Syswerda, S. P., B. Basso, S. K. Hamilton, J. B. Tausig, and G. P. Robertson. 2012. Long-term nitrate loss along an agricultural intensity gradient in the Upper Midwest USA. Agriculture, Ecosystems and Environment 149:10-19.
Nitrate (NO3−) loss from intensively farmed cropland is a long-standing, recalcitrant environmental problem that contributes to surface and groundwater pollution and coastal zone hypoxia. Here nitrate leaching losses are reported from nine replicated cropped and unmanaged ecosystems in southwest Michigan, USA. Ecosystems include four annual corn–soybean–winter wheat rotations under conventional, no-till, reduced-input, and organic/biologically-based management, two perennial cropping systems that include alfalfa and hybrid poplar trees, and three unmanaged successional communities including an early successional community analogous to a cellulosic biofuel system as well as a mature deciduous forest. The organic, alfalfa, and unmanaged systems received no synthetic, manure, or compost nitrogen. Measured nitrate concentrations were combined with modeled soil water drainage to provide estimates of nitrate lost by leaching over 11 years. Among annual crops, average nitrate losses differed significantly (p < 0.05) and followed the order conventional (62.3 ± 9.5 kg N ha−1 yr−1) > no-till (41.3 ± 3.0) > reduced-input (24.3 ± 0.7) > organic (19.0 ± 0.8) management. Among perennial and unmanaged ecosystems, nitrate loss followed the pattern alfalfa (12.8 ± 1.8 kg N ha−1 yr−1) = deciduous forest (11.0 ± 4.2) ≫ early successional (1.1 ± 0.4) = mid-successional (0.9 ± 0.4) > poplar (<0.01 ± 0.007 kg N ha−1 yr−1) systems. Findings suggest that nitrate loss in annual row crops could be significantly mitigated by the adoption of no-till, cover crops, and greater reliance on biologically based inputs, and in biofuel systems by the production of cellulosic rather than grain-based feedstocks.
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