Salt Distribution And Accumulation In Soil-Crop System With Saline Water By Under-film Drip Irrigation

The shortage of water resources has been an important restraint factor for agriculture development in arid and semiarid areas. Xinjiang as an extreme arid region, agriculture development relied on irrigation. The scarcity of fresh water makes saline water a valuable alternative water source for irrigation. Saline water has an agricultural potential but it is necessary to develop special management procedures to obtain maximum yield and high product quality. Drip irrigation under mulch film could save water and control salt accumulation. It is an effective way for utilization of saline water in arid and semiarid areas. Researches on irrigation with saline water through the way of drip irrigation under mulch film were not enough. A field experiment was conducted for three growing seasons (2004~2006) to evaluate the character of accumulation and distribution of salt in soil-crop systems which consequently affect the growth and yield of crop. The aim of present work is to estimate the characters of salt distribution and accumulation under surface and subsurface drip irrigation in soil-crop system and which consequently affect the growth and yield of cotton. The results obtained provide a promising option for develop saline water irrigation in arid and semiarid areas. Major finds as follows:1. In arid region, the soil water content of under-film drip irrigated farmland influenced by irrigation demands and evapotranspiration. The difference of the dynamic varieties of soil water content due to the location of water emitters between surface and subsurface drip irrigation. During the growing season, the soil salinity influenced by the condition of soil water content, and changed in accord with the soil water. Soil water content increased with increased irrigation water salinity levels in both surface and subsurface drip irrigationSoil salt accumulated with the continuing of applying saline water and increasing of the water saline concentration of irrigation water by under-film drip irrigation. Soil salt built up at topsoil in surface drip irrigation and accumulated significantly above the drip lateral layer in subsurface drip irrigation. Soil salt was leached to deeper layer in subsurface drip irrigation than that in surface drip irrigation. The average soil salinity in 0~100 cm soil profile was increased with increased irrigation water salinity levels in both surface and subsurface drip irrigation treatments. Soil salinity increased with increased irrigation water salinity levels in under-film drip irrigation. Those results suggested that salt accumulation increased significantly with saline water irrigation applied in arid region. Depending on water salinity, irrigation scheduling and seasonal salt load, salt can accumulate in the soil profile. The secondary saline leaching and drainage is necessary for maintaining agricultural production.2. Applying saline water continuously for irrigation through surface and subsurface drip irrigation, nitrogen and phosphorus concentration decreased and did not influenced by water salinity level and irrigation methods. K+ concentration of different organs of cotton changed steadily and increased with water salinity level; Cl- and Ca2+ mainly accumulated in shoots, accordingly, Cl- and Ca2+ concentration rise, and increased significantly with increasing of water salinity; Na+ concentration increased rapidly from boll formation stage, but Na+ concentration did not affected by water salinity.K+, Cl- and Ca2+ concentration of cotton increased significantly with water salinity which did not impacted Na+ concentration. Irrigation methods had no effects on K+, Cl- and Na+ concentration, but affected Ca2+concentration significantly. Ca2+concentration under surface drip irrigation higher than that under subsurface drip irrigation. Most of slat ions (K+, Cl- and Ca2+) uptaked by cotton accumulated in stems and leaves, but not buds and bolls. The results indicated that ion compartmentation in cotton which maintained the balance of ion of cotton could improve the salt tolerance. The order of K+/Na+ was: cottonseed>shell>root> stem>leave. The result indicated that K+ was selective uptake by cotton, and then transported to stems and leaves in order to maintain high K+/Na+ which is essential for ion balance in the plant, and becomes critical to plant salt-tolerance.3. Dry matter weight of cotton decreased significantly with increasing of water salinity level. Water salinity and irrigation methods had no effect on root dry matter weight, but the vertical distribution of root dry matter weight in soil influenced by water salinity. Irrigation with saline water reduced root dry matter weight at 0~30 cm depth, and root dry matter at 30~60 cm depth increased with increasing of water salinity level.Continuous saline water irrigation reduced the number of available bolls significantly and affected seed cotton yield, but did not decreased boll weight. The yield reduction was due to a reduction in the number of available bolls. The yield observed with the subsurface drip irrigation was higher than that with surface drip irrigation, while the effect of the irrigation system was less pronounced in subsurface drip irrigation treatment than in surface drip irrigation. The results indicated that for cotton yield, saline water irrigated by subsurface drip irrigation was better than surface drip irrigation.