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Entin Daningsih, Laurie Hodges, James R. Brandle, and Walter W. Stroup

Windbreaks can increase crop growth and improve crop quality. The effects of shelter on vegetable production varies with crop, location, and farming practices. While the advantages of minimizing wind stress on vegetable production is well-known, little research documents the specific response of vegetables to microclimate modification through the use of shelterbelts.

During the summer, 1991, a preliminary experiment was conducted on the effects of tree windbreaks (shelterbelts) on muskmelon plant growth, yield, and fruit quality. A split-plot design was used with shelter and exposed areas as main treatments with 3 replications. Subtreatments were 7 combinations of anti-transpirant and time of application. Leaf growth was measured 4 and 6 weeks after planting. Muskmelon fruit were harvested over a 6 week period at 2 day intervals. Muskmelon yield, fruit and cavity diameter, fruit color, and total sugar content were obtained.

The use of anti-transpirant did not significantly affect total yield, fruit or cavity diameter, total sugar content, or early leaf growth. The effect of shelter varied with the measured variable.

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John P. Edstrom*, William Krueger, and Wilbur Reil

Orchard hedgerow production systems have been used successfully in fruit and nut crops in California for decades to enhance yield, particularly in the early years of production. English walnuts (Juglans regia) are compatible with hedgerow techniques under prime soil conditions but are thought to require deep well drained soil to be commercially productive. Combining the production techniques of micro-irrigation, close spacing, minimal pruning and frequent fertilization in almonds has improved yield substantially on soils exhibiting a shallow, course textured topsoil underlain with a dense clay layer. Paradox hybrid rootstock (J. regia × J. hindsii) has shown greater tolerance to root lesion nematodes and heavier textured or poorly drained soils than Northern California Black (J. hindsii). Fourteen years of evaluation (1986-99) using `Chandler' and `Howard' Ctvs English walnuts in a replicated field trial on marginal soil has shown that 1) yields of 6700 kg·ha-1 (inshell) are attainable under these substandard soil conditions 2) Paradox hybrid rootstock out-yields Northern California Black by 30% on both cultivars tested, 3) kernels of high commercial quality for can be produced for both cultivars and 4) slip plow soil modifications may not improve tree growth, yield or crop quality in drip irrigated walnut hedgerow plantings.

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Rhuanito Soranz Ferrarezi, Geoffrey Matthew Weaver, Marc W. van Iersel, and Roberto Testezlaf

Subirrigation is a greenhouse irrigation method that relies on capillary action to provide plants with water and nutrients from below their containers. The first documented subirrigation system was described in 1895, and several variations on the basic design were used for research purposes before the modern ebb-and-flow type systems emerged in 1974. Most subirrigation systems apply the fertilizer solution to a waterproof bench or greenhouse section, allowing the substrate to absorb the water through holes in the bottom of the containers. Because there is little or no leaching, subirrigation typically allows for the use of lower fertilizer solution concentrations. Although excess fertilizer salts typically accumulate in the top layer of the substrate, this does not seem to have a negative impact on plants. Subirrigation can conserve nutrients and water, reduce labor costs, and help growers meet environmental regulations. A challenge with subirrigation is the potential spread of pathogens via the fertilizer solution. When this is a concern, effective disinfection methods such as ultraviolet radiation, chlorine, or ozone should be used. Sensor-based irrigation control has recently been applied to subirrigation to further improve nutrient and water use efficiencies. Better control of irrigation may help reduce the spread of pathogens, while at the same time improving crop quality. The primary economic benefit of subirrigation is the reduction in labor costs, which is the greatest expenditure for many growers.

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William D. Wheeler, Paul Thomas, Marc van Iersel, and Matthew Chappell

A soil moisture sensor-based automated irrigation system was trialed in a commercial floriculture greenhouse to determine what benefits these types of systems may offer to herbaceous ornamental producers. Water use, crop quality and growth, and grower behavior toward adoption of the new technology were monitored, when all decision making related to system operation was carried out by the grower. Two cultivars of poinsettia (Euphorbia ×pulcherrima) and three cultivars of geranium (Pelargonium ×hortorum) were produced in side-by-side trials over the course of 2 years while comparing grower-controlled, sensor-based automated irrigation with traditional grower-managed (timer-based) irrigation. Plant quality was equivalent between irrigation treatments across all five trials. Differences in plant size were noted in four of the five trials between irrigation treatments, but in all instances these differences were not judged by the commercial grower to impact marketability of the crop. No reductions in irrigation water use were noted with the sensor-based irrigation system, which differed from previous research using this technology in ornamental production. Over the course of 2 years, the number of plants produced using sensor-based irrigation control was scaled up, indicating increasing confidence in, and adoption of, the technology. Managers at the facility found that sensor-based irrigation facilitated reallocation of labor from irrigation management, which was especially valuable during peak production and shipping periods. The payback period calculated from labor savings would be roughly 1.5 years if the sensor-based irrigation system was implemented throughout the facility.

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Myung-Min Oh, Edward E. Carey, and C.B. Rajashekar

In a growth chamber study, lettuce (Lactuca sativa) plants were used to evaluate the effects of water deficits on health-promoting phytochemicals with antioxidant properties. Lettuce plants were treated with water stress by withholding water once at 6 weeks after sowing for 2 days or multiple times at 4 weeks for 4 days, at 5 weeks for 3 days, and at 6 weeks for 2 days. Water stress increased the total phenolic concentration and antioxidant capacity in lettuce. Young seedlings, 7 days after germination, had the highest total phenolic concentration and antioxidant capacity, and also, younger plants were typically more responsive to water stress treatments in accumulating the antioxidants than older plants. Phenylalanine ammonia lyase and γ-tocopherol methyltransferase genes, involved in the biosynthesis of phenolic compounds and vitamin E, respectively, were activated in response to water stress, although no activation of L-galactose dehydrogenase was detected. Lettuce plants subjected to multiple water stress treatments accumulated significant amounts of chicoric acid compared with the control plants. Although the increase in antioxidant activity in water stress-treated plants at harvest was not as great as in young seedlings, it was significantly higher than the control. One-time water stress treatment of lettuce at the time of harvest did not result in any adverse effect on plant growth. Thus, these results show that mild water stress in lettuce applied just before harvest can enhance its crop quality with regard to its phytochemical concentration without any significant adverse effect on its growth or yield.

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Paul R. Fisher, Royal D. Heins, Niels Ehler, Poul Karlsen, Michael Brogaard, and J. Heinrich Lieth

Commercial production of Easter lily (Lilium longiflorum Thunb.) requires precise temperature control to ensure that the crop flowers in time for Easter sales. The objective of this project was to develop and validate a greenhouse decision-support system (DSS) for producing Easter lily to predetermined height and flower date specifications. Existing developmental models were integrated with a knowledge-based system in a DSS to provide temperature recommendations optimized for Easter lily scheduling and height control. Climate data are automatically recorded in real time by linking the DSS to a greenhouse climate control computer. Set point recommendations from the DSS can be manually set or automatically implemented in real time. Potential benefits of the project include improved crop quality and the transfer, validation, and integration of research-based models. The DSS was implemented at several research and commercial locations during the 1994 Easter lily season. DSS recommendations were compared with the strategies of experienced growers. The system design, implementation, production results, quality of recommendations, and potential are discussed.

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Laurie Hodges and James R. Brandle

Windbreaks reduce wind speed and modify the microclimate in sheltered areas. Many producers use wind barriers in their production systems, but few producers recognize all of the benefits available or understand the principles involved in windbreak function and design. Wind has direct and indirect effects on plant growth and development. Direct effects include soil abrasion, increased transpiration, and lodging. Indirect effects are based on changes in the crop microclimate, which influence plant growth and yield. Windbreaks increase soil and air temperatures and can extend the growing season in sheltered areas, resulting in increased crop development, earlier crop maturity, and market advantage. Plant-water relations and irrigation efficiency are improved by shelter. Overall, modifications to the microclimate in sheltered areas contribute to 5% to 50% higher crop yields. Winds in excess of about 5 m·s−1 (1.0 m·s−1 = 2.25 miles/h; miles/h × 0.447 = m·s−1) result in wind erosion and soil abrasion and may cause a loss of crop stand. Wind speeds below 5 m·s−1 may have an equally adverse impact on crop quality and marketable yield. In both cases, wind-breaks can reduce damage effectively in sheltered areas. Wind protection reduces certain problems associated with plasticulture under windy conditions.

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Dario Ramirez and Harvey J. Lang

Production of holiday cactus has been limited by the common occurrence of marginal chlorosis of the phylloclades, which can lead to losses in crop quality. This work was conducted to determine if poor growth and phylloclade yellowing could be correlated to applied Fe concentration. Rooted cuttings of Schlumbergera truncata `White Christmas', `Twilight Tangerine', 'Christmas Charm', and `Lavender Doll' were transplanted into a modified Hoagland's solution, adjusted to a pH of 6.3, containing Fe-EDTA at either 0,10,20,30, or 40 mg·liter–1 Fe. Plants were grown in a controlled environmental chamber under 16 h daylength for 16 weeks at 22/18C day/night temperature. Plants grown under 0 and 10 mg·liter–1 Fe had significantly greater fresh weight, height, and root length than plants grown under higher Fe concentrations for all cultivars. Comparison of tissue analysis results revealed a direct correlation between poor growth and levels of Fe within the tissue. There was no correlation, however, between Fe concentration and phylloclade edge yellowing, as yellowing occurred sporadically in all treatments. Comparison studies in the greenhouse of plants grown in peat: perlite medium showed similar trends.

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Suzanne O’Connell, Cary Rivard, Mary M. Peet, Chris Harlow, and Frank Louws

Organic and heirloom tomatoes are high-value products with growing demand but there are many challenges to successful cultivation. A systems comparison study was carried out to evaluate the production of the popular heirloom tomato ‘Cherokee Purple’ (Solanum lycopersicum L.) under high tunnel and open field systems in North Carolina from 2007 to 2008. Management of the high tunnel (i.e., temperature and irrigation), weather events as well as pest and disease pressure influenced crop quality and yield. The high tunnel and field systems achieved similar total yields (100 t·ha−1) the first season but yields were 33% greater in the high tunnel system than the field system in the second year (100 t·ha−1 and 67 t·ha−1, respectively). Both years, the tomatoes were planted in high tunnels 1 month earlier and harvested 3 weeks earlier than the field. The accumulation of ≈1100 growing degree-days (GDD) was required in both systems before 50% of the fruit was harvested. Fruit cracking, cat-facing, blossom-end rot, and insect damage were the major categories of defects in both systems. Incidence of both Tomato Spotted Wilt Virus (TSWV) and Gray Leaf Spot (GLS) were lower in the high tunnel compared with the field in 2007 and 2008, respectively. Results of this study suggest that with proper management techniques, high tunnels can optimize yields, increase fruit quality, and provide season extension opportunities for high-value horticultural crops.

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Shawn D. Lyons, William B. Miller, H. Christian Wien, and Neil S. Mattson

When grown in containers, pineapple lily (Eucomis sp.) can produce excessively long foliage and tall scapes, particularly in cultivars with tall pineapple lily (Eucomis comosa) parentage. Height control, through the use of plant growth regulators (PGRs), is necessary to improve crop quality of potted pineapple lily. In year 1 of these trials, bulbs of cultivars Reuben, Tugela Jade, and Tugela Gem were given substrate drenches of flurprimidol or paclobutrazol, each at 2, 4, or 6 mg per 6-inch pot. Drenches were applied at the “visible inflorescence” stage. As concentration increased, scapes were generally shorter in all cultivars for both PGRs, but there was no effect on foliage length or production time. At the rates tested, the reduction in scape length was insufficient to produce marketable plants of the three cultivars. In the second year, substrate drenches were applied at an earlier stage than in year 1, at “leaf whorl emergence,” when shoots were about 7 cm tall. The PGR treatments were notably more effective at controlling plant height in the second year. As concentration increased, scape and foliage length was reduced relative to the controls in all three cultivars for both PGRs. For all cultivars, inflorescence leaning and toppling were sharply reduced at all application rates compared with untreated controls. The reduction in plant height observed in year 2, particularly in plants treated with 4 or 6 mg/pot, resulted in plants with compact scapes and foliage proportional with their 6-inch containers.