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Work supported in part by a grant from the Organic Farming Research Foundation for a project entitled “Are organic vegetables more nutritious?” and by Initiative for Future Agriculture and Food Systems Grant No. 2001-52101-11431 from the USDA

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Cabbage seed was germinated and grown to transplanting size in a 98-cell tray using an automatic irrigation system based on the principle of maintaining a constant water table (CWT) relative to the growing medium in transplant trays. Seedlings obtained a nutrient solution from a capillary mat with one end suspended in a trough containing the solution. The distance between the nutrient solution surface and the transplant tray bottom was regulated with a water level controller. The nutrient solution was resupplied from a larger reservoir. A polyester material on top of the capillary mat allowed solution movement to the roots but prevented root penetration into the mat. The water table placement below the tray determined the water content in the growing medium. Seedling growth was evaluated using two growing media combined with two water table placements. Excellent quality seedlings were produced; the CWT irrigation system satisfactory provided water and nutrients for the duration of the crop. The only problems observed were dry cells, less than 2%, because of no media–mat contact and algae growth on the media surface using the higher water table. The CWT irrigation system is adaptable to existing greenhouse vegetable transplant production systems. It is automatic and can provide a constant optimum amount of moisture for seedling growing. It can be adjusted for phases of seedling growing such as more water during germination and can create water stress near transplanting time to either harden off or hold plants because of unfavorable planting conditions.

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The utility of presidedress soil nitrate testing (PSNT) in irrigated lettuce (Lactuca sativa L.) and celery (Apium graveolens L.) production was evaluated in 15 commercial fields in California from 1996 to 1997. Fields were selected in which soil NO3-N (5- to 30-cm depth) was >20 mg·kg–1 at the time the cooperating grower made the first sidedress N application. The grower's N regime was compared with reduced N treatments established by reducing or eliminating one or more sidedress applications. All fields were sprinkler and/or furrow irrigated, with minimal in-season precipitation. Reductions in seasonal N application averaging 143 and 209 kg·ha–1 N in lettuce and celery trials, respectively, had no effect on marketable yield in any field. Crop biomass N at harvest in the lowest N treatment in each field averaged 94% (lettuce) and 88% (celery) of that in plots receiving the full grower N program. Based on controlled-environment aerobic incubation of soil from 30 fields in long-term vegetable rotations, in-season N mineralization averaged 1% to 2% of soil organic N. A soil NO3-N “quick test” procedure utilizing a volumetric extraction of field-moist soil and measurement by nitrate-sensitive colorimetric test strips was evaluated and proved to be a practical on-farm method to estimate soil NO3-N concentration. Lettuce midrib NO3-N concentration at cupping stage was poorly correlated with current soil NO3-N level. We conclude that PSNT can reliably identify fields in which sidedress N application can be delayed or eliminated without affecting crop performance.

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N ( Simonne and Hutchinson, 2005 ; Trenkel, 1997 ). Vegetable production in the United States often is located upstream and/or adjacent to large tracts of land set aside for water management, ecosystem restoration, or urban development. These lands

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farmers, termination at the flowering stage typically reduces the potential economic (i.e., food production) and N benefits compared with continuing crop growth and management for vegetable pod production. In a study of faba bean BNF and accumulation

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, vegetables, and cut flowers. High tunnels also allow small farmers to gain market share in the niche market of “locally grown” products at a time of the year when most fruits and vegetables are grown elsewhere. Extending the vegetable production season

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) and has now become a potential key vegetable crop worldwide because of its high nutritive and antioxidant properties ( Uddin et al., 2012b ; Wenzel et al., 1990 ). Recently, hydroponic production of purslane, as the easiest and cheapest growing method

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N availability and peak crop demand ( Liebman and Davis, 2000 ; Wortman et al., 2011 ). Nitrogen requirements are significant for most vegetable crops, yet plant available N is often limiting in organic production due to poor synchrony between N

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