Effect of Nitrogen Form and Oxygen Levels in Nutrient Solution on Growth and Some Macronutrients in Hydroponically Grown Lettuce (Lactuca sativa cv. Great leak)

In this study the effect of nitrogen form and different oxygen levels on growth and development and macronutrients concentrations in lettuce plants was investigated. This investigation showed that sole ammonium application caused fresh and dry weight reduction of shoot and root in lettuce plant. But different oxygen levels had no effect on them. Nitrogen concentration of shoot was higher in ammonium treatments compared to nitrate treatment and with increasing of oxygen levels in the presence of ammonium، nitrogen content also increased، although it was not the same in nitrate treatment. Phosphorous concentrations in shoot and root were not affected by any of treatments and their interaction. Ammonium also caused reduction of potassium concentration in shoots، but different oxygen levels and its interaction with nitrogen form had no significant effect on it. Magnesium content of shoot also decreased in the presence of ammonium، although it was not the same in root. With increase of dissolved oxygen level، magnesium content of shoot decreased in ammonium treatment، but in nitrate treatment the concentration of this element was not affected by oxygen levels. It is concluded that probably reduction of potassium and magnesium in ammonium-fed plants has a role in plant growth reduction، and it was also observed that in spite of increase in the concentration of shoot nitrogen and root magnesium with increase of dissolved oxygen level in ammonium treated plants، lettuce growth was not affected by oxygen levels.