The popularity of growers using only postemergence (POST) herbicides for weed management in soybean was enabled by the commercialization of glyphosate-resistant soybean. The efficacy and flexibility provided by this technology diminished the use of soil residual herbicides and arguably, increased soybean yield loss from early-season weed competition. While, the rapid evolution and biogeographical spread of herbicide-resistant weeds, especially glyphosate-resistant biotypes, has renewed interest into the use of soil residual products, herbicide-resistant soybean technologies continue to be developed that may once again entice growers into POST-only weed management systems. The commercial interest in soybean yield advancements justifies further characterizing the benefits provided by early-season weed control beyond those of herbicide-resistance management. Furthermore, as awareness heightens regarding techniques that will enhance the sustainability of agro-ecosystems, specific focus on resource utilization will help to evaluate the viability of this weed management strategy. Field experiments were conducted across four sites throughout southern Illinois in 2012 and 2013 to study the influence of early-season weed management strategies on soybean nutrient accumulation, grain yield parameters, and the acquisition of nutrients by broadleaved and grass weeds. Increasing periods of weed competition duration were established by removing weeds at heights of 10, 20, 30 or 45 cm with glyphosate. A weed-free treatment utilizing a comprehensive soil residual and POST herbicide program was included to implement a weed-free comparison. Two standard herbicide management strategies that simulate common grower practices were also evaluated for comparison: flumioxazin PRE followed by glyphosate POST and two sequential POST glyphosate applications. Averaged across all 11 mineral nutrients analyzed in this experiment, broadleaved weeds accumulated 149 and 108% more nutrients than grasses in 2012 and 2013, respectively. Competition from 20-cm weeds reduced the acquisition of N, P, Ca, Mg, S, Fe, B, Cu, and Zn by soybean in 2012; these nutrients in addition to K and Mn were reduced by the same level of competition in 2013. N and Fe were the nutrients in soybean most notably impacted by weed interference. Reductions in soybean grain yield were the result of competition with 30-cm weeds in 2012, and 10-cm weeds in 2013; while, both standard herbicide regimens yielded less than the weed-free treatment in 2013 only. Additionally in 2013, average soybean seed weight and grain oil content was reduced when weeds were not removed before a height of 10 and 20 cm, respectively. The rate of decomposition and nutrient release was measured for waterhemp and giant foxtail desiccated by glyphosate at heights of 10, 20, 30, and 45 cm in two southern Illinois soybean fields. Weed biomass was grown under greenhouse conditions to ensure homogeneity and litterbag methodology was utilized to track in situ mass and nutrient losses, expressed as a decay constant (k) regressed over time according to the single exponential decay model. The effect of specie and height both had a strong influence on the intrinsic properties of the weed biomass and the associated rate of decay. Concentrations of the recalcitrant cell wall components (cellulose, hemicellulose, and lignin) were generally greatest as weed height (plant age and development) increased and with giant foxtail compared with waterhemp. Ca, Mg, and S concentrations were greater in waterhemp, while N was greater in giant foxtail. N and K concentrations decreased with increasing weed height. After 16 weeks, 10-cm waterhemp and giant foxtail detritus had lost 10 and 12% more mass compared to the 45-cm height. Decomposition rates revealed mass loss was highest for 10-cm waterhemp (kD = 0.022) and lowest for 45-cm giant foxtail (kD = 0.011) and this process was negatively correlated to the overall amount of cell wall constituents (r = -0.73). Nutrient release rates followed a similar trend in that shorter (younger) weeds and waterhemp liberated nutrients more readily. Across all tested plant material, K was the nutrient most rapidly released, whereas, Ca was the most strongly retained nutrient. Although the pressing challenge of managing herbicide-resistant weeds justifies the implementation of early-season weed control tactics, this research suggests there are ancillary benefits that are provided by this strategy. The use of a robust, broad-spectrum soil residual herbicide program in conjunction with timely POST applications provides the foundation for early-season weed management, thereby minimizing non-crop nutrient use and enhancing the nutrient acquisition capacity in soybean. This strategy facilitates more sustainable crop production by requiring fewer supplemental nutritional inputs while also protecting grain yield.

In this study, biogeochemical regimes of Marguerite Bay and the adjacent part of the West Antarctic Peninsula (WAP) continental shelf were delineated through integration of nutrient, hydrographic, and biological measurements obtained during the LTER and SO GLOBEC studies during austral summer, autumn, and winter of 2001 and 2002. Marguerite Bay biogeochemical regime was found to differ from those of the adjacent WAP continental shelf. In terms of Treguer and Jacques (1992), Marguerite Bay is a combination of Coastal Continental Shelf Zone (CCSZ) and Seasonal Ice Zone (SIZ) distinguished by shallow mixing regime, high primary production and export production. At the end of the growing season (autumn) in both years, waters in Marguerite Bay were strongly depleted in nutrients (the deficits of total inorganic nitrogen (NO3-+NO2-+NH4+) and silica were >0.6 mol m-2 and >2.5 mol m-2, respectively). Observed ΔN/ΔP removal ratios of 10-12.5, lower than that of Redfield et al. (1963), and ΔSi/ΔN removal ratios as high as 4-5 indicated the dominance of diatoms. High autumnal ammonium stocks (>0.25 mol m-2) were observed in Marguerite Bay and were co-located with the areas of the highest nutrient deficits suggesting spatial coupling between primary and heterotrophic production during both years. Consistency of this feature was not disrupted by significant interannual variability of biological production in Marguerite Bay that resulted in ~30-50% reduction in nutrient deficits and ammonium stocks from the first year to the next.The other two biogeochemical regimes were at the central part of the continental shelf characterized by mixed phytoplankton community and at the outer shelf dominated by diatoms. Both regimes were characterized by considerably lower depletion of nutrients compare to those of the Marguerite Bay regime and were consistent between the two years. Interannual variability of biological production and possible sources of high ammonium stocks in Marguerite Bay were studied with a one-dimensional model, a modification of that of Walsh et al. (2001). The model attributed the decline in nutrient deficits to the difference in sea ice cover dynamics between two years. The greater sea ice presence led to the somewhat lower primary production during the second year compare to the fist one. Moreover, model's tight coupling between primary and bacterial production resulted in a decline of bacterial ammonification between the two years. Bacteria were found to be the primary source of ammonium in the Marguerite Bay model. Yet, 3-4-fold fluctuations in macro- and mesozooplankton biomass might have led to 15-25% variability in model's autumnal ammonium stocks.

A series of experiments were conducted to determine nutritional strategies to improve the efficiency of N utilization in dairy cows when feeding co-products including wheat-based (W-DDGS) and corn-wheat blend distillers grains with solubles (B-DDGS), and dried whey permeate (DWP). In Experiment 1, the objective was to determine the effects of replacing canola meal (CM) as the major protein source with W-DDGS on ruminal fermentation, microbial protein production, omasal nutrient flow, and animal performance. Cows were fed either a standard barley silage-based total mixed ration containing CM as the major protein supplement (0% W-DDGS, control) or diets formulated to contain 10, 15 and 20% W-DDGS (dry matter [DM] basis), with W-DDGS replacing primarily CM. Diets were isonitrogenous (18.9% crude protein [CP]). Inclusion of W-DDGS to the diet did not negatively affect ruminal fermentation, microbial protein production, and omasal nutrient flow. However, there was a 0.7- to 2.4-kg increase in DM intake, and a 1.2- to 1.8-kg increase in milk yield after the addition of W-DDGS in place of CM. In Experiment 2, the objective was to delineate the effects of including either W-DDGS or B-DDGS dried distillers grains with solubles as the major protein source in low or high CP diets fed to dairy cows on ruminal function, microbial protein synthesis, omasal nutrient flows, urea-N recycling, and milk production. The treatment factors were type of distillers co-product (W-DDGS vs. B-DDGS) and dietary CP content (15.2 vs. 17.3%; DM basis). The B-DDGS was produced from a mixture of 15% wheat and 85% corn grain. All diets were formulated to contain 10% W-DDGS or B-DDGS on a DM basis. Feeding up to 10% of dietary DM as B-DDGS or W-DDGS as the major source of protein did not have negative effects on metabolizable protein (MP) supply and milk production in dairy cows. However, reducing dietary CP content from 17.3 to 15.2% decreased milk production. This response was attributed to an insufficient supply of ruminally degradable protein (RDP) that suppressed microbial nonammonia N (NAN) synthesis in the rumen, thus decreasing intestinal MP supply. In Experiment 3, the objective was to determine the effects of replacing barley or corn starch with lactose (as DWP) in diets containing 10% W-DDGS on ruminal function, omasal nutrient flow, and lactation performance. The treatment factors were source of starch (barley vs. corn) and dietary inclusion level of DWP (0 vs. 6%; DM basis) as a partial replacement for starch. Diets were isonitrogenous (18% CP) and contained 3 or 8% total sugar. The starch content of the low sugar diet was 24% compared to 20% for the high sugar diet. Dry matter intake, and milk and milk component yields did not differ with diet. However, partially replacing dietary corn or barley starch with sugar up-regulated ruminal acetate and propionate absorption, and reduced ruminal NH3-N concentration, but had no effect on ruminal pH, microbial protein synthesis, omasal nutrient flow and production in dairy cows. In summary, data presented in this thesis indicate that W-DDGS and B-DDGS can be included as the major source of protein in dairy cow diets without compromising ruminal function, nutrient supply and milk production in dairy cows. Feeding medium to low CP diets, and partial replacement of starch with sugar in diets containing W-DDGS and B-DDGS can improve N utilization efficiency in dairy cows. Additionally, an upregulation of facilitated transport of acetate and propionate across epithelial cells possibly prevents the occurrence of ruminal acidosis when lactose partially replaces starch in cow diets.

This study was conducted to determine if nutrient utilization and enteric methane (CH4) emissions could be improved in overwintering beef cows consuming low-quality forage supplemented with protein in the form of dried distillers grain with solubles (DDGS) in thermal-neutral and cold-stressed environments. Thirty mature, dry and non-pregnant beef cows were divided into three treatment groups and fed diets consisting of low-quality (6.0% crude protein; CP) forage with no DDGS (control, CON), 10% DDGS (borderline sufficient CP, 8.7% CP), or 20% DDGS (excess CP, 11.6% CP). Cold acclimatization did not appear to affect nutrient intake and digestibility by beef cows, but increased N and P excretion by 1.2x and 2.5x, respectively. Cold acclimatized cows reduced energy excretion by 26.8% (7.1 vs. 5.2 ± 0.30% GEI in fall and winter, respectively; P < 0.0001) in accordance with a 33.8% increase in rumen fluid rate of passage (ROP). Supplementation with DDGS improved digestibility of N and P (40.6 vs. 61.2 ± 2.45% N and -23.9 vs. 5.7 ± 5.95% P for CON and 20%DDGS, respectively; P < 0.0001) by increasing digestible substrate in the diet. Protein supplementation increased rumen NH3-N concentrations (1.5, 2.1 and 3.1 ± 0.15 mg 100 mL-1; P < 0.0001) enough to increase rumen fermentation efficiency, resulting in 18.5% lower enteric CH4 emissions when CP was fed in excess of animal requirements. Total excretion of N and P were increased two- and 45-fold, respectively, when excess CP was fed. Reduced enteric CH4 emissions as a result of cold acclimatization suggest an advantage for the Canadian beef herd in terms of environmental sustainability. Supplementing CP in excess of cow requirements may improve nutrient utilization and rumen fermentation efficiency, and mitigate enteric CH4 emissions in beef cows fed low-quality forage diets, but may also contribute to greater N and P loading of soil and ground water.

This study was conducted to determine if nutrient utilization and enteric methane (CH4) emissions could be improved in overwintering beef cows consuming low-quality forage supplemented with protein in the form of dried distillers grain with solubles (DDGS) in thermal-neutral and cold-stressed environments. Thirty mature, dry and non-pregnant beef cows were divided into three treatment groups and fed diets consisting of low-quality (6.0% crude protein; CP) forage with no DDGS (control, CON), 10% DDGS (borderline sufficient CP, 8.7% CP), or 20% DDGS (excess CP, 11.6% CP). Cold acclimatization did not appear to affect nutrient intake and digestibility by beef cows, but increased N and P excretion by 1.2x and 2.5x, respectively. Cold acclimatized cows reduced energy excretion by 26.8% (7.1 vs. 5.2 ± 0.30% GEI in fall and winter, respectively; P < 0.0001) in accordance with a 33.8% increase in rumen fluid rate of passage (ROP). Supplementation with DDGS improved digestibility of N and P (40.6 vs. 61.2 ± 2.45% N and -23.9 vs. 5.7 ± 5.95% P for CON and 20%DDGS, respectively; P < 0.0001) by increasing digestible substrate in the diet. Protein supplementation increased rumen NH3-N concentrations (1.5, 2.1 and 3.1 ± 0.15 mg 100 mL-1; P < 0.0001) enough to increase rumen fermentation efficiency, resulting in 18.5% lower enteric CH4 emissions when CP was fed in excess of animal requirements. Total excretion of N and P were increased two- and 45-fold, respectively, when excess CP was fed. Reduced enteric CH4 emissions as a result of cold acclimatization suggest an advantage for the Canadian beef herd in terms of environmental sustainability. Supplementing CP in excess of cow requirements may improve nutrient utilization and rumen fermentation efficiency, and mitigate enteric CH4 emissions in beef cows fed low-quality forage diets, but may also contribute to greater N and P loading of soil and ground water.