Effects of different nitrogen and potassium sources on lettuce (Lactuca sativa L.) yield in a sandy soil

Lettuce plants were grown under sandy soil conditions in the private farm of Ahmed Orabi organization, Cairo Governorate Egypt, between 15th November 2009 and 15 January 2010. The experiment was conducted to assess the effects of different nitrogen sources, slow release N (urea-formaldehyde) and fast release N (urea) containing fertilizers at the rates of 0, 60, 90 and 120 kg N ha-1 applied alone or combined with potassium sulphate, on lettuce plant yield. Results indicated that application of different sources of N alone or combined with potassium sulphate gave the highest fresh dry weight per plant and total lettuce yield per hectare compared with the control. The highest dry weight of lettuce was achieved with the combination of urea and potassium sulphate. Although fertilization made with the combination of urea and potassium sulphate resulted in the highest P, K, Zn and Mn contents in lettuce plant, fertilization with urea alone gave the highest N and Fe contents. The lowest content of nitrate in lettuce plants was recorded with the fertilization of urea only or with the combination of urea and potassium sulphate. Application of the combination of urea and potassium sulphate induced the highest protein content in plants. The results indicated that application of urea-formaldehyde as a slow release nitrogen fertilizer solely or combined with potassium sulphate significantly improved yield and yield quality of lettuce plants grown in sandy soil.