| In order to respond to the zero-growth demand for chemical fertilizers,reduce environmental pollution,and develop green and sustainable agriculture,the application of organic fertilizers to replace chemical nitrogen fertilizers is being fully promoted.However,due to the diversity of soil types and crop varieties,it is not easy to accurately determine the substitution of organic fertilizers used to replace nitrogen fertilizers safely in different soil types and crop systems.And due to the relative lack of systematic studies on the effects of the partial substitution of organic fertilizers for chemical nitrogen fertilizers on soil quality,yield and safety quality of lettuce on different types of soil,a pot experiment of lettuce with organic fertilizers partially substituted for chemical nitrogen fertilizers in different ratios was conducted in 6typical soil types in Zhejiang Province,and a field lettuce cultivation verification test with organic fertilizers partially substituted for chemical nitrogen fertilizers in different ratios on diluvial gritty loamy paddy soil were studied.Then,from the dry farming system to the paddy field planting system,a two-year(2019-2020)rice planting field trial of organic fertilizers partially substituted for chemical nitrogen fertilizers in different ratios on the soil types of Diluvial gritty loamy paddy soil was carried out.In these studies,we explored the effects of organic fertilizers partially substituted for chemical nitrogen fertilizers in different ratios on soil environmental quality,crop yields and quality safety,and combined with multiple linear regression and soil environmental static capacity models,and finally clarified the safe substitution ratio of organic fertilizer for planting lettuce and rice and the static capacity of soil environment.The main results were as follows:(1)Through the lettuce pot experiment of organic fertilizers partially substituted for chemical nitrogen fertilizers in different ratios on 6 typical soil types,the results showed that partial substitution of chemical nitrogen fertilizer by organic fertilizer increased soil total nitrogen and soil organic matter(except fluvio-marine yellow loamy soil)content,and significantly increased the yield of lettuce(P<0.05).And the accumulation of heavy metals in soil and the shoot of lettuce differs greatly in different soil types,which increased the content of Cd in the paddy field on redeposit of red soil,diluvial gritty loamy paddy soil and blue clayey paddy soi,but significantly decreased the Cd content in fluvio-marine yellow loamy soil(P<0.05),while significantly increased the As content in it(P<0.05).The Cd content in shoot of lettuce grown in paddy field on desalting clayey polder and diluvial gritty loamy paddy soil was significantly increased(P<0.05),while it in yellow-red soil was significantly decreased(P<0.05).Considering the effects of partial substitution of chemical nitrogen fertilizers by organic fertilizers on soil environmental quality,lettuce yield,and heavy metal content in the shoot of lettuce,for the pot experiment with lettuce,the safety application ratios of organic fertilizer on blue clayey paddy soil,yellow-red soil,fluvio-marine yellow loamy soil and paddy field on desalting clayey polder were 20%,20%,30%,and 40%,respectively.In addition,as the number of years of organic fertilizer application increases,the environmental capacity of heavy metals in the soil decreases.Therefore,it is necessary to take corresponding measures to strictly control the application of organic fertilizers to ensure the quality of the soil environment and the quality and safety of agricultural products.(2)The lettuce planting verification test in different ratios of organic fertilizers partially substituted for chemical nitrogen fertilizers showed that soil p H value and soil organic matter content were increased by partial substitution of organic fertilizer(except M1 treatment),but the contents were significantly increased only at 40%application ratio(P<0.05)and each fertilization treatment can increase the soil EC value and total nitrogen content.Fertilization was conducive to the increase of lettuce yield,and the yield is significantly increased when the substitution ratio of organic fertilizer was 10% and 40%(P<0.05).The short-term application of organic fertilizer had no obvious effect on the accumulation of Cd and Cr in the soil,and the content of As and Pb in the soil showed a decreasing trend.The partial substitution of organic fertilizers for nitrogen fertilizers had little effect on the relative abundance of various species at the phylum level of soil bacteria.Among environmental factors,soil As content and soil EC value were significantly related to the relative abundance of soil bacteria from Actinomycota(P<0.05).Treatments M1,M3,and M4 had effects on the composition of soil bacterial community.And Soil EC value and soil Pb content are the main driving factors that affect the organization of soil bacterial communities.The partial substitution of organic fertilizers for nitrogen fertilizers did not significantly affect the Cd and Cr content in the shoots of lettuce,but increased the As and Pb content in the shoots of lettuce.In field planting,the ratio of safety application of organic fertilizer to partial substitution of nitrogen fertilizer in diluvial gritty loamy paddy soil is 40%.However,due to the cadmium pollution in diluvial gritty loamy paddy soil,the short-term application of organic fertilizer has no effect on the accumulation of heavy metals in the soil and the safety of the lettuce,the long-term application effect is uncertain,and it should be further studied.(3)A two-year(2019-2020)field experiment on the partial substitution of chemical nitrogen fertilizer with organic fertilizer with cultivation of rice found that the soil EC value increased significantly(P<0.05)with the increase of the ratio of partial substitution of chemical nitrogen fertilizer with organic fertilizer,and the soil p H did not change significantly.The results showed that the partial substitution of chemical nitrogen fertilizer by organic fertilizer had no significant effect on soil total nitrogen,organic matter,soil Cd,Cr and As content and rice yield(P<0.05).Considering the effects of partial substitution of nitrogen fertilizers with organic fertilizers on soil environmental quality,rice yields and heavy metal content in rice grains,the safety application ratios for the cultivation of Xiushui 14,Yongyou 1540,Jia 67 and Shaonuo 9714 were 10%,20%,30% and 30%,respectively.Among the four rice varieties,the environmental capacity of Cr in the soil and the environmental capacity of safe application of organic fertilizer for Yongyou 1540 are about 1/2 of other varieties.Therefore,when planting Yongyou 1540 rice,it is necessary to strictly control the application amount and application period of organic fertilizer. |
