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2016 TTREEE REPORT
2016 TTREEE Report
Effect of Surfactant and Fertilizer on Turfgrass Health and Water and Nutrient Retention Under Deficit Irrigation in Simulated Urban Lawns Ben Wherley, Jacqui Aitkenhead-Peterson, Baoxin Chang, and Richard White Department of Soil and Crop Sciences, Texas A&M University, College Station, TX
Introduction
Loss of water and nutrients from urban lawns via surface runoff has received increased scrutiny in recent years due to increasingly limited water supplies, and the environmental damage associated with nutrient losses from some ecosystems. With tighter scrutiny on landscape water use across the U.S., the use of wetting agents for improving soil water infiltration and retention has become widespread on golf courses and sports fields, where sand root zones predominate. More recently, there has been growing interest by manufacturers in determining potential benefits of wetting agents on commercial and home lawns. Preliminary results from other universities as well as limited testing at the Texas A&M University Urban Landscape Runoff Facility has shown potential benefits of surfactant applications under reduced irrigation scenarios across a range of soil types. If these products show benefits in terms of increasing water infiltration/retention and/or reducing irrigation runoff losses from urban soils, this could have widespread benefits on the sustainability of turfgrass systems, especially where water availability is limited. Unfortunately, limited to no information is published concerning the effectiveness of surfactants on nutrient uptake efficiency and runoff volume reductions. The objectives of this study were to 1) Determine the effects of regular applications of a surfactant on reducing the volume of runoff emanating from simulated home lawns, and benefits to soil moisture content and turfgrass health and quality, and 2) Determine if the use of surfactant reduces nutrient losses in runoff under two irrigation regimes, specifically those of 60% x ETo (full replacement) and 30% x ETo (deficit level) irrigation.
Methodology
This study was conducted at the Texas A&M Turfgrass Field Laboratory in College Station, TX on the urban runoff research facility described by Wherley et al. (2014). The facility contains 24 plots, each 13ft wide by 26ft long with a 3.5% slope and individual irrigation control. All plots are established with four-year-old ‘Raleigh’ St. Augustinegrass atop a fine sandy loam topsoil. At the toe of each plot is a runoff collection trough which empties through a flume connected to automated flow measurement and sample collection equipment. This gives full documentation of the amounts of water lost to runoff as well as samples for measurement of the chemical composition of the runoff. Twenty plots (4 reps/treatment) were used for this study, which accommodated the following treatments:
Trt 1: 60% ETo irrigation, – Fertilizer, -Surfactant (control) Trt 2: 30% ETo irrigation, + Fertilizer + Surfactant Trt 3: 30% ETo irrigation, + Fertilizer - Surfactant
Trt 4: 30% ETo irrigation, - Fertilizer, + Surfactant Trt 5: 30% ETo irrigation, - Fertilizer – Surfactant
Plots receiving surfactant (Scotts Synergy) were treated at a rate of 3 oz./1,000 square feet every 4 weeks beginning July 21, 2016 and ending Nov.1, 2016. Plots receiving fertilizer received Scotts Southern Turf Builder at the label application rate of 0.916 lbs. N/1,000 square feet on July 21 and September 22, 2016. The experiment began on July 15 and concluded December 10, 2016. Water samples and flow rate measurements were taken for each naturally occurring rainfall event during the 16-week period. Collected runoff water samples were analyzed for pH, EC, nitrate-nitrogen, ammoniumnitrogen, total dissolved nitrogen (TDN) and orthophosphate-P concentrations. Dissolved organic nitrogen (DON) were estimated for each sample by deducting NO3-N + NH4-N from TDN. Plots were irrigated every Wednesday morning to simulate home lawns being managed under “once per week” irrigation restrictions. Plots were visually rated for turf quality each Tuesday (1 day before irrigation) to evaluate quality under stressed (30% ETo) conditions. Moisture content for the upper 7 cm of soil in each plot was measured each Tuesday (1 day pre-irrigation) and Friday (2 days post-irrigation) morning using a hand held Spectrum Field Scout soil moisture meter. Digital light box images of representative areas within each plot were also taken every Tuesday to provide an unbiased estimate of percent green cover. Finally, it should be noted that water drop penetration time (WDPT) tests were conducted at the 1” depth in soil cores removed from plots during the study period, and indicated no evidence of hydrophobicity in soils within plots. At the end of the study, data were subjected to ANOVA with mean separation performed using Tukey’s HSD at P=0.05.
Results and Discussion Soil moisture content
Overall, the results showed little to no significant effects of surfactant applications on increasing soil moisture content within the 60% ETo (wellwatered) plots. When analyzing the effects of surfactant within only the deficit-irrigated (30% ETo) plots, significant effects from both surfactant and fertilizer on soil moisture content were also not found (Table 1). In addition, soil moisture content was also analyzed in more detail by splitting the data into Tuesday (1 day pre-irrigation) and Friday (2 Continued on page 12