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Sustainable agricultural systems could benefit from alfalfa (Medicago sativa L.) germplasm that reduce N losses to the ground water and decrease N fertilizer inputs. With the goal of producing alfalfa populations with altered nitrate N uptake, our objectives were to develop, assess, and refine an inexpensive selection method using Br as an analog for nitrate under field conditions. Two selection schemes using divergent herbage [Br.sup.-] concentration and/or divergent herbage [Br.sup.-] uptake, both in combination with high herbage N content, produced two Cycle 1 and four Cycle 2 alfalfa populations. We evaluated these populations for both [Br.sup.-] uptake and nitrate N uptake (estimated by N derived from fertilizer, Ndff [[sup.15]N-labeled]) for one regrowth period in two locations in each of 2 yr. Weak associations between [Br.sup.-] uptake and Ndff were found during the establishment year, but strong correlations were found between [Br.sup.-] concentration and fraction of Ndff (fNdff) (r = 0.83) and between [Br.sup.-] uptake and Ndff (r = 0.85 to 0.90) when populations were evaluated during the first production year. Populations selected for high [Br.sup.-] concentration or uptake had greater [Br.sup.-] concentration and uptake, fNdff, and Ndff than populations selected for low [Br.sup.-]. Our method of selecting alfalfa plants for differences in herbage [Br.sup.-] concentration or uptake in combination with high herbage N content is the first to successfully produce alfalfa populations that differ in nitrate N uptake in a field environment.

Perennial forages like alfalfa (Medicago sativa L.) or various perennial grasses, which are cut several times during the growing season, could provide an alternative land base and time management strategy for manure applications. Our objectives were to evaluate the response of two forage species to increasing rates of swine manure slurry applied in midsummer and to compare commercially available alfalfa cultivars for tolerance to swine manure applied during the growing season. The first experiment, hereafter referred to as the rate experiment, included four entries, two [N.sub.2]--fixing (UMN 3097 and 'Agate') and one non-[N.sub.2]--fixing (Ineffective Agate) alfalfa and reed canarygrass (Phalaris arundinacea L.), grown at two locations in Minnesota. Liquid swine manure was applied at five rates (0, 23.4, 32.7, 42.1, and 93.6 kL [ha.sup.-1]) within 4 d after the second forage harvest in July 1998 and 1999. In the second experiment, hereafter referred to as the cultivar study, six alfalfa cultivars, Magnagraze, 5312, Rushmore, Wintergreen, Winterstar, and WL 325 HQ, were evaluated for response to manures applied at three rates (0, 37.4, and 93.6 kL [ha.sup.-1]) as described above. Manure slurry containing less than about 3300 [ha.sup.-1] organic solids applied 4 d after cutting in July improved reed canarygrass yields and had no effect or slightly improved yields of normal [N.sub.2]--fixing alfalfa. Ineffective Agate yields improved with increasing manure rates, but insufficient N was applied to keep this entry productive. Alfalfa cultivars did not differ in yield response to manure applications. Organic solids in the manure slurries at one of the locations compromised forage yields and stand scores at the highest application rate by completely coating and smothering the plants. Results emphasized the importance of manure testing to reduce adverse effects on alfalfa and reed canarygrass yields., LIVESTOCK MANURES can be a source of N and other plant nutrients for crop production but must be managed properly to avoid negative impacts on the environment (Eghball and Power, [...]

Symbiotic [N.sup.2] fixation capacity may affect productivity of the perennial legume Illinois bundleflower [Desmanthus illinoensis (Michx.) MacMill. ex B.L. Rob. & Fernald]. Our objective was to estimate [N.sub.2] fixation of three Illinois bundleflower accessions managed for forage. Herbage yield ranged from 1.02 Mg [ha.sup.-1] to 3.69 Mg [ha.sub.-1] in Year 1, and 2.99 Mg [ha.sup.-1] to 8.27 Mg [ha.sup.-1] in Year 2. Accessions differed in herbage yield, aboveground N yield, and [N.sub.2] fixed at certain locations in Year 1, but not in Year 2. Percentage of N derived from the atmosphere (%Ndfa) varied with location but not with accession in either year. The [sup.15]N natural abundance method gave lower estimates of %Ndfa than the [sup.15]N enrichment method. In yr 1, [N.sub.2] fixation ranged from 0 to 30 kg [ha.sup.-1] N ([sup.15]N natural abundance method), 11 to 43 kg [ha.sup.-1] ([sup.15]N enrichment method), and 0 to 50 kg [ha.sup.-1] N (total N difference method), and in Year 2 these estimates at two locations were 60 to 67 kg [ha.sup.-1] N, 79 to 127 kg [ha.sup.-1] N, and 67 to 142 kg [ha.sup.-1] N, respectively. Differences in [N.sub.2] fixation among locations could have been due to rhizobial strains. At the high-yielding location with the greatest [N.sub.2] fixation, over one-half of the nodules were occupied by indigenous rhizobial strains, whereas at other locations, strains from commercial inoculaut accounted for most nodules. Symbiotic [N.sub.2] fixation by Illinois bundleflower could be enhanced by new rhizobial inoculums., ILLINOIS BUNDLEFLOWER, an herbaceous perennial legume (subfamily Mimosoideae) native to the central USA (Luckow, 1993), may fulfill the need for a persistent, high-quality forage legume to complement warm-season grasses. DeHaan [...]

Energy generation from biomass is an environmentally sound alternative to other energy producing technologies. Pilot studies have indicated that alfalfa (Medicago sativa L.) is a suitable feedstock for energy generation via the gasification process. The resulting ash is a potential liming agent and a source of plant nutrients. A growth chamber study was conducted with three soils to evaluate the potential use of this ash as a soil amendment. Corn (Zea mays L.) received 13 treatments: control, K and/or P fertilizer, seven ash rates (0.6 to 14.6 g ash [kg.sup.-1] soil), and one ash rate with K or P fertilizer. Soil pH increased with ash application on all soils. Ash application increased ammonium acetate-exchangeable K, Ca, and Mg, and Olsen P in soil and decreased DTPA-extractable soil Fe, Mn, Ni, and Pb. Averaged across the three soils, slopes of the cations recovered in plant and soil vs. cations applied in the ash were 0.48, 0.21, and 0.22 of total ash K, Ca, and Mg, respectively ([r.sup.2] > 0.97). Ash significantly increased plant K and Mo, and decreased Mg, Mn, and Zn concentration. Tissue P concentrations were not affected by ash, but increased with P fertilizer. Phosphorus fertilizer increased plant dry mass (DM), but K fertilizer did not, thus K did not limit yield. Alfalfa stem gasification ash is a potential liming agent, a source of K, and would not lead to excessive accumulation of trace elements in soil or plants when applied at rates based on lime or K need.

After an 8,000-year journey, the 'Queen of Forages' stands poised to enjoy renewed popularity Alfalfa holds the distinction of being the oldest forage crop for which we have a name, [...]