Phosphate (H3PO4) is the recognized P fertilizer source, while phosphite (phosphorous acid) (H3PO3) is often considered and labeled as a fungicide. However, the exact role of phosphite is unclear - is it functioning as a fertilizer, fungicide, or both? In turfgrass maintenance, phosphite is sometimes included in fertilizers, with no specific fungicidal claims attached. Previous work has shown that applications of phosphite can be detrimental to plant growth, especially if soil is low in phosphate. In the soil, phosphite will convert to phosphate, but the time required for that conversion is not well quantified. Thus, project objectives were: 1) evaluate how application of phosphite, phosphate and their combination affected turfgrass growth, and, 2) quantify the conversion of applied phosphite to phosphate, in soil. Two greenhouse studies and one soil incubation study were used to evaluate phosphite and phosphate, and their combined and separate effects on ryegrass and bentgrass, and soil conversion. Phosphite materials (labeled fungicides and phosphite-containing fertilizers) were applied based on P rate or at labeled rates. In the soil incubation study, phosphite was converted to phosphate within one month. In the greenhouse trials ryegrass was unaffected or positively benefited by application of phosphite, even at low levels of soil phosphate. In the bentgrass trials, root growth was reduced when phosphite was applied, but only when soil-test phosphate was < 2 mgkg(-1). When ryegrass and bentgrass were fertilized with any level of phosphate (> 15 kgPha(-1)) deleterious effects of phosphite on plant growth were not observed.

Given the rapid pace of urbanization and resulting pressures on water supplies in many regions, landscape water conservation has become increasingly important for many communities. To achieve this goal, programs incentivizing partial or complete removal of turfgrass lawns have been developed by many municipalities. While prior studies have been published examining effects of urban land change on stormwater runoff, few have addressed how the transition from traditional home lawns to alternative water-efficient landscapes alters runoff water quality. The objective of this 13-month study was to compare differences in stormwater runoff quality attributes among five commonly used urban residential mesocosms including established St. Augustinegrass lawn and four alternative residential mesocosms including xeriscaping, mulch, artificial turf, and sand-capped lawn. Runoff quality parameters including pH, electrical conductivity, nitrate–N, ammonium-N, dissolved organic N, total dissolved N, orthophosphate-P, total suspended solids, and dissolved organic carbon were monitored. Results demonstrated that export of nutrients via runoff, specifically N and P, were influenced by mesocosm type. In particular, artificial turf showed elevated runoff nitrate–N relative to other mesocosms, possibly due to minimal plant absorption of inorganic N coming onto plots as dry and wet deposition. However, an additional layer of compacted decomposed granite used for xeriscapes and artificial turf seems to have protected legacy soil P from leaving the system as runoff. Collectively, the findings of this study demonstrate that there is no one specific landscape that is best suited for mitigating runoff quality, but rather, alternative mesocosms should be selected based on local climate and environmental concerns.

Lawns have long been a primary feature of residential landscapes in the United States. However, as population growth in urban areas continues to rise, water conservation is becoming a key priority for many municipalities. In recent years, some municipalities have begun to offer rebate programs which incentivize removal of turfgrass areas and conversion to alternative ‘water-efficient’ landscapes, with the goal of reducing outdoor water use. The environmental impacts and changes to ecosystem services associated with such landscape alterations are not well understood. Therefore, a 2-year continuous research project was conducted at the Urban Landscape Runoff Research Facility at Texas A&M University to evaluate rainfall capture and runoff volumes associated with several commonly used residential landscape types (including, St. Augustine grass Lawn, Xeriscaping, Mulch, Artificial Turf, and Sand-capped Lawn) and to characterize the flow dynamics of surface runoff in relation to rainfall intensity for each landscape. The results demonstrate that runoff dynamics differ between landscapes, but also change over time as the newly converted landscapes become established. Following the initial months of establishment, the effects of landscape type on runoff volumes were significant, with Artificial Turf and Xeriscaping generating greater runoff volumes than Mulch and St. Augustine grass Lawns for most runoff events, which is partially due to the low infiltration rate of such landscapes. Overall, Artificial Turf and Xeriscaping showed the greatest cumulative runoff volumes (>400 L m−2), whereas Water Efficient- Mulch, Sand-capped Lawn and St. Augustine grass Lawn had a significantly lower cumulative runoff volumes, ranging from 180 to 290 L m−2. Information from this research should be useful to municipalities, water purveyors, and homeowner associations as they weigh the long-term hydrological impacts of lawn removal and landscape conversion programs.

In an effort to conserve water, conversion of irrigated lawns to "water-saving" landscape designs are being promoted in urban areas. Different materials, with different radiative and thermal properties, are used to accomplish this. We conducted a field study where we measured reflected spectral irradiance, albedo, energy balance, and soil and surface temperatures of grass (GR), artificial turf (AT), decomposed granite (DG), and hardwood mulch (MU) to better understand how surface temperature is controlled in landscapes composed of these materials. DG had the highest albedo and a large fraction of the reflected solar energy was in the visible band. AT had the lowest albedo and highest net radiation of the materials we tested. DG was the most efficient material in conducting energy into the subsurface, whereas MU was the least. Both AT and MU concentrated most of their thermal energy in the surface, indicating poor ability to diffuse thermal energy into the subsurface. Latent heat flux was the major component of the energy balance of GR, as expected. After GR, DG maintained the lowest surface temperature due to a combination of high albedo and high heat flux into the subsurface.

Shade is a major problem facing turf managers worldwide. Availability of low-cost devices and methods for quantifying daily light integral (DLI) offer the turf manager the ability to more precisely determine DLI levels in shade, yet minimal DLI requirements for acceptable turf quality (DLIm) for many commonly used warm-season turf cultivars grown under longer-term chronic shade stress have not been extensively tested. The objectives of this 2-yr field shade study were to (a) determine effects of growth regulator trinexapac-ethyl (TE) and season (summer or fall) on DLIm of nine commercially available bermudagrass (Cynodon spp.) and zoysiagrass (Zoysia spp.) cultivars; (b) determine effects of shade level and TE on summer percent green cover and root growth; and (c) determine effects of shade treatments on soil temperatures across the growing season. Significantly higher DLIm were noted during summer compared to fall for all cultivars in the study. The DLIm were generally higher for bermudagrass than zoysiagrass cultivars. 'Tifway' required the highest DLIm (ranging from 23.5 to 27.2 mol m(-2) d(-1)) of the bermudagrasses. 'TifGrand', 'Celebration', and 'Latitude 36' showed comparable DLIm during summer and fall. Fewer consistent differences were detected between zoysiagrasses, with 'Zorro' and 'Zeon' showing the lowest summer DLIm (18.1 and 19.1 mol m(-2) d(-1), respectively) and 'Geo' showing the lowest fall DLIm (11.7 mol m(-2) d(-1)). Trinexapac-ethyl reduced DLIm only in Zorro, 'Palisades', and 'JaMur' zoysiagrass, but had no effect on bermudagrass DLIm. The DLIm for a number of cultivars were higher than those previously reported in the literature, which may be attributed to lower mowing heights and/or use of permanent shade structures that were not removed for the duration of the 27-mo study. The findings should benefit turf managers by guiding data-driven, seasonal-based, warm-season turfgrass cultivar selection for shaded environments.

Given the growing adoption and use of recycled irrigation across the turfgrass industry, there is importance in understanding the effects of irrigation chemistry on N uptake efficiency as it relates to various soluble N sources. The objective of this study was to determine interactive effects of three soluble N sources (ammonium sulfate, potassium nitrate, and urea) and three irrigation water sources (reverse osmosis (R.O.), sodic potable, and 2.5 dS m(-1)saline (SA)) on turfgrass performance and(15)N nitrogen uptake efficiency following foliar N fertilization. Results demonstrated that although all water and N source treatments produced above-acceptable levels of quality in Champion bermudagrass, both N and water source significantly impacted nitrogen uptake efficiency. Following an eight-hour uptake period, approximately 40 to 70% of foliar-applied N (from a 0.5 g N m(-2)application) was recovered across all N sources. The highest uptake efficiency was noted with ammonium sulfate and urea treatments, with noticeably lower recoveries of N detected with potassium nitrate fertilization. Ammonium sulfate produced similar or improved turf quality to other N sources under R.O. and sodic potable irrigation, but reduced turf quality and green cover under saline irrigation. When water sources containing moderately high salinity levels (2.5 dS m(-1)) are used, potassium nitrate (KNO3) may provide the greatest turfgrass quality, however, its uptake efficiency may be lower than other N sources. The results suggest that soluble N source and tank mix and/or irrigation water chemistry may be important considerations for maximizing foliar uptake efficiency and minimizing potential for environmental loss.

Wetting agents have been widely used in the turf industry for ameliorating hydrophobic soil conditions and improving water use efficiency. However, limited information is available regarding potential benefits of wetting agents on fine textured soil lawns where wettable soils are commonly found, because most prior studies have been conducted in sand-based turf systems. This 2-year field study evaluated the potential for wetting agents to improve turf quality, as well as to reduce runoff losses of water and nutrients from st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] lawns. Over two seasons, turfgrass quality, percent green cover, and soil moisture in plots were evaluated in response to wetting agent and fertilizer treatments. During precipitation events, total runoff volumes were measured, as well as total export of nutrients including NO3-N, NH4-N, total dissolved N, dissolved organic N, dissolved organic C, and PO4-P. No runoff was detected from any treatments when precipitation was less than 13 mm. St. augustinegrass turfgrass quality and soil moisture were slightly improved by wetting agent and fertilizer treatments during the study, but no significant effects of either of the treatments were found on runoff volumes or nutrient exports. Although turf was managed under deficit irrigation levels of 0.3 × reference evapotranspiration, irrigation events were not withheld due to rainfall, and thus, little to no drought stress was observed during the study.

ABSTRACTSalinity stress is becoming a more prevalent issue for turf managers due to increased use of recycled water for irrigation. While published data are available on electrical conductivity (EC) thresholds for maintaining adequate turf growth and quality, data are lacking on the relationship between increasing irrigation and/or soil EC and turfgrass nutrient uptake efficiency. The objectives of this greenhouse experiment were to evaluate the effects of five irrigation water sources (reverse osmosis, sodic potable, 2.5 dS m−1 saline [SA], 5 dS m−1 SA, and 10 dS m−1 SA) and two soluble fertilizer N sources (15N‐labeled sources of ammonium sulfate and urea) on Tifway bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy] growth responses and N uptake efficiency. Results demonstrated that Tifway bermudagrass was capable of tolerating irrigation EC levels up to 5 dS m−1, which corresponded to final soil EC levels (at 2.5‐cm depth) of ∼2 to 2.6 dS m−1. However, with 10 dS m−1 irrigation (corresponding to soil EC levels of ∼3–5 dS m−1), turf quality declined to unacceptable levels and N uptake noticeably declined. Also, under increasing salinity (salinity levels of 2.5, 5, and 10 dS m−1), urea produced superior turf quality relative to ammonium sulfate. Collectively, the results indicate that for well‐watered, sand‐based Tifway bermudagrass, lower N fertilization rates should be considered once irrigation EC levels exceed 5 dS m−1 or corresponding soil EC levels at the 2.5‐cm depth exceed 2 dS m−1. Although N uptake efficiency of ammonium sulfate was greater than that of urea across all water sources in Year 1, results indicate that urea provided higher turf quality than ammonium sulfate under elevated salinity.