Crop Rotation, Tillage, and Climate Change Impact on Simulated Soil Organic Carbon Stocks.

Soil water is a major limiting factor for biomass production and soil organic carbon (SOC) stocks increase under dryland crop production systems. The objectives of this simulation study were to: 1) simulate SOC dynamics in the top 30-cm soil over a 20-yr (1993-2012) field study using CQESTR, a process-based soil C model; 2) examine the effects of projected climate change and spring wheat (Triticum aestivum L.) crop management on SOC stocks over the predictive period of 2013-2032; and 3) identify the best dryland cropping systems to increase SOC stocks under projected climate change in central North Dakota. Conversion from a spring wheat-fallow rotation under minimum tillage (SW–F/MT) to a continuous SW rotation under no-till (SW–SW/NT) increased annualized biomass additions by 2.77 Mg ha-1 (82%) and SOC by 0.22 Mg C ha-1 yr-1. Continuous crop rotations were predicted to have a greater impact on SOC stocks than tillage (MT or NT), as SOC was highly correlated to biomass input (r = 0.91; P = 0.00053). Under the assumption that crop production will stay at the 1993-2012 average, climate change is predicted to have a minor impact on SOC (~ -6.5%) relative to crop rotation management. The CQESTR model predicted the addition of another SW or rye crop would have a greater effect on SOC stocks in the top 30 cm depth than conversion from MT to NT or climate change during 2013-2032.