Simulated Soil Organic Carbon Responses to Crop Rotation, Tillage, and Climate Change in North Dakota.

Understanding how agricultural management and climate change affect soil organic carbon (SOC) stocks is particularly important for dryland agriculture regions that have been losing SOC over time due to fallow and tillage practices, and it can lead to development of agricultural practice(s) that reduce the impact of climate change on crop production. The objectives of this study were: (i) to simulate SOC dynamics in the top 30 cm of soil during a 20-yr (1993-2012) field study using CQESTR, a process-based C model; (ii) to predict the impact of changes in management, crop production, and climate change from 2013 to 2032; and (iii) to identify the best dryland cropping systems to maintain or increase SOC stocks under projected climate change in central North Dakota. Intensifying crop rotations was predicted to have a greater impact on SOC stocks than tillage (minimum tillage [MT], no-till [NT]) during 2013 to 2032, as SOC was highly correlated to biomass input ( = 0.91, = 0.00053). Converting from a MT spring wheat (SW, L.)-fallow rotation to a NT continuous SW rotation increased annualized biomass additions by 2.77 Mg ha (82%) and SOC by 0.22 Mg C ha yr. Under the assumption that crop production will stay at the 1993 to 2012 average, climate change is predicted to have a minor impact on SOC (approximately -6.5%) relative to crop rotation management. The CQESTR model predicted that the addition of another SW or rye ( L.) crop would have a greater effect on SOC stocks (0- to 30-cm depth) than conversion from MT to NT or climate change from 2013 to 2032.

Leaf Spot Diseases on Winter Wheat Influenced by Nitrogen, Tillage, and Haying after a Grass-Alfalfa Mixture in the Conservation Reserve Program.

When contracts for the Conservation Reserve Program (CRP) expire, highly erodible land that had a long-term vegetative cover composed of grasses or grass-legume mixtures may be converted back to cropland. Considering that some of the same leaf spot pathogens found on grasses can cause diseases on wheat, the management practices used to convert these lands were evaluated for their effect on winter wheat leaf spot diseases. In a 3-year spring wheat-winter wheat-pea crop rotation, the major leaf spot diseases on winter wheat were tan spot and Stagonospora nodorum blotch. Removal of hay or leaving hay in the plots when converting grassland to cropland had no significant effect on leaf spot diseases, indicating that the residue from the grass-alfalfa crop did not influence leaf spot diseases on winter wheat. Tillage treatments did not influence the amount of disease in 1996, but with higher precipitation levels in 1999, higher disease severities were associated with the no tillage treatment. Higher levels of crop residue associated with the no tillage treatment could potentially carry over plant pathogens from one crop to the next. The severity of leaf spot diseases was consistently lower when nitrogen was applied, indicating the importance of nitrogen application when converting grassland to cropland.