Nitrate Leaching from Continuous Corn, Perennial Grasses, and Poplar in the US Midwest

Leaching from annual corn (Zea mays L.) crops is a primary source of nitrate (NO₃⁻) pollution of ground and surface waters. Here, we compare NO₃⁻ losses from no‐till corn with losses from various alternative perennial cropping systems (switchgrass [Panicum virgatum L.], miscanthus [Miscanthus ×giganteus J.M. Greef & Deuter ex Hodkinson & Renvoiz], a native grass mixture, and restored prairie), as well as hybrid poplar (Populus nigra L. × P. maximowiczii A. Henry ‘NM6’), all grown on a well‐drained soil in Michigan. Soil water was sampled from below the root zone using suction cup samplers during nonfrozen periods (March–November) between 2009 and 2016. Leaching was estimated from NO₃⁻ concentrations in soil water and modeled drainage (percolation) rates. Drainage rates were not significantly different among crops, constituting ∼30% of total annual precipitation. Aboveground net primary production (Mg ha⁻¹ yr⁻¹) averaged across the 7 yr was highest in poplar (30.8 ± 1.9 [SE]) followed by miscanthus (23.9 ± 2.4) and corn (20.4 ± 0.9). Volume‐weighted mean NO₃⁻ concentrations (mg N L⁻¹) and NO₃⁻ leaching (kg ha⁻¹ yr⁻¹) averaged across the 7 yr were 9.2 and 34.1, 2.3 and 5.9, and 3.0 and 7.2, respectively, for corn, perennial grasses and poplar. Approximately 10 to 32% of applied N was lost as NO₃⁻ from these crops, with the highest percent losses from poplar (32%) followed by corn (20%). Perennial cropping systems leached considerably more NO₃⁻ in first few years after planting, but over 7 yr they lost much less NO₃⁻ than corn. Perennial crops may therefore help ameliorate NO₃⁻ pollution in agricultural landscapes even if they receive modest N fertilization. CORE IDEAS: Over 7 yr, perennial grasses and poplar trees leached much less nitrate than corn Nitrate leaching from grasses and poplar was comparable with corn for 1–2 yr after planting. Perennial crops can ameliorate nitrate pollution in agricultural landscapes.