Applying digestate, the residue from anaerobic digestion, to soil as a replacement for inorganic fertiliser is of growing interest in agriculture. However, the impacts of different fractions of digestate on the soil carbon (C) cycle remain unclear and provide the focus for the research reported here. We examined the effects of applying whole digestate (WD) and solid digestate (SD) on carbon dioxide (CO₂C) efflux, the concentrations of dissolved organic carbon (DOC), microbial biomass C (C_micro) and phospholipid fatty acids, alongside carbon use efficiency (CUE). A 21-day laboratory microcosm incubation was used to investigate the impacts of digestate when applied to two grassland soils of high versus low initial nutrient content. Application rates for SD and WD were based on recommended nitrogen (N) inputs to grassland soils for these organic materials. Compared to control treatments, cumulative CO₂C efflux and the concentration of DOC increased significantly after WD and SD application, although only within the low nutrient soil. Both C_micro and the fungal-to-bacterial ratio increased significantly following SD application, regardless of the initial soil nutrient content. These observations are likely to reflect the larger input of C, alongside the dominance of more strongly lignified compounds, associated with SD compared to WD to achieve a constant N application rate. Our results also indicate that the two digestate fractions generated significantly different CUE. The application of SD led to increases in C_micro and positive values of CUE, whereas decreases in C_micro and negative values of CUE were observed following WD application. These findings emphasize the need to carefully plan the management of digestate in agricultural production systems, to minimize negative impacts on C storage within soils whilst maximizing the agronomic value derived from digestate.

中文翻译：

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在土壤中加入不同比例的厌氧消化物后土壤微生物利用和碳归宿的变化

将厌氧消化的残余物作为无机肥料的替代物应用到土壤中的消化物在农业中越来越受到关注。然而，不同部分的消化物对土壤碳 (C) 循环的影响仍不清楚，并为这里报告的研究提供了重点。我们研究了应用全消化物 (WD) 和固体消化物 (SD) 对二氧化碳 (CO ₂  C) 流出、溶解有机碳 (DOC) 浓度、微生物生物量 C (C _micro) 和磷脂脂肪酸，以及碳利用效率 (CUE)。使用为期 21 天的实验室微观孵化来研究消化物应用于两种初始养分含量高与低的草地土壤时的影响。SD 和 WD 的施用率基于这些有机材料对草地土壤的推荐氮 (N) 输入。与对照处理相比，WD 和 SD 施用后累积 CO ₂  C 流出和 DOC 浓度显着增加，尽管仅在低营养土壤中。两者 C_微无论初始土壤养分含量如何，施用 SD 后真菌与细菌的比率显着增加。这些观察结果可能反映了更大的 C 输入，以及更强烈的木质化化合物的主导地位，与 SD 相比，与 WD 相关，以实现恒定的 N 施用率。我们的结果还表明，两种消化物级分产生了显着不同的 CUE。SD的应用导致C _micro和CUE的正值增加，而C _micro减少WD 应用后观察到 CUE 和负值。这些发现强调需要仔细规划农业生产系统中的消化液管理，以最大限度地减少对土壤中碳储存的负面影响，同时最大限度地提高源自消化液的农艺价值。