| Nearly half of the irrigated surface in the world is seriously affected by salinity and/or secondary alkalinity. In China, salinity is also an increasing serious social problem. In particular, in coastal plain lie to our country's north areas, seawater intrusion into the groundwater due to excessive withdrawals, cause increasing salinity of both groundwater resource and soil. Lack of freshwater resource has been one of the key limiting factors for sustaining development of local society and economy. Irrigation with seawater may be a feasible resolvent in present position.My experiment can mostly include two sections. In the Nanjing Agriculture University's experimental greenhouse, one section was studying the effects of freshwater (control), 20% seawater and 40% seawater on growth rate, oxidative metabolism, activity of protection enzyme, photosynthesis etc of sunflower seedlings leaves; In the other section, oleic sunflowers (Helianthus annuus L.) G101, a salt-tolerant economic plant, were irrigated with freshwater, 20% seawater, 40%, seawater 60% seawater and 80% seawater in the area of Laizhou, Shandong province where seawater intrusion was very serious. The main aims were to discuss the feasibility of irrigation with different diluent proportion of seawater and freshwater, and find the appropriate diluent proportion which can be applied in fact plant production. These primary growth indexes, ionic distribution, yield and mechanism of salinity migration were investigated during the course of Jul 20, 2002 to Oct27, 2002. The result show as the followers:To the aquaculture experiment carried out in greenhouse, the sunflower seedlings growth of roots and shoots were remarkably restrainted when treated by 40% seawater, but at the same time, 20% seawater promoted the growth of roots and increased the ratio of roots/shoots. Sunflower seedlings leaves also had great ability of membrane reconstruction because their self-adjusting mechanism could be motivated rapidly when stressed by salinity. Seawater is a compound saline system with abundant inorganic ions, microelement and some other organic matter, and more superior in simulating the field agricultural production to single salt such as NaCl, Na2COs and so on. 40% seawater also restrainted the photosynthesis of sunflower seedlings leaves. However, 20% seawater could promote the efficiency of photosynthesis and the growth of roots, for the photosynthate was transported from leaves to roots firstly.when treated by 0-40% seawater, the oleic sunflowers could maintain high Ca2+. Mg2+ content and the K+ selective transportation from roots to flower discs also was promoted. The great mass of Na+ was accumulated in the roots, just reverse to K+ content, and only a little was transported to leaves and flower discs. The mostly growth indexes of oleic sunflowers in early florescence, when treated by 20% seawater, were not significantly difference with that treated by freshwater (p=0.95). And the economical yield of oleic sunflower seeds was almost identical with that in control treatment. In a word, under our experimental conditions of rainfall, soil, plant, irrigation times, irrigation ration etc, 40% seawater was the critical irrigated water concentration mixed by seawater and freshwater. Therefore, we can safely make use of local saline groundwater (about 10% seawater to 20% seawater) or diluent marine culture wastewater (about 50% seawater) to irrigate oleic sunflower G101 in this coastal plain area and save considerable freshwater, realizing the unification of society, economy and environment finally.Distribution and migration of Na+,Cl-, Ca2+, Mg2+, K+ in 0~40cm soil irrigated by seawater were investigated, to attain the most fitting irrigation requirement. The results showed that salinity was accumulated conspicuous in 0~40cm soil layer and would broughton secondary salinization when the seawater irrigation concentration was excess by 60%; When by 40% concentration, slight content of salinity would be residued and some agricultural measure...
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