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Forage yield, nutritive value, and stand persistence are key metrics in alfalfa (Medicago sativa L.) management. The combination of cultivar improvement, longer growing seasons in the Midwest, and trends of shorter alfalfa rotations offer opportunity to reevaluate the effects of increasing cutting frequency (CF) on these metrics. We evaluated forage yield, nutritive value, milk production, and persistence of eight alfalfa entries with fall dormancy (FD) ranging from two (FD2) to five (FD5) under CF of four (CF4), five (CF5), or six (CF6) annual cuts during two production years in two environments in the upper midwestern United States. Nutritive value and milk kg–1 alfalfa increased with increased CF and differed among alfalfa entries. Cutting frequency and alfalfa entry interactively influenced forage yield and milk production ha–1 yet optimal CF depended on environment. At one environment, increasing CF from CF4 to CF5 and from CF5 to CF6 caused a 5 and 29% decrease in milk ha–1, respectively. At another environment, CF5 had about 16% greater milk production than CF4 and CF6. The CF6 reduced persistence of 3rd-year stand density with the effects especially severe for some entries. Alfalfa entry FD was not correlated to forage yield or persistence, but an entry with FD5 was consistently among those with the greatest in forage and milk yield ha–1 at CF5 and CF6. These results suggest that intensifying CF from four to five harvests per season of some cultivars can boost yield and nutritive value without negative effects on stand persistence in some environments. [ABSTRACT FROM AUTHOR]

Silphium integrifolium Michx. (silflower [Asteraceae]) is an emerging perennial oilseed and biomass crop with potential to supply ecosystem services, but optimum seeding dates for establishment are unknown. Our objective was to determine the effect of seeding dates from late summer to spring on establishment, biomass, and grain yield of wild and improved silflower populations. Germination was low, but plants established for all seeding dates, indicating that seed sown in the early fall (September and October) germinated and overwintered, and seed sown in late fall (November and December) overwintered as seeds, germinating in the following spring. Spring-sown (March through June) seed germinated without stratification. While this shows many planting date options for successful germination, only September planting dates produced acceptable seed and biomass yields within one full growing season of sowing. Spring seedings resulted in no grain yield in the following summer, confirming that vernalization was required for grain production. For use in Midwest cropping systems, the establishment of silflower at seeding dates early in September is currently recommended, but additional studies should consider summer planting dates, seed pretreatments, and the effects of the duration of the vegetative stage on plant traits such as drought resistance in addition to first-year seed and biomass production. [ABSTRACT FROM AUTHOR]

Various local factors influence the decision of when to harvest grassland biomass for renewable energy including climate, plant composition, and phenological stage. However, research on biomass yield and quality related to a wide range of harvest timing from multiple environments and years is lacking. Our objective was to determine the effect of harvest timing on yield, moisture, and mineral concentration of switchgrass ( Panicum virgatum L.) and native polyculture biomass. Biomass was harvested on 56 unique days ranging from late summer (2 September) to late spring (20 May) spanning 3 years (2009 to 2011) and seven sites in Minnesota, USA. Biomass yield varied considerably by location and year (range = 0.7-11.7 Mg ha) and was lowest during the winter. On average, there was no difference in biomass yield harvested in early fall compared to late spring. Biomass moisture content was lowest in late spring, averaging 156 g kg across all locations and years when harvested after 1 April. Biomass N concentration did not change across harvest dates; however, P and K concentrations declined dramatically from late summer to late spring. Considering the economic costs of replacing exported minerals and changes in revenues from biomass yield through time, biomass harvest should be conducted in late summer-early fall or late spring and avoided in winter. However, biomass managed for gasification should be harvested in spring to reduce concentrations of minerals that lead to slagging and fouling. Changes in biomass yield and quality through time were similar for switchgrass and native polyculture biomass. These biomass harvest recommendations are made from data spanning multiple years and locations and should be applicable to various growing conditions across the Upper Midwest. [ABSTRACT FROM AUTHOR]