Evaluation of automatic evapotranspiration-based irrigation scheduling controllers for water and energy savings in southern Florida tropical fruit orchards
Water use efficiency is becoming increasingly important in south Florida, particularly Miami-Dade County, due to the many demands on our potable water supply. Irrigation of landscape and turfgrass accounts for more than 50% of potable water use in some areas. Research has shown that use of soil moisture sensors to automatically control irrigation can result in water savings as high as 70-90% depending on brand and irrigation frequency (1, 2, or 7 d/wk). Earlier studies have also demonstrated the potential of evapotranspiration (ET)-based irrigation scheduling controllers to save over 40% irrigation water for turf and landscape applications.
The research goal was to evaluate and generate information on the suitability of evapotranspiration (ET)-based irrigation scheduling technologies for agricultural applications, specifically the technologies ability to estimate ET losses and provide water volumes to maintain a desired soil water content, to maintain root zone soil water content in an optimum range (close to field capacity) and to reduce volumes of irrigation water applied. To address this challenge, the following objectives were completed: 1) evaluation of ET-based irrigation water management in a tropical fruit orchard in south Florida and 2) comparison of various reference ET (ETo) estimation equations and spatial interpolation techniques in south Florida.
ET-based irrigation scheduling technologies adequately supplied the water needs of 15 year old Arkin carambola trees by replacing water that was daily lost through crop ET. In addition, the study revealed that substantial quantities of water were saved by the ET-based irrigation scheduling treatments compared to the typical irrigation practice (68% and 70% less irrigation water was applied by the real-time and historical ET-based treatments, respectively, compared to the typical irrigation practice for commercial carambola production in south Florida). ET-based irrigation scheduling methods also demonstrated their ability to maintain root zone soil water content below 10 kPa (close to field capacity of 34% volumetric water content). Evaluation of carambola physiological responses to real-time and historical ET-based irrigation scheduling, revealed that this type of irrigation water management did not appear to negatively affect stem water potential and leaf gas exchange which were used in the study as indicators of plant water stress. Yield data was also collected and results indicated no significant differences among treatments. ETo estimated from remote weather stations under estimated ETo estimated using onsite weather data probably due to the fact that weather conditions at the remote weather stations did not accurately represent the weather conditions at the study site.
The Turc (1961) radiation based ETo equation produced the best overall performance in predicting ETo estimated by the American Society of Civil Engineers-Environmental and Water Resources Institute (ASCE-EWRI) standardized equation. The Hargreaves method, the only temperature based ETo equation included in the study, had the lowest performance against the ASCE-EWRI standardized equation which was used as the bench mark. The results of the UF IFAS (1984) Penman and Priestley Taylor equations were satisfactory, although the two equations tended to overestimate ASCE-EWRI ETo especially in summer. The results of the South Florida Water Management District-Simple Method (SFWMD-SM) correlated well with the ETo estimated by ASCE-EWRI standardized equation, although the equation tended to slightly under ETo in winter. The surprisingly good performance of the simple Turc (1961) equation that only requires radiation and temperature as inputs provides an opportunity for improving irrigation scheduling algorithms for onsite or standalone ET-based controllers that are usually equipped with radiation and temperature sensor for agricultural applications. There was no substantial difference in the spatially distributed ETo surfaces generated using inverse distance weighted averaging and spline interpolation techniques. Spline ETo surfaces slightly improved ETo estimation between weather stations compared to using ETo from the closest weather station.
ET-based irrigation scheduling technologies provide a practical way of increasing water conservation in agriculture without negatively affecting the physiological development of the plant and with minimum inconvenience to the grower. Results of the study demonstrate that over 50% of irrigation water could be saved in tropical fruit orchards by adopting ET-based irrigation scheduling technologies. Increased water conservation in agriculture would also translate into reduced agro-chemical leaching and increased availability of water for other uses. However, their remain two main challenges that need additional research in order to improve performance of ET-based irrigation scheduling technologies in agriculture: 1) more work should be done to develop crop coefficient for the major commercial crops and 2) additionally studies should be conducted to evaluate the performance of onsite or stand alone ET-based irrigation technologies in agriculture settings, since these technology could accurately estimate location specific ETo using solar radiation and temperature sensors coupled with the Turc equation.
An example of a smart ET controller. (UF does not endorse any particular product.)
On-site weather station in carambola orchard.
Portions of this project were funded by USDA CSREES Integrated Water Quality Grant.
Thesis Web link : Kisekka Thesis
Publications: coming soon
Mr. Isaya Kisekka, MS graduate student in Agricultural and Biological Engineering, completed this project (Graduated Summer 2009).
Investigators