Effects of nitrogen and humic acid applications on the head weight, nutrient and nitrate contents in lettuce
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This study was conducted to investigate the effects of increasing amounts of nitrogen and humic acid applications on the head weight, nutrient and nitrate content in lettuce. Nitrogen doses of 0, 250, 500, 750 mg kg - 1 and humic acid doses of 0, 500, 1000, 2000 mg kg - 1 were applied into pots placed in a growth chamber. Nitrogen application significantly affected the head weight and nitrate, nitrogen, phosphorus, iron, manganese, copper and zinc contents. Humic acid application also significantly affected the head weight, nitrogen, nitrate and phosphorus contents, but also the contents of micronutrients, such as iron, manganese, copper and zinc, were markedly influenced. The combination of nitrogen and humic acids affected nitrogen, phosphorus and zinc contents, but not those of nitrate, copper and the head weight. It was observed that adverse effects of excessive nitrogen application could partly be eliminated by humic acid application.