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  • Author or Editor: Otho S. Wells x
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High tunnels are unheated, walk-in greenhouse-like structures which are used primarily for season extension of high-value crops. They are relatively inexpensive to build and maintain, but require manual labor for ventilation. Research with high tunnels at the Univ. of New Hampshire began in 1987 after assessing the international use of these structures. Because of the retail value of tomatoes, this has been the primary crop grown in tunnels. The average earliness of tomatoes is 1 month compared to field tomatoes. In 1988 in New Hampshire, there were 15 14 × 96 commercial high tunnels used for tomato production, with a gross income of $45,000. In 1997 the number of tunnels had increased to =160 units with a gross income of $912,000. Over the 10-year period, the cumulative income for commercial growers is estimated at $3.63 million. Because of earliness, this represents additional income to growers. Another very important benefit of high tunnels is the almost total reduction in diseases that are common in field production. Early blight, a serious field disease requiring several fungicide applications for control, is essentially nonexistent in high tunnels. Besides tomatoes, many other crops grow well in tunnels: pepper, summer squash, cucumbers, melons, lettuce and other salad crops, root crops, strawberries, and flowers. Although insects may be a problem, most of them can be controlled biologically. Particularly beneficial, especially for young, new-entry growers, is the relative low cost of high tunnels, $1.50/ square foot.

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Rowcovers and high tunnels are two intensive production systems used by commercial growers to extend the season and to improve yields of vegetables and strawberries. There are many types of rowcovers. These materials are summarized with descriptive information, primary use, and cost. The basics of high tunnel construction are presented to facilitate setting up a high-tunnel system.

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Tomato production in high tunnels is very intensive, although relatively low-input. However, optimal use of every square foot of growing space is critical to maximizing returns. Utilizing the basket-weave trellis system, `Ultrasweet' tomatoes were grown in 4 (replicated), 14-foot-wide high tunnels in 4 rows per tunnel at 3.5 ft between rows. In-row spacing of 12, 18, and 24 inches was combined with removal of sideshoots below the first flower cluster: one or three shoots at 18 and 24-inch spacing and none or one at 12-inch spacing. The highest marketable yield per plant was 22 lbs at 24 inches and three sideshoots, while the lowest yield per plant was 13.9 lbs at 12 inches and no sideshoots. The highest yield per sq ft was 4.2 lbs at 12 inches and no sideshoots, while the lowest yield per sq ft was 2.5 lbs at 24 inches and one sideshoot. The yield response to spacing and side-shoot removal was inverse for lbs per plant and lbs per sq ft. There was no difference in fruit size among any of the treatments. In a comparable experiment under field conditions, the highest yield per plant was 12.6 lbs at 24 inches and one sideshoot; and the highest yield per sq ft was 2 lbs at 12 inches and one sideshoot. The percentage of marketable fruit in the tunnels and in the field was 93.0 and 85.1, respectively.

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Experimental mulches which transmit high levels of solar infrared radiation and low levels of photosynthetically active radiation were compared to clear and black polyethylene mulches. Increases in soil temperature under infrared transmitting (IRT) mulches were intermediate between those under black and clear mulch. The IRT mulch with the highest solar transmittance (50%) produced soil temperatures close to those under clear mulch (T = 87%). Early leaf canopy development in muskmelon was enhanced more by both IRT and clear mulches than with black mulch. Minimal weed growth occurred under IRT mulches, but there was severe weed pressure from purslane under clear mulch with no herbicide.

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In 1992 and 1993, a run-down, infertile field was treated with 0, 12, 24, and 48 T/A (day weight) of compost. Timothy was grown on the plots each year and removed. In 1994 and 1995, `Earliqueen' muskmelon was grown in the same plots, along with four types of synthetic mulch (black plastic, IRT-100 plastic, IRT-200 plastic, and paper). Over the two years, there was a consistent crop response. As compost rates increased, crop yield increased. The highest yields were with the higher rates of compost coupled with the IRT mulches. After 2 years of cropping, the soil nutrient status remained at acceptable levels at the 24 and 48 T/A rates of compost. Generally, organic matter, pH, and CEC increased with increasing compost rates. Foliar diseases were suppressed with the compost at all rates.

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Abstract

Yields of muskmelon (Cucumis melo L.) were not significantly different between those grown under slitted polyethylene or those grown under polyester row covers, either with or without supporting wire hoops. Row covers combined with black polyethylene mulch increased both earliness and total yields of muskmelon as compared to those grown on black polyethylene mulch alone. Polyester appeared to be a potentially useful material for row cover culture of suitable crops because of its heat retention, light weight, relatively high tensile strength, and ease of installation.

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Abstract

“The French market gardens in the environs of Paris and other large cities are very curious-looking places.” Thus was the report in McCall's magazine in July of 1909 (1) in reference to the burgeon of bell glasses (cloches) used for winter and spring production of vegetables. Perhaps the gardening scenery around Paris was the fulfillment of the words of a classic English gardener, Mrs. Loudon, who in 1869 stated, “The cloche is quite unknown to the majority of amateurs, but nothing ever introduced to their notice will prove of greater or more varied utility” (4). By 1910, McKay (5) had placed the number of bell glasses in Paris at 2,160,000. Hence, the bell glass/cloche is the forerunner of the row cover/tunnel which is so prevalent in Europe and Japan today and which is becoming more popular in the United States.

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Abstract

Horticulturists have, from antiquity, attempted to circumvent climate-imposed limitations to crop production. The challenge has been to modify effectively both the predictive and nonpredictive elements of weather to take advantage of out-of-season production. Although there has been little, if any, success in actually controlling the weather, the progress in compensating for low temperatures has been phenomenal. One such compensatory factor has been the use of row covers for temperature modification. Accordingly, the purpose of this paper is to review the recent advances in using row covers for vegetable production, and to speculate on their potential uses in horticulture.

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High tunnels (unheated walk-in structures) are widely utilized in Europe, Asia, and the Middle East for early vegetable production. There are relatively few high tunnels used for vegetable production in the U.S. In a 2-year study, determinate tomatoes matured up to 32 days earlier than the same cultivars under standard field culture. Earliness was gained through 16 days earlier planting and 16 days earlier maturity than in the field. In tunnels, when ground grown, yield was 7.4 kg m-1; and when grown with a basketweave trellis, yield was 6.8 kg m-1. Even though these yields (for a 30-day period) were less than the yields from the field, the earlier harvest provides an extra marketing opportunity at premium prices. Under current production and marketing conditions in New Hampshire, at a conservative average selling price of $1.60/lb, the net return is $0.71/1b. By using relatively low cost tunnels, growers are able to economically extend their growing and marketing season without a high capital outlay.

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For 2 successive years, compost at rates of 0, 12, 24, and 48 t/acre were applied to a previously highly infertile field. Timothy was grown and harvested for these 2 years. Subsequently, for 3 consecutive years, through 1996, `Earliqueen' muskmelons were grown in the same plots without any additional compost being added. Subplots consisted of plastic and paper mulch and bare soil. Yields increased with increasing rates of compost for each of the 3 years, although yields for all treatments declined in the 3rd year. Highest yields were with the higher rates of compost coupled with IRT mulches and red mulch. Generally, organic matter and pH increased with increasing compost rates. Foliar diseases were suppressed with compost; however, there was an interaction of suppression with plastic mulches.

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