearly water use can be reduced by approximately 15% using soil moisture sensors or model simulation with no significant reduction in yield.