| With the rapid development of biogas construction in China, large amount of biogas slurry hasbeen produced. At the meantime, the problem of lacking irrigation water is serious, thus using thebiogas slurry for farmland irrigation should be an appropriate way to reuse the slurry. However,baseline data are limited related to the environmental impact of biogas slurry application on farmlands,especially for the condition of the wheat/maize rotation system in North China.This study was carried out on a typical wheat/maize rotation cropland, focusing on the impact ofswine farm biogas slurry application on the soil properties, water runoff and gas emissions, as well ason crop yield and quality, to explore the long-term environmental impact of biogas slurry application oncroplands, providing data for reference when utilizing biogas slurry from large-and-medium scalebiogas plants for irrigating. Two treatments were set concerning the ways of application of the slurry,namely the treatments of synthetic fertilizer plus slurry (referred to as F+S), and the slurry plus slurry(S+S). Within each of the treatment, three levels were set, the low, mediem and high levels representingapplying the slurry for once, twice and three times in the wheat growing season. The following findingswere obtained.The contents of copper, zinc, lead and cadmium of the soils of the treatments of F+S and S+S bothmet the standard requirements of NY/T851-2004, which requires that Cu≤100mg/kg,Zn≤300mg/kg,Pb≤350mg/kg,and Cd≤0.60mg/kg. Copper accumulation was found in the soil of thetreatmetns, although from the second year of treatment, accumulation rate had been low. The soilcopper contents of the F+S were18.8,22.5and22.8mg/kg for the first, the second and the third years,respectively, and those for the S+S were19.5,22.0and24.1mg/kg. The nitrogen loss through run-offwas less than seven percent, which posed little risk of eutrophication of the surface water.Application of biogas slurry enhanced the contents of soil organic matter, total and availablenitrogen and phosphorus, while lowering soil pH. After three years of slurry irrigation, soil organicmatter contents of F+S and S+S were13.5g/kg and12.6g/kg, increased for1.9g/kg and1.0g/kgcompared with the control (CK), and increased for3.2g/kg and2.3g/kg compared with the baselinevalue. Total nitrogen contents of the soils of F+S and S+S were0.98g/kg and0.97g/kg, increased for0.22g/kg and0.21g/kg compared with the CK, and higher than the baseline value, which was0.75g/kg.The highest level of the two treatments, T3and T6, reached soil nitrogen contents of1.04g/kg and1.14g/kg. The available nitrogen content of the soils of both F+S and S+S reached140mg/kg, higher thanthe baseline valee of76mg/kg, while that of the CK was about85mg/kg. Total phosphorus contents ofthe soils of F+S and S+S were0.92g/kg and0.95g/kg, increased for0.20g/kg and0.23g/kg comparedwith the CK. The highest level of the two treatments, T3and T6, reached soil phosphorus contents of1.01g/kg and1.07g/kg. The available phosphorus content of the soils of both F+S and S+S were97 mg/kg and111mg/kg, significantly higher than the CK, which was31mg/kg. The soil pH values ofF+S and S+S were7.9and7.8, significantly lower than the baseline value, which was8.3, and that ofthe CK (8.2).Application of biogas slurry did not affect winter wheat and summer maize production. Thenitrogen and phosphorus contents of the wheat grains of the F+S and S+S were significantly higher thanthose of the CK for the first two years, but were not for the third year. Carbon content of the wheat grainwas not affected by treatments. The carbon and nitrogen contents of the high level of the treatment ofF+S was significantly higher than that of the CK, and the phosphorus contents of the corns of the lowand medium levels of F+S treatment were significantly higher than that of CK for the second year, butwere not for the third year of treatment.The optimum application method of biogas slurry is T5, and3000tons of biogas slurry could beused if T5is employed..
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