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D.C. Sanders, J.C. Gilsanz, W.J. Snerry and G.D. Hoyt

A 3-year study of cover crops (rye + crimson clover or sudex) and vegetable rotation systems was conducted using a Norfolk sandy loam soil. Cash crops were planted on all plots each spring, and in the fall, crops were snap beans/squash, sudex, or fallow. Late incorporation of cover crops depleted soil water content, resulting in a need for irrigation before spring plantings. Sudex residue had a high C: N ratio, delaying the total mineralization of N. Potato yields were not affected by rotation treatments. Cover crops improved snap bean emergence and yield. Snap beans had a differential uptake of Fe, Al, and B with cover crops. Tomato growth and yield were reduced with winter cover crops. Fall squash yield was not influenced by rotations.

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N.K.D. Ranwala, K. Brock, C.L. Ray, K. Greene and D.R. Decoteau

The effects of two winter cover crops, rye and crimson clover, on bell pepper yield were studied. Cover crops were planted in fall and incorporated into the soil prior to bell pepper planting. Both cover crops increased the marketable number and weight of bell peppers, and reduced the cull number of bell peppers compared to fallow (control) treatment. Delaying the harvest increased the marketable yield in both cover crops. Since there was no difference in bell pepper yield between two cover crops, both cover crops can be used effectively for bell pepper production. Use of cover crops may reduce the production costs and harmful effects on the environment by reducing chemical dependency, and increase the crop yield.

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Aref A. Abdul-Baki, J.R. Teasdale, R. Korcak, D. Chitwood and R Huettle

Fresh-market tomatoes (Lycopersicon esculentum Mill) cvs. Sunny and Sunbeam were grown in bare soil (BS), Horto paper (HP), black polyethylene (BP), hairy vetch (HV), crimson clover (CC), and hairy vetch plus rye (HVR) mulches. Yields were highest in HV (85.8 t·ha–1), followed by HVR 69.3 t·ha–1) and CC (65.7 t·ha–1), and averaged 47% above BP for the 3-year period. A 5- to 9-day earliness was exhibited by BP over other treatments. Fruit weight was significantly higher in all three organic mulch treatments than in the other three treatments. Mulch biomass was highest in HVR (5.91 t·ha–1), whereas N fixation was highest in HV (188 kg·ha–1). Tomato harvest was extended by the HV treatment over the BP treatment by 3 to 4 weeks, during which tomato prices were higher than those in early or mid-season.

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Kathryn E. Brunson, Sharad C. Phatak, J. Danny Gay and Donald R. Sumner

Velvetbean (Mucuna deeringiana L.) has been used as part of the crop rotation in low-input vegetable production in southern Georgia to help suppress populations of root-knot nematode (Meloidogyne incognita) for the past 2 years. Over-wintering cover crops of crimson and subterranean clovers were used the low-input plots and rye was the plow-down cover crop in the conventional plots. Tomatoes, peppers, and eggplant were the vegetable crops grown in these production systems. Following the final harvest in 1992, use of nematicides in the low-input plots was discontinued and velvetbean was then planted into the low-input plots and disked in after 90 days. Results from the 1993–94 soil samples taken before and after velvetbean showed a continuing trend of reduced nematode numbers where velvetbean had been, while most conventional plots that had nematicides applied resulted in increases in nematode populations.

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D.R. Earhart, M.L. Baker and V.A. Haby

A factored experiment was established at the Texas A&M Univ. Research and Extension Center at Overton in Spring 1995. The objective was to investigate the use of warm- and cool-season legume cover crops in vegetable cropping systems for reducing phosphorus (P) accumulation from poultry litter (PL) and commercial blend (CB) fertilizer. PL rates were based on soil test nitrogen (N) requirement of the vegetable crop and percent N content of the litter. This was considered the 1X rate. Fertility treatments were applied to the vegetable crop only. PL was applied at O, 1X, 2X and 4X rates. CB was applied at recommended rates for N, P, and K. The vegetable crops were: Spring 1995—watermelon; Fall 1995—turnip; Spring 1996—tomato; Fall 1996—collard; Spring 1997—squash. The legumes were: spring—Iron and Clay cowpea; fall—crimson clover. Dry-matter yield of cowpeas and clover was not affected by fertility treatment in any of the years studied to date (Spring 1995, 1996, 1997). Plant concentration of P for both cover crops was increased all 3 years as rate increased. PL applied at the 1X rate maintained P levels in the surface 0—15 cm of soil at 60 mg·kg-1 over the five-season study period. CB maintained levels of P equal to the control. A cropping system of spring vegetable—fall legume greatly reduced P accumulation. A reduction in P was also noted from a system of fall vegetable—spring legume, but not as pronounced. The greatest accumulation was with a system of spring vegetable—fall vegetable.

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John Z. Burket, Delbert D. Hemphill and Richard P. Dick

Cover crops hold potential to improve soil quality, to recover residual fertilizer N in the soil after a summer crop that otherwise might leach to the groundwater, and to be a source of N for subsequently planted vegetable crops. The objective of this 5-year study was to determine the N uptake by winter cover crops and its effect on summer vegetable productivity. Winter cover crops [red clover (Trifolium pratense L.), cereal rye (Secale cereale L. var. Wheeler), a cereal rye/Austrian winter pea (Pisum sativum L.) mix, or a winter fallow control] were in a rotation with alternate years of sweet corn (Zea mays L. cv. Jubilee) and broccoli (Brassica oleracea L. Botrytis Group cv. Gem). The subplots were N rate (zero, intermediate, and as recommended for vegetable crop). Summer relay plantings of red clover or cereal rye were also used to gain early establishment of the cover crop. Cereal rye cover crops recovered residual fertilizer N at an average of 40 kg·ha-1 following the recommended N rates, but after 5 years of cropping, there was no evidence that the N conserved by the cereal rye cover crop would permit a reduction in inorganic N inputs to maintain yields. Intermediate rates of N applied to summer crops in combination with winter cover crops containing legumes produced vegetable yields similar to those with recommended rates of N in combination with winter fallow or cereal rye cover crops. There was a consistent trend (P < 0.12) for cereal rye cover crops to cause a small decrease in broccoli yields as compared to winter fallow.

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Lydia J. Stivers-Young and Frances A. Tucker

Surveys of vegetable growers in a six-county region in western New York were conducted in 1997 to determine which cover cropping practices were being used on commercial vegetable operations; to identify producers' needs for further research and information, and to assess the impact of cooperative extension programs in this area. In a broad survey, 118 responses were returned out of 315 surveys sent (37%). Respondents represented >37,000 acres (14974 ha) of vegetable production, or ≈53% of the vegetable acreage in the region. Vegetable acreage per operation ranged from 1 to 4000 acres (0.4 to 1619 ha). Sixty-nine percent responded that they grew cover crops on a total of 15,426 acres (6243 ha). Oats (Avena sativa L.), rye (Secale cereale), clover (Trifolium pratense), and wheat (Triticum vulgare) were the most commonly used cover crops. Seventy-six percent of the reported cover-cropped acres were planted to small grains, and 19% to legumes, almost entirely clovers. In open ended questions, the most important benefits of cover cropping identified by respondents were erosion control (46% of respondents) and organic matter additions (42%). The most important problems associated with cover crops were that they interfere with spring field work or fall harvest (26%), and that they are difficult to incorporate or plow under (24%). A targeted survey of nineteen onion (Allium cepa L.) producers in the same region measured the recent adoption of sudangrass (Sorghum sudanense Piper) and sorghum-sudan hybrid (Sorghum bicolor L. × S. sudanense) cover crops, the focus of the several years of extension research and educational programs. Nine of the onion producers had adopted the practice, and six of these had done so since the beginning of these extension programs. The implications of these results for research and extension are discussed.

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Glenn C. Wright, William B. McCloskey and Kathryn C. Taylor

Several orchard floor management strategies were evaluated beginning in Fall 1993 in a `Limoneira 8A Lisbon' lemon (Citrus limon) grove on the Yuma Mesa in Yuma, Ariz. and in a `Valencia' orange (Citrus sinensis) grove at the University of Arizona Citrus Agricultural Center, Waddell, Ariz. At Yuma, disking provided acceptable weed control except underneath the tree canopies where bermudagrass (Cynodon dactylon), purple nutsedge (Cyperus rotundus), and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermudagrass. Preemergence (norflurazon and oryzalin) and postemergence (glyphosate and sethoxydim) herbicides were used to control weeds in the clean culture treatment in Yuma. After three harvest seasons (1994-95 through 1996-97), the cumulative yield of the clean culture treatment was 385 kg (848.8 lb) per tree, which was significantly greater than the 332 kg (731.9 lb) and 320 kg (705.5 lb) per tree harvested in the disking and mowing treatments, respectively. In addition, the clean culture treatment had a significantly greater percentage of fruit in the 115 and larger size category at the first harvest of the 1995-96 season than either the disk or mow treatments. At Waddell, the management strategies compared were clean culture (at this location only postemergence herbicides were used), mowing of resident weeds with a vegetation-free strip in the tree row, and a `Salina' strawberry clover (Trifolium fragiferum) cover crop with a vegetation-free strip. The cumulative 3-year yield (1994-95 through 1996-97) of the clean culture treatment was 131 kg (288.8 lb) per tree, which was significantly greater then the 110 kg (242.5 lb) per tree yield of the mowed resident weed treatment. The yield of the strawberry clover treatment, 115 kg (253.5 lb) of oranges per tree, was not significantly different from the other two treatments. The presence of cover crops or weeds on the orchard floor was found to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on orange leaf nutrient content. The decrease in yield in the disked or mowed resident weed treatments compared to the clean culture treatment in both locations was attributed to competition for water.

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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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Kim Patten, Gary Nimr and Elizabeth Neuendorff

Blueberry production is enhanced by the use of an organic mulch. An alternative to off-farm sources of mulch is the production of winter and summer living mulch cover crops grown in the row middles of the blueberry planting. These crops are mowed and then windrowed for use as a mulch. We evaluated living mulch crops for blueberries for the following parameters: adaptation to low soil pH, mulch production, ease and cost of stand establishment, mowing tolerance, allelopathic weed control, and N contributed by mulch. Rye, ryegrass, and crimson clover were the most overall suitable crops for the winter; while for summer, pearl millet was best adapted. Nitrogen was the major limiting factor that affected nonlegume production. Legume yields were limited by deer foraging and low soil pH. Pearl millet had the greatest allelopathic response on weeds of all cover crops tested. Maximum dry matter production for the living mulches ranged from 6000 kg/ha for elbon rye in the winter, to 30,000 kg/ha for pearl millet in the summer. With the appropriate cover crop selection and adequate soil fertility living mulches appear to be a efficacious practice to aid blueberry production in the south.