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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #295535
Title: Do cover crops increase or decrease nitrous oxide emissions? A meta-analysis

Author
item BASCHE, ANDREA - Iowa State University
item MIGUEZ, FERNANDO - Iowa State University
item Kaspar, Thomas
item CASTELLANO, MICHAEL - Iowa State University

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2013
Publication Date: 11/1/2014
Citation: Basche, A.D., Miguez, F.E., Kaspar, T.C., Castellano, M.J. 2014. Do cover crops increase or decrease nitrous oxide emissions? A meta-analysis. Journal of Soil and Water Conservation. 69:471-482.

Interpretive Summary: Cover crops incorporated into agricultural systems can prevent erosion, recycle soil nutrients, and increase soil organic matter. The effect of cover crops on nitrous oxide emissions from agricultural systems is not well understood. In some studies cover crops have been shown to increase emissions, in others they have reduced emissions, and in the rest there has been little or no effect. Nitrous oxide is an important greenhouse gas and has been implicated in climate change. Nitrous oxide emissions from soil increase when conditions are favorable for denitrification (wet soil) and when soil nitrate levels are high. Because cover crops can both reduce or increase soil nitrate or soil water content, it is not surprising that they might have both positive and negative effects on nitrous oxide emissions. This study analyzed the results of 26 studies to determine what factors affect whether cover crops increase or decrease nitrous oxide emissions. The results of this analysis are important because they show that using a legume cover crop and tilling in cover crops residues increase nitrous oxide emissions. Alternately, using non-legume cover crops and leaving cover crop residues on the soil surface can decrease nitrous oxide emissions. This information will be useful to scientists in designing future experiments and to land managers, farmers, and government employees designing conservation plans that utilize cover crops.

Technical Abstract: Few studies have examined the factors that affect the impact of cover crops on nitrous oxide emissions. A meta-analysis of the data obtained from twenty-six peer reviewed articles was conducted using the natural log of the nitrous oxide flux with a cover crop divided by the nitrous oxide flux without a cover crop (LRR). The dataset included 106 observations and 18 additional environmental and management variables to investigate variability in LRRs. Forty percent of the observations had negative LRRs, indicating that the cover crop treatment had decreased nitrous oxide emissions, while 60% had positive LRRs indicating increased emissions. Legumes cover crops had higher LRRs than non-legume species, especially at lower nitrogen fertilizer rates. Nitrous oxide emissions were relatively higher when cover crop residues were decomposing, while emissions during cover crop growth were relatively lower. When cover crop residues were incorporated into the soil, nitrous oxide emissions were relatively larger than when cover crop residues were left on the soil surface. This analysis indicates that nitrous oxide emissions can be reduced by using non-legume cover crops and leaving their residues on the soil surface. Although this analysis looked at the direct effects of cover crops on nitrous oxide emissions, cover crops also prevent indirect losses of nitrous oxide that occur when nitrate is leached from agricultural fields and transported into surface water systems or wetlands where denitrification processes can also release nitrous oxide. Consideration of indirect losses of nitrous oxide as well as soil organic carbon changes must also be given when evaluating the full impact of cover crops on greenhouse gas emissions and global warming potential.