The Influence Of Pig-manure And Passivator Additions On The Transport And Transformation Of Copper In The Paddy Soil-Crop System

In recent years, with the vigorous development of livestock breeding, the withdrawal of the agricultural organic waste also increased remarkably, drawing more and more people's attention to the importance of the poultry and livestock's excrement to the agricultural production. It was discovered that heavy metal contents in most agricultural organic wastes have exceeded the allowed limits with an incresing tendency, which would pose risks to environment and ecology accordingly.Jiaxing County was selected in this study, where pig manure has been employed in the paddy soils for long time. This study simulated the effects of pig manure on the transport and transformation of copper with various levels in soil-crop system. Meanwhile, three kinds of amendments, pulverized coal ash, bentonite and apatite, were employed to study the passivating action on the copper in the soil. This study would put insight into the effects of long-term employment of agricultural organic wastes into soil on ecological environment, crop growth, and food security. This study would provide the theoretical basis for the reasonable employment of agricultural organic wastes and the amendment of contaminated soils.The results of this study mainly include the following:the employment of pig manure with high copper content can increase the copper content in the soil, the content of available copper in the soil increased with the increase of the copper content in the pig manure; the pig manure with highest copper content did not make the biggest effects on crop growth. In the potted experiment, the copper content in rice was highest after the application of pig manure with a 400 mg.kg-1 copper content,which achieving the national standard limit of copper content in grain, and would pose hazards to human health. The three kinds of amendments, pulverized coal ash, bentonite and apatite, can have influence on the characteristic of paddy soils. In wheat potted experiment, three kinds of amendments could enhance the soil pH. However, they could not increase the soil pH in the last stage of the rice potted experiment.The influence of passivating action of the amendments to the available copper content in the soil was obvious. The employment of amendments could reduce the available copper content in the soil, but in the later period of potted experiment, the employment of amendments did not significantly affect the available copper content in the soil, possibly because of the weak endurance ability of amendments. At the same time, there existed good relevance between paddy soil pH and the soil available copper content. Along with elevation of soil pH, the adsorptive capacity of soil to copper was strengthened, resulting in the precipitation of copper in the soil, which means that the available copper content in soil decreased. Of three kinds of amendments, the pulverized coal ash with high pH is best for the passivating action on the available copper content in soil.The toxic hazard of high copper content on the wheat is very serious. Simultaneously it was harmful for the wheat grow in the paddy soil. With a treatment of 400 mg.kg"1 copper content, the wheat experienced underdevelopment, even to death. But at the same time we also discovered that the employment of 2.5% bentonite could help the wheat grow well, and the employment of pulverized coal ash and apatite could also enhance the growth of wheat to some extent. So obviously the amendments can promote the crop growth. Under the cultivation of wheat-rice crop rotation, the employment of amendments had some enhancement, but not significantly, on the crop production such as the tiller numbers, the numbers of productive ear, plant heights and the weights of one thousand seeds.Compared with 200 mg.kg"1 copper treatment, the effects of the amendments on the crop growth condition in the 400 mg.kg"1 copper treatment were bigger. So with the increase of the copper content in the soil, the influence to the growth characteristics of rice was bigger, with more obvious passivating action of amendments. The copper content in the root, stem and grain increased with the accretion of copper content in the soil. For crops, the order of absorption ability of different tissues to copper was:root>stem>grain. The employment of three kinds of amendments in the copper treatment soil was able to reduce the copper content in the stem and grain. This effect is more remarkable in the high concentration copper treatment.The employment of amendments could improve the rhizosphere environment of wheat potted soil, enhance the absorption of nutrition and moisture to the wheat root, promote the transport of copper to the wheat root surface, increase the root adsorptive capacity of available copper, and cause the copper concentration in the root with the rise of copper content in wheat root. The employment of the amendments in the potted experiment could reduce the copper content in the root of rice. The treatment with 2.5% pulverized coal ash could significantly reduce the copper content in the root of rice.The copper mainly concentrated in the root of rice. The copper content in the stem increased with the increasing available copper content. But the increasing rate gradually reduced. Relative research indicated that the ability of copper transport to the overground tissues was weak with the high copper content treatment. In the potted experiment of the wheat-rice crop rotation cultivation, the copper contents in the grains were all below 10mg.kg-1, which would not cause negative problems to food safety according to the food sanitation standard (GB14935-1994) in China..