Impact of Cover Cropping and Landscape Positions on Nitrous Oxide Emissions in Northeastern Agroecosystems

Abstract:

Studies investigating agricultural nitrous oxide (N₂O) emissions tend to rely on plot-scale experiments. However, to understand the impacts of agricultural practices at a larger scale, it is essential to consider the variability of landscape characteristics along with management treatments. This study compared N₂O emissions from a fertilizer-based, conventionally managed farm and an organically managed farm that uses legume cover crops as a primary nutrient source. The objective of the study was to assess how management regimes and slope positions interact to impact N₂O emissions and soil characteristics. The field experiment was conducted in two adjacent grain farms in upstate New York that both have been under consistent management for 20 years. In the organic farm, red clover was frost-seeded into a winter grain (spelt), and then incorporated in the spring as a nutrient source for the subsequent corn plants. In contrast, the conventionally managed farm used inorganic fertilizer as the nutrient source. Gas measurement was conducted at two landscape positions at both farms: 1) shoulder and 2) toeslope positions. Comparable N₂O emissions were found in the clover-corn phase in the organic site and the bare fallow-corn phase in the conventional site. The spelt-corn phase in the organic farm had the lowest N₂O emissions. Soil nitrate concentration was the best predictor for seasonal average N₂O emissions. The impact of landscape position on N₂O emissions was only found in the conventional site, which was driven by higher denitrfication at toeslopes. In the organic farm, such effect was confounded by higher clover biomass at shoulder slopes. Our study shows that the impact of landscape characteristics on N₂O emissions could differ across sites based on the complex interplay between environmental conditions and management.