Energy conservation and application uniformity for irrigation systems

Abstract

The need for high energy input is one of the primary limitations to the sustainability of centre pivot irrigation. The purpose of this project was to evaluate a relatively new technology known as Low Elevation Spray Application (LESA) irrigation to obtain Saskatchewan specific performance data for this technology. Preliminary studies were conducted on small, research scale, linear and centre pivot systems. Afterwards, a two tower centre pivot irrigation system equipped with standard impact nozzles was modified by the addition of LESA equipment: drop tubes and low pressure nozzles with static spray pads. This system was capable of operating either standard above lateral mounted impact sprinklers or LESA technology on the same piece of land. Later, seven field scale systems with various makes of nozzles and spray pads were added to the study to ensure that the data collected from the research systems was applicable to field conditions. For all of the systems tested the, coefficient of uniformity, application efficiency and specific energy consumption were determined and compared for a variety of wind speeds. Results showed that for the two tower research centre pivot the coefficient of uniformity was similar for impact and LESA technology with static spray pads. The application efficiency for the impact nozzles and low pressure nozzles showed that, while they both had a trend in decreasing efficiency with increasing wind speeds, the low pressure nozzles had a better efficiency at all wind speeds. The trends showed that the application efficiency for the impact nozzles ranged from approximately 69% to 86% and the low pressure nozzles ranged from approximately 74% to 98% indicating an average efficiency gain of approximately 8% greater for the LESA technology. The energy consumed by both the impact and LESA systems indicated that both systems had an increasing energy consumption with increasing wind speed. However, the low pressure system showed a trend of using on average, one half of the energy required by the medium pressure system (0.107 kWh/m3 as compared to 0.057 kWh/m3)to deliver the same amount of water. Field comparisons indicated that the system equipped with the same LESA technology as the research system (drop nozzles and static spray pads) had similar results for coefficient of uniformity, application efficiency and specific energy consumption. Field systems equipped with spinner or rotator spray pads showed an increase in all factors measured. Results indicate that LESA technology offers promise for increasing the efficiency of centre pivot irrigation systems in Saskatchewan.