The production of the American lettuce type in greenhouse conditions using irrigation and fertilization, may contribute for the yield increase and expansion of the culture in the region of Lavras - MG, Brazil. In a greenhouse model chapel was carried out an experiment with the objective of evaluating the effects of irrigation frequencies and potassium doses on the yield of the American lettuce and the water use efficiency. The experiment was composed by the following treatments of irrigation frequency: (P1) - daily irrigation; (P2) _ every other day irrigation; (P3) - three in three days irrigation, and (P4) - four in four days irrigation. In the split plots four doses of potassium chloride (60% of K2O) were applied, by fertigation: (D1) - 100 kg KCl ha-1; (D2) - 150 kg KCl ha-1; (D3) - 200 kg KCl ha-1, and (D4) - 250 kg KCl ha-1. The variables evaluated were lettuce productivity in tons for hectare and water efficiency use, that is, the productivity for mm of water applied. It was possible to conclude that the highest productivity (44,06 t ha-1) was obtained with the dose of the 119,36 kg of K2O ha-1; the irrigation management for the American lettuce culture, in greenhouse conditions of Lavras can be carried out in irrigation interval of four days. The treatments with higher irrigation intervals presented greater water use efficiency.
irrigation; fertigation; water management
