Soil Carbon Dioxide Emission and Carbon Content Under Dryland Crops. I. Effects of Tillage and Crops (Gracenet Project)

Soil CO₂ emission and C content can be influenced by types of tillage and crops. The CO₂ flux at the soil surface, soil total C at 0- to 120-cm depth, and soil temperature and water content at 0- to 15-cm were measured under dryland no-tilled malt barley (NTB), no-tilled pea (NTP), no-tilled fallow (NTF), and conventional-tilled fallow (CTF) in a loamy soil from April to November, 2005 to 2007 in eastern Montana. The CO₂ flux in all treatments increased from May to July as soil temperature increased and then declined. Fluxes increased by 2- to 6-fold following substantial rain in June and July that increased soil water content. During these periods, fluxes were greater in NTB and CTF than in NTF in 2005, greater in NTP than in NTF in 2006, and greater in NTB and NTP than in NTF and CTF in 2007. In contrast, soil water content was greater in NTF and CTF than in NTB and NTP during drier periods in July and August. Averaged across measurement dates, CO₂ flux was greater in NTB than in other treatments in 2005 and 2007 and greater in NTB and NTP than in NTF in 2006. Soil temperature was greater in NTP and NTF than in NTB and CTF but soil water content was greater in NTF and CTF than in NTB and NTP. Soil total C content was not influenced by treatments. Although increased soil temperature and water content increased CO₂ emission, tillage and cropping increased the emission compared with no-tillage and fallow probably by increasing C mineralization due to increased microbial activities and root respiration. Malt barley increased CO₂ emission compared with pea in two out of three years.