Nitrous Oxide Emissions from Agricultural Fields: Assessment, Measurement and Mitigation

Abstract

In this paper we discuss three topics concerning N20 emissions from agricultural systems. First, we present an appraisal of N20 emissions from agricultural soils (Assessment). Secondly, we discuss some recent efforts to improve N20 flux estimates in agricultural fields (Measurement), and finally, we relate recent studies which use nitrification inhibitors to decrease N20 emissions from N-fertilized fields (Mitigation). To assess the global emission of N20 from agricultural soils, the total flux should represent N20 from all possible sources; native soil N, N from recent atmospheric deposition, past years fertilization, N from crop residues, N20 from subsurface aquifers below the study area, and current N fertilization. Of these N sources only synthetic fertilizer and animal manures and the area of fields cropped with legumes have sufficient global data to estimate their input for N20 production. The assessment of direct and indirect N 2 0 emissions we present was made by multiplying the amount of fertilizer N applied to agricultural lands by 2% and the area of land cropped to legumes by 4 kg N 2 0-N ha-I. No regard to method of N application, type of N, crop, climate or soil was given in these calculations, because the data are not available to include these variables in large scale assessments. Improved assessments should include these variables and should be used to drive process models for field, area, region and global scales. Several N20 flux measurement techniques have been used in recent field studies which utilize small and ultra-large chambers and micrometeorological along with new analytical techniques to measure N 2 0 fluxes. These studies reveal that it is not the measurement technique that is providing much of the uncertainty in N 2 0 flux values found in the literature but rather the diverse combinations of physical and biological factors which control gas fluxes. A careful comparison of published literature narrows the range of observed fluxes as noted in the section on assessment. An array of careful field studies which compare a series of crops, fertilizer sources, and management techniques in controlled parallel experiments throughout the calendar year are needed to improve flux estimates and decrease uncertainty in prediction capability. There are a variety of management techniques which should conserve N and decrease the amount of N application needed to grow crops and to limit N20 emissions. Using nitrification inhibitors is an option for decreasing fertilizer N use and additionally directly mitigating N20 emissions. Case studies are presented which demonstrate the potential for using nitrification inhibitors to limit N20 emissions from agricultural soils. Inhibitors may be selected for climatic conditions and type of cropping system as well as the type of nitrogen (solid mineral N, mineral N in solution, or organic waste materials) and applied with the fertilizers. • FAX No.: +19704908213 Plant and Soil is the original source of publication of this article. It is recommended that this article is cited as: Plant and SoU 181: 95-108, 1996. [589]