Safety Application Of Organic Manure Partial Substitution Chemical Nitrogen Fertilizer And Soil Environmental Capacity

A large number of chemical fertilizer utilization and irrational fertilization structure have caused severe waste of resources and environmental pollution.As the development of intensive livestock farming,there are 3.8 billion tons of livestock and poultry wastes in China annually.Organic fertilizer can improve soil properties and soil fertility,but the concentration of toxic pollutant is relatively high.Excessive application of organic fertilizer is bound to cause the risk of environmental pollution.Therefore,this research investigated the safety dosage of organic fertilizer partial substitution for chemical fertilizer and its impact on the soil environmental quality.The three representative soil types(silt-clayey yellow mettled paddy soil,powdery-loamy paddy soil and hapl fluvo-aquic loamy soil)were chosed in the pot experiment with lettuce and the three rice cultivars(Yongyou 17,Yongyou 538 and Xiushui 134)were selected in the plot experiment with rice.There are six different treatments:no fertilizer in the pot experiment with lettuce(CK)and 225 kg N ha-1 local conventional dosage of chemical nitrogen fertilizer in the plot experiment with rice(CK),180 kg N ha-1 nitrogen fertilizer(F),organic fertilizer substituted 10%of chemical nitrogen fertilizer(M1),organic fertilizer substituted 20%of chemical nitrogen fertilizer(M2),organic fertilizer substituted 30%of chemical nitrogen fertilizer(M3),and organic fertilizer substituted 40%of chemical nitrogen fertilizer(M4).In addition,soil heavy metal threshold value and environmental capacity for safety application of organic fertilizer were predicted by multiple liner regression model and soil environmental statistics model.The results are as followed:(1)Results showed the best substitution ratios of organic fertilizer for chemical nitrogen fertilizer for different soils were significant difference in the pot experiment with lettuce.Soil organic matter(SOM)and the yield of lettuce increased markedly when organic fertilizer partial substitution for chemical nitrogen fertilizer,but the concentration of heavy metals in soil and lettuce increased significantly at the same time.In conclusion,the optimal organic fertilizer substitution ratios on silt-clayey yellow mettled paddy soil,powdery-loamy paddy soil and hapl fluvo-aquic loamy soil are 30%,20%and 10%,respectively.(2)The optimal substitution ratios of organic fertilizer for chemical nitrogen fertilizer for planting different rice cultivars were significant difference in the plot experiment with rice.When Yongyou 17(YY17)harvested,Soil pH(H2O)decreased after organic fertilizer partial substitution for chemical nitrogen fertilizer,and soil Cd and Cu concentrations exceeded the risk screening values significantly.Meanwhile,Cd concentration in brown rice was out of the limit of National Food Safety Standard the Contamination Limit in Food(GB 2762-2017).When Xiushui 134(XS134)and Yongyou 538(YY538)harvested,soil pH improved and electrical conductivity(EC)reduced significantly when the substitution ratio was 30%and 40%.Soil Cd and Cu concentration were higher than the risk screening values,and the concentration of As in XS134 and YY538 brown rice was out of the limits when the substitution ratio was 30%and 10%.To sum up,although the concentration of soil Cd and Cu in research site exceed the risk screening values(slight pollution),organic fertilizer partial substitution for chemical nitrogen fertilizer still can be applied when XS134 and YY538 planted,and the organic fertilizer substitution ratio within 30%and 10%are optimal respectively.(3)Soil heavy metal threshold values and the environmental capacity were predicted by multiple liner regression models and soil environmental statistics model in the pot experiment with lettuce and the plot experiment with rice.The soil environmental capacity for heavy metals and safety application of organic fertilizer decreased as organic fertilizer application year increase.Therefore,application year of organic fertilizer should be controlled strictly to ensure soil environmental quality.