Fertilizers are commonly applied to turfgrass episodically, which usually causes a surge of absorption and growth intermittent with different degrees of deficiencies (Stiegler et al., 2011). In turfgrass management, yield is not the primary purpose of fertilization; rather stable color, vigor, and recuperation from damage are the goals of a fertilization program (Yust et al., 1984). To maintain constant turf qualities, slow-release fertilizers and different technologies, such as spoon-feeding program that relies on frequent and low-rate application, are used to simulate the natural mineralization in providing nutrients to turfgrasses at a regulated speed with high fertilizer use efficacy and low application cost (Spangenberg et al., 1986). Foliar application is one of those technologies, which was heavily investigated in the late 1940s and early 1950s (Fritz, 1978; Haq and Mallarino, 2000).
Compared with soil applied fertilizers, foliar applied fertilizers correct nutrient deficiencies faster, provide soil-immobile nutrients more efficiently, and reduce nutrient losses because of denitrification and leaching (Fageria et al., 2009). Micronutrients that are required in small amounts can be applied more uniformly in spray than in granular forms to soils. Additionally, spraying fertilizer along with other chemicals as a tank-mix allows for reduction in labor, machinery, and energy. However, foliar application requires repeated applications, especially macronutrients, to meet the demand of plants. Wind can affect uniformity of foliar application.
Foliar fertigation, fertilization through the irrigation system, was found as effective as soil application on bermudagrass (Cynodon dactylon × C. transvaalensis) (Snyder and Burt, 1976). In perennial ryegrass (Lolium perenne), daily foliar nitrogen (N) application resulted in increased shoot growth and decreased root biomass and length (Bowman, 2003). In creeping bentgrass, foliar N application provided better visual quality than granular fertilizers as reported by Steinke and Stier (2003). However, the results of foliar fertilization were not consistent in the study by Guertal (2010) and Stiegler et al. (2011). Zhang et al. (2003a) reported that applying seaweed extracts or humic acid together with liquid fertilizer did not improve the creeping bentgrass turf quality compared with fertilizer alone. However, addition of stimulants to fertilizer reduced dollar spot (Sclerotinia homoeocarpa) incidence during the summer because of improved plant health as reflected by the increase of antioxidants in treated plants.
Fernandez and Eichert (2009) provided a thorough review of the factors affecting the efficacy of foliar fertilizer application including the use of adjuvants. An adjuvant is a substance that is added to the spray tank to modify the activity of a.i. or spray characteristics and is one of the major technologies used to improve foliar fertilizer uptake (Hazen, 2000). Adding humectants to slow down drying process of foliar-applied chemicals has been reported effective in improving the performance of foliar nutrient application, especially in dry environments (Schonherr et al., 2005).
The results of foliar fertilization on creeping bentgrass are not consistent because of various environmental conditions, mowing height, nutrient forms, and addition of adjuvants. Many biostimulants such as humic substances are used by turfgrass managers either alone or in combination with tank-mixes of other chemicals (Karnok, 2000). Some of these humic substances also function as adjuvants (McWhorter et al., 1987). Since biostimulants are typically applied by spraying, their mixability with other foliar applications, such as liquid fertilizer, herbicides, and fungicides, is useful information for turfgrass managers. Rev™ (Dakota Peat, Grand Forks, ND) is a new organic amendment that is derived from naturally mined humic materials. The objective of this study was to investigate if the organic amendment sprayed tank-mixed with different N fertilizers affects fertilizer efficacy and turf quality.
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