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Guangyao Wang, Mathieu Ngouajio and Darryl D. Warncke

; Haramoto and Gallandt, 2004 , 2005 ; Matthiessen and Kirkegaard, 2006 ; Mojtahedi et al., 1991 ). This study was therefore undertaken to determine the effects of several brassica cover crops and sorghum sudangrass on nutrient cycling, weed suppression

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Qingren Wang, Waldemar Klassen, Yuncong Li, Merlyn Codallo and Aref A. Abdul-Baki

Intensive rainfall during summer causes substantial nutrient leaching in a subtropical region, where most vegetable lands lay fallow during this period. Also, an excessive amount of irrigation water supplied during the winter vegetable growing season leads to soil nutrient loss, which greatly impacts vegetable yields, especially in soils that possess a low capacity to retain soil water and nutrients. A 2-year field experiment was carried out to evaluate the effects of various summer cover crops and irrigation rates on tomato yields and quality, and on soil fertility in a subtropical region of Florida. The cover crops were sunn hemp [Crotalaria juncea (L.) `Tropic Sun'], cowpea [Vigna unguiculata (L.) Walp, `Iron Clay'], velvetbean [Mucuna deeringiana (Bort.) Merr.], and sorghum sudangrass [Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf.], with a weed-free fallow as a control. The cover crops were planted during late Spring 2001 and 2002, incorporated into the soil in the fall, and tomatoes [Lycopersicon esculentum (Mill.) `Sanibel'] were grown on raised beds during Winter 2001–02 and 2002–03, respectively. Irrigation in various treatments was controlled when tensiometer readings reached –5, –10, –20, or –30 kPa. The cover crops produced from 5.2 to 12.5 Mg·ha–1 of above ground dry biomass and 48 to 356 Mg·ha–1 of N during 2001–02 and from 3.6 to 9.7 Mg·ha–1 of dry biomass and 35 to 277 kg·ha–1 of N during 2002–03. The highest N contribution was made by sunn hemp and the lowest by sorghum sudangrass. Based on 2-year data, tomato marketable yields were increased from 14% to 27% (p ≤ 0.05) by growing cover crops, and the greatest increase occurred in the sunn hemp treatment followed by the cowpea treatment. Irrigation at –10, –20, and –30 kPa significantly improved marketable yields by 14%, 12%, and 25% (p ≤ 0.05) for 2001–02, and 18%, 31%, and 34% (p ≤ 0.05) for 2002–03, respectively, compared to yields at the commonly applied rate, –5 kPa (control). Irrigation at –30 kPa used about 85% less water than at –5 kPa. Yields of extra-large fruit in the sunn hemp and cowpea treatments from the first harvest in both years averaged 12.6 to 15.2 Mg·ha–1, and they were significantly higher than yields in the fallow treatment (10.2 to 11.3 Mg·ha–1). Likewise at –30 kPa yields of extra-large fruit from the first harvest for both years were 13.0 to 15.3 Mg·ha–1 compared to 9.8 to 10.7 Mg·ha–1 at –5 kPa. Soil NO3-N and total N contents in sunn hemp and cowpea treatments were significantly higher than those in fallow. The results indicate that growing legume summer cover crops in a subtropical region, especially sunn hemp and cowpea, and reducing irrigation rates are valuable approaches to conserve soil nutrients and water, and to improve soil fertility and tomato yields and quality.

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Qingren Wang, Yuncong Li and Waldemar Klassen

A pot experiment with summer cover crops and soil amendments was conducted in two consecutive years to elucidate the effects of these cover crops and soil amendments on `Clemson Spineless 80' okra (Abelmoschus esculentus) yields and biomass production, and the uptake and distribution of soil nutrients and trace elements. The cover crops were sunn hemp (Crotalaria juncea), cowpea (Vigna unguiculata), velvetbean (Mucuna deeringiana), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense) with fallow as the control. The organic soil amendments were biosolids (sediment from wastewater plants), N-Viro Soil (a mixture of biosolids and coal ash, coal ash (a combustion by-product from power plants), co-compost (a mixture of 3 biosolids: 7 yard waste), and yard waste compost (mainly from leaves and branches of trees and shrubs, and grass clippings) with a soil-incorporated cover crop as the control. As a subsequent vegetable crop, okra was grown after the cover crops, alone or together with the organic soil amendments, had been incorporated. All of the cover crops, except sorghum sudangrass in 2002-03, significantly improved okra fruit yields and the total biomass production (i.e., fruit yields were enhanced by 53% to 62% in 2002-03 and by 28% to 70% in 2003-04). Soil amendments enhanced okra fruit yields from 38.3 to 81.0 g/pot vs. 27.4 g/pot in the control in 2002-03, and from 59.9 to 124.3 g/pot vs. 52.3 g/pot in the control in 2003-04. Both cover crops and soil amendments can substantially improve nutrient uptake and distribution. Among cover crop treatments, sunn hemp showed promising improvement in concentrations of calcium (Ca), zinc (Zn), copper (Cu), iron (Fe), boron (B), and molybdenum (Mo) in fruit; magnesium (Mg), Zn, Cu, and Mo in shoots; and Mo in roots of okra. Among soil amendments, biosolids had a significant influence on most nutrients by increasing the concentrations of Zn, Cu, Fe, and Mo in the fruit; Mg, Zn, Cu, and Mo in the shoot; and Mg, Zn, and Mo in the root. Concentrations of the trace metal cadmium (Cd) were not increased significantly in either okra fruit, shoot, or root by application of these cover crops or soil amendments, but the lead (Pb) concentration was increased in the fruit by application of a high rate (205 g/pot) of biosolids. These results suggest that cover crops and appropriate amounts of soil amendments can be used to improve soil fertility and okra yield without adverse environmental effects or risk of contamination of the fruit. Further field studies will be required to confirm these findings.

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Samuel Y.C. Essah, Jorge A. Delgado, Merlin Dillon and Richard Sparks

and potentially cycle it to the following crop. Delgado et al. (2007) reported other benefits from summer cover crops grown with limited irrigation and observed a 12% to 30% increase in total yield and marketable tubers when potato followed sorghum-sudangrass

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Anthony M. Ortiz, Brent S. Sipes, Susan C. Miyasaka and Alton S. Arakaki

; Reynolds et al., 2000 ). Sorghum–sudangrass hybrids contain the cyanogenic glycoside dhurrin that, when hydrolyzed, yields cyanide, a nematicidal compound ( Widmer and Abawi, 2002 ). Brassicaceae species contain glucosinolates that react with myrosinase

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Raymond Kruse and Ajay Nair

plots were 612 ft 2 (25.5 ft long by 24 ft wide). Whole plot treatments were ‘Mancan’ buckwheat, ‘Iron & Clay’ southernpea, black oats, ‘Grazex II’ sorghum-sudangrass, or a no-cover crop (control). The subplot treatment was planting time of lettuce

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Alyssa H. Cho, Alan W. Hodges and Carlene A. Chase

to create partial budgets for five summer fallow treatments: sunn hemp, velvet bean, cowpea, sorghum-sudangrass, and use of tillage to manage weeds preceding a summer squash crop. Partial budget analyses are used to evaluate the relevant costs and

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George E. Boyhan, Julia W. Gaskin, Elizabeth L. Little, Esendugue G. Fonsah and Suzanne P. Stone

production, particularly in the southeastern United States. In onion production on muck soils in Michigan using brassica ( Brassica sp.) cover crops or sorghum × sudangrass (sudex) resulted in similar weed suppression and soil fertility regardless of the

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Nancy G. Creamer and Keith R. Baldwin

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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Jillene R. Summers, Gail R. Nonnecke, Cynthia A. Cambardella, Richard C. Schultz and Thomas M. Isenhart

Improving soil quality and suppressing weeds are two challenges facing strawberry growers. Cover crops, such as perennial ryegrass (Lolium perenne) and sorghum-sudangrass (Sorghum sudanense), have been used in rotation with strawberry in the Midwest. The objective of the field study was to investigate the effects of various cover crops on soil quality and weed populations for strawberry production. The experiment was established in 1996 at the Iowa State Univ. Horticulture Station, Ames, in plots that previously were planted continuously in strawberry for 10 years. Nine treatments were arranged in a randomized complete-block design with three replications. Treatments included cover crops of Indian grass (Sorghastrum avenaceum), switchgrass (Panicum virgatum), big bluestem (Andropogon gerardii), black-eyed susan (Rudbeckia hirta), marigold (Tagetes erecta `Crackerjack'), sorghum-sudangrass, perennial ryegrass, strawberry (Fragaria ×ananassa `Honeoye'), and bare soil (control). Data from 1998 showed that both annual and perennial cover crops were established more readily (higher treatment-plant populations and less weed populations) than in 1997. Water infiltration rates were highest in bare soil plots and lowest in P. virgatum plots. Bare soil plots and S. sudanense plots had the lowest percent soil moisture.