Nitrate Leaching from Sewage-irrigated Perennials as Affected by Cutting Management

A field study was conducted on two waste water-treated sites to evaluate the effectiveness of various cutting treatments for controlling nitrogen (N) leaching. Secondary municipal sewage effluent was applied at 7.5 cm/week during the growing season to Kentucky bluegrass (Poa praetensis L.), which received treatments of no cutting, biweekly mowing, and triannual hay harvest. Effluent was also applied at rates of 0, 5.0, and 10.0 cm/week to indigenous vegetation in an abandoned field which received treatments of no cutting, once, and twice-annual harvests. Soil-water was sampled with porous-cup samplers. The N concentration in the 120- to 150-cm depth was taken as a measure of N which escaped the root zone and which would leach to the ground water. Recharge volume was calculated from irrigation, rainfall, and potential evapotranspiration. Soil-water from the 150-cm depth in the Kentucky bluegrass consistently contained < 10 mg/liter of mineral N. Mineral N concentration of soil-water did not differ significantly among the cutting managements. Even though no vegetation was removed from the no-cutting and the mowed plots, they were as effective as the harvested plots in controlling N leaching past the 150-cm depth in the 2-year study. For the oldfield vegetation, there was no significant difference in mineral N concentration in soil-water at the 120-cm depth between the 5.0- and 10.0-cm/week irrigation rates. The mineral N concentration at 120 cm under both irrigation rates was affected by time of year and by cutting treatments. The twice-annual harvest controlled N leaching more effectively than not cutting. The once-annual harvest was more effective than not cutting for the 10-cm/week rate but not for the 5.0-cm/week rate. During the late summer and fall mineral N in the leachate increased to > 10 mg N/liter for the no cutting but not for the harvested oldfields. For reliable control of N leaching, removal of the N in harvested biomass was recommended.