Dinitrogen Fixation in Illinois Bundleflower

Although Illinois bundleflower is known to contribute N in forage systems (Dovel et al., 1990; Posler et al., Symbiotic N2 fixation capacity may affect productivity of the peren1993; Springer et al., 2001), there is a paucity of informanial legume Illinois bundleflower [Desmanthus illinoensis (Michx.) tion on its N2 fixation capability. Nodulation has been MacMill. ex B.L. Rob. & Fernald]. Our objective was to estimate N2 observed in 90% of the Mimosoideae (de Faria et al., fixation of three Illinois bundleflower accessions managed for forage. Herbage yield ranged from 1.02 Mg ha 1 to 3.69 Mg ha 1 in Year 1, 1989) including Illinois bundleflower (Allen and Allen, and 2.99 Mg ha 1 to 8.27 Mg ha 1 in Year 2. Accessions differed in 1981). Kulakow et al. (1990) found that mean acetylene herbage yield, aboveground N yield, and N2 fixed at certain locations reduction rates of 70-d-old seedlings of Illinois bunin Year 1, but not in Year 2. Percentage of N derived from the dleflower were comparable with those of soybean [Glyatmosphere (%Ndfa) varied with location but not with accession in cine max (L.) Merr.] and alfalfa (Medicago sativa L.), either year. The 15N natural abundance method gave lower estimates but also noted that rates varied significantly among acof %Ndfa than the 15N enrichment method. In yr 1, N2 fixation ranged cessions. However, the instantaneous rates of N2 fixation from 0 to 30 kg ha 1 N (15N natural abundance method), 11 to 43 kg measured by the acetylene reduction technique cannot ha 1 (15N enrichment method), and 0 to 50 kg ha 1 N (total N difference be extrapolated to obtain an accurate estimate of total method), and in Year 2 these estimates at two locations were 60 to N2 fixed across a growing season. 67 kg ha 1 N, 79 to 127 kg ha 1 N, and 67 to 142 kg ha 1 N, respectively. Integrated estimates of N2 fixation can be made by Differences in N2 fixation among locations could have been due to comparing N accumulation with non-N2–fixing plants rhizobial strains. At the high-yielding location with the greatest N2 (the total N difference technique) or by isotopic N methfixation, over one-half of the nodules were occupied by indigenous odologies. The latter depends on a 15N-labeled soil N pool, rhizobial strains, whereas at other locations, strains from commercial inoculant accounted for most nodules. Symbiotic N2 fixation by Illinois which is manifested in higher 15N concentrations in nonbundleflower could be enhanced by new rhizobial inoculums. N2–fixing reference plants dependent on soil N than in N2–fixing plants, which incorporate both soil and unlabeled atmospheric N. In the 15N enrichment or isotope I bundleflower, an herbaceous perennial ledilution technique, the soil N pool is labeled with an gume (subfamily Mimosoideae) native to the central 15N-enriched source, whereas the 15N natural abundance USA (Luckow, 1993), may fulfill the need for a persistent, method relies on the small but measurable elevation of high-quality forage legume to complement warm-season 15N already present in most soils relative to the atmograsses. DeHaan et al. (2003) found that in Minnesota, sphere (Chalk, 1985; Shearer and Kohl, 1986). In this northern accessions of Illinois bundleflower produce study, we compared both isotope methods and the total much of their biomass during July and August when N difference method as estimates of N2 fixation in monothe productivity of cool-season grasses and legumes in cultures of Illinois bundleflower. Our objective was to the region is low. determine the in-field N2–fixation of three accessions Illinois bundleflower is compatible in mixtures with a of Illinois bundleflower managed as a forage crop in diversity of warm-season grasses. In east-central Texas, pure stands during the first 2 yr after seeding. established kleingrass (Panicum coloratum L.) stands interseeded with ‘Sabine’ Illinois bundleflower had greater MATERIALS AND METHODS forage yields than kleingrass monocultures in the second, third, and fourth years after seeding (Dovel et al., Site and Climate Characteristics 1990). Mixtures of Illinois bundleflower accession PI The experiment was conducted at the Sand Plain Research 434011 with switchgrass (Panicum virgatum L.), sideoats Farm, Becker, MN (45 24 N, 93 53 W), the Rosemount Regrama (Bouteloua curtipendula Michx.), or indiangrass search and Outreach Center, Rosemount, MN (44 53 N, [Sorghastrum nutans (L.) Nash] in northeastern Kansas 93 13 W), and the Southwest Research and Outreach Center, had higher forage yield and crude protein concentration Lamberton, MN (44 15 N, 95 19 W). The soil at Becker was than grass monocultures in the fourth and fifth years a Hubbard loamy sand (sandy, mixed, frigid Entic Hapludoll). after establishment (Posler et al., 1993). Springer et al. At Rosemount, it was a Waukegan silt loam (fine-silty over (2001) showed that Sabine Illinois bundleflower was sandy, mixed, superactive, mesic Typic Hapludoll). At Lamhighly compatible in mixture with indiangrass. berton, the soil was a Normania clay loam (fine-loamy, mixed, superactive, mesic Aquic Hapludoll). Soil chemical characteristics for the three sites are reported in Table 1. Previous crops J. Byun, C.C. Sheaffer, N.J. Ehlke, and D.L. Wyse, Dep. of Agronomy at the three sites were rye (Secale cereale L.) at Becker, corn and Plant Genetics, 411 Borlaug Hall; M.P. Russelle, USDA-ARS (Zea mays L.), and soybean at Rosemount, and oat (Avena Plant Science Res. Unit and Dep. of Soil, Water, and Climate, 439 Borlaug Hall; and P.H. Graham, Dep. of Soil, Water, and Climate, sativa L.) at Lamberton. Manure had not been applied to the 439 Borlaug Hall, Univ. of Minnesota, 1991 Upper Buford Circle, sites within the previous 5 yr. On the basis of soil test results, St. Paul, MN 55108. Received 22 Nov. 2002. *Corresponding author 390 kg ha 1 K and 4.5 kg ha 1 B were applied at Becker in ([email protected]). Abbreviations: DAP, days after planting; PCR, polymerase chain Published in Crop Sci. 44:493–500 (2004).  Crop Science Society of America reaction; PNL, Perennial Native Legume; %Ndfa, percentage of N derived from the atmosphere. 677 S. Segoe Rd., Madison, WI 53711 USA