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Fig. 1. Distribution and irrigated history of soil sampling sites in the Shenfu irrigation area. Site A is located at the upstream area and was changed to ground water irrigation more than 30 yr ago. Site B is located at the upstream area and was changed to upland 30 yr ago. Site C is located at the third plot of the branch channel in the upstream area and has been irrigated by wastewater. Site D is located at the sixth plot of the branch channel in the upstream area and has been irrigated by wastewater. Site E is located at the ninth plot of the branch channel in the upstream area and has been irrigated by wastewater. Site F is located at the upper reach of the mid-stream area and has been irrigated by wastewater. Site G is located at the middle reach of the mid-stream area and has been irrigated by wastewater. Site H is located at the lower reach of the mid-stream area and has been irrigated by wastewater. Site I is located at the upper reach of the downstream area and was changed to ground water irrigation 10 yr ago. Site J is located at the middle reach of the downstream area and has been irrigated by wastewater. Site K is located at the lower reach of the downstream area and was changed to upland 10 yr ago. Site L is located at the lower reach of the downstream area and was changed to ground water irrigation 10 yr ago. Site M is located at the end of the channel and was changed to ground water irrigation 20 yr ago.
