52 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING / MARCH/APRIL 1999 SUBIRRIGATION SYSTEMS TO MINIMIZE NITRATE LEACHING By J. Wambua Kaluli, 1 Chandra A. Madramootoo, 2 Xiaomin Zhou, 3 Angus F. MacKenzie, 4 and Donald L. Smith 5 ABSTRACT: Nitrate leaching from corn production systems and the subsequent contamination of ground and surface waters is a major environmental problem. In field plots 75 m long by 15 m wide, the writers tested the hypothesis that subirrigation and intercropping will reduce leaching losses from cultivated corn and minimize water pollution. Nitrate leaching under subirrigation at a depth of either 0.7 m or 0.8 m below the soil surface was compared with leaching under free drainage. The cropping systems investigated were corn (Zea mays L.) monoculture and corn intercropped with annual Italian ryegrass (Lolium multiflorum Lam. cv. Barmultra). The effects of three fertilizer application rates (0, 180, and 270 kg N ha -1 ) on leaching were investigated in the freely drained plots. The greatest annual loss of in tile drainage water (21.9 kg N ha -1 ) occurred in - NO -N 3 freely draining, monocropped plots fertilized with 270 kg N ha -1 . Monocropped plots fertilized with 270 kg N ha -1 , with subirrigation at 0.7 m depth, resulted in annual nitrate losses into tile drainage of 6.6 kg N ha -1 , 70% less than under free drainage. Annual soil denitrification rates (60 kg N ha -1 ) with subirrigation at 0.7 m were about three-fold greater than under free drainage. Intercropping under free drainage resulted in a 50% reduction in tile drainage loss of compared with monocropping. Off-season (November 1, 1993, to May 31, 1994) - NO -N 3 tile drainage losses of (7.8 kg N ha -1 ) from freely draining monocropped plots accounted for 30% of - NO -N 3 the annual tile drainage losses. INTRODUCTION A high nitrate concentration in surface water may - (NO ) 3 cause environmental problems such as eutrophication and modify natural ecosystems (Keeny and Follett 1991). In hu- man blood, is reduced to nitrite which in turn - - NO (NO ), 3 2 converts blood hemoglobin to methemoglobin. This reduces the capacity of blood to carry oxygen, in turn causing a blood disorder known as methemoglobinemia or blue baby syndrome (Fletcher 1991). Under a St. Jude sandy loam soil cropped to potatoes, Mad- ramootoo et al. (1992) measured levels of nitrate nitrogen of up to 40 mg L -1 in the drainage water, well above - (NO -N) 3 the Canadian water quality guideline (10 mg L -1 ) for - NO -N 3 domestic water supplies. Using spatially separated field plots in North Carolina, Gilliam et al. (1979) found that controlled drainage reduced in drainage waters by up to 50%. In - NO -N 3 lysimeter studies, Madramootoo et al. (1993) showed that a water table depth (WTD) ranging from 0.6 to 0.9 m maxi- mized soybean yield while minimizing nitrate losses. Kalita and Kanwar (1993) measured maximum corn yields for WTDs of 0.6–1.0 m and observed that the use of 0.2–0.3 m WTD reduced corn yields because of waterlogging. Woodruff et al. (1984) showed that high water tables could lead to low fertil- 1 Formerly, Grad. Student, Dept. of Agric. and Biosys. Engrg., Facu. of Agric. and Envir. Sci., Macdonald Campus of McGill Univ., 21111 Lakeshore Rd., Sainte Anne-de-Bellevue, QC, Canada H9X 3V9. 2 Prof., Dir. of Ctr. for Drainage Studies, Dept. of Agric. and Biosys. Engrg., Facu. of Agric. and Envir. Sci., Macdonald Campus of McGill Univ., 21111 Lakeshore Rd., Sainte Anne-de-Bellevue, QC, Canada H9X 3V9. 3 Postdoct. Fellow, Dept. of Plant Sci., Facu. of Agric. and Envir. Sci., Macdonald Campus of McGill Univ., 21111 Lakeshore Rd., Sainte Anne- de-Bellevue, QC, Canada H9X 3V9. 4 Professor Emeritus, Dept. of Natural Resour. Sci., Facu. of Agric. and Envir. Sci., Macdonald Campus of McGill Univ., 21111 Lakeshore Rd., Sainte Anne-de-Bellevue, QC, Canada H9X 3V9. 5 New Sun Professor of Plant Sci., Dept. of Plant Sci., Facu. of Agric. and Envir. Sci., Macdonald Campus of McGill Univ., 21111 Lakeshore Rd., Sainte Anne-de-Bellevue, QC, Canada H9X 3V9. Note. Discussion open until September 1, 1999. To extend the closing date one month, a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review and possible publication on July 24, 1997. This paper is part of the Journal of Irrigation and Drainage Engineering, Vol. 125, No. 2, March/April, 1999. ASCE, ISSN 0733-9437/99/0002-0052 – 0058/$8.00 + $.50 per page. Paper No. 16279. izer use efficiency, perhaps due to excessive loss of - NO -N 3 through denitrification. Research has shown that subsurface drainage enhances leaching from the soil profile (Johnston et al. 1965; - NO -N 3 Carter et al. 1971; Devitt et al. 1976; Evans et al. 1995). Water table management is regarded as a best management practice to reduce leaching (Madramootoo et al. 1993). During - NO -N 3 subirrigation, supplemental water is supplied through subsur- face drainage pipes to raise the water table. The elevated water table provides moisture via capillary rise to help satisfy plant evapotranspiration (ET) requirements. The subsequent reduc- ing conditions in the root zone enhance denitrification, thereby minimizing nitrate leaching (Meek et al. 1969, Kimmelshue et al. 1995, Kliewer and Gilliam 1995). Elevation of the water table should be managed to provide moisture to the root zone and at the same time ensure adequate soil aeration for crop growth (Benz et al. 1981). Studies by Meisinger et al. (1991) and Lewan (1993), amongst others, have shown that ryegrass used as a nitrogen catch crop reduces levels in soil. Intercropping has - NO -N 3 been shown to increase N-uptake and consequently reduce leaching (Keeny 1986). Intercropping could also in- - NO -N 3 fluence the hydrology of an agricultural field through increased evapotranspiration (ET), thus reducing soil moisture content. The presence of a higher population of roots in the soil profile can also modify the soil structure and infiltration capacity. The objectives of this field experiment were: (1) to inves- tigate the effects of subirrigation and intercropping on growing season loss of through tile drainage and on root zone - NO -N 3 denitrification rates; (2) to evaluate the impact of N fertilizer application rates on leaching and denitrification; and (3) - NO 3 to evaluate the effect of subirrigation and intercropping on off- season loss of through tile drainage. - NO 3 MATERIALS AND METHODS Experimental Setup A field study was conducted during the 1993 and 1994 growing seasons on a 4.2 ha site located in Soulanges County, Quebec, about 30 km west of the Macdonald Campus of Mc- Gill University. Although the top soil was a well-drained Sou- langes sandy loam (fine, silty, mixed, nonacid, frigid Huma- quept), clay layers deeper in the soil profile impeded natural drainage. The surface topography was generally flat (average