Factors Affecting to Nitrate Accumulation in Lettuces of Hydroponically Farms Grown under Close and Open Greenhouses
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Abstract
Leaf vegetables can accumulate nitrate. Too much nitrate consumption is harmful to human. The objective of this research is to study nitrate accumulation in three salad vegetable varieties; green oak, red oak and cos, in hydroponic farms under close and open systems during winter and summer. Solution fertilizer factors; electrical conductivity (EC), pH and nitrate concentration in fertilizer were examined and weather condition factors; temperature, humidity and light intensity were recorded. The result shows that 36-day cos had a highest nitrate accumulation of 2,342.6 mg/kg FW under close system in summer and red oak and green oak in open system in summer (1,985.6 and 1,879.0 mg/kg FW, respectively). Factors affecting nitrate accumulation in vegetables were analyzed by using stepwise regression analysis. In winter, the factors affecting nitrate accumulation in green oak, red oak and cos were sample collecting date, age, pH, greenhouse system, fresh weight and EC value. The stepwise equations were able to predict nitrate accumulation in green oak, red oak, and cos correctly 80, 89 and 77%, respectively. In summer, the factors affecting nitrate accumulation in green oak are humidity and pH value. The equations can predict as correctly as 70%. In conclusion, adjustment of pH (5.5-7.0), humidity (63-74%), and decrease of adding fertilizer on a-week pre-harvesting period could reduce nitrate accumulation in vegetables.
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King Mongkut's Agricultural Journal
References
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