Product combos improve irrigation efficiency

Marco Schiavon, Ph.D., University of California-Riverside, discusses the effectiveness of plant growth regulators, soil surfactants and fertilizer treatment combinations to conserve water on golf course fairways. (Photo: Mike Kenna)

In California and in much of the Southwestern United States, golf courses irrigate to supplement annual precipitation for turfgrass growth. However, because of diminishing water resources and rising costs, sufficient evapotranspiration (ET) replacement may not be available during the summer months.

Replacement of some but not all ET requirements is considered deficit irrigation and is a viable water conservation strategy, especially in arid and semiarid regions. Deficit irrigation is essential in areas where the cost of water is too high to provide daily irrigation or where municipalities enforce water restrictions.

But, deficit irrigation on fairways can be detrimental to turfgrass quality and playability, especially when allocated irrigation water isn’t enough to sustain turfgrass growth. So, in addition to deficit irrigation, several management practices can make turfgrass irrigation more efficient.

Plant growth regulator (PGR), soil surfactant and fertilizer treatment list. (Table provided by author)

Efficient practices include (but aren’t limited to) the selection of drought-resistant, warm-season turfgrass cultivars adapted to the growing environment, increasing irrigation system efficiency and uniformity and using plant growth regulators (PGRs), soil surfactants and sufficient nitrogen fertilization. Best management practices for fairway water conservation should include several of these strategies, but researchers usually evaluate only one water conservation method at a time. Our experiment evaluates a combination of products applied to bermudagrass fairways that could improve turfgrass quality under deficit irrigation.

The setup

The experiment in 2016 and 2017 was on mature Princess 77 bermudagrass [Cynodon dactylon (L.) Pers.] at the University of California-Riverside Turfgrass Research Facility. The soil was a Hanford fine sandy loam (70.4 percent sand/19.8 percent silt/9.8 percent clay). Initial fertility status based on soil testing was 4 parts per million (ppm) nitrogen (N), 14 ppm Olsen phosphorus (P), 163 ppm potassium (K). We verticut the turf each year in April before treatment applications and mowed three times a week during the growing season at 0.5 inch with a reel mower, with clippings returned.

Figure 1 Turf visual quality, normalized difference vegetation indices (NDVIs) and percent green cover from May to October in 2016 and 2017 for Princess 77 bermudagrass [Cynodon dactylon (L.) Pers.] subjected to four treatment combinations of trinexapac-ethyl and Revolution under the 70-percent short-crop evapotranspiration (ET_os) irrigation regime. (Graph provided by author)

From May 19 to Oct. 31 of both years, we hand watered the plots three times a week to replace either 40 percent or 70 percent of the previous week’s short-crop reference evapotranspiration (ET_os) as determined by an on-site California Irrigation Management Information System (CIMIS) weather station. We restored full ETo replacement in November when ET_os rates were decreasing and differences in watering times were negligible.

Under both ET_os replacements, each plot received either: (1) fertilization only; (2) a combination of fertilizer and soil surfactant; (3) a combination of fertilizer and PGR; or (4) a combination of all three. Each plot received an equivalent of 1 pound N per 1,000 square feet per month, for an annual total of 5 pounds N per 1,000 square feet. The fertilizer products included Gro-Power (5-3-1) SeaBlend (12-4-5) plus Stress RX plus XP Micro, YaraMila Turf Royale (21-7-14) and YaraLiva CALCINT (15.5-0-0) (Table 1). We applied the PGR, Primo Maxx (trinexapac-ethyl or TE) and soil surfactant Revolution at label rates (Table 1). The first application of Primo Maxx, Revolution and fertilizer products occurred May 19, 2016. Following the application of Revolution and granular fertilizers, we irrigated the plots with approximately 0.25 inch of water.

Every two weeks, we evaluated plots for turf quality on a scale from 1 (worst) to 9 (best), naturalized difference vegetation index (NDVI), volumetric soil water content (VWC) using time domain reflectometry (TDR) and dark green color index (DGCI), as well as percent green cover using digital image analysis (DIA). We made visual turf quality ratings in late November and early December to measure the effect of fertilizer and chemical treatments on bermudagrass winter color retention. In March 2017 and 2018, we evaluated plots for NDVI and DIA to assess spring green-up.

Evaporation replacement impact

Figure 2 Turf visual quality and percent green cover from May to October in 2016 and 2017 for Princess 77 bermudagrass [Cynodon dactylon (L.) Pers.] untreated or treated with Revolution and irrigated at 40-percent short-crop evapotranspiration ET_os. (Graph provided by author)

Evaporation replacement treatments had a huge impact on bermudagrass performance. Although a few treatments had some positive effect on severely drought-stressed turf plots, none of the plots irrigated at 40 percent ET_os had acceptable turfgrass quality, NDVI or percent green cover compared with those irrigated at 70 percent ET_os (Figures 1 and 2).

At 70 percent ET_os, Primo Maxx, combined with Revolution, had the most positive effect on turfgrass quality (Figure 1). NDVI and percent green cover confirmed these findings, especially during the summer of 2017, when the combination of the PGR and the soil surfactant was better than any other treatment for each measured parameter. Except for May 2016 and 2017, bermudagrass irrigated at 70 percent ET_os always provided acceptable quality (Figure 1). Also, there were no differences in fertilizer treatments at 70 percent ET_os. Our results suggest that, under this level of irrigation replacement, the choice of N source does not affect bermudagrass performance. However, the surrounding turfgrass that did not receive N showed drastically lower turf quality than plots with N fertilization, stressing the importance of sufficient N fertilization for overall turf health.

At 40 percent ET_os, Revolution had the greatest impact on bermudagrass performance. Turfgrass quality, NDVI and percent green cover improved in plots that received Revolution (Figure 2). Revolution provided the most help in alleviating symptoms of drought, and we recommend its use before and during drought or water-use restrictions.

At 40 percent ET_os on plots that did not receive Revolution, SeaBlend plus Stress Rx plus XP Micro and Gro-Power showed improved quality and cover (Figure 3). Conversely, YaraLiva had the lowest turf quality. The lower performance of YaraLiva may be due to the high burn potential of calcium nitrate coupled with high temperatures during application. Also, the fertilizer may not dissolve with insufficient water at 40 percent ET_os irrigation treatment.

The restoration of full ETo replacements in November resulted in tissue restoration of severely droughtstressed bermudagrass. Plots fertilized with SeaBlend plus Stress Rx plus XP Extra Protection and Gro-Power had the highest percent green cover in December (95 percent and 9 percent, respectively). Plots receiving 40 percent ET_os greened up more quickly than those receiving 70 percent ET_os.

Turf visual quality and percent green cover from May to October in 2016 and 2017 for Princess 77 bermudagrass [Cynodon dactylon (L.) Pers.] that did not receive Revolution and were fertilized with either Gro-Power (5-3-1); SeaBlend (12-4-5) + Stress RX + XP Micro; YaraMila Turf Royale (21-7-14); YaraLiva CALCINT (15.5-0-0). (Graph provided by author)

The highest percent green cover in the spring was on plots receiving only Revolution and no Primo Maxx. The results indicate that the use of an appropriate combination of products such as soil surfactants, sufficient N fertilization and biostimulants can help sustain turf quality with less water.

It’s important to note that we hand watered plots in this experiment to ensure irrigation uniformity was near 100 percent. Your irrigation system needs to maximize uniformity and reliability. Without an efficient irrigation system and uniform distribution of water, you will not fully achieve the positive effects of cultural practices on turf quality while conserving water.

Research takeaways

Researchers tested a combination of plant growth regulators (PGRs), soil surfactants and sufficient nitrogen fertilization for water conservation on golf course fairways.

• None of the plots irrigated at 40 percent ET_os had acceptable turfgrass quality, normalized difference vegetation index (NDVI) or percent green cover
  comparable to those irrigated at 70 percent ET_os.
• At 70 percent ET_os, Primo Maxx combined with Revolution had the most positive effect on turfgrass quality, NDVI and percent green cover.
• Except for May 2016 and 2017, bermudagrass irrigated at 70 percent ET_os always provided acceptable quality.

Marco Schiavon, Ph.D., conducted this research as an assistant researcher at the University of California-Riverside. He is now an assistant professor at the University of Florida Fort Lauderdale Research and Education Center. You may reach Schiavon at marcoschiavon@ufl.edu for more information.

References

Cockerham, S.T., and D.D. Minner. 2011. Turfgrass nutrition and fertilizers. In: Adous, D.E. editor. International Turf Management. New York, NY. Routledge. p. 139-158.