Alfalfa stems, reed canarygrass, and switchgrass; perennial herbaceous species that have potential as biomass energy crops in temperate regions; were evaluated for their bioconversion potential as energy crops. Each forage species was harvested at two or three maturity stages and analyzed for carbohydrates, lignin, protein, lipid, organic acids, and mineral composition. The biomass samples were also evaluated for sugar yields following pretreatment with dilute sulfuric followed by enzymatic saccharification using a commercial cellulase preparation. Total carbohydrate content of the plants varied from 518 to 655 g kg À1 dry matter (DM) and cellulose concentration from 209 to 322 g kg À1 DM. Carbohydrate and lignin contents were lower for samples from early maturity samples compared to samples from late maturity harvests. Several important trends were observed in regards to the efficiency of sugar recovery following treatments with dilute acid and cellulase. First, a significant amount of the available carbohydrates were in the form of soluble sugars and storage carbohydrates (4.3-16.3% wt/wt). Recovery of soluble sugars following dilute acid pretreatment was problematic, especially that of fructose. Fructose was found to be extremely labile to the dilute acid pretreatments. Second, the efficiency at which available glucose was recovered was inversely correlated to maturity and lignin content. However, total glucose yields were higher for the later maturities because of higher cellulose contents compared to the earlier maturity samples. Finally, cell wall polysaccharides, as determined by the widely applied detergent fiber system were found to be inaccurate. The detergent fiber method consistently overestimated cellulose and hemicellulose and underestimated lignin by substantial amounts.

In the North Central region, producers typically initiate harvesting when alfalfa maturity reaches bud to early Alfalfa (Medicago sativa L.) has been considered as a biofuel flowering. This often results in three or four harvests feedstock. A system has been proposed to produce electricity from the stems and utilize the leaves as a livestock feed. We determined per season. Harvest maturity is determined by producer the effects of harvest regimes on yield and quality of leaf, stem, and need to optimize herbage yield, nutritive value, or nutritotal herbage of six alfalfa entries. We applied three harvest regimes ent yield. Highest herbage nutritive value and intake involving three harvests per year at bud stage or early flower, or two potential usually occur with preflowering alfalfa with the harvests per year at late flower. An early flower harvest regime had highest yields of nutrients at early flowering (Sheaffer et the highest leaf yield (average of 5.6, 4.5, and 4.5 Mg ha Ϫ1 for the al., 1988). Herbage harvested at full bloom is expected to early flower, late flower, and midbud regimes, respectively), and the have a higher stem proportion than less mature herbage late flower harvest regime had the highest stem yield (average of 5.8, (Fick and Holthausen, 1975; Kilcher and Heinrichs, 5.3, and 3.9 Mg ha Ϫ1 for the late flower, early flower, and midbud 1974). A biofuel production system that adds value to regimes, respectively). Leaf concentration decreased with increased stem components of alfalfa may favor a shift to harvestherbage maturity (average of 540, 517, and 458 g kg Ϫ1 for the midbud, early flower, and late flower regimes, respectively) and was associated ing at more mature stages with fewer harvests per with total herbage crude protein (CP) (r ϭ 0.65, P Ͻ 0.05) and acid-season. detergent fiber (ADF) and neutral-detergent fiber (NDF) (r ϭ Ϫ0.76, Recommended harvest schedules for modern alfalfa P Ͻ 0.05). Harvest regime did not affect total seasonal herbage yield cultivars in a biofuel system are unknown because the or stand persistence. Alfalfa entries differed in herbage quality, leaf relative value of leaf and stem components is expected concentration, and leaf yield, but did not consistently differ in total to vary with energy and livestock feed prices. Compared herbage or stem yield. Herbage yield and quality differences among with the currently used three-or four-cut schedules, a entries were similar for all harvest regimes. Producers can affect stem two-cut schedule with alfalfa harvested at full bloom and leaf yields by selection of harvest regime.

BackgroundAlfalfa, [Medicago sativa (L.) sativa], a widely-grown perennial forage has potential for development as a cellulosic ethanol feedstock. However, the genomics of alfalfa, a non-model species, is still in its infancy. The recent advent of RNA-Seq, a massively parallel sequencing method for transcriptome analysis, provides an opportunity to expand the identification of alfalfa genes and polymorphisms, and conduct in-depth transcript profiling.ResultsCell walls in stems of alfalfa genotype 708 have higher cellulose and lower lignin concentrations compared to cell walls in stems of genotype 773. Using the Illumina GA-II platform, a total of 198,861,304 expression sequence tags (ESTs, 76 bp in length) were generated from cDNA libraries derived from elongating stem (ES) and post-elongation stem (PES) internodes of 708 and 773. In addition, 341,984 ESTs were generated from ES and PES internodes of genotype 773 using the GS FLX Titanium platform. The first alfalfa (Medicago sativa) gene index (MSGI 1.0) was assembled using the Sanger ESTs available from GenBank, the GS FLX Titanium EST sequences, and the de novo assembled Illumina sequences. MSGI 1.0 contains 124,025 unique sequences including 22,729 tentative consensus sequences (TCs), 22,315 singletons and 78,981 pseudo-singletons. We identified a total of 1,294 simple sequence repeats (SSR) among the sequences in MSGI 1.0. In addition, a total of 10,826 single nucleotide polymorphisms (SNPs) were predicted between the two genotypes. Out of 55 SNPs randomly selected for experimental validation, 47 (85%) were polymorphic between the two genotypes. We also identified numerous allelic variations within each genotype. Digital gene expression analysis identified numerous candidate genes that may play a role in stem development as well as candidate genes that may contribute to the differences in cell wall composition in stems of the two genotypes.ConclusionsOur results demonstrate that RNA-Seq can be successfully used for gene identification, polymorphism detection and transcript profiling in alfalfa, a non-model, allogamous, autotetraploid species. The alfalfa gene index assembled in this study, and the SNPs, SSRs and candidate genes identified can be used to improve alfalfa as a forage crop and cellulosic feedstock.

Carbon flow in terrestrial ecosystems regulates partitioning between soil organic C (SOC) and atmospheric CO2. Our objectives were to assess SOC dynamics using natural 13C abundance in corn (Zea mays L., a C4 species)‐soybean [Glycine max (L.) Merr., a C3 species] sequences. Fifteen treatments of continuous corn, continuous soybean, various sequences of corn and soybean, and fallow were initiated in 1981 at Lamberton, MN, on a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll). In 1991, soil and aboveground shoot samples from all treatments were analyzed for total organic C and δ13C. Carbon inputs, δ13C, and SOC were integrated into a two‐pool model to evaluate C dynamics of corn and soybean. Total SOC was similar across all treatments after 10 yr; however, differences in soil δ13C occurred between continuous corn (δ13C = −17.2‰) and continuous soybean (δ13C = −18.2‰). Modeled C dynamics showed SOC decay rates of 0.011 yr−1 for C4‐derived C and 0.007 yr−1 for C3‐derived C, and humification rates of 0.16 yr−1 for corn and 0.11 yr−1 for soybean. Decay and humification rates were slightly lower than those found in other Corn Belt studies. Levels of SOC were predicted to decline an additional 7 to 18% with current C inputs from either corn or soybean, respectively. Annual C additions required for SOC maintenance averaged 5.6 Mg C ha−1, 1.4 to 2.1 times greater than previously reported estimates. Controlled variation in natural 13C abundance in corn‐soybean rotations during a 10‐yr period adequately traced C dynamics.