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

[black hollyhock (cv. Nigra); canola (cvs. Dwarf Essex and Sunrise Canola); cabbage (cv. Capitata); French marigold (cvs. French Brocade and Pesche’s Gold), sorghum–sudangrass (cvs. Piper and Sordan 79); sunn hemp; and yellow mustard (cv. Ida Gold)] were

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Jialin Yu, Nathan S. Boyd and Zhengfei Guan

-parasitic nematode populations ( Wang et al., 2002 , 2006 , 2007 ), and many of these, particularly legumes, increases soil fertility for the subsequent crops ( Wang et al., 2006 ). Sunn hemp ( C. juncea L.) is a legume cover crop and is thought to have important

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

, and must be managed with rotations of nonhost cover crops ( Clark, 2007 ). Crop rotation with cover crops has been found to reduce nematode populations. Sunn hemp and southernpea used as a summer rotation in Florida tomato plots were found to suppress

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Teresa Olczyk, Yuncong Li, Waldemar Klassen and Qingren Wang

Summer cover crops can improve soil fertility by adding organic matter, supplying nutrients through mineralization, reducing nutrient leaching, and improving soil water and nutrient holding capacity. Other benefits include weed suppression and reduction of soil parasitic nematodes. A series of field experiments have been conducted at the UF IFAS Tropical Research and Education Center in Homestead, Florida to evaluate several summer cover crops for use in vegetable production in South Florida followed by field demonstrations conducted in the growers' fields. Best performing cover crops were legumes: velvet bean (Macuna deeringiana) and sunn hemp (Crotalaria juncea L. `Tropic Sun') providing 13 and 11 Mt of dry matter/ha, respectively. Sunn hemp supplied 330 kg N/ha followed by velvet been with 310 kg N/ha. Traditional summer cover crop sorghum-Sudan produced 4 Mt of dry matter/ha and retained only 36 kg N/ha. In addition Sunn hemp significantly reduced soil parasitic nematodes for successive crops. Limitations in use of Sunn hemp by more vegetable growers in South Florida include cost and availability of seeds.

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Carlene A. Chase, Rosalie L. Koenig, Jeffery E. Pack and Clinton C. Warren

Weed management is a major constraint of organic vegetable production and perennial weeds such as purple nutsedge (Cyperus rotundus) are particularly difficult to control. A study was initiated in 2005 to determine how summer fallow techniques impact purple nutsedge population density, tuber number and tuber viability; and to evaluate the impact of the treatments on the yields of two fall crops differing in canopy size and rate of development. Clean fallow treatments accomplished with weekly tillage or weekly flaming were conducted for 12 weeks. Two sets of summer cover crop treatments of sunn hemp (Crotalaria juncea) were established by broadcasting 40 lb of seed per acre and were undercut at 13 weeks after seeding. Cover crop residue was either incorporated before transplanting or retained on the surface as mulch for the fall crops of lettuce and broccoli. Soil solarization was initiated on 2 July and the transparent solarization film was maintained in place until mid-October. A weedy fallow treatment was included as a control, which was tilled before establishing the fall crops. Before the initiation of the summer fallow treatments, no difference in viable tubers or nutsedge shoot density was observed. After fallow, flaming had the highest number of viable tubers, with all other treatments similar to the weedy control. Nutsedge shoot density was suppressed by all fallow treatments to lower levels than with the weedy control, but solarization was the least effective. Leaf-cutting insects eliminated the crops in the sunn hemp mulch treatment within days of being transplanted. Lettuce stands with all other treatments were similar and greater than with the weedy control. Highest broccoli stands were obtained with flaming, solarization, and tillage; but broccoli stand with incorporated sunn hemp was similar to the weedy control. Highest lettuce yields occurred with incorporated sunn hemp, solarization, and weekly tillage. However, lettuce yields with flaming and the weedy control did not differ statistically. Broccoli yields were greatest with flaming, solarization, and tillage. Broccoli development was delayed with the weedy control and incorporated sunn hemp treatments and no significant yield was obtained.

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Jose Linares, Johannes Scholberg, Carlene Chase, Robert McSorley and James Fergusson

Lack of effective weed control may hamper organic citrus establishment. Cover crop/weed biomass (CCW) indices were used to assess the effectiveness of annual and perennial cover crops (CC) in reducing weed growth. The CCW values for perennial peanut (PP) were 0.06, 0.14, 0.4, and 0.5 during 2002, 2003, 2004, and 2005, respectively (very poor to poor weed control). Initial PP growth was slow and repeated mowing was required, but, over time, PP became more effective in controlling weeds. Weed biomass with sunn hemp was 0.3 Mg/ha in 2002 (CCW = 25, outstanding weed control) compared to 1.4 Mg/ha with use of cowpea (CCW = 1) in 2004. In 2004, the dry weights (Mg/ha) for different summer CC were: hairy indigo = 7.6, pigeon pea = 7.6, sunn hemp = 5.3, cowpea = 5.1, alyce clover = 2.9, velvet bean = 1.3, and lablab bean = 0.8. Corresponding 2005 values were: 9.5, 3.7, 12.6, 1.0, 1.9, and 1.4. Respective CCWI values were: 7, 4, 2, 16, 28, 0.6, and 0.3 (2004) vs. 17, 2, 64, 80, 0.5, 2, and 14. In 2004, winter CC production (Mg/ha) was radish (R) = 3.2, crimson clover (CR) = 1.7, oats (O) + lupine = 1.6, and rye (WR)/vetch (V) mix = 1.1. Results for 2005 were: CR + R + WR = 8.0, WR = 6.0; CR + WR = 5.3, CR = 5.0, CR + O + WR = 5.0, R = 4.3, and O = 3.6 Mg/ha. Corresponding values for CCW-indices were 15, 2, 1, and 3 (2004) and 100, 25, 76, 35, 62, 11, and 16 (2005). Although OMRI-approved herbicides showed up to 84% weed injury for selected species, none of these products provided long-term weed control. Combination of repeated tillage, use of compact/reseeding CC mixes in tree rows, more vigorous annual CC and/or perennial PP in row middle and repeated use of organic herbicides near sprinklers and tree trunks are thus required to ensure effective weed suppression in organic citrus.

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Laura Avila, Johannes Scholberg, Lincoln Zotarelli and Robert McSorely

Poor water- and nutrient-holding capacity of sandy soils, combined with intense leaching rainfall events, may result in excessive N-fertilizers losses from vegetable production systems. Three cover cropping (CC) systems were used to assess supplemental N-fertilizer requirements for optimal yields of selected vegetable crops. Fertilizer N-rates were 0, 67, 133, 200, and 267; 0, 131, and 196; and 0, 84, 126,168, and 210 kg N/h for sweet corn (Zea mays var. rugosa), broccoli (Brassica oleracea), and watermelon (Citrullus lanatus), respectively. Crop rotations consisted of sunn hemp (Crotalaria juncea) in Fall 2003 followed by hairy vetch (Vicia villosa), and rye (Secale cereale) intercrop or a fallow. During Spring 2004, all plots were planted with sweet corn, followed by either cowpea (Vigna unguiculata) or pearl millet (Pennisetum glaucum), which preceded a winter broccoli crop. Hairy vetch and rye mix benefited from residual N from a previous SH crop. This cropping system provided a 5.4 Mg/ha yield increment for sweet corn receiving 67 kg N/ha compared to the conventional system. For the 133 N-rate, CC-based systems produced similar yields compared to conventional systems amended with 200 kg N/ha. Pearl millet accumulated 8.8 Mg/ha—but only 69 kg N/ha—and potential yields with this system were 16% lower compared to cowpea system. For a subsequent watermelon crop, trends were reversed, possibly due to a delay in mineralization for pearl millet. Because of its persistent growth after mowing, hairy vetch hampered initial growth and shading also delayed fruit development. Although CC may accumulate up to 131 kg N/ha actual N benefits, N-fertilizer benefits were only 67 kg N/ha, which may be related to a lack of synchronization between N release and actual crop demand.

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Rhuanito S. Ferrarezi, Stuart A. Weiss, Thomas C. Geiger and K. Paul Beamer

was managed using cover crops preceding pea planting. In Year 1, the experimental field was planted in ‘IAC-1’ sunn hemp [ Crotalaria juncea (800,000 plants/ha)] in Aug. 2013; followed by ‘Rongai’ lablab [ Lablab purpureus (400,000 plants

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Emillie M. Skinner, Juan Carlos Díaz-Pérez, Sharad C. Phatak, Harry H. Schomberg and William Vencill

allelopathic potential of leguminous summer cover crops: Cowpea, sunn hemp, and velvetbean HortScience 42 289 293 Akanvou, R. Bastiaans, L. Kroprr, M.J. Gourdrian, J. Becker, M. 2001 Characterization of growth, nitrogen accumulation and competitive ability of

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Ted S. Kornecki and Francisco J. Arriaga

Soil Sci. Soc. Amer. J. 57 506 512 Mansoer, Z.D. Reeves, W.R. Wood, C.W. 1997 Suitability of sunn hemp as an alternative late-summer legume cover crop Soil Sci. Soc. Amer. J. 61 246 253 Reeves, D.W. 1994 Cover crops and rotations 125 172 Hatfield J