Abstract
An analytical model is described that predicts air and soil temperatures under row tunnels used for early season microclimate modification for field grown vegetables and fruits. The model is time dependent and based on simultaneous solutions of thermal radiation and thermal energy balances for each component of the thermal system. The model's adequacy was tested by comparing its predictions to field data. Reasonable agreement was found considering the approximations used to determine values of required thermal parameters. Sensitivity analyses are presented to demonstrate uses of the model, and the significance of the more important thermal parameters.
Abstract
To appreciate the existing variation to horticulture in Texas, you need to realize the state has an area of more than 168,000,000 acres which are divided into 14 land resource areas based on soil types, topography, climate, and vegetation. The states annual rainfall varies from 58 to 8 inches East to West with forest free areas varying from 30 to 180 days South to North. The total horticultural economoc farm value in 1973 was about $326,571,000 of which 69% was attributed to vegetables, 18% to fruits and nuts, and 13% to ornamentals.
The Florida horticulture industry (vegetables, ornamentals, citrus, and deciduous fruit), valued at $4.5 billion, has widely adopted microirrigation techniques to use water and fertilizer more efficiently. A broad array of microirrigation systems is available, and benefits of microirrigation go beyond water conservation. The potential for more-efficient agricultural chemical (pesticides and fertilizer) application is especially important in today's environmentally conscious society. Microirrigation is a tool providing growers with the power to better manage costly inputs, minimize environmental impact, and still produce high-quality products at a profit.
Abstract
Stevens (4) has given a recent and thorough review of cultivar influence on nutritive value in fresh fruits and vegetables. Differences described in his paper indicate that there is great potential in breeding for nutritional value. The largest body of information is with respect to vitamins. Here it is not uncommon for one cultivar to have twice the vitamin concentration of another, and occasional differences may be much greater. Minerals and protein apparently vary to a lesser degree than vitamins, and less is known about cultivars which are consistently high or low in these nutrients. Nevertheless, there is a real potential for developing cultivars that have higher percentage composition of minerals and proteins as well as of vitamins.
Vegetables are grown throughout the U.S. on various soil types and in various climates. Irrigation is essential to supplement rainfall in all areas to minimize plant water stress. In the U.S., irrigated vegetable production accounts for about 1.9 million ha or 7.5% of the irrigated area. California, Florida, Idaho, Washington, Texas, Nebraska, Oregon, Wisconsin, and Arizona account for 80% of the U.S. production of irrigated vegetables. In the U.S., surface and subsurface (seepage) irrigation systems were used initially and are currently used on 45% of all irrigated crops with a water use efficiency of 33%. Sprinkler or overhead irrigation systems were developed in the 1940s and are currently used extensively throughout the vegetable industry. Sprinkler systems are used on 50% of the irrigated crop land and have a water use efficiency of 75%. In the late 1960s, microirrigation (drip or trickle) systems were developed and have slowly replaced many of the sprinkler and some of the seepage systems. Microirrigation is currently used on 5% of irrigated crops. This highly efficient water system (90% to 95%) is widely used on high value vegetables, particularly polyethylene-mulched tomato (Lycopersicon esculentum), pepper (Capsicum annuum), eggplant (Solanum melongena), strawberry (Fragaria ×ananassa), and cucurbits. Some advantages of drip irrigation over sprinkler include reduced water use, ability to apply fertilizer with the irrigation, precise water distribution, reduced foliar diseases, and the ability to electronically schedule irrigation on large areas with relatively smaller pumps. Drip systems also can be used as subsurface drip systems placed at a depth of 60 to 90 cm. These systems are managed to control the water table, similar to that accomplished with subsurface irrigation systems, but with much greater water use efficiency. Future irrigation concerns include continued availability of water for agriculture, management of nutrients to minimize leaching, and continued development of cultural practices that maximize crop production and water use efficiency.
Fresh-market spinach production has risen in the United States in the past few years as well as total value of the crop. Increased crop value may be attributed to more “value added” spinach products being produced and marketed. Public awareness of nutrition is rising due to more information being distributed concerning cancer prevention, antioxidants, and neutraceuticals. Spinach is high in the carotenoids beta-carotene and lutein, a known antioxidant for the prevention of age-related macular degeneration (AMD). It is also high in vitamins A, C, E, and folate, fiber, and the mineral iron. In this respect, spinach producers have an advantage over growers of salad vegetables such as lettuce. While this is an advantage, more innovative “value added” methods of marketing this product to the consumer are needed. A dark-green, semi-savoy spinach type developed at the Univ. of Arkansas was studied to determine shelf-life and storage capabilities of root cut plants in transparent clamshell containers. Plants were held at temperatures ranging from 1 to 6 °C. Leaf turgidity and visual characteristics were rated on a 1 to 5 scale. Acceptable characteristics and shelf-life of spinach stored in clamshell containers were seen up to 14 to 21 days when plants were stored at or near 1 °C. These results indicate that spinach packaged in transparent clamshell containers will maintain an acceptable shelf-life and could be beneficial to fresh market spinach producers.
Onion (Allium cepa L.) is an economically important vegetable in the United States. Though considered a minor crop in terms of total acreage, onions have high value when compared to other crops and, nationally, their value approaches $800 million. Because harvested onions are routinely stored for long periods, disease can be a major obstacle to the industry. The primary disease reported in stored onions is botrytis neck rot caused by the fungus Botrytis allii (syn. B. aclada). Losses from neck rot can approach 35% of the stored crop. In order to accurately quantify the level of B. allii inoculum in bulbs at harvest to be able to predict potential botrytis neck rot in storage, a quantitative real-time PCR test to quantify levels of B. allii DNA present in onion bulb tissue has been developed. We have employed the TaqMan real time PCR assay and report log-linear (R 2= 0.9915) relationship between B. allii DNA concentration and cycle threshold (Ct) value with a detection limit of 5 pico gram/microliter DNA. In addition, a log-linear standard curve plotting mycelial dry weight against Ct value has been developed to allow prediction of mycelial weight in onion tissue at harvest. Currently, the ability of this test to predict botrytis neck rot during storage is being tested.
Controlled plant growing systems have consistently used the standard earth day as the radiation cycle for plant growth. However, the radiation cycle can be controlled using automated systems to regulate the exact amount of time plants are exposed to irradiation (and darkness). This experiment investigated the influence of different radiation cycle periods on plant growth and carotenoid accumulation in kale (Brassica oleracea L. var. acephala DC.). Plants were grown in a controlled environment using nutrient solutions under radiation cycle treatments of 2, 12, 24 and 48 hours, with 50% irradiance and 50% darkness during each cycle. The radiation cycles significantly affected kale fresh weight, dry weight, percent dry matter, and the accumulation of lutein, β-carotene, and chlorophyll a and b. Maximum fresh weight occurred under the 2-hour radiation cycle treatment, whereas maximum dry weight occurred under the 12-hour treatment. Maximum accumulation of lutein, β-carotene, and chlorophyll a occurred with the 12-hour radiation cycle at values of 14.5 mg/100 g, 13.1 mg/100 g, and 263.3 mg/100 g fresh weight respectively. Maximum fresh weight production of the kale was not linked to increases in chlorophyll, lutein, or β-carotene. Consumption of fruit and vegetable crops rich in lutein and β-carotene carotenoids is associated with reduced risk of cancers and aging eye diseases. Increased carotenoid concentrations in vegetable crops would therefore be expected to increase the value of these crops.
Poster Session 21—Vegetable Breeding 1 28 July 2006, 1:15–2:00 p.m.
Demand for fresh fruits and vegetables is increasing worldwide in response to health concerns, wealth, and the desire for variety in the diet. However, consumption of produce is contingent on the ability of the industry to provide high quality fresh produce and on its convenience, as well as on consumer education and economics. Texture measurement is accepted by horticultural industries as a critical indicator of quality of fruits and vegetables. The fresh produce industry and, indirectly, consumers need methods for measuring produce texture to ensure the quality within a grade, and scientists need measurements to quantify the results of their treatments, whether treatments are genetic, chemical, or physical. The variety of attributes required to fully describe textural properties can only be fully measured by sensory evaluation by a panel of trained assessors. However, instrumental measurements are preferred over sensory evaluations for both commercial and research applications because instruments are more convenient, less expensive, and tend to provide consistent values when used by different people. Thus, instrumental measurements need to be developed that predict sensory evaluations of texture. Such instrumental measurements can then provide a common language among researchers, producers, packers, regulatory agencies, and customers. We compare sensory evaluations of specific critical textural attributes to instrumental force/deformation measurements on a wide variety of fruits and vegetables with relatively uniform bulk tissues, such as apples, bananas, carrots, jicama, melons, pears, potatoes, rutabagas, and several others.