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Organic coatings on sand particles can cause soil water repellency (SWR) where a soil does not spontaneously wet; this leads to challenges in water management and crop production. In laboratory studies, we evaluated a novel approach using direct application of 10 enzymes at three (low, medium, high) dosages to remediate SWR on two sand turfgrass soils in a 3-day incubation study and a second study at high dosage with 1-day incubation. A soil:solution ratio of 1:1 (10 g soil and 10 mL solution) was used and a deionized water control included. For Soil 7, a very strongly hydrophobic soil from a localized dry spot turfgrass area with a water drop penetration time (WDPT) of 7440 seconds (untreated) and 332 to 338 seconds (water-treated), the high dosage rates of laccase, chitinase, and protease at 1 and 3 days incubation resulted in WDPT of less than 60 seconds (i.e., hydrophilic soil). Pectinase exhibited similar results only in the 3-day incubation study. On the strongly hydrophobic Soil 21 (WDPT of 655 seconds untreated; 94 to 133 water-treated) from the dry area of a fairy ring-affected area on a turfgrass site, high dosages of chitinase, laccase, pectinase, and protease reduced WDPT to less than 60 seconds in both studies; and medium dosage rates were also effective for all but protease in the 3-day incubation study. Each of the four most effective enzymes for reducing WDPT, noted previously, demonstrated a significant exponential or logarithmic relationship between decreasing WDPT and increasing enzyme dosage. Further studies in field situations will be required to determine enzyme effectiveness on SWR and water management. Soil water repellency (SWR) is a condition in which a soil does not spontaneously wet when a drop of water is applied to the surface, indicating that the soil is hydrophobic (M€uller and Deurer, 2011). In recent years there has been greater attention to SWR as a result of increased awareness of its negative implications, especially on water management and associated environmental issues, which include reduced soil water intake, uneven wetting patterns, reduced irrigation efficiency and effective precipitation infiltration, increased preferential flow that may affect aquifer contamination, increased runoff and erosion, limited seed and vegetative establishment, and reduced plant growth and quality (Dekker et al., 2005; Doerr et al., 2000; M€uller and Deurer, 2011). Hydrophobic soils are found in many countries on traditional and no-till agricultural soils, pastures, coastal dune sands, shrub lands, parks, turfgrass soils, greenhouse potting media, fire-induced SWR in forestlands, and soils irrigated with treated wastewater (Bailey et al., 2012; Barton and Colmer, 2011; Blanco-Canqui, 2011; Fidanza et al., 2007; M€uller and Deurer, 2011; Nadav et al., 2011). Roper (2005) reported SWR occurring on more than 5 million hectares of western and southern Australia. Patterns of SWR differ with the field situation. On sandy turfgrass soils and grasslands, SWR is a recurring problem, where the normal situation is called ‘‘localized dry spot’’ (LDS) or dry patch, and SWR appears as irregular dry areas from a few centimeters to several meters diameter with the repellency usually extending from the surface to 5 to 10 cm depth (Doerr et al., 2000). A second SWR situation on turfgrass sites is within the dry area of basidiomycete induced ‘‘fairy ring’’ on all soil types (Barton and Colmer, 2011; Fidanza et al., 2007). Although SWR can occur in diverse climates and soils, it is most prevalent on sandy soils, which have low particle-surface area compared with soils higher in silt and clay content and sands are more prone to surface drying (M€uller and Deurer, 2011). On sand soils, SWR is universally attributed to hydrophobic organic matter coating on the sand particle surfaces and hydrophobic organic particulate matter from plant debris or added as an amendment, whereas high organic matter in the thatch/mat layer may also contribute (Barton and Colmer, 2011; Franco et al., 1995; M€uller and Deurer, 2011). For fine-textured soils exhibiting SWR, organic coatings are on soil aggregate surfaces. The sources of organic matter contributing to hydrophobic organic coatings are diverse and may include waxes, fatty acids, and lignin (a recalcitrant polymer of phenols) from plant leaves and other decomposing organic matter, plant root exudates, fungal hyphae/exudates, volatile organic compounds that condense on soil particles following forest or grassland fires, and organic matter in wastewater (Atanassova and Doerr, 2010). Regardless of soil type or organic matter source, soil drying increases repellency with air-drying greatly enhancing SWR severity (M€uller and Deurer, 2011). Many scientists have studied the chemical nature of the organic matter coatings, but there has been limited success in identification of specific compounds (Atanassova and Doerr, 2010). The generic types of organic compounds suggested to be involved with SWR include: 1) high-molecular-weight, polar fatty acids and their esters are the most often reported as contributing to hydrophobic coatings where these are alkanes-derived from plant and cuticular waxes; 2) other alkanes (paraffin-like compounds), microbial-derived waxes, alkanols, phytanols, and phytanes; 3) amphiphilic (partially hydrophobic) lipids, stigmasterols, and plant-derived sterols that have polar (hydrophilic) and non-polar (hydrophobic) groups; 4) other polar molecules such as sugars, glycosides, aromatic acids, and low-molecular-weight organic acids; 5) humic and fulvic acids from soil microbial activity or possibly added as amendments; and 6) hydrophobins and cysteine-rich proteins expressed only by filamentous fungi (Atanassova and Doerr, 2010; Doerr et al., 2005; Rillig, 2005). Difficulty in determining the nature of specific organic coatings may be the result of: 1) thin coatings of even a single layer on sand surfaces to small globules of organic matter on sand surfaces that are difficult to see even in scanning electron micrography or to selectively extract by chemical means; 2) changes occur in the orientation and hydrophobic– hydrophilic nature of compounds during drying and wetting but not the chemical composition; and 3) the extraction challenges presented by the complexity and diversity of various soil organic matter compounds present Received for publication 10 Dec. 2013. Accepted for publication 18 Feb. 2014. The study was supported in part by HATCH funds and a grant from Technology Commercialization Office, University of Georgia Research Foundation, Athens, GA. To whom reprint requests should be addressed; e-mail rcarrow@uga.edu. 662 HORTSCIENCE VOL. 49(5) MAY 2014 (Atanassova and Doerr, 2010; Doerr et al., 2000; Horne and McIntosh, 2000). M€uller and Deurer (2011) reviewed 12 SWR remediation strategies reported in the literature and noted that even with the major increase in SWR research over the past decade, current remediation strategies are limited in effectiveness. Application of wetting agents (surfactants) has been the most effective remediation practice, probably because it is focused on altering the hydrophobic organic matter properties and surface tension of water. However, this approach is costly and only renders short-term positive effectiveness with repeated applications needed to maintain hydrophilic conditions (Moore et al., 2010; M€uller and Deurer, 2011). Biological methods involving culturing microorganisms capable of degrading wax in soil is another remediation approach that concentrates on altering the nature of the organic matter associated with SWR and it has been shown to be effective at the laboratory scale (M€uller and Deurer, 2011; Roper, 2004). However, limitations exist in practical field applications such as costs and maintaining viable inoculation population levels (Roper, 2005, 2006). Sidhu et al. (2012, 2013) applied laccase directly to turfgrass ecosystems and induced decomposition of organic matter in the thatch/ mat, which were the first reports of success using direct enzyme applications of specific enzymes. Our hypothesis is that application of enzymes might directly alter or degrade the diverse organic materials contributing to SWR in a manner to reduce their hydrophobic nature and offer a new management option to this difficult field problem. In a laboratory study, Liu et al. (2013b) were the first to use this novel approach on SWR soils by applying enzymatic coproducts (mainly laccase mixed with other trace enzymes) from a biofuel research project on fungal pretreatment of switchgrass (Panicum virgatum) for improved saccharification to eight air-dried SWR soils from several golf courses with WDPT of 345 to 7439 s. All treated soils exhibited a WDPT of less than 60 s and the observed decrease in WDPT was positively related to the increased enzyme activity level for each soil in an exponential or logarithmic relationship. Based on the results observed by Liu et al. (2013b) with application of laccase to remediate SWR, additional proof-of-concept laboratory studies were conducted with the following objectives: 1) to evaluate the effectiveness of 10 diverse enzymes directly applied on two SWR soils at three dosages using a 3-d incubation to remediate SWR; and 2) to investigate the most effective enzymes in the initial study on the same soils but using a 1-d incubation period. Materials and Methods Soils and enzymes. The two soils used in all three experiments are described in Table 1. Samples were obtained in Feb. 2012 from the surface 0 to 3.8 cm within areas exhibiting field SWR symptoms using a soil profiler sampler and collecting 8 L volume of soil from four to six sites within an area. Soil 7 was from a golf course rough planted to ‘Salam’ seashore paspalum (Paspalum vagnitum O. Swartz) exhibiting normal localized dry spot, whereas Soil 21 was collected from the SWR zone of a fairy ring on a ‘Tifdwarf’ bermudagrass [Cyno

Evaluation of Direct Application of Enzymes to Remediate Soil Water Repellency