In the USA, biomass crop systems will be needed to meet future ethanol production goals. We estimated production costs, profits, and energy budgets for three potential crop systems for the Upper Midwest: continuous corn with stover harvest, an alfalfa-corn rotation with stover harvest, and switchgrass. Production costs, profits, and on-farm energy use were greatest for continuous corn, less for alfalfa-corn, and least for switchgrass. Energy to transport crops was similar for all crop systems. Both energy used to produce ethanol and energy output in ethanol was greatest for continuous corn, less for alfalfa-corn, and least for switchgrass. Co-product energy output was 32% greater for alfalfa-corn than continuous corn and 42% greater than switchgrass. Net energy produced (outputs-inputs) was greatest for switchgrass, followed by continuous corn, and then alfalfa-corn. Efficiency of energy production (outputs/inputs) was greatest for switchgrass, followed by alfalfa-corn, and then continuous corn. Our analysis emphasizes tradeoffs among crop systems. Corn may produce high rates of ethanol and net energy, but will do so least efficiently and with the greatest erosion and N leaching. Corn may have the greatest production costs, but return the greatest profit. Comparatively, alfalfa-corn will produce less ethanol and net energy, but will do so more efficiently, and with less erosion and little N leaching. Production costs, but also profits, may be less for alfalfa-corn than continuous corn. Switchgrass may produce the most net energy and will do so most efficiently and with the least erosion, but will also yield the least ethanol. Nitrogen leaching will be less for switchgrass than corn, but greater than alfalfa-corn. Switchgrass may be the least expensive to produce, but may return a profit only if selling prices or yields are high.

Corn (Zea mays L.) producers question the relative performance: of hybrids under different previous‐crop residue management systems. The objective of this study was to assess tillage system ✕ corn hybrid interactions for hybrids commonly grown in the northern United States. Field experiments were conducted at four locations in Wisconsin during 1984 and 1985, including sites with Plano and Nickin silt loam (Typic Argiudoll) and Meridian loam (Mollic Hapludalf) soils. Fifteen hybrids with a range of maturities (90–115 days based on the Minnesota Relative Maturity System) were compared under conventional (moldboard plowing and disking)(CT) and no‐till (NT) systems, in a corn‐following‐corn sequence. Stands were thinned after emergence. No‐till resulted in cooler soil temperatures (0.8–3.8°C cooler), lower emergence percentage (7–12% lower), delayed vegetative growth [4.4 (NT) vs. 7.9 (CT) g plant−1], later silking (2–5 days later), and increased grain moisture (10–20 g kg−1) compared to CT. For grain yield, differences occurred for all main effects (locations, years, tillage systems, and hybrids), and most interactions were significant. Yields under NT were 92% (cool spring, 1984) and 96% (warm spring, 1985) of CT yields. On silt‐loam soils, NT yields were 92 to 95% of CT yields, but tillage systems had similar yields on the loam soil. Superior‐yielding hybrids under CT were also good choices with NT, although delayed growth under NT limited the yield potential of later‐maturing (100–115 days) hybrids.

Improving grain yield in maize(Zea mays L.) can be facilitated by determining whether the source (leaf photosynthesis) or the economic sink (grain development)is more limiting. The long‐term effects defoliation and/or ear removal were measured on five maize genotypes (three inbreds and two hybrids) differing in relative source‐sink ratios. Plants were sown in the field on Clarion (fine‐loamy, mixed, mesic Typic Hapludoll) soils during the 1978 and 1979 growing seasons. Leaf carbon dioxide exchange rates (CER), stalk total nonstructural carbohydrates (TNC) and the dry weights of the leaves, sheaths, stalk, and ears were measuread at 10‐day intervals after source and/or sink manipulation (defoliation and/or ear removal).Grain yield, 100‐kernel weight, and the days to physiological maturity also were measured. The relative source‐sink ratio of the genotypes was the most important factor measured in determining how the imposed treatments affected leaf CER. Leaf CER increased after defoliation only in genotypes with large source‐slnk ratios in untreated plants and decreased following ear removal only in genotypes with small source‐sinkr atios in untreated plants. None of the treatments delayed leaf senescence. Defoliation caused a decrease in the weights of stalks, leaves, sheaths, ears, and stalk TNC of most genotypes. Ear removal increased these parameters, with the exception of leaf weight. The cob and grain weights, 100‐kernel weight, and the days to physiological maturity were decreased by defoliation. Both stalk TNC and stalk dry weight were reduced when plants were defoliated indicating increased mobilization of stored assimilates to other plant parts (i.e., the ear). These experiments showed that manipulation of source‐sink ratios affected leaf CER and utilization of stored assimilates according to the source‐sink ratio in untreated plants of that genotype.

Corn (Zea mays L.) producers question the relative performance of hybrids under different previous‐crop residue management systems. The objective of this study was to determine if tillage system × corn hybrid interactions were significant for corn growth parameters and grain yield for six commercial corn hybrids commonly grown in the Northern USA under conventional and no‐till systems in Wisconsin. A 2‐yr field study was conducted at River Falls, WI, on a Nickin silt loam soil (fine‐loamy over sandy or sandy‐skeletal, mixed Typic Argiudoll) in 1986 and a Whalen silt loam soil (fine‐loamy, mixed mesic Typic Hapludalfs) in 1987. Six hybrids with a range of maturities (90–115 d) were compared under conventional tillage (CT, mold‐board plowing and disking) and no‐till (NT, into a chemically killed alfalfa/grass sod) systems in a corn‐following‐alfalfa (Medicago sativa L.)/grass sod sequence. Emergence was reduced under NT in 1986, but was greater than CT emergence in 1987. No‐till resulted in cooler soil temperatures (2.3–4.9 °F cooler), and reduced vegetative leaf number, dry weight, and plant height. Days and growing degree days (GDD) after planting to 50% silking, mature plant height, and grain moisture were increased in NT. Although hybrid differences were observed for all of the traits measured, the only tillage system × hybrid interaction detected was for mature plant height. Tillage system × hybrid × year interactions, however, occurred for days and GDD to 50% silking, final stand, grain moisture, and grain yield, especially in 1986. Differences in growing season environments between 1986 and 1987, final stand, and GDD accumulated between silking and 30 September seem to account for the tillage system × hybrid interactions observed for grain yield in 1986. Corn producers may be able to select a hybrid for an NT system which is higher yielding than under a CT system, but the results of this study suggest that the potential benefit is limited. The top four yielding hybrids under CT in this study‐were also within the group of highest yielders under NT.