A Meta-analysis of Soil Carbon under Cover Crops
Abstract
Over two-thirds of global terrestrial carbon (C) is stored in the soil, meaning that soil C plays a critical role in the regulation of atmospheric CO2 concentrations. Increasing soil C levels also can improve soil quality and fertility. With increasing societal concern for agriculture sustainability, shifts in management practices, including the use of cover crops within rotations, have been proposed as a way to increase soil C sequestration. Many on-site experiments have been conducted to identify whether including cover crop increases soil C and improves soil quality, yet conflicting reports among studies means that a comprehensive quantitative assessment is necessary. In this study, we collected studies that compared agricultural production with and without cover cropping, and conducted t-tests and meta-analyses to explore interactions between cover crops, soils, and C. Our results show that when studies reported standard deviations, meta-analysis resulted in similar conclusion as t-test (cover crops significantly improve soil C); however, when standard deviations were not available and had to be estimated, the meta-analysis resulted in a conservative conclusion that cover crops do not significantly improve soil C. When applied to the overall dataset, both the t-test and meta-analysis found that cover crops resulted in significant increases in soil C in coarse-textured and fine-textured soils, but less increase was observed for medium-textured soil (mean increase of 13.2%, 11.3%, and 7.5%, respectively). Likewise, multi-species cover crop mixtures resulted in greater soil C increases than single-species cover crops (increase of 14% vs 8%), and using legumes as cover crops resulted in greater soil C increases compared to grasses and brassicas (increase of 11.5%, 5.5% and 9.8%, respectively). Carbon differences were mostly seen in shallow soils (< 20 cm), but significant increases were seen to 60 cm depth. A regression analysis revealed that soil C was positively correlated with cover crop dry biomass, but negatively correlated with C/N of cover crop biomass. Altogether, cover cropping caused a 9% mean increase in soil C (4% to 15%), indicating that the inclusion of cover crops into agricultural rotations can enhance soil C levels and thus increase the ability of soil to act as a C sink for atmosphere CO2.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B23I2635J
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 0486 Soils/pedology;
- BIOGEOSCIENCES