Sensor-Based Automation of Irrigation on Bermudagrass during Dry Weather Conditions

Transcription

1 Sensor-Based Automation of Irrigation on Bermudagrass during Dry Weather Conditions Bernard Cardenas-Lailhacar 1 ; Michael D. Dukes, P.E. 2 ; and Grady L. Miller 3 Abstract: Overirrigation of lawns with limited resources of potable water has increasingly become an issue for the state of Florida. A previous study showed that soil moisture sensors systems SMSs could lead to irrigation water savings during relatively wet/normal weather conditions. This research, as a follow-up comparison, was conducted under dry weather conditions. The first objective was to statistically evaluate the water savings potential of different commercially available SMSs during the first half of In the second half, the objectives were to quantify irrigation water use and to evaluate turfgrass quality differences among: 1 a time-based irrigation schedule system with and without a rain sensor; 2 time-based schedules compared to SMS-based systems; and 3 SMS-based systems under different irrigation frequencies. The experimental area was located in Gainesville, Fla. and consisted of common bermudagrass Cynodon dactylon L. Pers. plots. Four commercially available SMSs brands Acclima, Rain Bird, Irrometer, and Water Watcher were used to bypass scheduled irrigation cycles when the soil water content at the 7- to 10-cm depth was above field capacity. Time-based treatments with and without rain sensor feedback were set up as comparisons for irrigation depth applied, and a nonirrigated treatment for turf quality comparison purposes was implemented. Due to the dry weather conditions and/or infrequent rain events during the experiment, the nonirrigated plots as well as a broken SMS treatment resulted in turfgrass quality below the minimum acceptable level. The rest of the treatments had at least minimum acceptable turf quality. The treatment with rain sensor resulted in 13 to 24% less water applied than without the rain sensor treatment. Most SMS-based treatments resulted in significant irrigation water savings compared to the treatment without rain sensor, which ranged from 16 to 54% in the first half, and from 28 to 83% in the second half of 2006, for three of four SMS brands tested. DOI: / ASCE IR CE Database subject headings: Soil water; Moisture; Probe instruments; Rainfall; Irrigation; Scheduling; Automation; Water use; Drought. Author keywords: Soil water; Moisture; Sensors; Rainfall; Irrigation scheduling; Automation; Irrigation water; Water. Introduction Florida has dry and warm weather in spring and fall, as well as frequent rain events in summer National Oceanic and Atmospheric Administration NOAA These climatic conditions, coupled with low water holding capacity of the predominately sandy soils in Florida, make irrigation indispensable for the high quality landscapes desired by homeowners Haley et al. 2007; National Research Council NRC More than 15% of all new homes in the United States were built in Florida between 2005 and 2006 United States Census Bureau USCB 2008 ; most of them with automatic in-ground irrigation systems Tampa Bay Water TBW 2005; Whitcomb These 1 Research Associate, Dept. of Agricultural and Biological Engineering, Univ. of Florida, Gainesville, FL bernardc@ ufl.edu 2 Associate Professor, Dept. of Agricultural and Biological Engineering, Univ. of Florida, P.O. Box , Gainesville, FL corresponding author. mddukes@ufl.edu 3 Professor, Dept. of Crop Science, North Carolina State Univ., Raleigh, NC grady_miller@ncsu.edu Note. This manuscript was submitted on October 6, 2008; approved on August 3, 2009; published online on February 12, Discussion period open until August 1, 2010; separate discussions must be submitted for individual papers. This paper is part of the Journal of Irrigation and Drainage Engineering, Vol. 136, No. 3, March 1, ASCE, ISSN /2010/ /$ systems have been reported to result in higher water use compared to manual irrigation or manually moved sprinklers Mayer et al A recent study carried out by Haley et al in central Florida found that homeowners tended to irrigate two to three times the turfgrass requirements. Overirrigation wastes water and energy and can have a detrimental effect on landscape/turfgrass quality and the environment. Leaching of nutrients and/or agrochemicals, degradation of surface water supplies, potential increases in sediment-laden runoff, and erosion are all potential results of overirrigation. In addition, excessive irrigation strains water supply infrastructure by increasing peak demands, sometimes at or near system design limits. In turfgrass, overirrigation can promote the establishment and survival of turfgrass weeds Busey and Johnston 2006, increase the severity of some pathogens Davis and Dernoeden 1991, and increase evapotranspiration ET Biran et al Control of irrigation based on soil moisture or soil tension can reduce both overirrigation Augustin and Snyder 1984 and nitrogen leaching below the root zone Snyder et al Modern commercially available soil moisture sensor systems SMSs include not only a sensor to be buried in the soil but a controller that interfaces with the irrigation time clock. This controller is a milestone in the development of the soil moisture sensor industry because it sends a signal to the buried sensor and converts the response to a sensed soil water content SWC.At the same time, the controller acts as a switch that allows the 184 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010

2 operator to choose a desired SWC threshold, above which the scheduled irrigation events will be bypassed. Typically, the adjustable threshold can be set between relatively dry to relatively wet soil moisture conditions; depending on variables such as plant material, sensor installation depth, and soil type. In sandy soils, where the storage of water is minimal, coupled with shallow turfgrass root depth, the continuous and accurate monitoring of the SWC becomes of great consequence; hence, SMSs could be a useful tool for diminishing or avoiding overirrigation. Automatic control of irrigation, based on SMSs, has been successfully reported in coarse textured soils, achieving water savings without diminishing yields of vegetable crops Dukes and Scholberg 2005; Dukes et al. 2003; Muñoz-Carpena et al. 2005; Shock et al. 2002; Zotarelli et al nor quality of turfgrass Cardenas-Lailhacar et al while decreasing nutrient leaching Pathan et al Automatic irrigation systems with rain sensor feedback have been recommended to save water in Florida Cardenas-Lailhacar and Dukes 2008, but SMS-based systems have resulted in more than twice the water savings of rain sensors up to 88%, during normal/wet weather conditions in Florida Cardenas-Lailhacar et al The main goal of this project was to determine if a residential automatic irrigation system, when receiving feedback from a SMS, could reduce irrigation water application while maintaining acceptable turf quality compared to common time-based irrigation schedules implemented by homeowners. A previous study Cardenas-Lailhacar et al has shown that SMSs could lead to irrigation water savings under relatively wet/normal weather conditions. This research, as a comparison, was conducted under dry weather conditions. The first objective was to statistically evaluate the water savings potential of different commercially available SMSs. Afterward, the objectives were to quantify irrigation water use and to evaluate turfgrass quality differences among: 1 a time-based irrigation schedule system with and without a rain sensor; 2 time-based schedules compared to SMS-based systems; and 3 SMS-based systems under different irrigation frequencies. Materials and Methods This research was part of a project that began in Detailed materials and methods, and results from years 2004 and 2005 are reported in Cardenas-Lailhacar et al The experiment was installed in Gainesville, Fla., on a soil classified as Arredondo fine sand United States Department of Agriculture USDA 2008, with particle size distributions of 92.4, 4.5, and 3.1% for sand, silt, and clay, respectively; a bulk density of 1.53 g/ml, and an electrical conductivity of 0.05 ds/m, on the 0 20 cm depth, among other characteristics, according to Carlisle et al Sixty-four 3.7 m 3.7 m plots were established on a field with common bermudagrass Cynodon dactylon L. Pers.. Each plot was irrigated with four quarter-circle pop-up spray heads Hunter 12A, Hunter Industries, Inc., San Marcos, Calif., which were pressure regulated at 172 kpa, and with an average application rate of 38 mm/h. Turfgrass management was carried out according to recommendations by the University of Florida Trenholm et al and plots were mowed twice weekly at a height of 5.5 cm. Four commercially available SMSs were tested: Acclima Digital time domain transmissometry TDT RS-500 Acclima Inc., Meridian, Id., Watermark 200SS-5 Irrometer Company, Inc., Riverside, Calif., Rain Bird MS-100 Rain Bird International, Inc., Glendora, Calif., and Water Watcher DPS-100 Water Watcher, Inc., Logan, Utah, codified as AC, IM, RB, and WW, respectively. The working principles of these systems are TDT and soil water matric potential for AC and IM, respectively, and frequency domain reflectometry for the RB and WW systems. Each one of these SMSs included probe s to be installed in the soil and a controller that could be adjusted to different SWC thresholds. Each probe was installed in 2004, in the center of a different plot, in the top 7 to 10 cm of the soil, where most of the roots were observed. Each plot with a sensor was used to control irrigation in three other plots, simulating an irrigation system with four zones controlled by one sensor. Specific sensor locations were discussed by Cardenas-Lailhacar et al Because homeowners/contractors typically would not calibrate these commercially available sensors, the different SMS tested were used directly out of the box, following manufacturer instructions for installation and set points. The SMS controllers were set at thresholds close to field capacity. The AC controllers were set on their display at a volumetric water content of 7%, which was taken as approximately field capacity based on soil column dehydration tests Cardenas-Lailhacar Permanent wilting point for this soil series has been reported as 3% Carlisle et al Following manufacturer recommendations to find a set point close to field capacity, the RB and WW controllers were set at their thresholds 24 h after a significant rainfall event that filled the soil profile with water. The RB controllers were set at 2.5 and, on the WWs, the knob was set in the middle of the scale dimensionless and the calibration button was pushed, which allowed its autoset point. As reported in Cardenas-Lailhacar and Dukes 2007, the lowest volumetric SWC at which the different brands allowed irrigation were 7.3, 6.4, and 7.3% for AC, RB, and WW, respectively, indicating that their set points were similar. Brand IM, however set at 1, which according to the manufacturer represents 10 kpa or field capacity, was reported to allow irrigation at a volumetric SWC of 12% or more, meaning that this brand/model was reading a dryer than actual SWC, and did not bypass as many cycles as the other SMS brands tested. Therefore, in an attempt to initiate irrigation bypass at soil moisture levels close to field capacity, the IM controllers were set slightly higher; at Set Point 2 or 15 kpa of soil tension, according to the manufacturer. Treatments Three basic types of treatments were defined: time-based, SMSbased, and nonirrigated treatments Table 1. Within the timebased treatments, an irrigation frequency of 2 days/week was selected since this frequency is common in Florida due to water restrictions established by state regulatory agencies St. John s River Water Management District SJRWMD Two of these treatments 2-WRS and 2-DWRS were connected to a rain sensor Mini-click II, Hunter Industries, Inc., San Marcos, Calif., which was set at 6-mm rainfall threshold, to simulate requirements imposed on homeowners by Florida Statutes Chap In addition, a without rain sensor treatment 2-WORS was included to simulate household irrigation systems with a nonfunctional or absent rain sensor. This last treatment was used as the main time-based comparison treatment since rain sensors are thought to be absent or nonfunctional on many homes in Florida Whitcomb Also, a nonirrigated treatment 0-NI was implemented as a control for turfgrass quality. Two experiments were performed during 2006 Table 1. The first experiment occurred from March 25 to July 15, where all the JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010 / 185

3 Table 1. Irrigation Treatments from March 25 to July 15 and from July 22 to December 10, 2006 Treatment description or SMS brand Set point or controller position March 25 to July 15 July 22 to December 10 Treatment code Irrigation frequency days/week Treatment code Irrigation frequency days/week Time-Based Without rain sensor N/A 2-WORS 2 2-WORS 2 With rain sensor 6 mm 2-WRS 2 2-WRS 2 80% of 2-WRS 6 mm 2-DWRS 2 2-DWRS 2 SMS-Based Acclima 7% VWC AC 2 1-AC 1 2-AC 2 7-AC 7 Rain Bird #2.5 RB 2 1-RB 1 2-RB 2 7-RB 7 Irrometer #2 IM 2 1-IM 1 2-IM 2 7-IM 7 Water Watcher #0 WW 2 a a Nonirrigatated N/A NI 0 0-NI 0 Note: SMS=soil moisture sensor system, N/ A=not applicable, and VWC=volumetric water content. a During this testing period the three WW systems malfunctioned, thus they were not included in this part of the research. SMS-based treatments were set at an irrigation frequency of 2 days/week Mondays and Thursdays to statistically evaluate whether the different SMS brands tested had the same water savings potential while maintaining an acceptable turf quality. The second experiment occurred from July 22 to December 10, where the different SMS brands were set to run with three different irrigation frequencies: 1, 2, and 7 days/week, respectively to analyze their performance under different watering frequency scenarios. The 1- and 2-day/week frequencies represent typical watering restrictions imposed in Florida Florida Department of Environmental Protection FDEP 2008; St. John s River Water Management District SJRWMD The 7-day/week watering frequency was chosen to analyze the possibility of allowing the SMS to decide when to irrigate according to plant needs independent of the day of the week water restrictions. It should be noted that during this last testing period, the three WW systems presented malfunctioning problems; thus, they were not included in this part of the research. This brand is no longer commercially available. The irrigation cycles were programmed on five time clocks, which were set to start between 1 and 5 a.m., to diminish wind drift and decrease evaporation, and to mimic water use restrictions in the study area. The weekly irrigation depth was programmed to replace 100% of the monthly net irrigation requirement based on recommendations by Dukes and Haman 2002 and with monthly application amounts as given by Cardenas-Lailhacar et al All treatments were programmed to have an equal opportunity to apply the same amount of irrigation per week, except for treatment 0-NI nonirrigated and 2-DWRS 80% of 2-WRS. Therefore, differences in water application among treatments would be the result of sensors bypassing scheduled irrigation cycles. Data Collection Pulse-type positive displacement flowmeters PSMT 20 mm 190 mm, Amco Water Metering Systems, Inc., Ocala, Fla. were used along with a CR 10X datalogger Campbell Scientific, Logan, Utah to continually record the irrigation date and volume applied to each plot. An automated weather station Campbell Scientific, Logan, Utah was located at the experimental site to record rainfall and other weather parameters to enable daily evapotranspiration ET calculation, which was computed from the ASCE-Environmental and Water Resources Institute EWRI standardized equation for short crops ASCE-Environmental and Water Resources Institute ASCE-EWRI 2005 ET o = R n G T u 2 e s e a u 2 where ET o =reference ET mm/day ; R n =net radiation at the crop surface MJ/m 2 day ; G=soil heat flux density MJ/m 2 day, T =mean daily air temperature at 2-m height C ; u 2 =wind speed at 2-m height m/s ; e s =saturation vapor pressure kpa ; e a =actual vapor pressure kpa, e s e a =saturation vapor pressure deficit kpa ; =slope vapor pressure curve kpa/ C ; and =psychrometric constant kpa/ C. Turfgrass quality was visually assessed and rated using a scale of 1 to 9, where 1 represents brown, dormant, or dead turf, and 9 represents the best quality Skogley and Sawyer A rating of 5 was considered the minimum acceptable turf quality. The first rating was carried out by the end of the first half of 2006, on July 15, and the second rating was conducted by the same person on October 26, 2006, when differences in turf quality were apparent after 42 days with no rainfall / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010

4 Table 2. Weather Conditions and Reference ET ET o at the Experimental Site during March 25 to July 15 and from July 22 to December 10, 2006 Month Mean air temperature C Mean relative humidity % Mean wind speed m/s Total rainfall mm a March 25 to July 15 March April May June July Total b July 22 to December 10 July August September October November December Total a Calculated from the ASCE-EWRI standardized equation for short crops, as described in ASCE-Environmental and Water Resources Institute ASCE- EWRI ET o a mm Treatments were replicated four times, for a total of 64 plots, in a completely randomized design. Statistical data analyses were performed using the general linear model procedure of the Statistical Analysis System software Statistical Analysis System SAS ANOVA was used to determine treatment differences and Duncan s multiple range test was used to identify mean differences. Results and Discussion Table 2 summarizes the monthly mean air temperature, relative humidity, wind speed, total rainfall, and ET o measured on site during both experimental periods. In general, favorable temperatures prevailed for the growth and development of the bermudagrass, except in late November and December when temperatures began to gradually decline until dormancy December 10 and research was discontinued. During March 25 to July 15, total rainfall was less than ET o 323 and 523 mm, respectively, suggesting that supplemental irrigation would be necessary to maintain adequate turfgrass quality, and the opposite occurred during July 22 to December 10, when total rainfall was greater than ET o 567 and 499 mm, respectively. bermudagrass around 15 cm, it can be considered that drought conditions prevailed during this period. In comparison, and for the same period during 2005 Cardenas-Lailhacar et al. 2008, 38% of these days presented rainfall events with a cumulative amount of 561 mm, which could be considered as normal/wet conditions compared to historical records. These observations were corroborated by the drought monitor archives for this area The Drought Monitor Table 3 shows the cumulative irrigation depth applied to treatments, statistical comparisons, and percent water savings compared to 2-WORS. During this experiment, one WW unit failed for unknown reasons, and was not included in this analysis. Results show that when a rain sensor was connected to the irrigation system, the volume of water applied decreased from 602 to 525 mm 2-WORS versus 2-WRS, respectively, a 13% water savings. During 2004 and 2005, water savings of 34% were reported for 2-WRS Cardenas-Lailhacar et al. 2008, clearly influenced by First Half of 2006 Fig. 1 shows the rainfall pattern compared to a historical average During this 123-day experiment, every month exhibited less rainy days than historically. On average, 18% of the days presented rainfall events compared to a historical of 35% of rainy days for this period. The cumulative precipitation was 323 mm, which represents a 38% deficit from the historical average of 523 mm. Moreover, 77% of this amount 247 mm fell in five large rain events 4% of the total days. Therefore, and taking into account the high infiltration rate 133 mm/h Gregory et al and the low water holding capacity of this sandy soil Cardenas- Lailhacar 2006, plus the observed shallow rooting system of the Fig. 1. Rainy days per month and cumulative rainfall; March 25 to July 15, 2006 versus historical values JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010 / 187

5 Table 3. Total Cumulative Irrigation Depth Applied to Treatments, Statistical Comparisons, and Percent Water Savings Compared to 2-WORS, from March 25 to July 15, 2006 Treatment Cumulative depth mm Comparisons a A B Water savings % Time-based 2-WORS WRS DWRS Time-Avg 513 a b SMS-based AC 279 b c 54 RB 266 b 56 IM 552 a 8 WW 504 a 16 SMS-Avg 400 b 34 CV % Note: For treatment acronyms description, see Table 1. SMS=soil moisture sensor system; Avg=average; and CV=coefficient of variation determined by the overall ANOVA model. a A=time-based versus SMS-based treatments and B=between SMS brands. b Different letters within this column indicate statistical difference at P 0.01 Duncan s multiple range test. c Different letters within this column indicate statistical difference at P Duncan s multiple range test. the more abundant and frequent rainfall conditions. Treatment 2-DWRS applied 31% less water compared to 2-WORS and 21% less water than 2-WRS. Table 3 Comparison A shows that, on average, the SMSbased treatments applied significantly less water P 0.01 than the time-based treatments 400 mm versus 513 mm, respectively. Compared to 2-WORS, all SMS brands applied less water, ranging from 266 to 552 mm, which represents from 8 to 56% in water savings, with an average of 34%. Furthermore, sensors from brands AC and RB saved 47 and 49% more water, respectively, compared to an irrigation system having a rain sensor added 2-WRS. The water applied by the different SMS brand/units could be due to a number of factors, including soil spatial variability, probe burial depth, and difference in the threshold setting. In this experiment, these factors were managed by analyzing moisture retention of all plots and selecting plots with similar conditions for probe burial, by burying all probes in the observed turfgrass root zone at similar depths, and by setting thresholds on all controllers at field capacity as practically as possible; with comparable results for AC, RB, and WW, as described earlier. Therefore, water savings by these different brands/models were estimated to be mainly a result of their particular accuracy and consistency to measure SWC. As reported in Cardenas-Lailhacar and Dukes 2007, AC and RB resulted in a narrowest range of SWC over which they allowed irrigation 3.9 and 2.5 percentile points, respectively suggesting that they were more accurate and consistent to measure SWC than IM and WW which allowed irrigation within 5.5 and 4.5 percentile points, respectively. As noted previously, the IM controllers were set at a SWC content slightly lower than field capacity according to the manufacturer calibration Position 2 or 15 kpa of soil tension to investigate if this set point would bypass as many irrigation cycles as the other brands. Fig. 2. Relationship between water depth applied and turfgrass quality, averaged by treatments, March 25 to July 15, Dotted line indicates minimum acceptable turfgrass quality and error bars are standard error of the mean. Note: One WW system controlling four plots noted as WW-broken in the graph failed for unknown reasons and was considered as a separate treatment for turfgrass quality purposes. For treatment acronyms description, see Table 1. Table 3 Comparison B shows that brands AC and RB applied a significantly P lower depth of water compared to IM and WW 279 and 266 mm versus 552 and 504 mm, respectively. The irrigation savings compared to 2-WORS averaged 54 and 56% for AC and RB, versus 8 and 16% for IM and WW, respectively. Similar trends in water savings were reported for these brands in Cardenas-Lailhacar et al but, due to the dryer weather conditions that prevailed in the spring of this experiment, lower irrigation savings were obtained compared to previous results, which ranged from 27 to 92%. Both groups resulted in an absolute and a relative threshold set point brand AC and RB, respectively, versus IM and WW, also respectively, suggesting that there was not a systematic error in the setup of the absolute versus the relative controllers. However, these results indicate that Set Point 2 in the IM controllers was still higher than the field capacity. Note that the threshold for the IMs was set up at 6 for short periods, verifying that they were functional. This suggests that in this sandy soil and with the manufacturer calibration, the IMs operate like relative controllers rather than absolute controllers. Other explanations could be found in previous studies, where it was stated that granular matrix sensors, like the IM probes, have limitations to respond accurately in sandy soils Irmak and Haman 2001 at low soil water tensions Taber et al. 2002, and that their readings have high variability Intrigliolo and Castel Some differences in turf quality between the plots were apparent by July To assess the extent of a treatment effect, the average turf quality was plotted against the average depth of water applied per treatment Fig. 2. A positive correlation was obtained between them and, according to the linear regression, 89% of the variation in turf quality between treatments could be explained by the amount of the irrigation water applied. Supplemental irrigation of over 250 mm was necessary to achieve acceptable turf quality during this period, differing from previous wetter years, where the resultant turf quality of the nonirrigated treatments was not significantly different from the SMS-based treatments Cardenas-Lailhacar et al / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010

6 Table 4. Turfgrass Quality Ratings per Treatment on July 15, 2006 Comparisons a Treatment Rating A B C D Time-Based 2-WORS 6.8 NS 2-WRS 6.0 NS 2-DWRS 6.3 NS Time-Avg 6.4 a b NS SMS-Based AC 5.7 b RB 5.8 b IM 7.0 a WW 7.0 a SMS-Avg 6.4 a NS WW-broken c 4.3 b Fig. 3. Rainy days per month and cumulative rainfall; July 22 to December 10, 2006 versus historical values Control 0-NI 3.8 b CV % Note: Turfgrass quality was visually assessed and rated using a scale of 1 to 9, where 1 represents brown, dormant, or dead turf; 9 represents the best quality; and 5 was considered the minimum acceptable turf quality, based on Skogley and Sawyer For treatment acronyms description, see Table 1. SMS=soil moisture sensor system; Avg =average; NS=no statistical difference; and CV=coefficient of variation determined by the overall ANOVA model. a A=time-based versus SMS-based versus 2-WW versus nonirrigated treatments; B=time-based versus SMS-based treatments; C=between time-based treatments; and D=between brands. b Different letters within a column indicate statistical difference at P 0.01 Duncan s multiple range test. c Unit failed to control irrigation, but was considered as a different treatment for turf quality purposes. Table 4 shows statistical comparisons between treatments for the resultant turfgrass quality on July 15, 2006, where the broken WW was considered as a separate treatment. The turf qualities of the broken WW and 0-NI treatments declined to unacceptable levels 4.3 and 3.8, respectively, and were significantly lower P 0.01 than the time-based and the SMS-based treatment averages, which remained above the minimum quality rating Comparison A. Significant differences were not found between the averages of the time-based versus the SMS-based treatments Comparison B, neither among the time-based treatments Comparison C, suggesting that the incorporation of a rain sensor or soil moisture sensor to an automatic irrigation system could lead to irrigation water savings without compromising the turf quality beyond unacceptable levels. Even when turf quality did vary across brands AC and RB resulted in a significantly P 0.01 lower turfgrass quality compared to WW and IM Comparison D all SMS-based treatments resulted in an average quality that was at least acceptable rated as 5 or above. It is important to remark, however, that some AC and RB replications were just at the minimum acceptable quality level or slightly above, suggesting that their thresholds/run times were at the limit to maintain acceptable turf quality during the dry weather conditions of this monitoring period. Second Half of 2006 Fig. 3 shows the percent of rainy days per month and the cumulative rainfall for the second half of 2006 compared to historical records. Even when the cumulative rain for the 142-day experimental period was 10% higher than a historical year 567 mm versus 517 mm, 76% of the rain fell in only 6 days 4% of the experimental days. When taking into account the frequency of rainfall, on average, rain occurred on 20% of the days, when in a historical year 30% of the days recorded rain events. Moreover, from July through October a lesser amount of rainy days occurred compared to a historical year, coinciding with high ET o values. It should be pointed out that for more than a month from September 15 to October 26 only 0.25 mm of rain was recorded, coupled with high temperatures. As a comparison, during the second half of 2004, in the same experimental period, 32% of the days had rainfall events normal with a cumulative amount of 943 mm, 82% more than a normal year Cardenas-Lailhacar et al Therefore, the second half of 2006 could be considered as dry corroborated also by The Drought Monitor 2008 and a lesser amount of irrigation cycles bypassed by the SMSs should be expected, compared to normal/rainy years. The cumulative irrigation depth applied by the different treatments as well as statistical comparisons and percent water savings compared to 2-WORS are presented in Table 5. Treatment 2-WORS was programmed to allow every scheduled irrigation cycle independent of the weather and/or SWC conditions, and resulted in a cumulative depth of 659 mm. The treatment that included a rain sensor 2-WRS applied a total of 500 mm, equivalent to 24% water savings compared to 2-WORS. Cardenas-Lailhacar et al reported that in 2004 and 2005, this amount was higher 34% ; however, it should be remembered that 2006 was a dryer year and, during this specific period, almost no rain fell for more than a whole month. Consistent with previous years, the time-based treatments applied significantly P more water than the SMS-based treatments, averaging 532 mm versus 303 mm, respectively Table 5, Comparison A. This means that the average of the SMS-based treatments saved 54% of the water applied by 2-WORS, even during relatively dry weather conditions. When comparing the three SMS irrigation frequencies tested Table 5, Comparison B, all of them were significantly different P 0.001, with the 1 day/week frequency applying the most water, followed by 2 days/week, and then by 7 days/week, with 378, 296 and 234 mm, respectively. Compared to 2004 and 2005, the 7-day/week irrigation frequency also resulted in the least irrigation, as reported in Cardenas-Lailhacar et al This trend JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010 / 189

7 Table 5. Total Cumulative Irrigation Depth Applied to Treatments, Statistical Comparisons, and Percent Water Savings Compared to 2-WORS, from July 22 to December 10, 2006 Treatment Cumulative depth mm Comparisons a A B Water savings % Time-based 2-WORS WRS DWRS Time-Avg 532 a b SMS-based 1-AC RB IM Avg 378 a 43 2-AC RB IM Avg 296 b 55 7-AC RB IM Avg 234 c 64 SMS-Avg 303 b 54 CV% 47 9 Note: For treatment acronyms description, see Table 1. SMS=soil moisture sensor system, Avg=average, and CV=coefficient of variation determined by the overall ANOVA model. a A=time-based versus SMS-based treatments and B=between irrigation frequency averages. b Different letters within a column indicate statistical difference at P Duncan s multiple range test. appears to be because a higher frequency of irrigation windows leads to a greater probability that rain will be used for plant needs, even at a low rainfall frequency. Moreover, the 7-day/week irrigation frequency was scheduled to apply a lower amount for a given irrigation event, which tends to minimize water losses due to deep percolation, increasing the irrigation efficiency. However, in practice, the irrigation system runtimes should be long enough to ensure that the minimum application amount at least replaces 1 day of ET o. Lower application amounts could result in inefficiency due to pipe filling, as well as a higher proportion of the applied water evaporating relative to longer irrigation run times. Considering the RB treatments a discontinued system, 1-RB applied a greater amount of water than the other frequencies, 474 mm, or 28% in water savings. The other two frequencies tested, 2-RB and 7-RB, applied a similar total amount of irrigation, 122 and 140 mm, respectively. These two last frequencies represent water savings of 81 and 79%, respectively, compared to 2-WORS; a slightly lesser amount than those recorded during the wetter weather conditions of 2004 and 2005, respectively, 88 and 90% Cardenas-Lailhacar et al After the end of this project, in March 2007, the field site was altered for another project and, in the process, all sensors were removed. One of the sensor rods from 2-RB exhibited corrosion, which may be the reason for the inconsistent behavior observed in the final phase of this study. At every irrigation frequency tested, the IM treatments applied Fig. 4. Aerial view of the experimental site. Lighter plots show drought stress. more water than the other brands, as what had occurred in the first half of This is also consistent with years 2004 and 2005 Cardenas-Lailhacar et al. 2008, even when the IM controllers were set at Position 2 instead of Position 1, which should have kept the lawn on a dryer condition Position 1 corresponds to a soil tension of 10 kpa, or field capacity, and Position 2 corresponds to 15 kpa of soil tension, according to the manufacturer. The 2-IM treatment applied almost the same amount of water than 2-WORS, with water savings of just 9%, which was lower than that obtained with the rain sensor 24%. The other two frequencies tested, 1-IM and 7-IM, applied 484 and 448 mm, a respective savings of 27 and 32%, compared to 2-WORS. During 2004 and 2005, these water savings were higher, 48 and 53% for 1-IM and 7-IM, respectively. Again, this is consistent with the different weather conditions of both periods. Finally, all the Acclima systems behaved similarly with respect to the total amount of water that they allowed to be applied during this testing period. Treatments 1-AC, 2-AC, and 7-AC applied 177, 166, and 114 mm, respectively, which represent water savings of 73, 75, and 83% compared to 2-WORS, respectively. These results are similar to but slightly lower than to those obtained by the Acclima systems during the wetter 2004 and 2005 periods, when they recorded respective water savings of 81, 77, and 92% Cardenas-Lailhacar et al In contrast to uniform good turfgrass quality results in previous SMS research, regardless of water application depths Cardenas-Lailhacar et al. 2008, drought stress was apparent on some plots in this study in the dry episode that occurred from September 15 to October 26. Fig. 4 shows an aerial view of the experimental site, where plots with different turfgrass qualities can be seen. Fig. 5 shows the relationship between the amount of water applied and the resultant turfgrass quality during this period, averaged by treatment, where a linear regression of R 2 =0.80 was obtained. Less than 60 mm of irrigation over the dry period of 42 days resulted in unacceptable turf quality on two experimental treatments 0-NI and 2-RB and in minimum acceptable turf quality on other two SMS-based treatments 7-RB and 7-AC. Thus, this amount of irrigation could be considered the minimum to maintain acceptable turfgrass quality during this period. It should be noted that 2-RB was probably not working properly when it began to allow scheduled irrigation cycles after October 4. Thereafter, it behaved normally and the turf quality improved gradually. This behavior could be due, in part, to the corrosion of one of its rods as described earlier. Table 6 shows statistical comparisons P 0.05 between treatments for the resultant turfgrass quality on October 26, The control treatment for quality purposes 0-NI resulted in 190 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010

8 Table 6. Turfgrass Quality Ratings by Treatment at the End of the Dry Period on October 26, 2006 Comparisons a Treatment Rating A B C D E Time-based 2-WORS 7.0 NS 2-WRS 6.3 NS 2-DWRS 6.5 NS Time-Avg 6.6 a b a Fig. 5. Relationship between water depth applied and turfgrass quality, averaged by treatments, September 15 to October 26, Dotted line indicates minimum acceptable turfgrass quality and error bars are standard error of the mean. For treatment acronyms description, see Table 1. lower quality compared to the averages of the time-based and the SMS-based treatments Comparison A meaning that irrigation was necessary to maintain an acceptable turf quality. The timebased treatments resulted in better average turf quality than the SMS-based treatments Comparison B, mainly due to the higher depth of water that the plots received during this part of the experiment Fig. 5, yet the SMS-based treatments average was above the minimum acceptable turf quality 5.7. No differences between the time-based treatments were detected Comparison C, with average quality ratings that ranged between 6.3 and 7.0. The irrigation frequencies averages Comparison D resulted in no significant turf quality differences even when they allowed significantly different amounts of water to be applied Table 5. Finally, statistical differences were found between the SMS-based treatments Comparison E, where the lowest turf quality was found on 2-RB, as a result of the low amount of water applied to this treatment Fig. 5. Treatment 7-RB was just in the level of the minimum acceptable turf quality and a similar situation happened with all the AC frequencies, with turf qualities between 5 and 5.5. Considering these results, the set points and/or the run times for these systems mainly for the 2 and 7 days/week irrigation frequencies were possibly at the limit for sustained dry weather conditions. In the case of the IM systems, which applied more water than the other brands Table 5, turfgrass qualities between 6.0 and 6.8 were observed, with an average of 6.4; which was significantly higher than the AC and RB averages 5.3 and 5.3, respectively. Summary and Conclusions During this research project, dry weather conditions prevailed at the experimental site. Supplemental irrigation was necessary to maintain acceptable turf quality during this period, which was evidenced by unacceptable turf quality on the plots with minimal or no supplemental irrigation. During the first half of 2006, an experiment was set up to evaluate the water savings potential of different commercially available SMSs. On average, treatments from brands AC and RB SMS-based 1-AC 5.5 ab 1-RB 6.8 a 1-IM 6.0 ab 1-Avg 6.1 NS 2-AC 5.5 ab 2-RB 4.0 c 2-IM 6.8 a 2-Avg 5.4 NS 7-AC 5.0 bc 7-RB 5.0 bc 7-IM 6.5 a 7-Avg 5.5 NS SMS-Avg 5.7 a b Control 0-NI 3.3 b CV % Note: Turfgrass quality was visually assessed and rated using a scale of 1 to 9, where 1 represents brown, dormant, or dead turf, 9 represents the best quality, and 5 was considered the minimum acceptable turf quality, based on Skogley and Sawyer For treatment acronyms description, see Table 1. SMS=soil moisture sensor system; Avg =average; NS=no statistical difference; and CV=coefficient of variation determined by the overall ANOVA model. a A=time-based versus SMS-based versus nonirrigated treatments; B =time-based versus SMS-based treatments; C=between time-based treatments; D=between irrigation frequency averages; and E=between SMSbased treatments. b Different letters within a column indicate statistical difference at P 0.05 Duncan s multiple range test. resulted in substantial irrigation reductions while maintaining good turf quality. Turf quality was enhanced by time-based irrigation schedules and less functional soil moisture sensor controllers at the expense of water conservation. Three time-based treatments were established to mimic the operation of irrigation systems carried out by different homeowner profiles. The treatment with a functional rain sensor 2- WRS, set at a 6-mm threshold, applied between 13 and 24% less water than the treatment without a rain sensor 2-WORS, showing that even under dry weather conditions rain sensors can save substantial amounts of irrigation water in Florida. On the other hand, treatment 2-DWRS, saved between 13 and 21% of water compared to 2-WRS and between 31 and 34% compared to 2-WORS. These time-based treatments resulted in good turfgrass quality during the entire experiment. Thus, using a rain sensor, and decreasing time clock runtimes at the same time, can reduce the irrigation water applied 2-WORS versus 2-WRS versus 2-DWRS, while maintaining good turf quality. All of the properly working SMS-based treatments applied JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING ASCE / MARCH 2010 / 191

9 less water than 2-WORS, ranging from 8 to 54% in the first half, and from 9 to 83% less water in the second half of 2006; with averages of 35 and 54% for the first and second half of 2006, respectively. These savings results are lower than those obtained during the previous rainier years where the SMS-based treatments recorded irrigation water savings that ranged from 27 to 92%. Except for some IM treatments, the SMS-based treatments also saved more water compared to the treatment with rain sensor. These experimental treatments had savings ranging from 5 to 77% beyond a rain sensor alone. All three irrigation frequencies tested in the second half of , 2, and 7 days/week were significantly different, with the 7 days/week schedule applying the least amount of water; the same result that was obtained in previous rainier years. However, runtimes for the 7-days/week schedule were often very short on the order of a few minutes. In practice, irrigation runtimes should be long enough to fill the irrigation system and compensate for site-specific conditions such as high evaporative potential. SMS-based treatments resulted in average turf qualities that were at or above the minimum acceptable over the monitoring period, with the exception of the broken WW treatment and, in the second half of 2006, treatment 2-RB. However, the ACs and the rest of the RB treatments resulted in turf qualities at or slightly above the minimum acceptable level. This means that the thresholds set on these controllers might be too low for sustained drought situations or less drought-tolerant turfgrasses, and/or that the run times might be increased to assure or improve turf quality above the minimum acceptable level. Finally, the goal of this research was fulfilled, when the SMSs appear to be a technology that could lead to substantial savings in residential irrigation water while maintaining acceptable turf quality during both dry and normal/wet weather conditions. Testing this technology on actual household/light commercial irrigation systems is recommended to validate these results. Acknowledgments The writers thank Engineer Larry Miller for his assistance and to numerous undergraduate and graduate students for their help on this project. This research was supported by the Pinellas-Anclote Basin Board of the Southwest Water Management District, the Florida Department of Agriculture and Consumer Services, the Florida Turfgrass Association, the Florida Nursery Growers and Landscape Association, and the Florida Agricultural Experiment Station. 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