The Effect Of Irrigation With Swine Wastewater On Heavy Metals (Zn, Cu, As) In Soil

With the serious shortage of agricultural irrigation water in China, water resources has become an important factor to restrict agricultural development. Sewage contains N, P, K, Cu, Zn, and other nutritional elements which crops can absorb and utilize. After properly treatment, sewage has become one of the important irrigation water sources to relief the scarcity, while the water-saving effect is significant with additional fertilizer. Because sewage contains heavy metals, non-metallic, toxic substances, inorganic materials e.tc, the harm on soil, groundwater and crop quality caused by non-scientific wastewater irrigation has been caused for concern.The field trial was conducted from September, 2007 to September, 2008, in Yang Liuqing Town, Xiqing district, Tianjin, China. And the experimental materials ware winter-wheat and Summer-maize, which were main crops in North China. There were 4 types irrigation water sources (raw water, effluent of anaerobic tank, effluent of ecological pond and groundwater). There were 8 treatments and each treatment had 3 experimental plots. We set three irrigation amounts of anaerobic effluent,which were: 830m³/hm², 500 m³/hm² and 160 m³/hm²; We also set three types treated swine wastewater (Origin, Anaerobic, Eco-ponds) mix with groundwater of 1:5 scale, and the irrigation amount was 830m³/hm² and another treatment was anaerobic water mix with groundwater of 1:1 scale, and the irrigation amount was 830m³/hm²; The irrigation amount of the treatment witch was irrigated with groundwater was 830m³/hm².Through field trial we tried to find the effect of heavy metals (T-Zn, T-Cu, T-As, B-Zn, B-Cu, B-As) irrigated by swine wastewater in surface soil (0-20cm layer), and the vertical distribution characteristic of the heavy metals (T-Zn, T-Cu, T-As, B-Zn, B-Cu, B-As) in the soil profile with a depth of 100 cm.The results showed that:1) After two crop growing seasons of winter-wheat and summer maize, the T-Zn, T-Cu, T-As contents of each treatment had no significant differences, except for the T_ori:gw1:5. While the B-Zn, B-Cu, B-As contents of each treatment had no significant differences by each other. T-Zn, B-Zn, T-Cu, B-Cu, T-As, B-As contents of T_Hanae, T_Manae, T_Lanae, T_ori:gw1:5, T_anae:gw1:5, T_eco:gw1:5, T_anae:gw1:1 in surface soil layer (0-20cm) increased compared with Tgw basically. There was a trend that with the greater amount of irrigation water, the higher heavy metal concentration in swine wastewater, the greater input of heavy metal, the heavy metal contents in surface soil was higher. The T-Zn, B-Zn, T-Cu, B-Cu, T-As, B-As contents of T_ori:gw1:5 and T_Hanae was the highest generally. The heavy metal contents of T_eco:gw1:5 was the lowest. The heavy metal contents of each treatment had an increasing trend. Long-term swine wastewater irrigation could increase the heavy metal pollution risks of soil.2) After two crop growing seasons of winter wheat- summer maize, T-Zn, T-Cu, T-As, B-Zn, B-Cu and B-As contents in soil (0-100cm) presented the same longitudinal distribution, namely the heavy metal content in 0-20cm soil layer was highest, with the increasing of depth of soil, the heavy metal content reduced, while the heavy metal contenr of 80-100 cm soil layer also increased, this may be related to the physical and chemical properties of soil. The heavy metal contents of each treatment in 0-20cm soil layer increased compared with Tgw, the heavy metal contents of T_ori:gw1:5 and T_Hanae also had an increasing trend. Long-term swine wastewater irrigation could increase the heavy metal pollution risk of soil and groundwater.3) The conclusion was that: the proper irrigation water amount was middle amount (500m³/hm²) effluent of anaerobic tank and the proper irrigation source was eco-pond water. On this condition, we can obtain high quality and yield of winter wheat, summer maize, while reduce heavy metal pollution of soil environment effectively.