38-21 Leaching Export of Dissolved Organic Carbon and Dissolved Nitrogen from Agricultural Soils in Southern Michigan.
Monday, October 23, 2017: 3:00 PM
Marriott Tampa Waterside, Grand Ballroom B
Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are two closely linked components of dissolved organic matter leaching from soils. DOC can be significant to soil C balance and affects the bioavailability of trace metals, and DON may be significant to soil N balance and a source of reactive N to surface waters. while leaching losses of nitrate (NO3-) are often studied because of eutrophication and public health concerns, leaching of DOC or DON from agricultural soils is rarely reported. This study examines leaching of DOC, DON, ammonium (NH4+), and NO3- from no-till maize, perennial herbaceous crops (switchgrass, miscanthus, native grasses and restored prairie), and a tree plantation (poplar). Pore-water was sampled below the root zone (1.2 m soil depth) in non-frozen periods (March-November) between 2009 and 2015. Leaching was estimated on a crop-year basis from concentrations in pore-water and modeled drainage rates. DOC leaching rates and volume-weighted mean concentrations were similar in all crops, averaging 12.1 kg ha-1 y-1 and 3.6 mg L-1, respectively, with the exception of poplar, which was lost more DOC (21.5 kg ha-1 y-1 and 6.8 mg L-1). DON averaged 9.8 kg ha-1 y-1 and 2.5 mg L-1 for maize, which was higher than perennial herbaceous crops (mean: 1.1 kg ha-1 y-1 and 0.35 mg L-1) and poplar (1.8 kg ha-1 y-1 and 0.6 mg L-1). Nitrate-N leaching averaged 13.0 kg ha-1 y-1 and 4.5 mg L-1 while ammonium-N leaching from these crops was comparatively small (less than 5% of NO3-). Nitrogen leaching occurred in all crops with or without N fertilization but higher N rates led to increased leaching in maize. Perennial crops leached more nitrogen in first few years after planting, but N leaching significantly decreased as the crops matured. Our study shows how perennial crops can minimize N leaching and consequent movement into aquifers and surface waters, but mainly via reduced NO3- leaching rather than affecting DON. DON was a significant component constituting ~20 percent of the total N leaching. Fertilization of annual crops resulted in enhanced NO3- and DON leaching with little effect on DOC or NH4+ leaching.