Productivity of Vegetable Crops Grown under Shade in Hawaii

Abstract

Waimanalo Long' eggplant (Solanum melonaena L.), 'Kahala' soybean ^Glvcine max (L.) Merrill), 'Jumbo Virginia' peanut (Arachis hvpoaea L.), 'Waimanalo Red' sweet potato flpomea batatas (L.) Lam.), and 'Green Mignonette' semihead lettuce fLactuca sativa L.) were field-grown in two seasons at Waimanalo, Oahu, Hawaii with five artificially produced levels of shade (0, 30, 47, 63, and 73%). Yields and vegetative growth of eggplant, soybean, peanut, and sweet potato were linearly decreased with increasing shade levels. Compared to unshaded controls, yields of semihead lettuce increased significantly from 8100 kg•ha-1 to 13,600 kg•ha-1 by 30% shade in Fall 1986. During Spring 1987, semihead lettuce yields were reduced only slightly from unshaded levels of 22,000 kg•ha-1 by increasing shade up to 47%. Eggplant, soybean and lettuce maintained index leaf areas similar to unshaded controls as shade intensity increased, at the expense of leaf dry weight. By comparison, both leaf area and leaf dry weight of peanut index leaves decreased as shade increased. Leaf area and leaf dry weight of sweet potato did not respond to shading. To further investigate the effects of shade on leafy vegetables, 'Green Mignonette', 'Salinas', 'Parris Island Cos', and 'Amaral 400' lettuce (Lactuca sativa L.), 'WR-55 Days' Chinese cabbage (Brassica raoa L. Pekinensis Group), 'Waianae Strain' green mustard cabbage (Brassica iuncea (L.) Czerniak), 'Tastie Hybrid' head cabbage (Brassica oleracea L. Capitata Group), and an unnamed local selection of bunching onions (Allium ceoa L. Aggregatum Group) were field-grown in two seasons at the same location with the same five artificially produced levels of shade. Yields of cos lettuce, green mustard cabbage, and bunching onions were irresponsive or negatively affected by shade in both seasons. Yield responses of the other crops to shade varied seasonally. Optimum shading of 30 to 47% increased 'Green Mignonette', 'Salinas', and 'Amaral 400' lettuce by 36% and head cabbage and Chinese cabbage yields by 23% and 21 %, respectively, compared to full-sun plots in some trials. Index leaf areas similar to unshaded controls were maintained as shade intensity increased, at the expense of leaf dry weight in all crops except 'Salinas' and 'Parris Island Cos' lettuce. Maximum rates of net photosynthesis (Pn) were attained at about two-thirds of full sunlight (1500 umol • s-1•m-2).