Nitrate Loading and Isotopic Signatures in Subsurface Agricultural Drainage Systems
- E. L. Smith * and
- L. M. Kellman
Artificially draining soils using subsurface tiles is a common practice on many agricultural fields. High levels of nitrate-nitrogen (NO3−–N) are often released from these systems; therefore, knowledge on the sources and processes controlling NO3−–N in drainage systems is needed. A dual isotope study (δ15N and δ18O) was used to investigate three subsurface drainage systems (shallow, conventional, and controlled) in Onslow, Nova Scotia, Canada. The objectives of this study were (i) to identify which drainage system more effectively reduced the NO3−–N loading, (ii) to examine differences in isotopic signatures under identical nutrient and cropping regimes for a fixed soil type, and (iii) to identify the utility of different drainage systems in controlling nutrient flows. Nitrate concentrations measured ranged from 0.92 to 11.8, from 2.3 to 17.3, and from 2.1 to 19.8 mg L−1 for the shallow, conventional, and controlled drains, respectively. Total NO3−–N loading from shallow and controlled drains were 20 and 5.6 kg ha−1, respectively, lower than conventional (39.1 kg ha−1). The isotopic composition of NO3−–N for all drainage types appeared to be a mixture of two organic sources (manure and soil organic matter) via the process of nitrification. There was no evidence that denitrification played a significant role in removing NO3−–N during transport. Overall, shallow drainage reduced NO3−–N loading but offered no water conservation benefits. Combining the benefits of decreased NO3−–N loading from shallow systems with water control capability may offer the best solution to reducing nutrient loadings into water systems, achieving optimal crop yield, and decreasing drainage installation costs.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2011. . Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.