Cover crop effects on soil carbon dioxide emissions in a semiarid cropping system

Cover crops improve soil health and environmental quality by enhancing soil organic carbon (SOC) sequestration and nutrient cycling in agroecosystems. This study evaluated the effect of cover crops on soil CO2-C emissions, temperature, and water content during cover crop growth from April to October, 2017 and 2018. Treatments included fallow, pea (Pisum sativum L.), oat (Avena sativa L.), canola (Brassica napus L.), pea-oat (POmix), pea-canola (PCmix), pea-oat-canola (POCmix), and POC-hairy vetch (Vicia villosa L.)-forage radish (Raphanus sativus L.)-barley (Hordeum vulgare L.) (six species mixture; SSmix). The CO2-C emissions were monitored weekly from April to October each year using a portable infrared-gas analyzer. Seasonal changes in CO2-C emissions varied with cover crops and peaked as soil temperature and water content following precipitation events. Average CO2-C emissions across sampling dates was 46-70% greater under pea than under fallow, canola, and POmix in 2017, but not different among cover crops in 2018. Although the emissions were higher than fallow, canola and POmix plots had lower CO2-C emissions than other cover crops. Pea as sole cover crop or in mixtures (PCmix, POCmix, SSmix) increased CO2-C emissions and microbial activity whereas canola and POmix mixture reduced the emissions during the period with higher precipitation.