Water Conservation by Systematic Injection of Wetting Agents
By Dr. Sowmya Mitra
Introduction
Irrigation water quantity and quality are becoming the limiting factors in maintaining high quality turf for sport fields and golf courses all around the world.
Issues surrounding water quality and availability have led Turf Managers to blend water supplies from different sources, while others have had to rely on recycled water supplies.
Objectives
Develop a protocol to optimize irrigation scheduling based on evapotranspiration (ET) demand.
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 (Kc) of the Bermuda grass maintained under fairway mowing conditions.
Materials and Methods
Twenty four (3 m by 3 m) 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 3 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 m 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) were measured once a month.
Irrigation scheduling: 100% ETo during May 2003, 70% ETo during June 2003, 30% ETo during July 2003, 10% ETo during August 2003; Etc = ETo x 0.65 for Bermuda grass
Surfactant Rates: Irrigade 24 fl oz/acre every 2 weeks, Dispatch 12 fl oz / acre every week, ACA 1897 12 fl oz / acre every week
Time Domain Transmission
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.
Benefits of TDT
When compared to TDR, TDT data measures a larger volume, thus considered more accurate.
TDT measures a soil core 3 m long with a 2.52 cm radius of measurement along the entire sensor.
6 liters of soil measured. No equilibration problems. System longevity (10y) Volumetric Water Content
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° C to 34° C during the summer months.
All the surfactant treatments significantly reduced the presence of localized dry spots (LDS) in the plots compared to the untreated control but there was no statistical difference between the surfactant treatments.
Irrigation at 100% Eto
During the month of May, 2003 the turf grass plots received 100% of the cumulative ET demand (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% 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% Eto
The turf experienced drought stress and localized dry spots 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% 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 -10% 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
