Management Practices Influence On Dryland Soil Carbon Dynamics.

Information is needed on novel management practices to increase dryland C sequestration and soil quality. We evaluated the effects of tillage, crop rotation, and cultural practice on dryland crop biomass (stems and leaves) yield from 2004 to 2007 and surface residue and soil C fractions at the 0-20 cm depth in a Williams loam in 2007 and 2008 in eastern Montana, USA. Treatments were two tillage practices (no-tillage [NT] and conventional tillage [CT]), two crop rotations (continuous spring wheat [CW] and spring wheat-barley hay-corn-pea [W-B-C-P]), and two cultural practices (regular [conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height] and ecological [variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height]). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop biomass was 24 to 39% greater in W-B-C-P than in CW in 2004 and 2005. Surface residue C was 36% greater in NT than in CT in the regular practice. At 5-20 cm, SOC was 14% greater in NT with W-B-C-P and the regular practice than in CT with CW and the ecological practice. In 2007, POC and PCM at 0-20 cm were 23 to 54% greater in NT with CW or the regular practice than in CT with CW or the ecological practice. Similarly, MBC at 10-20 cm was 70% greater with the regular than with the ecological practice in NT with CW. All C fractions declined from autumn 2007 to spring 2008. No-tillage with early planting increased surface residue and soil C storage and microbial biomass and activity compared with conventional tillage with delayed planting. Without additional crop C input, mineralization of residue and soil organic matter reduced C storage and microbial activity from autumn to the following spring.