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Previous research has implied that forage yield in released alfalfa (Medicago sativa L.) cultivars declined slightly between 1978 and 1996. Our objective was to compare alfalfa cultivars released during the past five decades side by side in replicated yield trials to test for any changes in forage yield across time. Ten cultivars, two from each of the five decades, four recently released cultivars, and two check cultivars were compared for forage yield, persistence, and nutritive value at four locations. Cultivars were established in May 1999 at Iowa, Wisconsin, Ohio, and Minnesota. Forage was harvested three to four times in each of four production years depending on location. Plots were subsampled for nutritive value analyses for the first and third harvests in 2000 and 2001. Year × location × cultivar‐release date interactions demonstrated that forage yield and final stand densities differed among the cultivars in each year of the experiment at each location. Nutritive value traits were similar among all cultivars. Evidence for changes in forage yield for cultivars released between 1940 and 1995 was environmentally dependent. In environments where conditions lead to plant stand losses, recently released cultivars with multiple disease resistance had a yield advantage over older cultivars, but in environments where no differences in plant density occurred across time, older cultivars yielded the same as recent cultivars.

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An understanding of the factors and relationships affecting wholeplant digestibility is needed to improve the nutritional quality of maize (Zea mays L.) forage. The objectives of this study were to: (i) determine the ranges among 24 maize genotypes for fiber composition and digestibility of stover and whole-plant forage, and (ii) determine the relationships between fiber composition and digestibility. Twenty-four S 0 ., families (S 0-derived families in S,) exhibiting a range in neutral detergent fiber (NDF) and lignin at mid-flower, were testcrossed to two commercial inbred lines (FR23 and LH74) to form two groups of F, hybrids. A third experimental group was created by self-pollinating the S 0 .i families to form S 0. 2 families. These germplasms were evaluated in three Wisconsin environments. Ranges in S,. 2 family means for fiber and digestibility were: NDF, 439 to 582 g kg-1 for the whole plant and 579 to 654 g kg-1 for the stover; and in vitro true digestibility (IVTD), 714 to 820 g kg-1 for the whole plant and 689 to 757 g kg-1 for the stover. Narrower ranges were observed among LH74 and FR23 testcrosses. For S,. 2 families, correlation coefficients for stover IVTD with stover NDF and lignin were-0.76 and-0.85, respectively. Correlation coefficients for whole-plant IVTD with stover IVTD and lignin of S 0. 2 families were 0.44 and-0.49, respectively. The results of this study show that (i) significant variation exists for nutritional quality traits of the stover and whole-plant forage and (ii) stover quality is an important factor influencing whole-plant nutritional quality within the germplasm studied.

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.