Influence of Overwatering and Fertilization on Nitrogen Losses from Home Lawns

Fertilized home lawns represent a potential source of NO,-N contamination to groundwater and surface waters. The waterborne losses of inorganic N from Kentucky bluegrass (Poa pratensis L.) turf subjected to three levels of N fertilization (0, 97, and 244 kg N ha"' yr~' as urea and methylene urea) and two irrigation regimes (scheduled by tensiometer and overwatering with 3.75 cm of water per week in addition to rainfall) were measured. The site was located on a Merrimac sandy loam (sandy, mixed, mesic Typic Dystrochrept). Soil-water percolate was collected by suction plate lysimeters placed below the root zone. Surface runoff was quantified with orifice flow splitters. Soilwater percolate flux comprised >93% of the total water and inorganic-N discharged from all treatments. Mean annual flow weighted concentrations of inorganic N in soil-water percolate were below the U.S. drinking water standard on all treatments and ranged from 0.36 mg L' on the overwatered, unfertilized, control treatment to 4.02 mg L" on the over-watered, high N treatment. Annual losses ranged from 32 kg ha"' on the overwatered high N rate treatment to 2 kg ha' on the scheduled irrigation, unfertilized, control treatment. Overwatering in conjunction with fertilization generated significantly higher annual flow weighted concentrations and mass loss than the unfertilized controls. Nitrogen loss and concentrations from the scheduled irrigation treatments were not significantly different from the controls. Additional Index Words: Nitrate-nitrogen, Turfgrass, Groundwater pollution, Water quality, Irrigation scheduling. Since 1970, pesticide and fertilizer use on home lawns has steadily increased (Watschke, 1983). The growth of chemical use suggests the possibility for an increase in off-site losses and subsequent environmental contamination. Lawn care chemicals may be applied in close proximity to impervious zones with high potential for surface runoff. Miller et al. (1974), in their study of groundwater contamination in the northeastern USA, stressed the need for long-term studies to determine if home lawn agrichemicals have penetrated the soil zone and entered the groundwater system. Several researchers have described conditions under which they found substantial NO3-N leaching from fertilized cool season turf grass (Owen and Barraclough, 1983; Rieke and Ellis, 1974). Nitrate-N is a drinking water contaminant with a U.S. drinking water standard of 10 mg L" (USEPA, 1976). Leaching of NO3 is of particular T.G. Morton and A. J. Gold, Dep. of Natural Resources Sciences, and W.M. Sullivan, Dep. of Plant Sciences, Univ. of Rhode Island, Kingston, RI 02881-0804. Contribution from the Rhode Island Agric. Exp. Stn. as Journal Paper no. 2380. Received 2 Mar. 1987. "Corresponding author. Published in J. Environ. Qual. 17:124-130 (1988). 124 J. Environ. Qual., Vol. 17, no. 1, 1988 concern on Long Island, NY, and the southern New England states where permeable, outwash soils overlie unconfined drinking water aquifers. Coastal estuaries and bays have been found to be N limited, and may be degraded by concentrations of NO3-N much less than the drinking water standard of 10 mg L-~ (Ryther and Dunstan, 1971). Other researchers have shown little increase in NOrN leaching from fertilized turfgrass (Starr and DeRoo, 1981; Snyder et al., 1984). Starr and DeRoo (1981) monitored the fate of N applied to cool season turfgrasses in southern New England and found low concentrations of NOrN in leachate when moderate rates of N were applied and no supplemental irrigation water was used. Irrigation has been shown to significantly increase NOrN leaching (Snyder et al., 1984; Endelman et al., 1974; Timmons and Dylla, 1981; Rieke and Ellis, 1974). Home lawns are typically watered with little regard for soil moisture status or the water holding capacity of the soil. Where irrigation is automatically controlled, rates are often selected to meet maximum evaporative demands, resulting in routine overwatering (Snyder et al., 1984). Excessive watering will increase antecedent soil moisture, thereby promoting additional leaching and surface water runoff from natural storm events or from the supplemental water alone. The goal of this study was to quantify N losses from turf subjected to the range of fertilization and watering practices generally used on home lawns. Commercial applicators often employ several practices that past studies have shown to minimize off-site transport of N (Rieke and Ellis, 1974; Brown et al., 1982). Nitrogen is frequently applied in the form of urea in combination with some form of slow release materials, rather than in immediately available forms. The fertilizer is usually applied in small increments throughout the growing season, which is thought to minimize high N concentrations in the root zone. However, commercial home lawn care companies often apply greater annual amounts of N than individual homeowners. A survey of 460 households on Long Island found that homeowners applied an average of 122 kg N ha-’ yr-’ to their lawns (Koppelman, 1978). Many commercial operations apply 220 to 293 kg N ha-’ yr"~ (J.F. Wilkinson, Old Fox Lawn Care, Inc., 1985, personal communication). The objective of this study was to determine the effects of varying N fertilization rates and irrigation regimes on waterborne losses of inorganic N from home lawns. MATERIALS AND METHODS