Abstract:

Nearly half the irrigated fields in the world are becoming saline and alkaline. Soil salinization is becoming a serious problem in China, especially in the seashore plain of north China where there is a highly developed industrial and agricultural economy and a huge population. With the high speed of industrial development and rapidly increasing population, groundwater overuse is leading to an influx of seawater and further expediting salinization of freshwater resources and soil. Lack of freshwater is a main factor restricting social and economic development in the seashore plain of north China.
Irrigation of crops with diluted seawater has been proposed as a way to conserve freshwater supplies. This experiment was conducted to study the characteristics and effects of irrigation with diluted seawater on a salt tolerant economic plant and provide recommendations for saline water irrigation in these drought/semi-drought seashore areas. `Oleic sunflower G101' (Helianthus annuus), a salt-tolerant economic plant, was irrigated with different proportions of diluted seawater in the Laizhou, Shandong Province, where seawater intrusion is a very serious problem. The effects of irrigation with diluted seawater on various growth indices, the accumulation and distribution of ions in the plant, and total yields of `G101' planted under local rainfall conditions were investigated during two growing seasons, 2002 (drought year) and 2003 (wet year). The sunflower was irrigated twice during the growing season, one at early bud and the other at early florescence. The results showed that 1) In both the drought year (2002) and the wet year (2003), a 40% seawater irrigation solution was a safe dilution ensuring economic yields for the 100 day growth period of `G101'. During the drought year, `G101' seed yields decreased significantly when irrigated with 40% seawater or greater, while there were no differences in seed yields in the wet year when irrigated with 40% or 60% seawater. Thus, irrigation with a 40% seawater solution was economically feasible. 2) During the drought year, most growth indices of oleic sunflowers when treated with 20% seawater were not significantly different with that irrigated with freshwater (p=0.95), except for stem thickness and disc fresh weight during early florescence. However, in the wet year, all measured growth indices were not significantly different from the freshwater treatment when treated with up to 40% seawater (p=0.95). 3) When irrigated with 0-40% seawater, Ca²⁺ and Mg²⁺ homeostasis was maintained in the leaves and root K⁺ selective ion transport to the disc was strong. Accumulation of Na⁺ was mainly in the root and stem, while Na⁺ concentrations in the leaves and disc were lower. Chloride content was the greatest in the stem as compared to other parts of the oleic sunflowers.

Key words: Rainfall, Seawater irrigation, Oleic sunflower, Morphologist, Yield