Soil Amendments and Fertilizer Source Effects on Creeping Bentgrass Establishment, Soil Microbial Activity, Thatch, and Disease

Natural organic fertilizers require microbial degradation for nitrogen (N) release, but their ability to promote rapid turfgrass establishment has not been well documented in newly constructed sand-based rootzones. This 2-year field study evaluated the influence of two general fertilizer and soil amendment programs for their effect on establishment and quality of three creeping bentgrass (Agrostis stolonifera L.) cultivars—‘Crenshaw’, ‘Penn G-2’, and ‘Providence’. Turf was grown on a 4 sand : 1 sphagnum peat (by volume) rootzone mixture. Four treatments consisting of surface-applied synthetic fertilizer (SF; mostly water-soluble N in 1999 and methylene urea thereafter); surface-applied hydrolyzed poultry meal (PM); preplant-incorporated granular humate (GH) with surface-applied SF; and preplant-incorporated PM with surface-applied PM. Turf cover data collected 42 days after seeding (DAS) showed that the rate of establishment was SF+GH incorporated = SF surface-applied >PM surface-applied + PM incorporated >PM surface-applied. Turf cover was ≥96% among all treatments 90 DAS. Rootmass density was greater (18% to 29%) at 103 DAS in GH incorporated plots combined with SF, when compared to all other treatments, but no rootmass differences subsequently were observed. Soil microbial activity generally was highest in PM-treated plots during the first 14 months following seeding, but not thereafter. Turf treated with SF had less microdochium patch (Microdochium nivale (Fr.) Samuels and I.C. Hallett) and more bentgrass dead spot (Ophiosphaerella agrostis Dernoeden, M.P.S. Camara, N.R. O’Neill, van Berkum et M.E. Palm), when compared to PM-treated plots. Slightly less thatch developed in PM-treated turf when compared to plots receiving SF alone by the end of the second year. Penn G-2 and SF generally provided the best overall turf quality. This study demonstrated the beneficial effects of readily available N from SF for rapid establishment and that preplant incorporation of GH initially aided root development. Golf greens normally are constructed with high sand content rootzone mixtures (>80% by volume) to resist compaction and maintain drainage (USGA Green Section Staff, 1993). Despite the aforementioned benefits of a sand-based rootzone, these synthetically prepared soils initially may support a less numerous microbial community than native soils because of their reduced organic matter and clay contents (Alexander, 1977). Organic matter additions have been shown to increase soil microbial activity, water retention, cation exchange capacity, nutrient transformation, cycling and retention, and pesticide degradation (Elliott and Des Jardin, 2001; Mancino et al., 1993; Stevenson, 1994). The positive effects of organic substances like humates on plant these earlier studies are useful, however, these studies were of relatively short duration and the longer term effects of these materials on rooting under field conditions where adequate nutrients are supplied is unclear. In addition to humic sources for amending sand-based rootzones, there is an industry trend to supply turfgrass nutrients as naturally occurring organic N sources, like hydrolyzed poultry meal (PM) products. Besides being N sources, the suppressive effects of these materials on common turfgrass diseases like dollar spot (Sclerotinia homoeocarpa F.T. Bennett) have been reported (Davis and Dernoeden, 2002; Hoyland and Landschoot, 1993; Liu et al., 1995; Nelson and Craft, 1991, 1992). The disease suppressive effects in these studies were attributed to several factors including stimulation of shoot growth by the N components of these products, the introduction of antagonistic microbes, stimulation of native microbes or a combination of one or more of these factors. Liu et al. (1995) found higher microbial populations on the leaves, thatch and soil of turf treated with a poultry meal-based fertilizer, ammonium nitrate or sulfur-coated urea compared to other fertilizers. They suggested that this increase in microbial population may be related to the dollar spot suppression observed in the study. Davis and Dernoeden (2002) found that a natural-organic PM product delayed dollar spot incidence and reduced outbreaks to within an acceptable threshold when disease pressure was low to moderately severe. The response, however, was not significantly different than urea or sulfur coated urea. They also found that none of the N sources tested were consistently associated with higher soil microbial activity and concluded that N availability was more important than soil microbial activity in suppressing dollar spot. The aforementioned studies, however, were conducted on mature turfgrasses grown on older sand rootzones or native soils. While dollar spot can be a chronic problem on creeping bentgrass, take-all (Gaeumannomyces graminis (Sacc.) Arx and D. Olivier var. avenae (E.M. Turner) Dennis) and bentgrass dead spot often are a problem on newly constructed greens or older greens that have been fumigated with methyl bromide (Kaminski and Dernoeden, 2002; Smiley et al., 1992; Smith et al., 1989). In both cases, these diseases often are most severe in the first few years after seeding and generally decline in subsequent years. This decline is believed to be in response to increasing soil microbial populations (Kaminski and Dernoeden, 2002; Smiley et al., 1992; Smith et al., 1989). Little information exists regarding the influence of N source on disease suppression and soil microbial activity during creeping bentgrass establishment in a sand-based medium. Many turfgrass managers are curious about the potential benefits of using natural-organic fertilizers as their sole N source for nutrition during establishment, and the long term effects on disease suppression, soil microbial activity, thatch production and aesthetic turfgrass growth properties. The objectives of this study were to compare the effects of various growth in the Poaceae family have been well documented (Chen and Aviad, 1990). The effects of some organic soil amendments and nitrogen (N) sources on the establishment of creeping bentgrass grown on sand media have been evaluated. In a field study, creeping bentgrass established on a 85 sand : 15 peat (by volume) rootzone had greater rootmass where granular humate (GH) was preplant incorporated, compared to an unamended control (Dorer and Peacock, 1997). In a greenhouse study involving creeping bentgrass in sand culture, Cooper et al., (1998) showed that GH incorporated to a depth of 10 cm in a 30-cmdeep rootzone increased bentgrass rootmass and maximum root length when compared to bentgrass grown on unamended sand. In a related solution culture study, creeping bentgrass net photosynthesis, root dehydrogenase activity and root regrowth increased with increasing rates of humic acid in liquid solution (Liu et al., 1998). When grown in soil with a high soil moisture content (–0.03 MPa), Zhang and Schmidt (2000) found that foliar applications of a soluble humic acid increased rooting of creeping bentgrass seedlings. Information from HORTSCIENCE 39(3):620–626. 2004. Received for publication 6 Jan. 2003. Accepted for publication 23 July 2003. Mention of trademark or proprietary product does not constitute a guarantee or warranty of the product by the University of Maryland or the authors and does not imply its approval to the exclusion of other products that also may be suitable. A contribution of the Maryland Agricultural Experiment Station. Corresponding author; e-mail [email protected].