Irrigation scheduling performance by evapotranspiration-based controllers

Stacia L. Davis

doi:10.1016/j.agwat.2010.07.006

Irrigation scheduling performance by evapotranspiration-based controllers

2010-12-01

113

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AI

DOI：10.1016/j.agwat.2010.07.006

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Evapotranspiration-based irrigation controllers also known as ET controllers use ET information or estimation to schedule irrigation Previous research has shown that Er controllers could reduce irrigation as much as 42% when compared to a time-based irrigation schedule The objective of this study was to determine the capability of three brands of ET-based irrigation controllers to schedule irrigation compared to a theoretically derived soil water balance model based on the Irrigation Association Smart Water Application Technologies (SWAT) protocol to determine the effectiveness of irrigation scheduling Five treatments were established T1-T5 replicated four times for a total of twenty field plots in a completely randomized block design The irrigation treatments were as follows T1 Weathermatic SL1600 with SLW15 weather monitor T2 Toro Intelli-sense T3 ETwater Smart Controller 100 T4 a time-based treatment determined by local recommendations and T5 a reduced time-based treatment 60% of T4 All treatments utilized rain sensors set at a 6 mm threshold A daily soil water balance model was used to calculate the theoretical irrigation requirements for comparison with actual irrigation water applied Calculated in 30-day running totals irrigation adequacy and scheduling efficiency were used to quantify under- and over-irrigation respectively The study period 25 May 2006 through 27 November 2007 was drier than the historical average with a total of 1326 mm of rainfall compared to 1979 mm for the same historical period It was found that all treatments applied less irrigation than required for all seasons Additionally the Er controllers applied only half of the irrigation calculated for the theoretical requirement for each irrigation event on average Irrigation adequacy decreased when the ET controllers were allowed to irrigate any day of the week All treatments had decreased scheduling efficiency averages in the rainy season with the largest decrease of 29 percentile points with a timer and rain sensor (T4) and an average decrease of 20 percentile points for the Er controllers indicating that site specific rainfall has a significant effect on scheduling efficiency results Rainfall did not drastically impact the average irrigation adequacy results For this study there were two controller program settings that impacted the results The first setting was the crop coefficients where specific values were chosen for the location of the study when calculating the theoretical requirement whereas the controllers used default values The second setting was the soil type that defines the soil water holding capacity of the soil The ET controllers were able to regularly adjust to real-time weather unlike the conventional irrigation timers However the incorporation of site specific rainfall measurements is extremely important to their success at managing landscape water needs and at a minimum a rain sensor should be used (c) 2010 Elsevier B V All rights reserved

Keyword:

Smart controller

Soil water balance

SW AT protocol

Tui fgrass

Evapotranspiration irrigation controller

Irrigation scheduling performance by evapotranspiration-based controllers

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