Does the application of biogas slurry reduce soil N 2 O emissions and increase crop yield?-A systematic review

The use of organic fertilizer for agricultural production can reduce the use of chemical fertilizer (CF), reduce greenhouse gas emissions, and maintain crop production. However, biogas slurry (BS), a liquid with a high moisture content and a low C/N ratio, differs from commercial organic fertilizer and manure in terms of its impact on the soil N cycle. Replacing CF with BS needs to be reconsidered regarding soil nitrous oxide (N O) emissions and crop production in terms of fertilization, agricultural land type, and soil characteristics. For this systematic review, the results of 92 published studies worldwide were collected. Based on the findings, the combined application of BS and CF can significantly increase soil total N (TN), microbial biomass N (MBN), and soil organic matter (SOM) levels. The Chaol and ACE index values of soil bacteria were increased by 13.58% and 18.53%, whereas those of soil fungi were decreased by 10.45% and 14.53%, respectively. At a replacement ratio (rr) ≤ 70%, crop yield was promoted by 2.20%-12.17%, and soil N O emissions were reduced by 1.94%-21.81%. A small rr (≤30%) was more conducive to growth, and a moderate rr (30%