Soil Carbon Dioxide Emission and Carbon Content Under Dryland Crops. II. Effects of Tillage, Cropping Sequence, and Nitrogen Fertilization (Gracenet Project)

Management practices are needed to reduce soil CO₂ emission and increase C sequestration under dryland cropping system. The effects of tillage, cropping sequence, and N fertilization were evaluated on soil surface CO₂ flux, soil total C content at 0- to 120-cm depth, and soil temperature and water content at 0- to 15-cm from April to October, 2006 and 2007 in eastern Montana. Tillage and cropping sequences were no-tilled continuous malt barley (NTCB), no-tilled pea-malt barley (NTP-B), no-tilled fallow-malt barley (NTF-B) and conventional-tilled fallow-malt barley (CTF-B) with split plot application of two N rates (0 and 80 kg N ha^-1) to barley. Tillage and cropping sequence did not influence CO₂ flux in the second phase of the cropping sequence. In 2006, CO₂ flux was greater with 80 than with 0 kg N ha^-1 in NTCB, NTF-B, and CTF-B in June and August following substantial rain. In 2007, CO₂ flux was greater with 80 than with 0 kg N ha^-1 in NTP-B and CTF-B in June and July but was greater with 0 than with 80 kg N ha^-1 in NTCB and NTF-B in July following rain. Soil temperature varied with treatments. Averaged across measurement dates, CO₂ flux was greater in NTCB and NTP-B with 80 kg N ha^-1 than in NTF-B with 0 and 80 kg N ha^-1. Soil temperature was greater in CTF-B with 0 kg N ha^-1 than in NTP-B and CTF-B with 80 kg N ha^-1 in 2006. Soil water content was greater in CTF-B with 0 kg N ha^-1 than in other treatments. Soil total C was not influenced by treatments. Although NTF-B reduced CO₂ emission, continuous cropping with N fertilization increased the emission probably by increasing root respiration due to increased biomass production.