A USDOE and USDA study concluded that more than 20 million U.S. hectares of cropland, idle cropland, and cropland pasture could be converted from current uses to the production of perennial grasses from which biomass could be harvested for use as biorefi nery feedstock. Th is study was conducted to determine the most effi cient species, level of N, and harvest frequency from among four perennial grass species {'Midland 99' bermudagrass [Cynodon dactylon (L.) Pers.], 'Carostan' fl accidgrass (Pennisetum fl accidum Griseb.), 'SL 93-3' (a selection from 'Alamo') switchgrass (Panicum virgatum L.), and weeping lovegrass [Eragrostis curvula (Schrad.) Nees]}. Each species was established in 2002 on a Kirkland silt loam soil near Stillwater, OK. Treatments in postestablishment years consisted of four N fertilization levels (34, 67, 134, and 269 kg ha −1 yr −1 ) and two harvest systems (once year −1 in October, and twice year −1 in July and October). Plots were harvested in 2003, 2004, and 2005. For bermudagrass, fl accidgrass, and lovegrass, the greatest biomass yield year −1 was produced from plots harvested twice year −1 . Switchgrass produced signifi cantly more biomass than the other three species. Biomass yield to N response functions were estimated for switchgrass. For most biomass price and N price combinations, the optimal strategy is to establish switchgrass, and in postestablishment years, to fertilize with 65 kg N ha −1 yr −1 and harvest once year −1 aft er senescence.

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Eight 4-ha mixed warm-season grass pastures in southwestern Arkansas (33°40'4″ N, 93°35'24″ W, and elevation 107 m) were stocked with either large mature size (571 kg [SD 55.2] BW) or small mature size (463 kg [SD 58.2] BW) spring-calving cows at 4 stocking rates (SR; 1, 1.5, 2, or 2.5 cow-calf pairs/ha) over 4 yr to test the effects of SR and mature body size on cow and calf performance and system economics. Each pasture received 112 kg/ha N as ammonium nitrate in May and was broadcast seeded to annual ryegrass ( Lam.) in mid October each fall along with 112 kg/ha N as ammonium nitrate. Data were analyzed by regression to determine the effects of cow size and SR on calf performance, cow BW change, calf gain, weaning weight per hectare, hay feeding requirements, and net returns. As SR increased, cow BW and BCS at weaning decreased ( < 0.01) by 26 kg and 0.36 condition scores, respectively, for each additional cow stocked per hectare ( = 0.44). Calf BW at weaning in October increased ( < 0.01) 19 kg for each 100-kg increase in cow BW but was not affected ( = 0.66) by SR. As cow BW increased, calf BW at weaning per 100 kg cow BW decreased ( < 0.01) 6.7 kg for each 100-kg increase in cow BW but was not affected ( = 0.44) by SR. Neither cow BW nor SR affected ( ≥ 0.53) pregnancy percentage, which averaged 88% over the 4-yr experiment. Calf BW weaned per hectare was not affected ( = 0.75) by cow BW but linearly increased ( < 0.01) by 217 kg for each additional cow per hectare SR. Hay feeding days and cost of hay per cow increased ( ≤ 0.05) and kilograms of hay offered per cow tended ( = 0.09) to linearly increase with increasing SR, yet cow BW had no effects ( > 0.22). Although there were no effects ( ≥ 0.38) of cow BW on carrying cost or net returns, increasing SR decreased ( < 0.01) total expenses by US$102/cow and increased net returns by $70/cow and $438/ha for each cow per hectare increase in SR. These data indicate that increasing cow size can increase weaning BW of calves but does not affect total production per hectare or profitability, even though weaning weight efficiency ratios were reduced. Increasing SR reduced cow BW and BCS at weaning and increased feeding of conserved forages but did not affect pregnancy rates and led to increases in total calf BW weaned per hectare and net returns.

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Limited information is available explaining the economics of supplying N and P fertilizers on established stands of switchgrass growing in phosphorus-deficient soils. The objective of this study was to determine the most economical fertilizer supply system for producing feedstock in phosphorus-deficient soil in the southern Great Plains. Data collected from field trials conducted at two locations in south-central Oklahoma along with prices quoted by local input suppliers and custom service providers and assumptions about the farm-gate price of feedstock were used to estimate expected values for production costs, gross revenue and net return to owner's labor, management, and overhead for eight fertilizer supply systems. The systems included a zero fertilizer check system (0/0), three P systems (0/34, 0/67, and 0/101), one N system (135/0), and three N and P systems (135/34, 135/67, and 135/101). Random-effects mixed ANOVA models were used to determine the effects of fertilizer system on the values of total cost and net return. For the base-case price scenario (feedstock, N and P prices of $110 Mg −1 and $1.28 and 1.17 kg −1 , respectively), the 135/0 system was the most profitable system, producing 10.2 Mg of feedstock and $263 of net return per hectare. Economic results were most sensitive to the prices of feedstock, N and P. Net return was negative for all eight systems for the scenario where the farm-gate price of feedstock was relatively low ($55 Mg −1 ) and prices for N and P were relatively high ($2.20 kg −1 ).