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

Abstract

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.