Nitrate and Tracer Leaching from Aerated Turfgrass Profiles

Macropore flow has received increased attention in the recent years due to its importance on solute flow through the vadose zone and contamination of groundwater. The effects of man-made macropores resulting from cultivation of turfgrass sites on the mobility of nitrates and tracer chloride were studied. Treatments included two soil profiles (a sandy profile, simulating a US Golf Association style putting green and a sandy clay soil) and three cultivation practices (shallow hollow tines, 80 mm deep and 19 mm internal diameter (I.D.); deep drill, 220 mm deep and 19 mm I.D.; and high pressure water injection). Free draining lysimeters sodded with Agrostis stolonifera ssp. palustris Huds. var. 'Providence' were used in greenhouse to perform three studies. In the first study, turfgrass was fertilized with a solution fertilizer at a rate of 24 kg N ha-1 and a daily irrigation of 6.8 mm in excess of the predetermined field capacity. In the second greenhouse study the irrigation rate was increased to 13.7 to 27.4 mm d-1 simulating an overwatering regime. In the third study turfgrass was fertilized with (NH4)2SO4 as nitrogen (N) source at a rate of 49 kg N ha-1 and 13 mm of daily irrigation was applied while the plants were sufficient in N. In addition chloride was utilized as a nitrate tracer. In the first study, NO3 was detected after 2 L of effluent volume from the sand profiles and peaked at 13 to 14 mg NO3-N L-1 at 3 L of effluent volume. Nitrate leaching was not affected by the cultivation treatments. However, at a higher daily irrigation schedule (13.7 to 27.4 mm d-1), NO3 concentration from the sand profiles reached 18 to 20 mg NO3-N L-1 but the differences between cultivated and uncultivated profiles were less pronounced compared with the low irrigation regime. Nitrate leaching was not detected from the sandy clay profiles for any of the two irrigation regimes due to a large amount of N plant uptake. In the third study, NO3 leaching from the sandy profiles peaked more rapidly from the shallow and deep cultivated profiles reaching 54 mg NO3-N L-1 for both treatments. Water injected and uncultivated profiles peaked at 45 mg NO3-N L-1. Chloride analysis suggested that macropore flow through cultivation holes did not affect solute flow past the root zone in the sand profiles. The mass of NO3-N lost by leaching differed between studies according to the irrigation rates and the level of N sufficiency of the plants. It was concluded that under proper management