Do cover crops increase or decrease nitrous oxide emissions? A meta-analysis

Abstract

There are many environmental benefits to incorporating cover crops into crop rotations, such as their potential to decrease soil erosion, reduce nitrate (NO 3 ) leaching, and increase soil organic matter. Some of these benefits impact other agroecosystem processes, such as greenhouse gas emissions. In particular, there is not a consensus in the literature regarding the effect of cover crops on nitrous oxide (N 2 O) emissions. Compared to site-specific studies, meta-analysis can provide a more general investigation into these effects. Twenty-six peer-reviewed articles including 106 observations of cover crop effects on N 2 O emissions from the soil surface were analyzed according to their response ratio, the natural log of the N 2 O flux with a cover crop divided by the N 2 O flux without a cover crop (LRR). Forty percent of the observations had negative LRRs, indicating a cover crop treatment which decreased N 2 O, while 60% had positive LRRs indicating a cover crop treatment which increased N 2 O. There was a significant interaction between N rate and the type of cover crop where legumes had higher LRRs at lower N rates than nonlegume species. When cover crop residues were incorporated into the soil, LRRs were significantly higher than those where residue was not incorporated. Geographies with higher total precipitation and variability in precipitation tended to produce higher LRRs. Finally, data points measured during cover crop decomposition had large positive LRRs and were larger than those measured when the cover crop was alive. In contrast, those data points measuring for a full year had LRRs close to zero, indicating that there was a balance between periods when cover crops increased N 2 O and periods when cover crops decreased emissions. Therefore, N 2 O measurements over the entire year may be needed to determine the net effect of cover crops on N 2 O. The data included in this meta-analysis indicate some overarching crop management practices that reduce direct N 2 O emissions from the soil surface, such as no soil incorporation of residues and use of nonlegume cover crop species. However, our results demonstrate that cover crops do not always reduce direct N 2 O emissions from the soil surface in the short term and that more work is needed to understand the full global warming potential of cover crop management. Key words: cover crops-global warming potential-meta-analysis-nitrous oxideAgricultural soils account for 69% of nitrous oxide (N 2 O) emissions in the United States (USEPA 2013). This occurs because nitrogen (N) is an essential nutrient for agricultural production; N is added to soil as N fertilizer and manure, released from soil organic matter, and has high reactivity and mobility in terrestrial ecosystems (Robertson and Vitousek 2009). Fertilizer N recovery efficiency for major cereal production is less than 50% and even as low as 20% (Cassman et al. 2002), which potentially makes large quantities of N available for the biological processes that release N 2 O. Nitrous oxide, which ...

Non‐Legume Cover Crops Can Increase Non‐Growing Season Nitrous Oxide Emissions

“…In part, this is because cover crops release labile C and N through root exudates and rhizodeposition during their growth phase and freeze-thaw cycles, which can stimulate microbial activity and increase N 2 O emissions (Petersen et al, 2011;Gul and Whalen, 2013;Mitchell et al, 2013). This may counter the crop N uptake and explain why there is no clear consensus on how non-legume cover crops effect N 2 O emissions (Basche et al, 2014). A better understanding of N 2 O emissions and the substrates that drive N 2 O production during the non-growing season could improve cover crop management practices for optimized environmental and agronomic performance.…”

“…About 39 to 90% of annual N 2 O emissions occur during the non-growing season (Teepe et al, 2000;Jayasundara et al, 2007;Yanai et al, 2011;Abalos et al, 2016), mostly through the winter to spring thaw period in temperate regions (Nyborg et al, 1997;Wagner-Riddle and Thurtell, 1998;Dörsch et al, 2004;Ellert and Janzen, 2008). In cover cropped soils, decomposing root and aboveground tissues may supply organic C and NO 3 for N 2 O production (Basche et al, 2014), exacerbating N 2 O emissions during freeze-thaw events (Mørkved et al, 2006). Typically, WEOC is considered a surrogate of the C available for microbes (Appel and Mengel, 1993;Kalbitz et al, 2000;Chantigny, 2003;Zsolnay, 2003).…”

Meta‐Analysis Constrained by Data: Recommendations to Improve Relevance of Nutrient Management Research

“…By combining multi-study data with robust statistical methods, meta-analysis of agricultural experimental data can be used to fi nd overall benefi ts of management practices that may otherwise be difficult to fully understand with individual, often short-term, research projects, most of which are limited to particular climatic and soil conditions. For example, recent meta-analyses have improved the scientific certainty as well as the understanding of the implications of tillage on nitrous oxide (N 2 O) emissions (van Kessel et al, 2013), the impact of cover crops on N 2 O emissions (Basche et al, 2014), and the effect of nitrogen (N) fertilizer on N 2 O emissions and the interaction effect between fertilizer rate, fertilizer type, and soil organic carbon (Qian et al, 2010).…”

KringloopToets Mestverwerking

“…Echter kunnen groenbemesters een stijging van N2O emissies veroorzaken -vnl. als leguminosen worden toegepast (Basche, Miguez, Kaspar, & Castellano, 2014).…”