Effect of Deficit Irrigation on Pigment Content, Photosynthesis, Growth, and Yield of Cabbage

Water is an increasingly scarce resource in Northwestern U.S. agricultural region. Deficit irrigation strategy, a practice that deliberately allow crops to sustain some degree of water deficit with no or marginal yield loss, has the potential to increase water use efficiency and save water. Field experiments were conducted in the Wintergarden of Texas to investigate the responses of leaf pigments, gas exchange, plant growth, and yield of cabbage (Brassica oleracea L. cv. Pennant) to deficit irrigation. Each fall, cabbage was seeded and thinned in the field at 0.90 m between rows with two lines per row and 0.30 m between plants. Irrigation was applied with subsurface drip at 100%, 75% and 50% of evapotranspiration (ETc) in the first season and 100% and 70% of ETc in the second season. Although chlorophyll index were marginally and temporally increased under deficit irrigation, the pigment (chlorophyll a, b, a+b, and carotenoids) contents were not affected by deficit irrigation based on either leaf area or dry weight. Deficit irrigation at 50% ETc reduced leaf area per plant, and during late development it marginally reduced leaf fresh weight and increased leaf relative water content and specific leaf area. The plant height and width were temporarily reduced while the photosynthetic rate and transpiration decreased under 50% ETc irrigation. Deficit irrigation reduced both head size (height and width) and fresh weight, resulting in decreases in marketable and total yield.  However, the difference in head dry weight among the three irrigation rates was not significant, suggesting most of the increases in yield under 100% ETc irrigation are just water content. These results suggest that deficit irrigation (75% ETc) could save water though moderate decreases in yield and head size is expected.