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  • Author or Editor: Wlodzimierz Bres x
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`Buttercrunch', `Grand Rapids', and `Summer Bibb' lettuce (Lactuca sativa L.) seedlings were grown with the nutrient film technique (NIT). The influence of two K concentrations (150 and 225 mg·liter-1) and four solution pH levels (5.0, 5.5, 6.0, and 6.5) on lettuce tipburn was investigated in four experiments. Additionally, the influence of pH on foliar nutrient concentration was examined. Even though tipburn was observed in `Buttercrunch' and `Summer Bibb' lettuce, neither K nor pH level consistently affected tipburn incidence. No tipburn was observed in `Grand Rapids'. Solution pH generally did not affect concentration of total N and NO3-N in lettuce tissue. Increasing the pH increased K concentration and resulted in increased proportions of K compared to Mg or Ca. Although the influence of solution pH on P, Ca, and Mg concentration was significant, nutrient accumulation differences were not reflected in lettuce fresh-weight differences. The influence of K solution concentration and pH on lettuce yield was not significant. Tipburn incidence in NIT-produced lettuce appears to be primarily affected by environmental conditions maintained during greenhouse growth.

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Experiments were conducted to evaluate the effect of incorporated hydrogel amendments to a soilless growth medium on ammonium, nitrate, and water retention and tomato (Lycopersicon esculentum Mill.) seedling growth. HydroSource and Agri-gel were incorporated into a 1 peat: 1 perlite: 1 vermiculite soilless medium at rates of 1, 2, or 3 g·liter-1 with 0.88 g of ammonium nitrate fertilizer. Water retention by the growth medium increased linearly with gel application; HydroSource generally was more effective than Agri-gel. Between 90% and 96% of the applied nitrate-N was recovered in the resulting leachate of the gel-amended media, while 33% to 55% of the ammonium-N was recovered. Nitrate-N and ammonium-N retention was higher when 3 g·liter-1 of either gel was added to the growth medium than when lower amounts or no gel was added. Gel amendment did not affect tomato seedling growth. Total foliar N concentration in tomato leaves was significantly higher in the HydroSource treatments than in the control or Agri-gel treatments.

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