Field evaluation of wetting agent efficacy against localized dry spot, soil moisture, and root system growth on creeping bentgrass putting green turf - 21 trial. K. Carey, A.J. Porter, E.M. Lyons and K.S. Jordan Department of Plant Agriculture and the Guelph Turfgrass Institute, University of Guelph, Ontario. The objective was to determine efficacy of wetting agents on creeping bentgrass putting green turf on a high sand rootzone. Efficacy against localized dry spot, effects on soil moisture content, and on root system growth and health were to be determined. MATERIALS/METHODS The experiment was located on the alternative construction putting green at the GTI, which is a typical industry standard green of this type, with 3 cm of USGA specification rootzone mixture (8% sand, 2% peat v/v) on a graded subsoil with tile drains but no gravel drainage layer (Figure 1). Permanent turf cover on this green is 'Cobra' creeping bentgrass (Agrostis stolonifera) and invasive weedy Poa annua. The green has developed hydrophobic layers in previous seasons. Standard cultural practices were maintained (mowing at 5 mm, regular fertility). Test Design: The test was a complete randomized block design with four replicates per treatment. Each plot measured 2 m x 2 m. Treatments: Treatments listed in Table 1 were applied via a calibrated compressed air sprayer (2 psi, Teejet 81VS flat fan nozzles, 2 ml sec-1) on May 13, June 1, July 7, August 6, September 2, and September 3, 21. All liquid applications were made in 1 ml of water per square meter (1 L 1 m -2 ). Control plots were treated with water only. Treatments were watered following application. Data collected included Environmental Data: Environmental data collected included daily max/min air temperature, irrigation records (turfgrass site manager), rainfall and an initial soil analysis: macro and micronutrients, soil type, particle size, % organic matter. Evaluation: Turf health and uniformity were assessed with canopy reflectance measurements (normalized-difference vegetation index; Greenseeker). The NDVI values are decreased by phytotoxicity, drought, localized dry spot, and have been shown to be well correlated with visual estimates of turf quality. Plots were evaluated for visual rating of localized dry spot when it occurred. The extent of the symptoms was recorded as the percentage exhibiting symptoms. Table 1. Treatments. Treatment Rate Application schedule 1 Liquid 1/2X.95 ml m -2 2 Liquid 1X 1.9 ml m -2 3 Liquid 2X 3.8 ml m -2 4 Granular 1/2X 7.3 g m -2 5 Granular 1X 14.6 g m -2 6 Granular 2X 29.3 g m -2 7 Respond 3 1.3 ml m -2 Monthly (May 13, June 1, July 7, August 6, September 2, September 3) 8 Control All treatments were watered in immediately with 2 min of irrigation. All liquid treatments were applied in 1 L water 1 m -2 ; granular treatments were applied with a hand shaker. Guelph Turfgrass Institute 21 Annual Research Report 1
Figure 1. Plot area on research green, May 28, 21. Soil moisture readings (% volumetric water) were recorded using a ThetaProbe soil moisture meter. Water droplet absorption tests were made on 4-6 cm soil cores: 4 soil cores, approximately 15 cm each, were taken from each plot, air dried for two weeks at room temperature, and evaluated for hydrophobicity using the water droplet penetration test (time to penetration of a 35 μl droplet of distilled water placed at 1 cm intervals along the core starting at the thatch-air interface and ending at 6 cm). Data Analysis: Data were analysed and means compared using appropriate statistical methods (ANOVA). RESULTS Environmental data. Rainfall and temperature data were recorded at the Environment Canada weather station in the research ranges at the GTI (Figures 2 and 3). The season was wetter than average, with ~5 mm of rainfall during the course of the experiment. Temperatures were Rainfall (mm) 6 4 2 M J J A S O 12 15 18 21 24 27 3 Julian day 6 4 2 Figure 2. Daily and cumulative precipitation - summer 21 Data are from the Environment Canada weather station at the GTI. Cumulative rainfall (mm) Air temperature ( C) 35 3 25 2 15 1 5 Maximum Minimum -5 M J J A S O 12 15 18 21 24 27 3 Julian day Figure 3. Daily maximum and minimum air temperatures - summer 21. Data are from the Environment Canada weather station at the GTI. 2 Guelph Turfgrass Institute 21 Annual Research Report
slightly below normal for summer in Guelph, with only four days above 3 C. To increase the likelihood of localized dry spot development, irrigation was withheld from the plots after the middle of July. Turf performance: canopy reflectance. Canopy reflectance readings were significantly different among the treatments on all observation dates (Table 2.) The Greenseeker is very sensitive to NDVI variation, which reflects turf health (chlorophyll content, photosynthetic activity, growth rate), as well as stresses (phytotoxicity from treatments, drought stress, localized dry spot development). Early in the season (April and May), prior to treatment applications, there were some residual differences among treatments from the 29 applications. The treatments which had had the least hydrophobicity and LDS symptoms in 29 (Respond 3 and the three Neptune liquid treatments), had lower canopy reflectance values. The absolute value of the differences was small, and there was no visible difference among the plots in turf quality or color. Once applications began on May 28, there was no evidence of phytotoxicity, which would have appeared as a decline in NDVI immediately following applications compared to the control plots, in any of the treatments; this confirmed visual assessments of the plots. Over the course of the trial, the performance of the liquid application treatments as assessed by canopy reflectance was consistently higher than the control (Figure 4). The granular treatments were often not significantly better than the control, although the 1x and 2x rates were better than the 1/2x rate. Localized dry spot. The wet summer resulted in localized dry spot development only the second Granular 1/2x.2.1. -.1 -.2 Liquid 1/2x.15.1.5. -.5 -.1 -.15 Granular 1x.2.1. -.1 -.2 Liquid 1x.15.1.5. -.5 -.1 -.15 Respond 3.15.1.5. -.5 -.1 -.15 Granular 2x.2.1. -.1 -.2 Liquid 2x.15.1.5. -.5 -.1 -.15 Figure 4. Increase in canopy reflectance in treated plots relative to untreated check. LOWESS spline curves indicate trends of mean values. Principal periods of significant treatment effects are evident in late July (days 9-11) and in September (days 14+). Blue arrows indicate treatment applications. Guelph Turfgrass Institute 21 Annual Research Report 3
Table 2. Canopy reflectance (normalized-difference vegetation index) in treated plots. Treatment 4/16 4/22 4/3 5/1 5/16 5/17 5/19 5/2 5/25 Control.67 a 1.545 a.546 ab.575 b.6 b.63 b.572 ab.534 b.563 c Granular 1/2X.572 c.517 b.513 d.542 c.56 d.561 d.536 c.498 d.56 c Granular 1X.594 ab.524 b.554 a.599 a.63 b.68 ab.578 a.545 ab.595 a Granular 2X.593 b.515 b.533 c.575 b.62 b.61 ab.581 a.554 a.599 a Liquid 1/2X.538 de.477 c.484 e.53 c.554 d.556 d.513 d.472 ef.545 d Liquid 1X.577 c.57 b.536 bc.68 a.621 a.614 a.563 b.511 c.579 b Liquid 2X.526 e.471 c.55 d.538 c.62 b.584 c.528 c.483 e.57 bc Respond 3.548 d.469 c.492 e.537 c.576 c.557 d.55 d.46 f.558 c msd p=.5.13.19.13.17.9.11.11.12.13 5/27 5/29 5/31 6/4 6/8 6/11 6/14 6/16 6/21 Control.582 ef.576 cd.621 d.628 d.62 b.611 c.62 c.599 b.579 c Granular 1/2X.574 f.562 e.61 e.629 d.63 a.614 c.631 a.69 a.598 ab Granular 1X.68 ab.592 b.641 ab.648 ab.576 c.599 d.619 b.61 a.589 bc Granular 2X.611 a.61 a.647 a.651 a.631 a.582 e.6 c.596 b.576 c Liquid 1/2X.576 f.568 e.614 de.632 d.577 c.63 b.626 ab.617 a.69 a Liquid 1X.597 cd.582 c.637 bc.644 bc.597 b.614 c.589 d.58 c.554 d Liquid 2X.599 bc.59 b.639 bc.645 bc.576 c.642 a.618 b.591 b.577 c Respond 3.588 de.574 d.633 c.641 c.591 bc.617 c.66 c.591 b.581 c msd p=.5.9.6.8.6.16.7.11.1.16 6/23 6/28 6/3 7/6 7/12 7/15 7/19 7/23 7/27 Control.533 cd.67 c.537 b.525 c.548 c.472 cd.553 d.569 d.643 e Granular 1/2X.563 a.626 ab.566 a.581 b.591 b.483 bc.597 bc.593 c.669 c Granular 1X.56 ab.633 a.564 a.525 c.54 d.449 d.548 d.548 e.654 d Granular 2X.548 abc.61 c.536 b.512 c.511 d.415 e.52 e.572 d.629 f Liquid 1/2X.568 a.636 a.571 a.66 a.621 a.518 a.612 ab.614 ab.679 bc Liquid 1X.512 d.67 c.534 b.516 c.572 b.472 cd.581 c.599 bc.676 c Liquid 2X.55 abc.617 bc.559 a.65 a.632 a.57 ab.62 a.621 a.689 ab Respond 3.541 bc.61 c.542 b.593 ab.626 a.517 a.62 a.624 a.689 a msd p=.5.21.12.13.24.22.28.18.19.1 8/3 8/9 8/19 8/26 8/3 9/1 9/7 9/9 9/14 Control.62 e.611 cd.562 e.571 f.514 f.454 d.365 bc.397 abc.344 bcd Granular 1/2X.616 cd.614 c.592 d.569 f.53 e.449 d.353 c.378 cd.331 cd Granular 1X.584 f.64 d.66 c.599 d.549 d.494 c.395 a.417 a.381 a Granular 2X.67 de.67 cd.614 c.59 e.559 d.484 c.353 c.386 bc.357 abc Liquid 1/2X.621 bc.641 b.629 b.617 c.628 bc.544 b.365 bc.398 abc.312 de Liquid 1X.62 bc.65 ab.639 ab.625 b.622 c.555 ab.38 ab.47 ab.378 ab Liquid 2X.635 a.659 a.643 a.629 ab.642 ab.572 a.346 c.36 d.294 e Respond 3.628 ab.656 a.645 a.631 a.65 a.56 ab.286 d.3 e.244 f msd p=.5.1.1.12.6.15.19.21.26.35 9/2 9/23 9/27 Season mean Control.399 c.58 cd.475 d.576 de Granular 1/2X.418 bc.526 bc.493 cd.576 e Granular 1X.473 a.569 a.553 ab.584 b Granular 2X.44 ab.535 abc.529 abc.58 cd Liquid 1/2X.416 bc.526 bc.527 bc.582 bc Liquid 1X.473 a.564 ab.567 a.59 a Liquid 2X.386 c.478 d.471 d.591 a Respond 3.299 d.364 e.382 e.584 b msd p=.5.4.41.4.3 1 Normalized-difference vegetation index: mean of ~5 readings x 4 replicates; means within columns followed by the same letter are not significantly different (Tukey s HSD test, p=.5) 4 Guelph Turfgrass Institute 21 Annual Research Report
half of July and in September. Irrigation was withheld from the plot areas during this period. On the dates when LDS differences were significant, the pattern was similar to that observed in the canopy reflectance data (Table 3). The localized dry spot was relieved best by the liquid wetting agent treatments at label rate. The granular treatments were less efficacious, particularly at low rates. Volumetric water content. There were significant differences among treatments for volumetric water content as measured with the ThetaProbe on all dates (Table 4). Water contents were well into adequately watered range on all dates (field capacity on a USGA sand rootzone is typically 25-3%). During the drought periods in July and September, there were areas in the most significantly affected plots with volumetric water contents less than 1%. The pattern of treatments increasing volumetric water content was similar to the patterns observed in LDS and canopy reflectance, with the liquid treatments having the best effect, and the higher rate granular treatments some limited effectiveness. Correlations among performance characteristics. The efficacy of the treatments as measured by Table 3. Localized dry spot development. Treatment 5/25 6/4 7/6 7/28 8/1 Control 4.8 a 2.8 a 4.5 a 3.3 a 4.3 a Granular 1/2X 3.8 ab 2. ab 2.8 ab 2.3 ab 3.5 ab Granular 1X 1.8 cd.3 b 4.5 a 3.8 a 4.3 a Granular 2X 2.5 bcd 1. ab 3.5 a 3.8 a 4.5 a Liquid 1/2X 3. abc 1.8 ab.5 b.5 b 1.5 bc Liquid 1X 1.8 cd.8 ab 2.3 ab 2.5 ab.8 c Liquid 2X 1. d.8 ab.8 b.5 b.5 c Respond 3 2. bcd.3 b.8 b.5 b.3 c msd p=.5 1.82 2.31 2.58 2.55 2.57 1 Visual rating of dry spot development (-1, 1=full plot area affected). Means of 4 replicates; means within columns followed by the same letter are not significantly different (Tukey s HSD test, p=.5) Table 4. Volumetric water content in treated plots Treatment 5/21 6/4 6/21 7/2 7/29 Control 18.22 d 23.34 c 16.36 c 18.76 cd 14.58 bc Granular 1/2X 18.29 d 25.29 bc 18.66 bc 19.62 cd 15.84 b Granular 1X 22.92 ab 26.59 ab 19.88 b 16.65 d 13.59 c Granular 2X 19.73 bcd 25.48 bc 19.98 b 18.29 cd 14.46 bc Liquid 1/2X 18.96 cd 27.3 ab 23.34 a 24.5 ab 19.32 a Liquid 1X 23.1 a 26.77 ab 22.44 a 2.62 bc 15.52 b Liquid 2X 21.87 abc 27.51 ab 23. a 23.97 ab 18.15 a Respond 3 21.4 abcd 28.5 a 23.56 a 25.83 a 18.8 a msd p=.5 3.19 2.29 2.38 3.54 1.76 1 Percent volumetric water content measured with ThetaProbe. Means of 9 readings x 4 replicates; means within columns followed by the same letter are not significantly different (Tukey s HSD test, p=.5) Guelph Turfgrass Institute 21 Annual Research Report 5
localized dry spot development was correlated with other observed variables on the dates when LDS was significant. There was a clear decline in canopy reflectance with an increase in localized dry spot (Figure 5). A similar pattern was seen between LDS and the soil moisture (Figure 6), though the Localized dry spot 8 6 4 2 5/25 6/4 7/6 7/27 8/9 -.1 -.5..5.1 NDVI relative to control Figure 5. Association between localized dry spot and canopy reflectance. The correlation coefficients were.37 (5/25),.55 (6/4),.72 (7/6),.74 (7/27), and.67 (8/ 9). Charted values are plot means for the 32 plots. association was not as strong, in part because of the smaller number of VWC observations (9 as opposed to ~5 canopy reflectance measurements per plot). The association between soil moisture and canopy reflectance was positive (Figure 7), and strongest when the plots were more stressed on July 27. VWC mean 3 5/2 6/4 7/6 25 7/27 2 15 1 2 4 6 Localized dry spot Figure 6. Association between localized dry spot and soil moisture (VWC). The correlation coefficients were.59 (5/2),.57 (6/4),.89 (7/6), and.85 (7/27). Charted values are plot means for the 32 plots. VWC mean 25 2 15 1 5 7/27 -.1 -.5..5.1 NDVI relative to control Figure 7. Association between canopy reflectance and soil moisture (VWC). The correlation coefficients was.63. Charted values are plot means for the 32 plots. Water drop penetration tests / hydrophobicity. Data from the cores collected during the trial indicate that the rootzone in these plots continues to be severely hydrophobic. In fact, comparison of WDPT tests done in connection with various trials over several years show a steady increase in depth and severity of hydrophobic conditions up until 29 (Figure 8). In other trials on the same green the increase in hydrophobicity continued through 21, but in this trial there was a slight decline at all depths in hydrophobicity, though the overall levels remain high. The water drop penetration tests from this trial showed the most consistent treatment effect patterns in the upper layers of the rootzone ( and 1 cm deep) (Table 5). There were few significant pre-treatment differences (residual effects from 29 treatments), although there was a correlation between the 29 and 21 values (Figure 9). The levels of hydrophobicity that developed later in the season were only relieved by treatments at or near the surface. There was a rate effect in the liquid treatments at the and 1 cm depth, but no significant effects with the granular treatments. Significant difference in deeper layers indicate a noisy background. When differences among treatments were significant, the best effects were with the 1x and 2x rates, which were not statistically different. The Respond 3 treatments were no better than the best experimental treatments at reducing hydrophobicity. 6 Guelph Turfgrass Institute 21 Annual Research Report
Table 5. Water drop penetration test timings for cores removed from treated plots. Treatment 6/11 8/1 1/14 6/11 8/1 1/14 cm depth 4 cm depth Control 33.8 6. 512.1 a 252.3 595.2 a 29.2 Granular 1/2X 4.6 493.3 456.5 ab 225.7 439.9 ab 34.4 Granular 1X 348.2 6. 46.4 ab 211.1 574.2 ab 162.3 Granular 2X 393.3 6. 553. a 257.8 6. a 354.1 Liquid 1/2X 423.6 48.9 36. bc 267.4 422.7 b 327.4 Liquid 1X 326.5 567.7 17.7 d 36.1 6. a 111.1 Liquid 2X 377.4 519.4 112. d 41.5 542.3 ab 23.1 Respond 3 397.5 57.8 191.5 cd 34.1 51. ab 354.6 msd p=.5 NS NS 179.7 NS 166.6 NS 1 cm depth 5 cm depth Control 469.3 6. 532.4 a 162.1 548.6 a 211.3 ab Granular 1/2X 444.6 56. 516.1 a 139.2 423.9 ab 315.9 a Granular 1X 458.2 6. 549.5 a 124.1 475.8 ab 98.3 b Granular 2X 56.1 6. 585.4 a 185. 586.7 a 33.4 ab Liquid 1/2X 444.3 479.6 468.9 a 152.4 342.4 b 196.4 ab Liquid 1X 374.7 59.2 172.1 b 18.9 578.6 a 9.3 b Liquid 2X 427.6 532.3 167.4 b 299.6 441.6 ab 156.7 ab Respond 3 391.6 557.3 253.8 b 251.9 451.7 ab 229.5 ab msd p=.5 NS NS 166.1 NS 193.2 215.8 2 cm depth 6 cm depth Control 389.3 589.8 546.8 ab 63. b 441.1 abc 152. ab Granular 1/2X 454.5 454.7 491.5 ab 54.9 b 322.1 abc 12.9 ab Granular 1X 395.8 584.2 469.1 ab 17.8 ab 467.1 ab 53.1 b Granular 2X 53.7 6. 564.7 a 119.9 ab 57.6 a 242.9 a Liquid 1/2X 485.8 47.4 429.8 ab 78.5 b 226.8 c 117.5 ab Liquid 1X 428.3 6. 335. b 66.4 b 39.8 abc 49.6 b Liquid 2X 46.6 552.7 337.4 ab 28.5 a 361.9 abc 113. ab Respond 3 422. 572.2 436.7 ab 166.5 ab 25.1 bc 156. ab msd p=.5 NS NS 228.6 12.2 223.6 158.1. 3 cm depth Control 292.7 6. a 368.6 Granular 1/2X 199.1 456.8 bc 366.8 Granular 1X 254.6 597.1 ab 27.7 Granular 2X 287.3 593. ab 421.7 Liquid 1/2X 29.7 444.1 c 356.4 Liquid 1X 23.4 6. a 23.1 Liquid 2X 44.5 569.8 abc 243.7 Respond 3 327.8 578.9 abc 426.5 msd p=.5 NS 141.9 NS 1 Time (sec) for a 35 μl droplet of distilled water to penetrate core (max 6 sec). Mean of 4 cores x 4 replicates. Means within columns followed by the same letter are not significantly different (Tukey s HSD, p=.5). Guelph Turfgrass Institute 21 Annual Research Report 7
Hydrophobicity 6 Mean WDPT 6 4 2 22 24 25 29 21 21 pre-treatment 4 2 2 4 6 8 Depth (cm) Figure 8. Historical pattern of increase in hydrophobicity and depth of affected rootzone on the California green. Data for 29 and 21 are grand means from the plots of the present trial. Data for previous years are from trials on different areas of the green, so are not strictly comparable to each other, but indicate the trend. 2 4 6 29 end of season Figure 9. Association between wdpt data for end of season 29 and pre-treatment 21. Treatment means by depth are plotted (7 depths per treatment). The association is statistically significant (Pearson r=.74). CONCLUSIONS Wetting agent treatment effects on localized dry spot were limited to late July and then in September, in large part because the wet summer did not allow LDS to persist. During the most stressed period, the 4 liquid wetting agent treatments all provided significant relief from LDS compared to the control. The two higher rates of granular wetting agent provided some relief, but the ½ rate of granular wetting agent was not significantly different from the control. These results are in very good agreement with the 29 trial results. The canopy reflectance data, which is indicative of photosynthetic activity and plant health, showed similar clear patterns, particularly in the September dry period. Soil moisture readings also showed a similar pattern, though the absolute moisture contents were rarely down to the permanent wilting point (<1%). The general ranking of the treatments across all three data sets was Respond 3 = Liquid 2x > Liquid 1x >Liquid 1/2x > Granular 2x > Granular 1x > Granular 1/2x, Control Treatment effects on hydrophobicity of the soil as measured by the water drop penetration tests were limited to the upper 2 cm of the soil profile, and only appeared at the end of the season. The liquid treatments at 1x and 2x were as effective as the positive control (Respond 3). Sponsor: United Agri Products Canada Inc. 8 Guelph Turfgrass Institute 21 Annual Research Report