Use of conservation tillage and narrow row spacing in soybean [Glycine max (L.) Merr.] production has led to increased use of herbicides for weed control. Some producers are seeking alternative weed control methods, such as smother crops, that would reduce dependence on chemical weed control. A successful smother crop must compete strongly with weeds but minimally with the crop. In four environments, we intercropped three annual Medicago spp. (medics) with soybean to test their utility as a smother crop for weed control. Annual medics were intercropped with soybean at rates of 0, 85, 258, or 775 seeds m(-2) , and the intercrops were grown with and without weed control. Increasing medic seeding rate decreased weed yields but also reduced soybean herbage and grain yields. For the weed-controlled treatment, average soybean grain yields declined 7 kg ha(-1) for every 10 seeds m(-2) increase in medic seeding rate. Soybean grain yield was lower when grown with Medicago scutellata L. cv. Sava than when grown with Medicago polymorpha L. cv. Santiago or Medicago lupilina L. cv. George. Soybean grain yield was negatively related (r = -81) to medic herbage production. In the autumn following soybean harvest, medic residue ranged from 200 to 3700 kg ha(-1) depending on the location and seeding rate. Medics provided residue for soil protection, suppressed weeds, but also reduced soybean yields.

Information is scarce on sampling techniques for field studies of alfalfa forage quality. Standard formulas are available for estimating the number of samples needed for reducing error in a study, but little is known about the impact of plot sampling on forage quality. Our objectives were to compare the strategy of manual harvesting from small areas within plots with that of grab sampling mechanically harvested forage, and to determine whether the within-plot location of sampling affected forage quality in any systematic way. Alfalfa forage was sampled from swaths of mechanically clipped forage (grab samples) and from hand-clipped areas within field plots (area samples). Systematic sample location within a plot had no discernable effect on forage quality. Calculations of predicted standard errors and required sample numbers indicated that one area or one grab sample per plot with three replicates would provide an acceptable standard error for comparison of alfalfa entries for protein and fiber concentration. Within-plot variability was greater at late-summer harvests than earlier harvests, but at all harvests one sample per plot with three replicates gave adequate precision for forage quality comparisons. Higher forage quality from grab samples than from area samples at spring harvests suggested the need for caution when comparing forage quality studies done with different harvest methods; however, there were few entry × sampling strategy interactions, which suggests that relative performance of entries would be similar regardless of the method of sampling. Key words: Alfalfa, forage quality, Medicago sativa L.; field sampling, bootstrap

Tall forage soybean [Glycine max (L.) Merr.] cultivars in maturity groups V, VI, and VII have been developed to supply forage. Our objective was to determine the effect of harvest date and row spacing on the forage yield and quality of these new soybean cultivars. We grew forage and standard grain soybean in Minnesota with harvests in early and late September. Average maturity of tall forage soybean was R3 (early harvest) to R4 or R5 (late harvest) and average maturity of grain soybean was R6 (early harvest) to R7 (late harvest). Herbage of forage soybean was mostly leaves and stems at both harvests, whereas herbage of grain soybean contained an average of 400 and 595 g kg−1 pods at the early and late harvests, respectively. There was no harvest date × soybean entry interaction for forage yield or forage quality. Forage and grain soybean had similar forage yields (∼8.8 Mg ha−1). Because adapted grain soybean was more mature and had a greater pod proportion than forage soybean, grain soybean had greater crude protein (CP) and lower fiber concentration than forage soybean. Average forage CP for forage and grain types was 146 and 218 g kg−1, respectively, while neutral‐detergent fiber (NDF) concentration was 523 and 400 g kg−1, respectively. Decreasing row width from 76 to 25 cm increased forage yield 0.8 Mg ha−1 but had no effect on total herbage quality.

Commercial lots of alfalfa (Medicago sativa L.) hay are often bought and sold on the basis of forage quality. Proper sampling is essential to obtain accurate forage quality results for pricing of alfalfa hay, but information about sampling is limited to small, 20‐ to 40‐kg rectangular bales. Our objectives were to determine the within‐bale variation in 400‐kg rectangular bales and to determine the number and distribution of core samples required to represent the crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and dry matter (DM) concentration in commercial lots of alfalfa hay. Four bales were selected from each of three hay lots and core sampled nine times per side for a total of 54 cores per bale. There was no consistent pattern of forage quality variation within bales. Averaged across lots, any portion of a bale was highly correlated with bale grand means for CP, ADF, NDF, and DM. Three lots of hay were probed six times per bale, one core per bale side from 55, 14, and 14 bales per lot. For determination of CP, ADF, NDF, and DM concentration, total core numbers required to achieve an acceptable standard error (SE) were minimized by sampling once per bale. Bootstrap analysis of data from the most variable hay lot suggested that forage quality of any lot of 400‐kg alfalfa hay bales should be adequately represented by 12 bales sampled once per bale.

Alfalfa (Medicago sativa L.) has been considered as a biofuel feedstock. A system has been proposed to produce electricity from the stems and utilize the leaves as a livestock feed. We determined the effects of harvest regimes on yield and quality of leaf, stem, and total herbage of six alfalfa entries. We applied three harvest regimes involving three harvests per year at bud stage or early flower, or two harvests per year at late flower. An early flower harvest regime had the highest leaf yield (average of 5.6, 4.5, and 4.5 Mg ha−1 for the early flower, late flower, and midbud regimes, respectively), and the late flower harvest regime had the highest stem yield (average of 5.8, 5.3, and 3.9 Mg ha−1 for the late flower, early flower, and midbud regimes, respectively). Leaf concentration decreased with increased herbage maturity (average of 540, 517, and 458 g kg−1 for the midbud, early flower, and late flower regimes, respectively) and was associated with total herbage crude protein (CP) and acid‐detergent fiber (ADF) and neutral‐detergent fiber (NDF) Harvest regime did not affect total seasonal herbage yield or stand persistence. Alfalfa entries differed in herbage quality, leaf concentration, and leaf yield, but did not consistently differ in total herbage or stem yield. Herbage yield and quality differences among entries were similar for all harvest regimes. Producers can affect stem and leaf yields by selection of harvest regime.

Alfalfa (Medicago sativa L.) cultivars are available that produce high-quality forage; however, information is lacking on the consistency of cultivar forage quality over environments and the influence of stand age on quality. Our objectives were to evaluate alfalfa cultivars for consistency of forage quality over time and environments and to test the validity of sampling seeding-year stands for forage quality. We sampled eight alfalfa entries (seven cultivars and one experimental germplasm) at bud and flower maturity stages in the seeding year (one harvest) and first production year (two harvests) in six states (Indiana, Kentucky, Minnesota, New York, Washington, and Wisconsin). ANOVA and orthogonal contrast analyses were conducted to assess entry X environment interactions for forage quality. First-cut forage in the first production year had lower forage quality than third-cut forage, and differences between entries were more pronounced at the first cutting. Including seeding-gear data in the ANOVA produced a complex Location X entry X stand age interaction, indicating that seeding year data alone cr ere insufficient to characterize alfalfa entries for forage quality. 'Cimarron VR', 'Arrow', and '5432' had the greatest stability for forage quality and could serve as high, medium, and low forage-quality checks, respectively, in forage quality testing trials. 'WL 322 HQ' and 'Pacesetter' often had high quality, but were not stable for forage quality over environments, Correlations between crude protein, acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro digestible dry matter were consistent across locations, entries, cuttings, and maturities. The high correlation between NDF and ADF (r greater than or equal to 0.97, P less than or equal to 0.05) suggests that it may not be necessary to use both procedures to predict entry differences in forage quality.

Alfalfa (Medicago sativa L.) cultivars have been developed for modern forage production systems with three or four cuts per year. Little is known about persistence of alfalfa cultivars in unharvested systems such as Conservation Reserve Program (CRP) fields. Our objective was to determine the stand persistence of alfalfa cultivars that were not harvested or harvested once per year. Twenty-three alfalfa cultivars representing a range of fall dormancy and disease resistance were established in binary mixture with timothy (Phleum pratense L.) at Pecker Grand Rapids, Morris, Rosemount, and Waseca, MN. Cutting treatments, which included a single cut per year (about 1 August) or no cutting were applied for 3 yr. Cutting treatment effects at Rosemount, Becker, Grand Rapids, and Waseca suggest that annual cutting of alfalfa-grass mixtures on CRP land would enhance alfalfa persistence, but stand survival of many cultivars was lower than that normally observed in cultivar trial plots cut three or four times per year. At Becker and Morris, fall dormancy was a good predictor of stand survival. There was no relationship between stand survival and disease resistance of cultivars. Annual mowing should be considered as a tool for maintaining alfalfa in CRP fields at some locations, but cultivars designed for the CRP program, which normally does not allow cutting, are needed.

The federal Conservation Reserve Program (CRP), which had goals including reduced soil erosion and increased wildlife habitat, funded diversion of land from annual crops into permanent vegetation, The survival of grasses and legumes planted in CRP fields was not known, Our objectives were to assess the persistence and coverage of grasses and legumes in 6- to 8-yr-old CRP fields and to determine changes in soil pH, P, and K levels, We studied 151 CRP fields chosen from 10 counties in four geographical regions of Minnesota: 108 in the conservation practice 1 (CP-1) cover type (planted cool-season perennial grasses and legumes); 17 in the CP-2 cover type (planted warm-season native grasses); and 26 in the CP-10 cover type (existing vegetation), Statewide, legumes persisted in 82% of CP-1 fields planted to legumes, with 23% groundcover. Grasses persisted in 90% of the planted CP-1 fields with 47% groundcover. Alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculaturs L.), the most persistent legumes, persisted in 90 and 67% of the planted fields with 21 and 32% groundcover, respectively, Smooth bromegrass (Bromus inermis Leyss), reed canarygrass (Phalaris arundinacea L.), and switchgrass (Panicum virgatum L.) persisted in over 90% of the planted fields and had 50% groundcover or more, Other legumes and grasses persisted in 50% or less of the planted fields and had 10% groundcover or less, To maintain legumes in CRP fields, clipping is required or cultivars should be developed that persist without defoliation. Generally, soil pH, P, and K levels did not change from initial to final samples and should be adequate to obtain low levels of forage production.

The federal Conservation Reserve Program (CRP) funded the conversion of eroding cropland to grass or grass-legume cover that was not to be tilled, hayed, or grazed for 10 yr. It was not known what the species composition of CRP fields would be after years of minimal disturbance. Our objective was to document the presence and percentage groundcover of weeds in 151 CRP fields located in 10 Minnesota counties; including 108 Conservation Practice (CP)-1 (cool-season legumes and grasses) fields, 17 CP-2 (native grasses) fields, and 26 CP-10 (existing vegetation) fields. Groundcover of each species present and of bare ground was scored in six 106-sq-ft sample plots per field. The most prevalent species were the primary noxious weed Canada thistle [Cirsium arvense (L.) Scop.], the secondary noxious weed quackgrass [Elytrigia repens (L.) Desv. ex. Nevski], and the non- noxious weeds dandelion (Taraxacum officinale Weber.) and goldenrod (Solidago spp.). Weed percentage groundcover was higher in CP-10 fields than in CP-1 or CP-2 fields, probably because many CP-10 stands were already thinning at the start of the CRP contract. Volunteer legumes and grasses were common in CP-10 fields. In CP-1 fields, legume and grass percentage groundcover usually was correlated negatively with weed percentage groundcover. Weed percentage groundcover and species richness were correlated positively Gopher mounding was correlated positively with the amount of bare ground and with the percentage groundcover of annual and biennial weed species. Primary, secondary, and non-noxious weeds were each found in nearly 90% of the fields studied. Widespread presence of noxious weeds on CRP fields is a cause for concern. Weed control issues should be addressed in planning a new CRP.