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  • Author or Editor: James M. White x
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`Orlando Gold' carrots (Daucus carota L.) were grown in plastic containers filled with an organic soil and placed in a greenhouse in the fall and spring. Three (high, medium, and low) soil water concentrations of 48% (low), 54% (medium), and 60% (high) were used. The number of marketable roots was higher following the fall than the spring planting. The high and low soil water concentrations significantly reduced the number of marketable roots over the medium concentration, but only the high concentration reduced the total marketable weight in both plantings. Application of the high soil water concentration reduced root length but not width measured at 2.5 cm below the crown relative to the medium and low soil water concentrations. Carrots will produce marketable roots when grown in a wide range of soil water concentrations, but the high concentration reduced yield more than the low concentration.

Free access

Abstract

Seed treatments and soil covers were used to assess stand establishment and uniformity of direct-seeded cabbage (Brassica oleracea L. var capitata) under high and low soil temperatures. Generally, primed seeds did not result in increased or more uniform seedling emergence compared to untreated seeds. Germinated seeds sown with a magnesium silicate gel (Laponite) or a starch-acrylamide-acrylate polymer gel (Liquagel) resulted in incomplete stands under heat stress, and stands for all plantings were generally lower when cabbage seeds were sown in a gel than when sown without a gel. Peat-vermiculite (Plug-mix) and calcined clay (GrowSorb) seed covers improved stands regardless of seed treatment when average soil temperatures were ≥30°C. Under normal (25°) to cooler soil conditions stands were not improved by seed treatment or seed cover.

Open Access

Proper water management is a major responsibility of managers of creeping bentgrass grown on putting greens in the hot and humid southern states. The combination of shallow root systems, sand-based root zones, high temperatures, and high evaporative demands frequently results in severe drought stress on bentgrass (Agrostis palustris Huds.) greens. This study was initiated to determine the effects of irrigation frequency on creeping bentgrass turgor pressure and on the O2 and CO2 concentrations in a sand-based root zone mixture. In total, 81 plots, 1.5 × 1.5 m each, were established on a USGA-type root zone mixture and organized into 9 groups of 9 plots each. Each group could be irrigated individually. One plot in each group was planted to either `A-4', `Crenshaw', `Mariner', `L-93', or `Penncross' creeping bentgrass. Irrigation frequency treatments of 1-, 2-, and 4-day replacement of historical PET were imposed on three groups each. After establishment, measurements of the leaf water potential, osmotic potential, soil oxygen concentration, and soil carbon dioxide concentrations were made over a 1- to 2-year period. Bentgrass irrigated every 1 or 2 days had significantly (P = 0.05) greater turgor pressures at 0600 hr as compared to turf irrigated every 4 days in 1997. No differences were seen in 1998 due to drier environmental conditions. Concentrations of O2 and CO2 in the soil air remained in the optimal range for all treatments, indicating that lack of O2 in the root zone as a result of frequent irrigation may not be the primary cause for reduced rooting depth of bentgrass grown on highly permeable sand-based root zone mixtures.

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Integrating hydroponic and aquaculture systems (aquaponics) requires balanced pH for plants, fish, and nitrifying bacteria. Nitrification prevents accumulation of fish waste ammonia by converting it to NO3 -N. The difference in optimum pH for hydroponic cucumber (Cucumis sativa) (5.5 to 6.0) and nitrification (7.5 to 9.0) requires reconciliation to improve systems integration and sustainability. The purpose of this investigation was to: 1) determine the ammonia biofiltration rate of a perlite trickling biofilter/root growth medium in an aquaponic system, 2) predict the relative contribution of nitrifiers and plants to ammonia biofiltration, and 3) establish the reconciling pH for ammonia biofiltration and cucumber yield in recirculating aquaponics. The biofiltration rate of total ammonia nitrogen (TAN) removal was 19, 31, and 80 g·m−3·d−1 for aquaponic systems [cucumber, tilapia (Oreochromis niloticus), and nitrifying bacteria (Nitrosomonas sp. + Nitrobacter sp.)] with operating pH at 6.0, 7.0, and 8.0, respectively. With the existing aquaponic design (four plants/20 L perlite biofilter/100 L tank water), the aquaponic biofilter (with plants and nitrifiers) was three times more effective at removing TAN compared with plant uptake alone at pH 6.0. Most probable number of Nitrosomonas sp. bacteria cells sampled from biofilter cores indicated that the aquaculture control (pH 7.0) had a significantly higher (0.01% level) bacteria cell number compared with treatments containing plants in the biofilter (pH 6.0, 7.0, or 8.0). However, the highest TAN removal was with aquaponic production at pH 8.0. Thus, operating pH was more important than nitrifying bacteria population in determining the rate of ammonia biofiltration. Early marketable cucumber fruit yield decreased linearly from 1.5 to 0.7 kg/plant as pH increased from 6.0 to 8.0, but total marketable yield was not different. The reconciling pH for this system was pH 8.0, except during production for early-season cucumber market windows in which pH 7.0 would be recommended.

Free access

Abstract

Carotenes from vegetables and fruits are vitamin A precursors that contribute about half of the vitamin A in the U.S. diet (3) and two-thirds of the world diet (5). Carrots typically contain 65 to 90 ppm carotenes (1) and are estimated to be the major source of carotene for U.S. consumers (3). Few pro-vitamin A sources surpass the carotene content of typical carrots, although red palm oil can contain >825 ppm carotenes (2). Genetic selection for higher carotene levels in carrots could increase the dietary consumption of carotene and consequently vitamin A. A high carotene mass carrot population was developed for use in breeding, genetic, and biochemical studies of carrot (Fig. 1).

Open Access