Sustainable Landscapes: Water Conservation by Systematic Injection of Wetting Agents

By Dr. Sowmya Mitra

Diminishing resources and client demands have made Sustainable Landscapes extremely important.  Water-wise (or Xeriscape) native plant material, best management practices and water-efficient irrigation systems are crucial components of sustainability.

Objectives

Develop a protocol to optimize irrigation scheduling based on evapotranspiration demand (ETo). Reduce water usage by injecting wetting agents into the irrigation line. Monitor changes in turf quality. Analyze plant tissues to monitor any abnormal element accumulations. Measure crop coefficient of the Bermuda grass maintained under fairway mowing conditions.

Materials and Methods

Twenty four 3-meter by 3-meter individually irrigated plots were laid out in a split-plot design. 12 plots receive potable water and 12 plots receive reclaimed water. Three surfactant treatments and a control were evaluated.

Each treatment was evaluated under potable and reclaimed water with three replications. Water meters were installed on the lines to measure the amount of water used for irrigation. The results of the project were evaluated by monitoring volumetric moisture content using 3-meter-long Aquaflex sensors buried in the soil. The Aquaflex sensors use time domain transmission (TDT) principle in measuring moisture content. Turf quality was evaluated on a weekly basis. Soil and water chemical analysis was conducted once a month. Electrical conductivity (EC) and total dissolved solids (TDS) were measured once a month.

Plots were rated for localized dry spots (LDS) and were measured once a month. Irrigation scheduling: 100 percent ETo during May, 70 percent ETo during June, 30 percent ETo during July, 10 percent ETo during August, etc. = ETo x 0.65 for Bermuda grass. Surfactant Rates: IrrigAid 24 fl. oz./acre every two weeks, Dispatch 12 fl. oz./acre every week, ACA 1897 12 fl. oz./acre every week

Time domain transmission

With TDT, an electrical pulse is sent along a transmission line embedded within the probe. A transient electrical field is created around the transmission line interacts with the surrounding medium and soil water. Aquaflex extracts information from the shape of the pulse, which gives a good indication of soil conductivity. The electrical pulse data is used to correlate soil moisture.

Results

Overall, all the surfactant treatments helped retain higher levels of soil moisture between irrigation cycles at 15 cm from the soil surface compared to the untreated plots. The surfactant treatments did not have an effect on the soil temperature. The soil temperature varied from 28 degrees Celsius to 34 degrees Celsius during the summer months. All the surfactant treatments significantly reduced the presence of LDS in the plots compared to the untreated control but there was no statistical difference between the surfactant treatments.

Irrigation at 100 percent Eto: During the month of May, the turf grass plots received 100 percent of the cumulative ETo for the month. The bermudagrass turf experienced little moisture stress during the month and there was no significant difference in turf color or quality between the treatments.

Irrigation at 70 percent Eto: The Dispatch treatment resulted in the highest amount of volumetric moisture content in soil for both the water sources. There was no statistical difference between the IrrigAid and ACA 1897 treatments in the potable water source. In the recycled water irrigated plots the ACA 1897 treatment had higher amount of soil moisture compared to the IrrigAid treatment. There was no statistically significant difference between the IrrigAid and the untreated check plots with the recycled water source.

Irrigation at 30 percent Eto: The turf experienced drought stress, and LDS started to appear, but there was no significant difference between the treatments. The Dispatch treatment helped to maintain a higher amount of soil moisture compared to the other treatments followed by IrrigAid in the recycled water and ACA 1897 in potable water. There was no statistically significant difference between the IrrigAid and ACA 1897 treatments with the recycled water source.

Irrigation at 10 percent Eto: During this month, all the Dispatch treated plots irrigated with potable water and recycled water had a significantly higher amount of volumetric soil moisture content at 15 cm from the soil surface compared to the other treatments. The IrrigAid and ACA 1897 treated plots had significantly higher amounts of soil moisture compared to the untreated plots, but there was no statistical difference between the two treatments

Conclusion

Overall, all the wetting agents helped in retaining higher moisture in the soil profile compared to the untreated controls. Under moisture stress (30 to10 percent ETo) Dispatch treatments maintained significantly higher moisture content in soils compared to the other treatments. IrrigAid and ACA 1897 treatments recorded higher moisture content in soils compared to the untreated plots but there was no significant difference between the treatments. The efficacy of the wetting agents was not affected by water quality

Dr. Sowmya (Shoumo) Mitra is global technical manager for turf at Syngenta in Switzerland. Previously an assistant professor in the Department of Horticulture/ Plant and Soil Sciences at California State Polytechnic University, Pomona, his primary responsibilities included teaching and research with turfgrasses. His research areas of interest are turfgrass physiology — mainly environmental stress management, soil and water quality, soil fertility and fertilizers, fate of pesticides, chemical and biological control of weeds.