Effect of irrigation and drainage engineering control on improvement of soil salinity in Tianjin

Abstract: Since the 1950s, China has begun to develop irrigation and water conservation project construction to control the saline-alkali soil. However, there are few reports about the effect on soil salinity improvement resulting from large-scale farmland and water conservancy engineering construction. So to check the effect of irrigation and drainage engineering on soil salinity improvement action, this research took Tianjin, in which the saline-alkali soil area is wide, as an example for the discussion and analysis of the improvement effect on soil salinity of farmland and water conservancy engineering construction. This study illustrated the relationship of interaction and change between farmland and water conservancy engineering construction and soil salinity improvement from the formation environment of saline-alkali soil and salinity change based on ArcGIS9.3 and laboratory analyses. The results showed that with the constant improvement of irrigation and drainage engineering construction and facilities, during the period from 1982 to 2002, the area where the salinity soil was easy to form reduced from 65.55×104 hm2 to 54.60×104 hm2, which was down by up to the percentage of 9.96%. During the period from 1982 to 2008, the salinity soil area reduced from 49.40×104 hm2 to 32.42×104 hm2, in the meantime, 18.76% of the saline alkali soil had completed the desalinization with other areas whose soil salinity degree was also reduced substantially further. During the period from 2006 to 2010, newly increased cultivated land which originally belonged to saline-alkali land had decreased by 2.54×104 hm2, at the same time the area that the irrigation canals and ditches had exchanged into the cultivated land was up to 1.11×104 hm2. As for the profiles (0 -60 cm) of the coastal saline-alkali land, more than 69.81% of the cultivated land was under the slight salinity which had a perfect drainage system. On the contrary, more than 40% of the wasteland was the solonchak, with only 14.85% of it under the slight salinity whose drainage system was relatively poorer. During the period from 1982 to 2005, the soil which was easy to undergo salinization was reduced from 65.55×104 hm2 to 49.60×104 hm2. In addition, the spatial distribution pattern of the reduced area was in accordance with the area where the degree of soil salinity had lowered. In conclusion, irrigation and water conservancy projects control the saline-alkali by decreasing the area of salinity soil, lowering the salinization rank, and reducing the newly increased cultivated land that originally belonged to saline-alkali soil by means of improving the forming environment of the saline-alkali soil. For some areas that had completed the desalinization, there were almost no floods and they were crisscrossed by irrigation canals and ditches in where the original abandoned and dilapidated irrigation canals and ditches should be classified into the reserved land resources suitable for cultivation. Through the scientific planning of irrigation and water conservancy engineering and competitive land consolidation, the cultivated lands that are cut to pieces can connect with each other and improve farmland scale, which relieves the pressure of the protection and requisition-compensation balance of cultivated land.