Composts Obtained by Mixing Hop Leaves with Wheat Straw or Farmyard Manure Improved Soil Properties and Increased Microbial Communities

Abstract

Hop (Humulus lupulus L.) leaves are rich in nutrients, particularly nitrogen (N). After harvest, they can be recycled through composting for use as a soil amendment. In this study, we report the effect of composts obtained from mixtures of hop leaves with other organic materials (wheat straw, farmyard manure, and ash from hop stems) at different ratios on soil properties and microbial diversity. Data on total N, total organic carbon (TOC), microbial N (Mic-N), microbial C (Mic-C), soil basal respiration (SBR), metabolic quotient (qCO2), Mic-C/TOC ratio, acid phosphatase activity (APA), microbial density, and species identification were assessed after each one of the two growing seasons of potted lettuce (Lactuca sativa L.). The diversity of microbial species was evaluated using Simpson and Shannon diversity indexes, and the interactions between soil properties and the microbial community were explored. Higher microbial activity was found among the soils amended with leaves plus straw (HS), which exhibited higher levels of TOC, APA, Mic-N, and total N in the first growing cycle and higher levels of Mic-C, Mic-C/TOC, SBR, TOC, and Mic-N in the second growing cycle. Fungi identified belong to the Ascomycota and Zygomycota phyla, while bacteria belong to the Actinobacteria, Bacillota, Bacteroidetes, Firmicutes, and Proteobacteria phyla. Differences in the prevalent microbial genera were observed between compost treatments and growing cycles. Correlation analysis revealed significant relationship between soil bacteria and fungi abundance and higher levels of N and C in the soils, indicating the relevance of specific microbial genera, such Acrostalagmus, Doratomyces, Talaromyces, and Aspergillus fungi, as well as Gordonia and Bacillus bacteria. Overall, the results indicate that hop leaves-based compost, particularly with a higher proportion of leaves and straw, influenced the composition of the soil microbial community, ultimately enhancing soil N availability for plant development.