Purpose

This study investigated the C and N mineralisation potential of solid fractions (SFs) from co-digestated pig manure after P-stripping (P-POOR SF) in comparison with P-rich SFs, as a means to estimate their organic matter stability in soil. Compost (COMP) and biochar (BCHR) (made from P-POOR SF) were also included in the study as reference biosolids.

Methods

The SFs were incubated in a sandy-loam soil under moist conditions to determine production of CO₂ and mineral N. At specified intervals, CO₂ evolution in the mixtures was measured via the alkali trap method and titration over a period of 81 days, while mineral N was measured using a flow analyser after KCl extraction over a period of 112 days.

Results

The various SFs showed similar patterns of C mineralisation (15–26% of added total C in 81 days) that were clearly higher than for COMP and BCHR (6% and 7%, respectively). Temporary N immobilisation was observed in biosolids with a high C/N ratio. The effective organic matter (EOM) of the SFs was calculated based on the C mineralisation data and varied between 130 and 369 kg Mg⁻¹.

Conclusions

The SF with a reduced P content had a high EOM/P ratio which is beneficial in areas where P status of the soil is already high. Moreover, the N mineralisation patterns confirm that a high C/N ratio may also reduce risks for N leaching due to temporary N immobilisation.

中文翻译：

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分离的消化物的固体部分作为土壤改良剂：对土壤肥力和碳固存的影响

目的

这项研究调查了与富含P的SFs相比，P剥离（P-POOR SF）后共同消化的猪粪中固体部分（SFs）的C和N矿化潜力，以此来评估其在土壤中的有机物稳定性。堆肥（COMP）和生物炭（BCHR）（由P-POOR SF制造）也包括在研究中作为参考生物固体。

方法

将这些SFs在潮湿的沙质壤土中温育，以确定CO ₂和矿物质N的产生。在指定的时间间隔内，通过碱捕获法测量混合物中的CO ₂释放量，并在81天的时间内进行滴定，同时氯化钾萃取112天后，使用流量分析仪测量矿物N。

结果

各种SF表现出相似的C矿化模式（81天之内总C的15–26％），明显高于COMP和BCHR（分别为6％和7％）。在具有高C / N比的生物固体中观察到了暂时的N固定化。SF的有效有机物（EOM）是基于C矿化数据计算得出的，介于130至369 kg Mg ^-1之间。

结论

P含量降低的SF具有较高的EOM / P比，这在土壤P状况已经很高的地区是有利的。此外，N的矿化模式证实，高的C / N比还可以减少由于暂时固氮而导致N浸出的风险。