Interactive role of topography and best management practices on N2O emissions from agricultural landscape

Abstract

Global greenhouse gas emissions have reached an unprecedented level. Agriculture and land-use change, one of the most diverse sectors, emits 66 % of global anthropogenic nitrous oxide (N2O) into the atmosphere. A plethora of research has been compiled to estimate and quantify the N2O emissions from agricultural systems and understand the underlying processes (nitrification and denitrification). These processes are controlled by natural (e.g., environment, soil, and topography) and anthropogenic factors (e.g., agricultural management practices). Complexity in topographical attributes such as elevation, slope, and aspect contribute to spatial variability in soil properties and controls N2O emissions. Additionally, a set of agricultural best management practices (BMPs) such as conservation tillage (CT), cover cropping (CC), and soil organic amendments have been adopted to improve soil health. However, the potential impact of these BMPs on N2O emissions has not been considered in detail. Simultaneously, the inter-connectedness of these natural and anthropogenic factors makes soil N2O emissions extremely variable and complex. Recent studies reported the varied impacts of CT, CC, and organic amendments on N2O emissions. However, the landscape level and integrated impact of natural and anthropogenic factors and processes from temperate regions have not been reviewed, which is an obvious gap in the literature. In this review, we critically analyzed 226 recent studies (mainly from temperate regions) to investigate the status and progress of our understanding of N2O emissions from the agricultural crop production system. Most of the studies reported that topography increases spatial variations in N2O emissions by regulating soil physical, chemical, and biological properties. Landscape positions with higher soil moisture (foot slope, toe slope, localized depressions) had significantly higher contributions towards N2O emissions. Moreover, agricultural BMPs also increase soil N2O emissions alone and integrated with topographical variations. We identified potential mechanisms accelerating these emissions, mitigation options, and future research directions under each section based on critical literature analysis.