| It is an important measure for the national strategic planning of planting and breeding combined with circular agriculture to absorb livestock manure biogas slurry in farmland.In the past,significant progress has been made in the evaluation of biogas slurry dosage and usage,as well as the effects of heavy metals.However,the previous conclusions of relevant studies are inconsistent yet.This makes it difficult for a long time to decide whether to return biogas slurry to farmland for consumption or treat it in the form of water pollution.One of the important reasons for the differences in the assessment results of the crop yields,ecological and environmental effects of biogas slurry application depends on the production process,pretreatment and application areas of biogas slurry.The coastal area is an important crop production base in China.At the same time,there are also the most concentrated large-scale intensive breeding enterprises in China.Different from decentralized livestock and poultry breeding,intensive enterprises produce a large amount of biogas slurry.However,due to the standardized process of feces collection,fermentation,biogas slurry separation,storage and use,the biogas slurry has stable properties and low pollutant content.Obviously,the promotion of biogas slurry instead of chemical nitrogen fertilizer in coastal farmland is a win-win measure for the sustainable development of regional agriculture with high efficiency and low consumption and to solve the worries of biogas slurry disposal with high cost for large breeding enterprises.However,because the biogas slurry is generally alkaline,the soil p H of coastal farmland is also at a high level,as well as the large amount of biogas slurry and the presence of heavy metals and other pollutants,the promotion and use of biogas slurry in coastal agricultural areas has been hovering and wait-and-see.The impacts of biogas slurry application on crop yield,soil quality and potential ecological environment risks are thus lack of systematic research and assessment.Therefore,a timely and in-depth study on the impact of biogas slurry on crop yield and quality and soil ecological and environmental risks in coastal rice-wheat cropping farmland is a major demand for sustainable,efficient and safe development of regional planting and breeding combined with circular agriculture.In the present dissertation,the rice-wheat cropping farmland in Dongtai,Jiangsu Province were taken as an example,and the field observation was carried out for two consecutive years through the field plot test method with the biogas slurry under the current standardized feces treatment mode of large-scale intensive pig raising enterprises(feces collection-full mixed anaerobic reactor-biogas slurry and biogas residue precipitation separation).The effects of biogas slurry application on crop yield and soil properties were investigated by setting three groups of treatments with different biogas slurry dosages(rice/wheat season dosage were 0/0,250/160,500/320,and 750/480 m~3/ha),biogas slurry substitution for conventional fertilizers(0%,33%,67%,and 100%substitution,total nitrogen application 225/150 kg/ha for rice and wheat,respectively),and the combination of biogas slurry and biochar(0 and 15 t/ha).The risk of heavy metal pollution in soil and crops were analyzed,aiming to define the appropriate biogas slurry dosage and the substitution ratio of chemical nitrogen fertilizer.Further,with the help of the second generation high-throughput sequencing technology,the change of soil bacterial community structure and diversity was studied to evaluate the potential ecological impact of biogas slurry application.At last,a measurement system for the integrated absorptive capacity of livestock and poultry breeding biogas slurry was built to explore the sustainable mechanism of biogas slurry consumption,providing a theoretical basis for the development of biogas slurry consumption in coastal agricultural areas and recycling agriculture based on combination with planting and breeding.The main results and conclusions are following:(1)Biogas slurry substitution of 33%-100%chemical nitrogen fertilizer had no significant effect on rice and wheat yields in the region.This indicates that biogas slurry can completely replace chemical nitrogen fertilizer in rice and wheat fields.When the amount of biogas slurry was0-250 m~3/ha,the rice yield increased from 5404 kg/ha to 7924 kg/ha,and when the amount increased to 500-750 m~3/ha,the yield had a little decrease(7098-7099 kg/ha).In the absence of biochar,when the biogas slurry dosage was 250 m~3/ha,the rice yield arrived to the highest of 6891-8957 kg/ha.In contrast,In the presence of biochar,rice yield was the highest of 7309-8599 kg/ha when applying 500 m~3/ha biogas slurry.When the amount of biogas slurry was 0-480 m~3/ha,the wheat yield increased from 3462 kg/ha to 7663 kg/ha.In addition,the wheat yield was the highest of 7643-8284 kg/ha when applying 480 m~3/ha biogas slurry.(2)There was no significant difference in soil p H of rice and wheat fields when applying biogas slurry.This indicates that the application of alkaline biogas slurry does not cause an increase of soil p H in coastal farmlands.However,biogas slurry application significantly increased the soil EC,which increased with the increasing biogas slurry dosage.Compared with chemical fertilizer,the total replacement of chemical nitrogen fertilizer with biogas slurry significantly increased soil organic carbon and total nitrogen content.The content of total nitrogen and total phosphorus in soil increased with the increase of biogas slurry application amount in the presence of biochar.This shows that the combined use of biochar with biogas slurry helps to improve nutrient utilization and reduce potential non-point source pollution risk.(3)After two years of continuous application of biogas slurry,the total replacement of chemical nitrogen fertilizer had no significant effect on the content of Cu,Zn,Pb and Cd in soils.Compared with CK,when the biogas slurry dosage in rice/wheat season was 250/160 m~3/ha,soil Cu and Zn content did not change significantly,but when the dosage increased to 500/320-750/480m~3/ha,the soil Cu and Zn content increased significantly.The content of Cu in paddy soils increased by 9.7%and 11.1%respectively,under the biogas slurry dosage of 500 m~3/ha and 750m~3/ha.At the same time,the content of Zn in paddy soil increased by 8.3%when applying 500m~3/ha biogas slurry.In contrast,Zn contents in wheat field increased by 42.5%under the biogas slurry dosage of 320 m~3/ha.In addition,biochar addition had no significant effect on the content of Cu,Zn,Pb,Cd.All the content levels were far lower than the limit values of soil quality standards for agricultural land in China,although biogas slurry application increased the content of Cu and Zn in soil.This shows that no worry should be paid on heavy metal risks when applying biogas slurry in rice and wheat fields in coastal areas.(4)The total replacement of chemical nitrogen fertilizer with biogas slurry increased the content of Cu and Zn in rice and wheat grains to 4.07-5.17 mg/kg and 26.2-29.9 mg/kg,with an increase of 9.2%-15.1%and 19.1%-32.3%,respectively.There was no significant changes on the content of Pb and Cd in rice and wheat grains.Compared with no fertilization treatments,when the biogas slurry dosage was 500/320-750/480 m~3/ha,the content of Cu and Zn in rice/wheat grains increased by 24.5%-60.4%and 51.4%-73.3%.When biochar was added,the corresponding increases decreased to 9.0%-32.7%and 40.9%-52.1%,respectively.This indicated that adding biochar can effectively reduce the migration of Cu and Zn from soil to rice.All the content levels were lower than the limits of China’s agricultural product quality standards,although the observed increase of Cu and Zn contents in grains.Considering the content of heavy metals in soil and crop grains,the evaluation results of soil and agricultural products comprehensive quality index method show that,when applying the biogas slurry in rice/wheat cropping farmlands,the heavy metal pollution degree belongs to a clean level.(5)There was no significant difference in soil bacterial community diversity of rice and wheat fields when applying different rates of biogas slurry.Compared with chemical fertilizer,the total replacement had no significant effect on soil bacterial community diversity.The difference is that,after two years of continuous application of biogas slurry,the soil bacterial diversity was increased by 30.5%in the presence of biochar,when the biogas slurry usage in rice/wheat season was500/320 m~3/ha.Further analysis showed that the replacement of chemical nitrogen fertilizer with biogas slurry significantly reduced the relative abundance of Planctomycotes community.Soil total nitrogen and organic carbon were proved to be the greatest impact on soil bacterial community composition under different biogas slurry dosage.Network analysis showed that biogas slurry substitution of chemical nitrogen fertilizer increased the number of nodes in the soil bacterial network.(6)Based on the six modules of biogas slurry nutrient supply,cultivated land area,unit area yield,proportion of fertilizer supply nutrients,proportion of biogas slurry in fertilizer application,and biogas slurry utilization efficiency,a calculation system for the integrated absorptive capacity of livestock and poultry breeding biogas slurry was constructed.According to the calculation,the theoretical livestock and poultry carrying capacity of integrated biogas slurry farming and breeding farmland in coastal areas of China is 1.162 billion pigs,and the required area of rice/wheat farmland is 6.0445 million ha.The actual capacity accounts for 36%of the theoretical capacity.In addition,the calculation shows that the integrated consumption of livestock and poultry breeding biogas slurry in coastal areas in China can effectively reduce the use of commercial fertilizer urea by 2.62 million tons/a and saving 1.34 billion m~3/a of irrigation water.To sum up,the biogas slurry under the mode of feces collection-full mixed anaerobic reactor-biogas slurry and biogas residue precipitation separation in large-scale intensive breeding enterprises can be continuously used in the coastal rice-wheat double cropping farmland.The recommended dosage in rice and wheat fields is 250 m~3/ha and 160 m~3/ha respectively.When combined with biochar,the dosage can be increased to 500 m~3/ha and 320 m~3/ha.The application of biogas slurry instead of chemical nitrogen fertilizer can maintain and increase crop yield,and no heavy metal environmental risk is investigated,and no noticeable change in soil microbial community diversity has been found.The integrated absorptive capacity measurement system of livestock and poultry breeding biogas slurry can provide planning and evaluation basis for sustainable biogas slurry consumption at regional scale.Biogas slurry consumption in coastal farmland is the need of recycling agriculture and regional ecological environment management in China.The long-term observation of crop production,ecological and environmental risks of biogas slurry application in the future will be necessary for the efficient,safe and sustainable development of cropping combined with breeding. |
PDF Full Text Request