| Excessive discharge of biogas slurry can seriously pollute the environment.Biogas slurry treatment by biological method has the problem of high energy consumption.Field treatment is a feasible biogas slurry treatment method.However,there is a potential risk of accumulation of heavy metals in the soil during returning to the field.Meanwhile,the effect of biogas slurry application on the most active dissolved organic matter（DOM）of organic matter in the soil is still unclear.In this paper,pot experiments and field experiments were conducte d to study the effects of biogas slurry from swine farms on soil nutrient content,soil DOM fluorescence characteristics,soil heavy metal content,corn growth,corn yield and content of Zn in corn grains.The pot experiments showed that application of biogas slurry can significantly increase soil nutrient content.In the early stage of the experiment,biogas slurry combined with chemical fertilizer and single application of biogas slurry have significant improvement effects on soil total nitrogen,alkali-hydrolyzed nitrogen,ammonium nitrogen,organic matter and dissolved organic carbon（DOC）.Compared with CKA without exogenous fertilizer,the above indexes can increase up to 10.09%,117.37%,477.54%,12.31%and 98.57%.As time went on,the above indexes were still higher than that of CKA treatment at the end of the experiment.In the early stage,there was no significant difference between the soil p H of treated with biogas slurry and that of CKA.However,at the end of the experiment,the soil p H of CKA treatment was 7.87,and the soil p H value of treated with biogas slurry decreased to 7.44-7.67,and the more biogas slurry was applied,the lower the soil p H was.Parallel factor（PARAFAC）was used to analyze the fluorescence spectral data of the soil DOM in the pot experiment,and it was found that there were four independent components of C1,C2,C3 and C4 in the soil DOM.The application of biogas slurry can significantly increase the content of fluorescence components in soil DOM.The application of biogas slurry significantly increased the content of humus and proteins substances in soil DOM,especially proteins substances in the early stage.Compared with CKA,the application of biogas slurry in the early stage of the experiment increased the Fmax of humic substances（C1 and C2）in the soil DOM by16.90%-91.03%,and the Fmax of protein substances（C3 and C4）increased by 37.32%-369.76%.At the end of the experiment,biogas slurry still had an increasing effect on the content of humus in soil DOM.At 60 days,the Fmax of humus substances（C1 and C2）in the soil DOM treated with biogas slurry increased by 15.57%-34.49%compared with that of CKA.At the end of the pot experiment,the treatment with the highest total nitrogen content of corn plants was MFA.Compared with CKB using only chemical fertilizers,the total nitrogen content of MFA corn plants increased by 18.49%.The corn plant height,biomass,soluble sugar and soluble protein of MFA were at the same level as CKB and higher than CKA.Application of biogas slurry increased the content of copper（Cu）and zinc（Zn）in the field soil,but had little effect on the content of arsenic（As）in the soil.Compared wi th CK,the content of Cu and Zn in soil treated with biogas slurry increased by 1.21-2.67 mg/kg and 0.08-7.99 mg/kg,respectively.In this experiment,Cu was the limiting element of three heavy metals.After continuous application of biogas slurry,the Cu content in the soil first reached the soil risk value.Different application methods,different ratio of biogas slurry and chemical fertilizer ha d great influence on corn yield in the field.Compared with CF treatment with conventional chemical fertilizer,the yields of spraying+deep tillage A33 treatment and injection Z100 treatment increased by 3.36%and 3.72%respectively.In addition,the application of biogas slurry with nitrogen supply greater than 58 kg/hm2 spraying+deep tillage treatment and biogas slurry with nitrogen supply greater than 175 kg/hm2 injection treatment with the increase of biogas slurry application,the corn production overall showed a downward trend.Compared with spraying+deep tillage treatment,injection treatment can guarantee higher corn yield at higher biogas slurry consumption.For the content of Zn in corn grains,the content of Zn in corn grains in each treatment ranged from 14-15 mg/kg.The cumulative effect of biogas slurry on Zn in corn grains was not obvious. |
