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  • Author or Editor: Nancy G. Creamer x
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Five grasses, six broadleaf species, and five legume/grass mixtures were evaluated for their production of aboveground biomass (AGB), nitrogen contribution, C: N ratio, ability to compete with weeds, and susceptibility to three methods of mechanical kill. Of the legume species, sesbania, cowpea, and soybean produced the most biomass, which totaled 5542, 4227, and 3934 kg·ha–1, respectively. Nitrogen in the AGB of these species was 109, 95, and 83 kg·ha–1, respectively. AGB production of the grass species ranged from 8677 kg·ha–1 for sorghum–sudangrass to 5247 kg·ha–1 for pearl millet. Nitrogen in the AGB for the grass species ranged from 68 to 38 kg·ha–1. In general, the cover crops most competitive with weeds were those that had an excess of 3900 kg AGB/ha. The broadleaf species were effectively controlled by mowing, while undercutting controlled five of the species, and rolling provided little control. Undercutting provided the best control of the grasses, while rolling was effective on the most mature species, and mowing provided little control.

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Summer cover crops can produce biomass, contribute nitrogen to cropping systems, increase soil organic matter, and suppress weeds. Through fixation of atmospheric N2 and uptake of soil residual N, they also contribute to the N requirement of subsequent vegetable crops. Six legumes {cowpea (Vigna unguiculata L.), sesbania (Sesbania exaltata L.), soybean (Glycine max L.), hairy indigo (Indigofera hirsutum L.), velvetbean [Mucuna deeringiana (Bort.) Merr.], and lablab (Lablab purpureus L.)}; two nonlegume broadleaved species [buckwheat (Fagopyrum esculentum Moench) and sesame (Sesamum indicum L.)]; and five grasses {sorghum-sudangrass [Sorghum bicolor (L) Moench × S. sudanense (P) Stapf.], sudangrass [S. sudanense (P) Stapf.], Japanese millet [Echinochloa frumentacea (Roxb.) Link], pearl millet [Pennisetum glaucum (L). R. Br.], and German foxtail millet [Setaria italica (L.) Beauv.)]}, were planted in raised beds alone or in mixtures in 1995 at Plymouth, and in 1996 at Goldsboro, N.C. Biomass production for the legumes ranged from 1420 (velvetbean) to 4807 kg·ha-1 (sesbania). Low velvetbean biomass was attributed to poor germination in this study. Nitrogen in the aboveground biomass for the legumes ranged from 32 (velvetbean) to 97 kg·ha-1 (sesbania). All of the legumes except velvetbean were competitive with weeds. Lablab did not suppress weeds as well as did cover crops producing higher biomass. Aboveground biomass for grasses varied from 3918 (Japanese millet) to 8792 kg·ha-1 (sorghum-sudangrass). While N for the grasses ranged from 39 (Japanese millet) to 88 kg·ha-1 (sorghum-sudangrass), the C: N ratios were very high. Additional N would be needed for fall-planted vegetable crops to overcome immobilization of N. All of the grass cover crops reduced weeds as relative to the weedy control plot. Species that performed well together as a mixture at both sites included Japanese millet/soybean and sorghum-sudangrass/cowpea.

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Row intercropping sweet corn (Zea mays L.) with a living mulch of buckwheat (Fagopyrum esculentum Moench) may reduce weed competition without reducing sweet corn yields. The objective of this experiment was to examine competition for nutrients, crop water use, and plant growth between weeds, buckwheat, and organically grown sweet corn, and examine the impact of buckwheat on weed densities and corn yields. In 1999, `Bodacious' (sehybrid) sweet corn was planted to 41,000 plants/ha stand and the following treatments were applied: 1) `Manor' buckwheat planted at 0 kg·ha–1, 56 kg·ha kg·ha–1, and 112 kg·ha–1, 2) buckwheat planted at three times: planting corn, at four-leaf corn and eight-leaf corn stage. A RCB design with four replications including a weedy/weed-free split was used. Above ground biomass of buckwheat was measured within a 1/2-m2 quadrat 8WAP and analyzed for C and N. Weed densities were taken within a 1/2-m2 quadrat 4WAP and 8WAP following each buckwheat planting. Buckwheat and corn tissue samples were analyzed for total nutrient content 8WAP. Soil samples were taken in corn and buckwheat interrows at emergence, 4 WAP, 8 WAP, and at harvest, and evaluated for inorganic nitrogen and soil moisture. Within rate treatments, yield was highest in weed and buckwheat-free (16.3 MT·ha–1) and lowest in weed-free 112 kg·ha–1 buckwheat (8.5 MT·ha–1). Within buckwheat timing treatments, yield was highest in 8 leaf (18.2 MT·ha–1) relative to at plant buckwheat. Weed densities were highest in no buckwheat (281 no/m2) and lowest in 56 kg·ha–1 buckwheat (28 no/m2) compared to the controls. These findings indicate buckwheat rate influences yield and weed density more than timing of buckwheat plant.

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A mixture of rye, hairy vetch, barley, and crimson clover was seeded on raised beds at two locations in Ohio in August, 1992. The following May, the mixture was killed with an undercutter and left on the surface as a mulch. Processing tomatoes (OH 8245) were planted into the killed cover crop mulch immediately following undercutting. Four systems of production were evaluated including: conventional (without cover crop mulch), integrated (with reduced chemical input), organic, and no additional input. At the Columbus site, above ground biomass (AGB) was 9,465 kg ha-1 with 207 kg ha-1 N in to AGB. In Fremont, the AGB was 14,087 kg ha-1 with 382 kg ha-1 N in the AGB. Annual weeds were suppressed by the killed cover crop mulch, and no additional weed control for the annual weeds was necessary. Weed suppression by the mulch was equivalent to weed suppression by the herbicides used in the conventional system. Other data that will be reported include soil moistures and temperatures; impact on insects end diseases; and, tomato growth, development, and yield.

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Regional growers have expressed an interest in the feasibility of producing potatoes on wide beds. Using wide beds decreases compaction and may increase water available to the crop due to the elimination of postplanting cultivation, or hilling, required in conventional rows. The middle row of wide beds may have cooler soil temperatures than the other rows in the bed. In addition, wide beds allowed for a planting density 1.5-times greater than conventional rows, which could significantly increase yields. Potatoes, `Atlantic', were planted mid-March into conventional rows on 38-inch centers and 6-foot 4-inch-wide beds, each bed with three rows. Plots were 50 feet long. Initial soil moisture contents in the middle of the bed, the outer rows of the bed and the conventional rows were not significantly different. Initial soil temperature data suggests that fluctuations in temperature are greatest in the conventional rows and least in the middle row of the wide beds. Soil temperature and soil moisture are reported. Marketable yields from wide beds are compared to marketable yields from conventional rows. Influence on potato size distribution and quality factors also are reported.

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Planting polyculture mixtures of cover crops can optimize the benefits of their use. Thirteen polyculture mixtures of cover crops were evaluated in Columbus and Fremont, Ohio, to find a species mix that would establish quickly for erosion control, overwinter in Ohio, contribute sufficient N and have a C : N ratio between 20:1 and 30:1 to optimize N availability for subsequent crops, be killable by mechanical methods, and have high weed control potential. All of the mixtures in Columbus had achieved 30% ground cover 1 month after planting, but only four of the mixtures achieved this in Fremont due to poor conditions at planting. Above-ground biomass (AGB) accumulation in the mixtures ranged from 3631 to 13,642 kg·ha-1 in Columbus, and 449 to 12,478 kg·ha-1 in Fremont. Nitrogen in the AGB ranged from 74 to 269 kg·ha-1 in Columbus, and 10 to 170 kg·ha-1 in Fremont. Weed cover in the cover crop plots ranged from 1% to 91% eight weeks after cover crop kill in Columbus, and 12% to 90% seven weeks after cover crop kill in Fremont. Because one or more species in each screened mixture was determined not to be suitable, none of the mixtures was optimum. However, information gained about performance of individual species within the mixtures is also useful. `Nitro' alfalfa (Medicago sativa L.), ladino clover (Trifolium repense L.), subterranean clover (Trifolium subterraneum L.), Austrian winter peas [Pisum sativum ssp. Arvense (L.) Poir], and annual ryegrass (Lolium multiflorum Lam.) did not overwinter dependably in Ohio. Tall fescue (Festuca arundinacea L.), perennial ryegrass (Lolium perenne L.), and orchardgrass (Dactylis glomerata L.) did not compete well with taller, more vigorous species, and were not persistent in the mixtures. Medium and mammoth red clover (Trifolium pratense L.), annual and perennial ryegrass, and white and yellow blossom sweetclover [Melilotus alba Desr., and Melilotus officianalis (L). Desr.], were not killable by mechanical methods. Individual species that established quickly, were competitive in the mixtures, overwintered dependably, and were killed by mechanical methods were rye (Secale cereale L.), barley (Hordeum vulgare L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa Roth.)

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Polyculture mixtures of several species of cover crops may be the best way to optimize some of the benefits associated with cover crop use. In the first year of a three year study, 16 polyculture mixtures of cover crops (4 species/mixture) were screened at seven sites throughout the state. Five of the mixtures were seeded at two planting dates. Fall evaluation of the cover crop mixtures included ease of establishment, vigor, percent groundcover, plant height, and relative biomass. The two mixtures with the highest percent groundcover were (1): sudex, rye, mammoth red clover, and subterranean clover (62% and 80% groundcover, one and two months after planting respectively), and, (2), annual alfalfa, hairy vetch, ryegrass, and rye (56% and 84% groundcover one and two months after planting respectively). The six mixtures with the highest percent groundcover did consistently well, relative to other mixtures, at all locations. Mixture (1) above also had the highest relative biomass throughout the state. Yellow and white sweet clovers, hairy vetch, winter oats, subterranean clover, red clover, rye and barley established well and maintained high vigor ratings throughout the fall. Ladino clover, timothy, and big flower vetch consistently had poor vigor ratings.

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The effects of eight summer cover crop treatments combined with two arbuscular mycorrhizal (AM) fungal inoculants on strawberry growth and yields were examined in a 2-year field experiment. Cover crop treatments included 1) sudangrass [Sorghum bicolor (L.) Moench cv. Piper]; 2) pearl millet [Pennisetum glaucum (L.) R.Br. cv. 102 M Hybrid]; 3) soybean [Glycine max (L.) Merrill cv. Laredo]; 4) velvetbean [Mucuna deeringiana (Bort) Merr. cv. Georgia Bush]; 5) sudangrass/velvetbean combination; 6) pearl millet/soybean combination; 7) a non-mycorrhizal host consisting of rape (Brassica napus L. var. napus cv. Dwarf Essex) and buckwheat (Fagopyrum esculentum Moench) in Year 1 and Year 2, respectively; and 8) no cover crop control. Strawberry tips were inoculated with either a native mixture of several AM fungal species or a single species sold commercially, Glomus intraradices. Cover crop treatments were assessed for their aboveground biomass and nutrient uptake as well as their impacts on weed abundance and diversity, soil nutrients, and parasitic nematode populations. Cover crop and AM treatments were assessed for their impact on strawberry growth, yields, AM root colonization, and nutrient uptake. Grass-based cover crop treatments, particularly pearl millet, produced the most aboveground biomass. In both years, all cover crop treatments reduced summer weed biomass compared with the control. Neither cover crop nor AM treatments had an effect on overall strawberry plant growth or yields in either year, although some differences existed at specific growth periods. The results suggest that cover crops are a viable strategy for reducing summertime weeds and that background, native populations of AM fungi in the soil may be just as effective as a commercially available species. It is likely that no overall yield benefit was found among treatments for two reasons: 1) nutrients, especially nitrogen, were not limiting; and 2) the cover crop growth window may have been too short for a significant impact on strawberries over two seasons.

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Field and laboratory studies were conducted to investigate the mechanisms of weed suppression by cover crops. High-performance liquid chromatograph analysis and a seed germination bioassay demonstrated that rye (Secale cereale L.) can be leached of its allelochemicals, redried, and used as an inert control for separating physical suppression from other types of interference. In a field study, rye, crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth.), barley (Hordeum vulgare L.), and a mixture of the four species suppressed the emergence of eastern black nightshade (Solanum ptycanthum Dun.). Crimson clover inhibited the emergence of eastern black nightshade beyond what could be attributed to physical suppression alone. The emergence of yellow foxtail [Setaria glauca (L.) Beauv.] was inhibited by rye and barley but not by the other cover crops or the cover crop mixture.

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Conservation tillage using residue from a cover crop grown before potato (Solanum tuberosum L.) production has been infrequently and inconclusively studied. The objectives of this study were to 1) conduct a field study to evaluate soil physical properties, and potato growth and yield, in conventional-tillage (CT), no-tillage (NT), and subsurface-tillage (SST) systems and 2) conduct a greenhouse study to evaluate the effect of soil bulk density (ρb) on potato growth and yield. Potatoes (`Atlantic') were planted into residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench × S. sudanense (Piper) Staph] at two sites in eastern North Carolina—Plymouth into Portsmouth fine sandy loam and Lewiston into Norfolk sandy loam. Potatoes in the NT and SST system emerged more slowly than potatoesplanted conventionally. There were no differences in plant population or size by 8 weeks after planting at Plymouth, but plant population and size were less in NT and SST systems at Lewiston. Reducing tillage also affected soil compaction, increased soil moisture early in the season at both sites, and increased ρb at Lewiston. Yield of U.S. No. 1 potatoes planted in NT and SST systems were comparable to potatoes planted in a CT system at Plymouth, but were less than potatoes planted in a CT system at Lewiston. There were no differences in yield between potatoes planted with NT and SST. In the greenhouse study, ρb did not affect leaf area or tuber yield or tuber grade. Specific sites and soils may allow for comparable potato production with no or SST, but further research, conducted on different soil types would promote further understanding of the impacts of reducing tillage in potato production.

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