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Lewis Jett* and Andrew Read

High tunnels are passive solar greenhouses that are used to extend the traditional growing season for many horticulture crops. Growing conditions within a high tunnel are significantly different from growing conditions encountered in field production. Tomatoes (Lycopersicon esculentum Mill.) are wells suited for high tunnel culture having an upright growth habit and a significant economic premium for precocious harvest. The objective of this research was to investigate three planting dates (15 Mar., 30 Mar., and 10 Apr.) and three mulch types (black plastic, bareground, and clear plastic) with or without row covers, for early tomato production within a high tunnel in the Central Great Plains. High tunnels increased the average daily temperature by ≈6 °C. Early planting (i.e., mid- to late March) resulted in significantly earlier yield (i.e., early July). Using clear plastic mulch increased total marketable yield, but was not significantly different from black plastic. Row covers and plastic mulch are necessary for early tomato production. Row covers are specifically necessary for frost protection, but can be removed when the risk of frost has decreased.

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Lewis W. Jett

Skinning of sweetpotatoes [Ipomoea batatas (L.) Lam] can reduce marketable yield and quality. The `Beauregard' sweetpotato, despite its consistent high yield and quality, is very susceptible to skinning injury during harvest. A research project was initiated to investigate chemical and mechanical methods to improve skinset of `Beauregard' sweetpotato. Approximately 14 days before harvest, Desicate II and Enquik (dihydrogen tetraxosulfate) were applied to the sweetpotato vines as a broadcast spray. Mechanical methods evaluated included mowing with a flail-type mower or pulling (vine detachment) 7 days before harvest. Skin-set was measured using a Halderson periderm shear tester fitted to a torquometer. The Enquik + Desicate II treatment significantly desiccated the vines relative to application of Desicate II alone. The skin set testing device was sensitive enough to detect differences between treatments. The highest skin-set reading was obtained from the pulled vine treatment. Marketable yield was not affected by application of any chemical or mechanical treatment. Curing of skinned sweetpotatoes(4 days; 30 °C; 90% relative humidity) significantly reduced postharvest moisture loss and disease incidence.

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Lewis W. Jett

Growth of the sweetpotato [Ipomoea batatas (L.) Lam.] is subject to environmental variation. High soil temperatures can restrict storage root initiation and development. Moreover, fluctuating soil moisture can have a pronounced effect on yield and quality. Cover crops, used in a conservation tillage system, could modify the soil environment. The objective of this research was to investigate the effects of conservation tillage on sweetpotato growth. A rye cover crop was broadcast seeded in Fall 1996, and sweetpotatoes were transplanted into the undisturbed residue the following spring. A fallow, unseeded plot represented the conventional method of sweetpotato culture. Plants were harvested at 14-day intervals commencing at 21 days after transplanting. Leaf area and dry weights of the storage roots and vines were recorded. Soil moisture was measured by taking soil cores at the depth of rooting (10 cm). The sweetpotatoes growing in the undisturbed rye residue had a significantly greater leaf area, vine weight, root set, and yield (particularly large grade class) relative to conventional-tilled sweetpotatoes. The rye residue was very effective in reducing soil evaporation.

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Lewis W. Jett and Gregory E. Welbaum

Various osmotic solutions and solid carriers have been used to prime (controlled hydration followed by drying) seeds. Broccoli (Brassica oleracea L., var. italica, cvs. Brigadier and Earlidawn) seeds were primed in solutions of polyethylene glycol, potassium nitrate (KNO3), and mannitol or calcium silicate (Micro-ccl E) and vermiculite to determine which treatment provided the greatest enhancement of germination. Germination percentage and rate as well as head yield were determined in a series of laboratory, glasshouse, and field experiments over a three year period. Water potentials (Y) ranged from -0.8 to -2.6 MPa at 20°C for both osmotic solutions and carriers. The duration of the priming treatments were 3, 7, or 10 days. All priming treatments, except KNO3 and mannitol, consistently reduced the mean time to germination in the laboratory, reduced the mean time to field emergence, increased final stands, but did not affect the mean time to harvest. However, solid phase was more effective than osmotic priming at each Ψ tested. The best solid priming mixture was 1.0:0.8:1.8 (seed:carrier:water) for 7 days at 20°C using Micro-cel E. This treatment was measured to have a Y = -1.2 MPa, and other types of priming at the same Y were less effective. The Y threshold below which no priming effect was obtained was Ψ= -2.4 MPa. Priming response was closely associated with, but not entirely dependent on, the Ψ of the treatment.

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Lewis Jett*, Edward Carey and Laurie Hodges

There is great interest by horticulture producers in the Central Great Plains in methods to extend the traditional growing season, increase value of crops and provide more locally grown produce. High tunnels are low-cost, unheated greenhouses that can accomplish these goals. In 2002, the Central Great Plains High Tunnel Project was initiated through funding support by the Initiative for Future Agriculture and Food Systems (IFAFS). The Univ. of Missouri, Kansas State Univ., and the Univ. of Nebraska have constructed 24 high tunnels to conduct research on vegetables, small fruits and cut flowers. Each year, a multi-state workshop is conducted along with several on-farm and research center tours. Growers are collaborating with extension personnel on projects ranging from high tunnel temperature management to pest management. A web site for high tunnel information has been constructed (www.hightunnels.org). Production guides on specific high tunnel crops have been printed. From 2002-03, a significant number of high tunnels have been constructed in the Central Great Plains.

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Lewis W. Jett and T.P. Talbot

`Beauregard' and `Darby' sweetpotato cultivars were developed and released by the Louisiana Agricultural Experiment Station in 1987 and 1994, respectively. In total acreage, `Beauregard' is the dominant cultivar of sweetpotato grown in Louisiana and the remaining United States. However, very little is known about the growth characteristics of these two cultivars. Therefore, the objectives of this research were to examine storage root and shoot growth. Uniform transplants of both cultivars were transplanted in mid-July 1995 at the LSU Sweet Potato Research Station and sequentially harvested biweekly. Optimum leaf area of both cultivars was attained ≈60 days after transplanting. `Beauregard' had less leaf area than `Darby' at each stage of development, but partitioned more assimilates to the storage roots. At harvest, the harvest index of `Beauregard' was ≈75% compared with 50% for `Darby'. `Beauregard' had a significantly greater total yield of storage roots than `Darby'.

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Lewis W. Jett and W.A. Mulkey

Nitrogen effects on `Beauregard' sweetpotato were investigated from 1992 to 1995 at the LSU Sweet Potato Research Station to determine the optimal rate and timing of nitrogen application. Five rates of preplant nitrogen were applied: 0, 33.6, 50.4, 67.2, and 84 kg·ha–1. Increasing the rate of nitrogen to 50.4 kg·ha–1 significantly increased marketable yield. Five treatments of pretransplant/sidedress nitrogen (kg·ha–1) were applied: 0/0, 50.4/0, 0/50.4, 33.6/16.8, and 16.8/33.6. Withholding nitrogen resulted in significantly more storage root initiation 21 days after transplanting (DAT). Application of 50.4 kg N/ha 21 DAT resulted in significantly greater yields of US #1 sweetpotatoes in 1992 and 1995 and equaled the pretransplant nitrogen treatment in 1993 and 1994.

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Lewis W. Jett and Timothy P. Talbot

A cultural practice that can modify and conserve the soil environment is needed in sweetpotato [Ipomoea batatas (L.) Lam.] production. The objective of this research was to evaluate conventional and conservation tillage of sweetpotato with four cover crop species (fallow, ryegrass, rye, and wheat). The cover crops were seeded in late Oct. 1995, and the sweetpotato transplants (`Beauregard') were transplanted at two dates the following spring (May and June). Conservation tillage significantly lowered soil temperature (10 cm depth) during storage root initiation and development. Moreover, each cover crop significantly reduced weed emergence and soil erosion. The ryegrass conservation tillage treatment significantly increased marketable yield of sweetpotato in the first planting date, while rye and wheat performed equally well in the second planting date. In the second planting date, white grub (Phyllophaga ephilida Say) injury to storage roots was significantly higher in the conservation tillage treatments. However, conservation tillage seems to be a viable alternative to the conventional method of sweetpotato production.

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Lewis W. Jett, Ronald D. Morse and Charles R. O'Dell

Consumer attitudes and preferences towards fresh market broccoli (Brassica oleracea L. Group Italica) are changing. Consumers desire large-head broccoli with more florets per unit weight, which we term single unit broccoli. Single unit broccoli could be field established by transplanting, alleviating the problems of poor stand establishment encountered with direct-seeded broccoli in the Southeast. The objectives of this research were to determine the feasibility of producing single unit broccoli and the optimal plant arrangement and spacing to maximize the yield of single unit broccoli. Two spatial arrangements (single vs. twin row) and five plant densities (10.8, 7.2, 5.4, 4.3 and 3.6 plants/m2) were examined in 1990 and 1991 for production of single unit broccoli. Spatial arrangement had no significant effect on any measured variable, although the twin row arrangement resulted in less plant damage with each multiple harvest. For exclusive production of high quality, single unit broccoli with high yields of marketable florets, a planting density of 3.6 plants/m2 (46 cm within row spacing) should be used in a twin row arrangement.

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Lewis W. Jett, Ronald D. Morse and Charles R. O'Dell

There is a strong consumer demand for single-head broccoli (Brassica oleracea L. var. italica) that yields more florets per unit weight than bunching broccoli. Two spatial arrangements (single vs. twin row) and five plant densities (10.8, 7.2, 5.4, 4.3, and 3.6 plants/m2) were examined for single-head broccoli production. Spatial arrangement had no significant effect on any measured attribute, although the twin-row arrangement resulted in less plant damage with each harvest. For exclusive production of quality, single-head broccoli with high yields of marketable florets, 3.6 plants/m2 (46-cm within-row spacing) should be used.