Nutrient scarcity in organic farming is an important obstacle to the growth of the sector. This study aimed to design a novel anaerobic digestion system for enhancing nitrogen (N) availability and abundance by co-digestion of grass-clover biomass and cattle slurry and a series of post-treatments. The digestates were separated, and the solid fraction was dried and stripped of ammonia. By a novel approach, the liquid fraction was used in a desulfurizing filter for the biogas producing an acidic liquid that was enriched with ammonia resulting in a sulphur-nitrogen-rich fertilizer product (LiqNS). The fertilisers were assessed for their fertilizer value under organic field conditions by direct injection before sowing spring barley. Two field studies were conducted to compare the N fertilizer replacement value (NFRV) of cattle slurry, digestates from co-digestion of cattle slurry and grass-clover, the liquid fractions, the dried fibre fraction of digestates, LiqNS, and mineral fertilizers under organic crop management. A third field study also compared the effect of crop management practices (organic vs. conventional) on NFRV. The field trials showed that cattle slurry, co-digested digestates, liquid digestates, and LiqNS had high NFRV of 80–90 %, with liquid digestates showing consistent performance. Co-digestion of grass-clover and cattle slurry did not change NFRV significantly compared to untreated cattle slurry. Conversely, the dried fibre fraction (DF) exhibited negative NFRV in spring barley due to nitrogen immobilization but no negative yield effect in a N-fixing faba bean crop. Anaerobic mono-digestion of cattle slurry improved NFRV by 16 % compared to untreated cattle slurry. By organic crop management, higher NFRV was estimated than by conventional management, due to lower yield response to mineral fertilization by organic management (11.9 percentage points lower nitrogen use efficiency), but mostly similar responses to organic fertilization under organic and conventional management. A reason for this could be the use of surface application of mineral N fertilizer favouring weed growth in the organic system, while such effects were avoided in both systems by injection of the slurries. Anaerobic digestion and post-treatments of digestates are valuable methods for enhancing nutrient efficiency and availability in organic farming. However, assessing the N fertilizer value of organic manures requires careful consideration of experimental management practices. Additional research is necessary to understand the different responses to mineral N fertilizers by organic management.

中文翻译：

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利用牛粪浆、沼气沼渣和通过注入有机管理的春大麦分离的沼渣


有机农业的营养物质短缺是该行业发展的重要障碍。本研究旨在设计一种新型厌氧消化系统，通过三叶草生物质和牛粪浆的共消化以及一系列后处理来提高氮 （N） 的可用性和丰度。分离沼渣，干燥固体组分并剥离氨。通过一种新颖的方法，液体组分被用于脱硫过滤器，用于沼气产生富含氨的酸性液体，从而产生富含硫氮的肥料产品 （LiqNS）。在播种春大麦之前，通过直接注射评估肥料在有机田条件下的肥料价值。进行了两项田间研究，比较有机作物管理下牛粪浆、牛粪浆和草三叶草共消化的沼渣、液体组分、沼渣的干燥纤维组分、LiqNS 和矿物肥料的氮肥替代值 （NFRV）。第三项实地研究还比较了作物管理实践（有机与传统）对 NFRV 的影响。田间试验表明，牛粪浆、共消化沼渣、液体沼渣和 LiqNS 的 NFRV 高达 80-90%，液体沼渣表现出一致的性能。与未处理的牛粪液相比，草三叶草和牛粪液的共消化不会显着改变 NFRV。相反，由于氮固定化，干纤维组分 （DF） 在春大麦中表现出负 NFRV，但在固氮蚕豆作物中没有负产量效应。与未处理的牛粪浆相比，牛粪液的厌氧单消化将 NFRV 提高了 16%。 通过有机作物管理，估计 NFRV 高于常规管理，因为有机管理对矿物肥料的产量反应较低（氮利用效率降低 11.9 个百分点），但在有机和常规管理下对有机肥的反应大多相似。造成这种情况的一个原因可能是在有机系统中使用有利于杂草生长的矿物氮肥的表面施用，而在两个系统中，通过注入浆料可以避免这种影响。沼渣的厌氧消化和后处理是提高有机农业养分效率和可用性的宝贵方法。然而，评估有机肥料的氮肥值需要仔细考虑实验管理实践。需要进行额外的研究，以了解有机管理对矿物氮肥的不同反应。