C 4 perennial grasses are being considered as environmentally and economically sustainable high yielding bioenergy feedstocks. Temporal and spatial variation in yield across the conterminious United States is uncertain due to the limited number of field trials. Here, we use a semi-mechanistic dynamic crop growth and production model to explore the potential of Miscanthus 9 giganteus (Greef et. Deu.) and Panicum virgatum L. across the conterminous United States. By running the model for 32 years (1979-2010), we were able to estimate dry biomass production and stability. The maximum rainfed simulated end-of-growth-season harvestable biomass for M. 9 giganteus was ca. 40 Mg ha À1 and ca. 20 Mg ha À1 for P. virgatum. In addition, regions of the southeastern United States were identified as promising due to their high potential production and stability and their relative advantage when compared with county-level maize biomass production. Regional and temporal variation was most strongly influenced by precipitation and soil water holding capacity. Miscanthus 9 giganteus was on average 2.2 times more productive than P. virgatum for locations where yields were ! 10 Mg ha À1 . The predictive ability of the model for P. virgatum was tested with 30 previously published studies covering the eastern half of the United States and resulted in an index of agreement of 0.71 and a mean bias of only À0.62 Mg ha À1 showing that, on average, the model tended to only slightly overestimate productivity. This study provides with potential production and variability which can be used for regional assessment of the suitability of dedicated bioenergy crops.

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Compared with traditional cropping systems, integrated crop-livestock systems have shown greater effi ciency in improving soil quality and crop yield. Th e objective of this study was to determine how an integrated crop-livestock system aff ected soil properties and corn (Zea mays L.) yield when compared with continuous corn (CC). Th e study was conducted from 2004-2008 on a large-scale research farm located near Pana, IL, USA. We evaluated the following soil and crop variables: soil organic matter (SOM) fractions, total nitrogen (TN) and total organic carbon (TC), soil microbial biomass carbon (SMBC), water aggregate stability, soil penetration resistance (PR), and corn yield. Th ree treatments were used in this study: winter cover crops (WCCs) and cool-season pastures (CSP), considered integrated system treatments and a nonintegrated CC monoculture. In the integrated system, CSP and WCC treatments combined, had signifi cantly higher TN (P = 0.0926) than CC. Water aggregate stability was also higher in the integrated system (P = 0.0039). Greater percentages of TC and TN were represented by particulate organic matter (POM) POM-N and POM-C in the WCC treatment, followed by CSP, and CC. Th e PR for CSP (928 kPa) was not signifi cantly diff erent than WCC (921 kPa). However, both were signifi cantly diff erent than CC (655 kPa). Averaged across years, corn grain yield for WCC (11.5 Mg ha −1 ) was signifi cantly higher than CC (10.8 Mg ha −1 ) (P = 0.0780). Th ese results confi rm that WCC and CSP used within integrated crop-livestock systems should improve soil quality, SOM dynamics, and crop yield despite moderate soil compaction caused from cattle presence.

Warm‐season grasses (WSG) can supply badly needed forage in summer when cool‐season grasses (CSG) are often unproductive. This study was conducted from 2005–2007 in central Illinois to compare annual and perennial WSG pasture types integrated into a CSG grazing system. The objective was to compare summer herbage mass, forage nutritive value, cattle (Bos taurus) performance, and variable costs between CSG systems integrated with either annual (AWSG) or native, perennial warm‐season grass (NWSG) pastures. The AWSG pastures were established with sorghum‐sudangrass cultivars [Sorghum bicolor (L.) Moench], and eastern gamagrass [Tripsacum dactyloides (L.) L.] dominated NWSG pastures. Beef cow–calf groups were moved between CSG and WSG pastures during summer based on forage availability. Both WSG pasture types averaged 61% more herbage mass (493 g m−2) in mid‐summer compared with CSG pastures (204 g m−2). Except for one sampling date, herbage mass on NWSG pastures either exceeded (P < 0.05) or was equal to AWSG pastures. The nutritive value of AWSG forage was consistently higher than NWSG (P < 0.05), but cow and calf performance was similar on both pasture types. A simple cost analysis showed that AWSG pastures were more expensive to maintain even though establishment costs of NWSG pasture were much higher. Our results suggest NWSG pastures may be the better option for livestock producers seeking a longer‐term solution to summer forage deficits associated with CSG.