A gronomy J our n al • Volume 10 0 , I s sue 6 • 2 0 0 8 1703 Stover from corn grain production has been identifi ed as a probable source of biomass feedstock for cellulosic ethanol production (Graham et al., 2007). Furthermore, the replacement of fossil fuels with renewable fuels has been identifi ed as an eff ective method of reducing greenhouse gas (GHG) emissions (Griffi n and Lave, 2006). However, the loss of SOC associated with the removal of corn fodder for cellulosic ethanol feedstock is of agricultural and environmental concern. Th e decline of SOC in agricultural systems combined with increased awareness of the importance of the terrestrial ecosystem in global C budgets has stimulated evaluations of land management eff ects on soil C dynamics and storage (Lal et al., 1995). Past and present farming practices have resulted in loss of an estimated 4 ± 1 × 10 9 Mg of C from soils of the United States, and 78 ± 12 × 10 9 Mg from the world's soils, a large fraction of which ended up in the atmosphere (Lal, 1999). Soils play a major role in the global C budget not only because of the large amount of C stored in soil, with estimates ranging from 1395 to 1636 × 10 8 Mg (Torbert et al., 1999;Schlesinger, 1984) but also because the annual fl ux of CO 2 to the atmosphere from soil is 10 times the amount of CO 2 contributed by fossil fuel usage (Post et al., 1990). Land use practices that may increase C sequestration include a switch to no-tillage (NT), greater cropping frequency (Bremer et al., 1994;Campbell et al., 1995), and application of organic amendments such as manure (Sommerfeldt et al., 1988), although Janzen et al. (1998) regarded applications of C amendments as a C transfer rather than a gain. Many of these practices (manure, forage production, and reduced harvest removal) that favor C storage appear to interact synergistically with each other, so that increases in SOC under one practice are greater when combined with other practices (Grant et al., 2001).Additional input of organic substances containing high amounts of C, such as farmyard manure or the incorporation of crop residues will increase organic C content in soil (Dersch and Bohm, 2001). Beef cattle feedlot manure contains essential nutrients in addition to approximately 15% C that can be used to improve soil physical and chemical properties (Eghball, 2002).Despite increased oxidative losses it was estimated that approximately half of the added manure C is retained in the soil at the end of the season (Rochette and Gregorich, 1998). Iazurralde et al. (2001) determined that the addition of farmyard manure was a key management component leading to SOC increases. Drinkwater et al. (1998) compared manure and conventional systems and found that even though both systems received equal amounts of C, the manure system showed a signifi cant increase in C stored in soil. Rate of SOC change was directly related to C input from crop residues and amendments (Rasmussen and Parton, 1994). Compared with senescent-crop residues, a larger proportion of manure...

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Biennial wormwood has become an important weed for soybean producers in the northern Great Plains states of the United States. Research was conducted at Fargo, Leonard, and Wyndmere, ND, in 2000 and 2001 to evaluate postemergence control of biennial wormwood in soybean. Biennial wormwood densities at Fargo, Leonard, and Wyndmere were 290, 290, and 130 plants/m2in 2000 and 22, 670, and 88 plants/m2in 2001, respectively. Across years, biennial wormwood control with postemergence herbicides 4 wk after treatment was 81 to 97% at Fargo, 5 to 89% at Leonard, and 2 to 95% at Wyndmere. Biennial wormwood control was greater at Fargo than at the other locations probably because of smaller seedling size at the time of treatment. Bentazon split applied at the rate of 560 g ai/ha followed by 560 g/ha approximately 12 d after the first treatment generally provided the least amount of injury to soybean, the greatest control of biennial wormwood, and the fewest escaped plants. Lactofen at 220 g ai/ha or split applied at 110 g/ha followed by 110 g/ha approximately 12 d after the first treatment provided 84% or greater biennial wormwood control at Fargo but less than 40% control at Leonard and Wyndmere. The 4.5:1 bentazon plus acifluorfen premix full-rate and split treatments provided slightly better control than the 2:1 bentazon plus acifluorfen premix full-rate and split treatments. High levels of biennial wormwood control can be achieved with a better understanding of seedling emergence patterns and by targeting postemergence herbicide applications to seedlings less than 5 cm tall.

Biennial wormwood has become a problem for soybean producers in the northern Great Plains of the United States. Research was conducted to evaluate control of biennial wormwood with preemergence (PRE) herbicides alone or followed by postemergence (POST) herbicides in 2000 and 2001 at Fargo, Leonard, and Wyndmere, ND. Favorable soil moisture conditions at Leonard resulted in continual emergence and greater densities of biennial wormwood, whereas the soil at Fargo and Wyndmere was dry and few biennial wormwood seedlings emerged at these locations. Biennial wormwood control with PRE herbicides was greater than 89% at Fargo and Wyndmere but was 80% or lower at Leonard. PRE biennial wormwood control was higher with flumetsulam than with sulfentrazone. When POST treatments were applied after PRE herbicides, biennial wormwood control 4 wk after treatment was 92% or better at Fargo and Wyndmere but was 76% or less at Leonard. The combination of PRE and POST herbicide treatments did not improve control greatly at Fargo or Wyndmere but at Leonard reduced the number of biennial wormwood plants.