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Robert Wiedenfeld and Robert Stubblefield

Plastic mulch ground cover and drip irrigation have produced substantial increases in yield and earliness of melons. However, such practices affect water movement, and nutrient and salt distribution in the soil. Salt levels in the soil after a melon crop using drip or flood irrigation increased in bare soil but decreased where plastic mulch had been used. Apparently capillary rise of water in response to surface evaporation brought salts up into the root zone. Very little of the applied N was detectable at the end of the study. However, enhanced early vine growth due to N application where drip irrigated but not where flood irrigated indicated that flood irrigation may have caused earlier N losses. Yield responses to N regardless of irrigation method indicated that early availability may have been most important. Yield increases were found for drip vs flood irrigation, and for plastic mulch vs bare soil, both of which may have been earliness effects; but the later treatments did not get the chance to catch up due to the occurrence of vine decline.

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Youbin Zheng, Thomas Graham, Stefan Richard, and Mike Dixon

To determine whether currently used commercial nutrient solution concentrations can be reduced during the final stage (last 4 to 5 weeks) of production of potted gerbera (Gerbera jamesonii `Shogun') under recirculating subirrigation conditions, plants were grown under one of four nutrient levels (10%, 25%, 50%, and 100% of full strength). Nutrient concentration levels did not affect leaf area, flower number and appearance, and plant total dry weight. There were no significant differences in the greenness (as measured by SPAD meter) of leaves from plants that received the 50% and 100% strength nutrient solutions. However, leaves from plants that received the 10% and 25% strength solution showed significantly less greenness than that of the plants that received 50% and 100% strength nutrient solutions. There were interveinal chlorosis symptoms on the younger leaves of some plants in the 10% and 25% strength nutrient treatments. It is suspected that this interveinal chlorosis was due to iron (Fe) deficiency caused by the increased substrate pH. It is concluded that the nutrient solution concentrations typically used for potted gerbera production in commercial greenhouses at the final stage (4 to 5 weeks) under recirculating subirrigation conditions, can be safely reduced by at least 50% without adversely affecting crop production. Nutrient salts accumulated in the top section of the growth substrate under all treatments levels; however, no phytotoxic effects were observed. No differences in water use (141 mL per plant per day) were observed amid the various nutrient levels. Fertilizer inputs were reduced in the 50%, 25%, and 10% treatments by 54%, 75%, and 90% respectively, relative to the 100% treatment. After 4 weeks under recirculating conditions, the qualities of the nutrient solutions were still within acceptable limits.

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Genhua Niu, Denise S. Rodriguez, Rosa Cabrera, John Jifon, Daniel Leskovar, and Kevin Crosby

disturbing seed germination and seedling emergence. Furthermore, to investigate the effect of irrigation method on salt accumulation at the top soil layer, additional flats with pots filled with both soil types without seed were included and irrigated with

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Jinrong Liu, W. Roland Leatherwood, and Neil S. Mattson

, 1988 ). Pepper growth. Fresh weight and DW of pepper were significantly affected by fertilizer and irrigation method ( Table 2 ). Subirrigated pepper appeared sensitive to soluble salt accumulation. The greatest pepper FW and DW occurred at 200 mg·L −1

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Mario Perches and Don Wilkerson

Ebb and Flood systems provide an efficient means of sub-irrigating greenhouse crops. However, substrate accumulations of soluble salts can limit plant growth.

Two treatment irrigation regimes, consisting of 1.70 EC and 0.86 EC, were applied to 7.0 cm pots filled with a standard peat:perlite growing medium. Treatment solutions were changed weekly. All containers were irrigated daily and substrate EC levels measured weekly in the upper, middle, and lower 2.33 cms of the container.

Following 6 weeks of observation, mean EC substrate levels ranged from 1.23 mmhos/cm to 4.42 mmhos/cm. Significant differences occurred between the upper and middle/bottom portions of the container. There was also a significant interaction between treatment irrigation regimes, substrate layer and week.

In both treatment regimes, salt accumulations in the middle and bottom layers of substrate were within acceptable levels for plant production.

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Elio Jovicich and Daniel J. Cantliffe

A physiological disorder, “Elephant's Foot”, can develop in greenhouse hydroponic sweet pepper (Capsicum annuum L.). In a plant with this disorder, the base of the stem becomes swollen below the cotyledon level and wounds develop at the base of the stem's epidermis, what might predispose it to a localized rot and result in a sudden permanent plant wilt. Salt accumulation at the base of the stem could be a possible cause of the epidermis wounds. The effects of soilless media type (perlite, coconut coir, pine bark, and peat–perlite–vermiculate mix), transplant depth, and amount of nutrient solution applied per day were studied to evaluate the development of “Elephant's Foot” on a summer–fall sweet pepper greenhouse crop in Gainesville, Fla. Seedlings grown in polyethylene containers were transplanted 29 June 1999 into 11.4-L pots at three transplant depths: a) at half of the cell height, discarding only the bottom of the container (TOP); b) at the cotyledon level (LEVEL), and c) at the second stem node (DEEP). Plants were irrigated with 2, 2.5, 3, 3.5, and 4 L/day per plant of solution. The percentage of plants with epidermis wounds at the base of the stem was highest (82.5%) on TOP plants, compared to LEVEL (5.8%) and DEEP plants (0%). TOP plants had higher values of electrical conductivity on the stem epidermis than LEVEL and DEEP plants. There was a positive linear relationship (r = 0.82) between the percentage of plants with epidermis wounds and the electrical conductivity. Early yield of extra large and large fruits was higher in DEEP (1.05 kg·m–2) than in TOP plants (0.82 kg·m–2). Transplanting sweet pepper with the cotyledonary node under the soilless media could minimize salt accumulation and epidermis damage at the base of the stem level.

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Hee-Ju Lee, Sang-gyu Lee, Changhoo Chun, and Jung-Myung Lee

Use of grafted seedlings is a practical method to overcome salt accumulation, deterioration of physicochemical properties of soil, and accumulation of soil-borne pathogen that farmers, as well as commercial plug seedling producers, in Korea mainly adapted. Graft-take, subsequent growth, and quality characteristics of grafted hot pepper (Capsicum annuum L.) seedlings composed of three scions and 10 rootstocks were investigated. `Manita', `Chungyang', and `Nokkwang' were cultivars of scions used—they are the major hot pepper cultivars in Korea. The ten rootstock cultivars can be categorized into three groups: cultivars specially bred for rootstocks (`Konesian Hot', `PR-380', `R-Safe', and `Tantan'); cultivars recently bred in NHRI, Korea with the potential to be rootstocks (`Wonkwang1' and `Wonkwang2'); and cultivars originally bred for fruit harvest, but used as rootstocks due to their tolerance to soil-borne pathogens (`Kataguruma', `PR-Data', `PR-Gangza', and `PR-Power'). All the plants were treated with 5 mg·L-1 diniconazole solution 2 weeks after grafting and were soaked into 1.4% salt solution for 48 hours about 5 weeks after grafting. All the grafted seedlings showed feasible growth, including normal flowering and fruit set, and any symptoms of phytophthora blight and anthracnose were not found during 17-day-long experiment. Seedlings grafted onto `Tantan' rootstock showed stronger tolerance to high salt concentration than those grafted onto other rootstocks. Use of some, such as `Wongang 1', `PR-Data' and `Kataguruma', was alleviated the salt-induced growth inhibition.

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W. Voogt

In the Netherlands, many crops in protected cultivation changed from soil to soilless culture in recent years. The reasons for this development were problems with soil sterilization and better growth control with soilless culture, which led to considerable yield increases. However, the growing systems used, with free leachate drainage, contribute highly to pollution of the ground and surface water with minerals (N and P). To reduce this emission, closed growing systems were developed, i.e., systems with recirculating nutrient solutions. Inherent to these systems, however, were problems such as the rapid spread of pathogens in the root environment. Methods were developed for disinfestation of the nutrient solution. Salt accumulation was also a concern, the concentrations of ions in the water used for closed systems must be lower than the uptake capacity of the plants. To avoid depletion and accumulation of certain nutrients. the addition of nutrients should be adapted to the demand during the cropping period. For this purpose, nutrient solutions and guidelines for adjustments during the cropping period were developed for several crops.

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A. Erez, Z. Yablowitz, and R. Korcinski

Fresh fruits of stone fruit species are either lacking or in short supply in the months of March and April on the world market. This results from the absence of late-maturing cultivars in most of these species and from their poor storage capabilities. In March–April, supply from the Southern Hemisphere is dwindling or finished, while supply from the Northern Hemisphere has not started yet. A horticultural system was developed in Israel to get early fruit ripening of stonefruit species. The system developed is based on early completion of dormancy requirements followed by greenhouse tree growing. The system uses the following elements: 1) Improve chilling accumulation in winter by using evaporative cooling, to prevent chilling negation by high day temperatures. 2) Monitor salt accumulation level to prevent damage to branches and buds. 3) Monitor bud temperature and evaluate dormancy development according to the dynamic model. 4) Use dormancy breaking chemicals to compensate for part of the chilling not applied. 5) Cover of the trees with polyethylene having the appropriate characteristics of light filtering. 6) Keep the temperature in the greenhouse lower than the maximal temperature allowed, at every specific stage of development by ventilation. By using this system, fruit ripening was advanced by 4 to 6 weeks in peaches and nectarines (harvested from late March) and by 4 weeks in sweet cherries (harvested from April 11). Yields of 20 to 30 tons/ha were obtained in both species with high fruit quality.

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Genhua Niu, Denise S. Rodriguez, and Terri Starman

and Rodriguez, 2006a , 2006b ). Salt accumulation in the root zone is affected by the physical and chemical properties of the substrate, plant size, and environmental conditions because these factors influence the substrate moisture content and cation