Abstract: 【Objective】Returning organic manure into field soil is one of the important ways to achieve cyclic utilization of waste resources. A large number of studies proved that pig manure could improve soil fertility and crop yield. However, long-term pig manure amendments also would lead heavy metal elements such as Cu, Zn and As accumulation in soil, due to the feed additive are widely used which contain high content of heavy metals, and then threat the soil quality and food safety. Therefore, the effect of long-term amendments of pig manure on environment carrying capacity was conducted in red paddy field. 【Method】The changes of rice grain yield and the contents of soil organic carbon and heavy metals such as Cu, Zn, Cr and As were investigated based on samples from the long-term field experiment with continuously pig manure amended since 1981 (it contained samples of initial soil, 5, 16, 22, and 30 years fertilization), in order to assess the environment carrying capacities of red paddy field regarding to the side effects of pig manure amendments based on the Grade Ⅱ thresholds according to the national soil environmental quality standard (GB15618-1995). 【Result】The results showed that long-term amendments of pig manure significantly increased both rice yield and soil organic carbon content by 10.3%-12.0% and 18.8%-23.7%, respectively, compared with long-term chemical fertilizer (NPK) amendment. Soil pH value for both OM1 and OM2 treatments (i.e. pig manure amendments in the early and late rice season) after three decades compared to the initial soil pH before the experiment set up. This indicated that long-term pig manure could not alleviate soil acid status. Moreover, pig manure amendments also significantly increased the contents of heavy metals such as Cu, Zn, Cr and As in soil. After continuous amendments for three decades, the contents of Cu, Zn, Cr and As were increased by 72.0%-82.6%, 29.1%-55.2%, 194.8%-262.6% and 90.5%-192.7%, respectively, compared with the chemical fertilizer (NPK) treatment, but still below the Grade Ⅱ thresholds according to the national soil environmental quality standard (GB15618—1995). Based on the present amendment rate of pig manure, the contents of heavy metal measured in soil would exceed the Grade Ⅱ thresholds if continuously amended pig manure for 22, 67, 44 and 14 years, respectively. From a different perspective, considering the 50-year continuously amended pig manure as an essential prerequisite, the amendment rate of pig manure should not exceed 6.40 t•hm-2•a-1 to ensure the soil heavy metal contents of Cu, Zn, Cr and As is still below the Grade Ⅱ thresholds. 【Conclusion】Long-term amendments of pig manure unambiguously increased both the rice grain production and soil fertility development. Meanwhile, it should not be neglected that the accumulation of heavy metal would lead to environmental pollution. Taking together, the results highlight that tradeoffs between crop production, soil fertility and ecological benefits and environmental carrying capacities subjected to long-term pig manure amendments could help the sustainable development of agriculture and the improvement of the ecological environment in red paddy field.

Key words: red paddy soil , pig manure , heavy metals , carrying capacities