The Response of Summer Lettuce to Irrigation at Different Stages of Growth

The greatest growth response of summer cabbage lettuce to irrigation was found to occur when the soil was restored to field capacity about one week before the first harvest; at this time the ground cover was almost complete and the mean fresh weight was increasing rapidly.Irrigation at 3 weeks or at 5½ weeks after sowing gave only a small increase in the mean fresh weight at harvest, but the crop was slightly earlier. Unirrigated lettuce and those irrigated once only, after 3 weeks, were of poor quality and had a significantly lower moisture content than the good-quality lettuce obtained by irrigating 5½ weeks after sowing or later.