Nitrogen Dynamics among Cropland and Riparian Buffers

Abstract

Nitrate (NO3-) leaching to ground water poses water quality concerns in some settings. Riparian buffers have been advocated to reduce excess ground water NO3- concentrations. We characterized inorganic N in soil solution and shallow ground water for 16 paired cropland-riparian plots from 2003 to 2005. The sites were located at two private dairy farms in Central New York on silt and gravelly silt loam soils (Aeric Endoaqualfs, Fluvaquentic Endoaquepts, Fluvaquentic Eutrudepts, Glossaquic Hapludalfs, and Glossic Hapludalfs). It was hypothesized that cropland N inputs and soil-landscape variability would jointly affect NO3- leaching and transformations in ground water. Results showed that well and moderately well drained fields had consistently higher ground water NO3- compared to more imperfectly drained fields receiving comparable N inputs. Average 50-cm depth soil solution NO3- and ground water dissolved oxygen (DO) explained 64% of average cropland ground water NO3- variability. Cropland ground water with an average DO of <3 mg L(-1) tended to have <4 mg L(-1) of NO3- with a water table depth (WTD) of <or=1 m. Water table depth and DO explained 83% of ground water NO3- variability among buffers. More poorly drained buffers had low ground water NO3- and DO, a shallow WTD, and higher ground water ammonium and soil organic matter. Chloride patterns indicated that dilution was minor in most buffers, suggesting that denitrification losses were important. Soil-landscape factors strongly influenced NO3- behavior and suggest the importance of accurately characterizing soil variability along cropland-riparian zones.