Impact of Digestate Application on Chemical and Microbiological Properties of Two Different Textured Soils

Agricultural application of anaerobic digestates can play an important role in plant nutrition. The effects of digestate treatment were studied in pot experiments, using sandy and loamy textured soils with distinct characteristics. Three different treatments were studied and compared: control, digestate, and irrigation treatments. Nitrogen loading was calculated on the bases of the digestate analysis. The same amounts of digestate and irrigation water were applied in the different treatments before sowing and at the V4–V6 stages of maize. Besides the conventional soil chemical analysis, invertase, dehydrogenase, catalase, and the abundance of some cultivable microbes were measured in two consecutive years. According to our results, irrigation and digestate treatments had greater impact in the case of sandy soils than in loamy textured soils. Digestate provides more effective phosphorus and potassium sources than nitrogen. Based on the results of discriminant analysis, the digestate application had a greater influence on soil chemical properties, followed by microbiological parameters.     

Effects of biogas and raw slurries on grass growth and soil microbial indices

Biogas slurry is increasingly used as fertilizer. Earlier research was focused on plant growth and soil chemical properties, with only little information available regarding the effects of biogas slurry on soil and root microbial indices. For this reason, a 70 d pot experiment was conducted in which biogas and raw slurries obtained from six biodynamic farms were added to a soil. Italian ryegrass (Lolium multiflorum Lam.) was cultivated to investigate the effects on plant yield, N uptake (two harvests), soil microbial biomass, soil fungi, and root‐colonizing microorganisms. Biogas slurries increased the mean total above‐ground plant biomass by 66% and raw slurries by 35% in comparison to the control. The mean plant N‐uptake increased under biogas and raw slurry application by 166% and 65%, respectively, compared with the unfertilized pots. The effects of biogas and raw slurry application on soil microbial indices were similar except for the lower fungal biomass after biogas slurry amendment. In contrast to biogas slurries, the raw slurries significantly increased microbial biomass C and N by roughly 25% in comparison to the control. The application of biogas slurries significantly decreased the soil ergosterol content in comparison with raw slurry and control treatment, leading to a significantly lower ergosterol : microbial biomass C ratio. In the roots, biogas and raw slurry application significantly decreased the concentrations of the amino sugars galactosamine and glucosamine by 39 and 27%, respectively, but not that of ergosterol in comparison with the control. This was most likely due to a reduced colonization with arbuscular mycorrhizal fungi in the presence of highly available plant nutrients.     

水力停留时间对猪粪厌氧发酵残留物中磺胺类抗生素分布的影响

针对厌氧消化中磺胺类抗生素(SAs)残留及在沼渣、沼液中分配特征不清等问题,以猪粪为发酵原料,采用完全混合式反应器(CSTR)在中温(37±1℃)条件下进行室内模拟试验,探讨不同水力停留时间(HRT)对磺胺嘧啶(SD)、磺胺二甲嘧啶(SM)和磺胺氯哒嗪(SCP)的去除及其在固/液相中分配的影响。研究结果表明:厌氧消化对3种SAs的去除率表现为SMSDSCP。水力停留时间(HRT)=20 d时,猪粪中3种SAs的去除率均达90%以上;HRT=15 d时,三者的去除率均有所下降,特别是SCP去除率降为72.8%左右。厌氧发酵后残留的抗生素主要分布在猪粪沼渣中,其中SCP在沼渣中占有绝对优势。同时,HRT=15 d的处理中,SM和SCP的固/液分配比率明显高于HRT=20 d的处理。厌氧消化过程中不同磺胺类抗生素的降解过程和影响因子存在差异,延长反应体系中抗生素与厌氧微生物作用的反应时间,对中温厌氧消化过程中SAs的去除有积极的作用。为降低其环境危害,猪粪沼渣在还田利用前应进一步消减其中残留的SAs。     

沼肥种类及不同施氮量对芹菜品质影响研究

沼渣沼液作为厌氧发酵后的产物,因其量大消纳难,已逐渐成为限制沼气工程发展的制约因素。因此研究沼渣沼液作为肥料施用于农田对作物生长发育的影响具有重要的意义。该研究分别以猪粪厌氧发酵剩余物和秸秆牛粪厌氧发酵剩余物作为肥料,设置不同氮浓度施用水平(0,8.5,17,34,68 gTN·m-2 y-1),具体以沼渣作为底肥、沼液作为追肥的施肥方式,实际施用量以总氮(TN)作为标定指标,沼渣沼液施用比例为1∶2。研究结果表明:不同来源厌氧发酵剩余物对芹菜品质的影响效果不同;中低浓度氮条件下的猪粪沼肥和高氮浓度条件下的秸秆牛粪沼肥更有利于芹菜的营养物质的积累。     

大中型沼气工程厌氧发酵液的后处置技术

沼气生产之后的厌氧发酵液处置是制约大中型沼气工程发展的重要因素之一,国内外沼液处置相继出现了低成本的资源性利用、低成本的自然生态净化、高成本的工厂化处理和高附加值的开发性处理等四种方式。前二者属于"生态型",适用于全混式发酵,且具有足够消纳的生态单元;后二者属于"环保型",适用于干湿分离发酵。     

沼液深度处理技术研究与应用现状

针对我国大中型沼气工程沼液产生量巨大,沼液还田无法广泛实施,而直接排放又会造成环境污染的问题,通过对大量的文献资料和研究结果进行分析,得出沼液处理的2种主要途径:①降解其中的污染物使其能够达标排放或安全回用,②浓缩并回收沼液中营养物,使沼液体积减量化。建议今后的研究应选择适合的工艺,克服技术难题,以沼液高效利用为目标,以防止环境污染为前提,探索低运行费用的沼液处理方法。     

Does acidification increase the nitrogen fertilizer replacement value of bio‐based fertilizers?

Acidification of manure, digestate and their processed derivatives has been proposed as a technique to, amongst others, mitigate ammonia emissions related to application in the field. The current study investigated whether acidification of (1) pig slurry (PS), (2) liquid fraction of pig slurry (LFPS), (3) digestate (DIG), and (4) liquid fraction of digestate (LFDIG) increases their nitrogen (N) fertilizer replacement value (NFRV) as compared to non‐acidified counterparts, a synthetic N fertilizer (calcium ammonium nitrate; CAN) and an unfertilized control. Product performance was evaluated from the perspective of (1) crop development (yield, nutrient uptake, and crop quality assessment) via a pot experiment with Lactuca sativa L. and (2) soil N dynamics [net N release (N_rel,net) and net N mineralization] via a soil incubation experiment. Crop yield of pots receiving bio‐based fertilizers performed ‘on par' with CAN as compared to unfertilized control, implying that bio‐based fertilizers derived from digestate or manure could potentially play a role in replacing synthetic N fertilizers. However, our findings also suggest that acidification did not result in an increased use efficiency of applied N. NFRVs of acidified products were below those of non‐acidified products and CAN, with crop yield on average 6–13% and 11–18% lower compared to non‐acidified products and the CAN treatment, respectively. A possible explanation for lower performance as compared to non‐acidified products could be an inhibitory delay in the N_rel,net, which in our experimental design proved to be negative for crops with short production cycles. This pattern was revealed in the incubation experiments in which N_rel,net in acidified products remained below that of non‐acidified, in this study tentatively attributed to immobilization of mineral N. However, this negative effect on N availability should be reaffirmed in crops with longer production cycles. Finally, some interesting findings with regard to plant composition also warrant further in‐depth investigation, e.g ., Zn uptake by lettuce in acidified treatments was significantly higher than that of non‐acidified treatments. This implies that product pre‐treatment may play a future role in biofortification and amelioration of (trace) element composition of crops (arguably for crops with longer production cycles). Improving crop nutritional value by increased uptake of micronutrients is receiving increasing attention.     

Unbalanced nutrient ratios in pelleted compound recycling fertilizers

The aim of this study was to contribute to the development of pelleted compound recycling fertilizers with favourable handling and spreading characteristics and balanced nutrient ratios by combining nitrogen (N)‐ and phosphorus (P)‐rich waste resources (meat bone meal, fish sludge or food waste) with potassium (K)‐rich bottom wood ash. Pelleted compound recycling fertilizers with good durability and low dusting tendency were produced by roll‐pelleting preheated waste resources at a suitable moisture content. However, the nutrient ratios in the final products were insufficiently balanced, with too low N concentrations relative to P and K to meet crop demands. In a bioassay using barley (Hordeum vulgare ) and a nutrient‐deficient sand/peat mixture, the relative agronomic effectiveness (RAE ) of pelleted compound recycling fertilizers and reference recycling fertilizers was 22–42% of that of mineral compound fertilizer. Growth limitation was due to reduced N availability (mineral fertilizer equivalent ‐ MFE = 35–57%) or reduced P availability (MFE  = 20–115%), with the greatest P fertilizer value obtained for digestate based on dairy manure and fish sludge. Availability of K in bottom wood ash was masked by the experimental soil.     

Potential of anaerobic digestate of dairy manure in suppressing soil‐borne plant disease

Frequent use of pesticides to control soil‐borne plant disease leads to environmental pollution and the development of pesticide resistance in phytopathogens. Soil amendment is considered to have the potential of suppressing plant disease because of its biological properties. However, information on anaerobic digestate is limited. In this study, potential of antagonistic activities of anaerobic digestate against phytopathogens were investigated by detecting the amounts of antagonistic bacteria (Bacillus and Pseudomonas) in anaerobic digestates of dairy manure. The results showed that anaerobic digestion increased the total amounts of Bacillus and Pseudomonas in digestate. Bacillus suppressed growth of phytopathogens, while Pseudomonas did not show any antagonistic activities. These results indicated that Bacillus was an effective antagonistic bacterium in digestate against phytopathogens. Furthermore, two selected isolates, B11 (Bacillus subtilis) and B59 (Bacillus licheniformis), were applied in field experiments and showed significant reduction in percent infection of potato late blight (Phytophthora infestans). These results demonstrate the benefits of digestate in suppressing soil‐borne plant diseases caused by antagonistic bacteria.     

Effects of 5 years of digestate application on biomass production and quality of cocksfoot (Dactylis glomerata L.)

Anaerobic digestion of biomass produces biogas for combustion and also provides a residual digestate. Although sometimes regarded as a waste product, the nutrient‐rich chemical composition of digestate makes it a potential organic fertilizer for agriculture. The goal of this study was to evaluate the effectiveness of digestate as a fertilizer on the biomass yield and chemical composition of cocksfoot (Dactylis glomerata L.). In a 5‐year small‐plot field experiment digestate fertilization treatments supplying 90, 180, 270, 360 and 450 kg N ha^?1 were compared with untreated plots and plots fertilized with 180 kg N ha^?1 of mineral N fertilizer. Swards fertilized with digestate produced higher biomass yield compared with the control. The same rate of nitrogen fertilizer (180 kg N ha^?1) supplied as digestate and from mineral fertilizers gave similar results on biomass yield. Herbage in swards fertilized with digestate contained less nitrogen, but the C:N ratio was much more suitable for biogas production. Digestate fertilization resulted in higher concentrations of cellulose and hemicellulose in biomass and lower contents of the inhibitors of anaerobic digestion—sulphur, calcium, magnesium and phosphorus—compared with those of swards receiving mineral fertilizers.