# Vermicompost Alters Soil Microbial Communities and Decomposition but Increases Nitrate Leaching in Tropical Sugarcane

## TL;DR

Vermicompost boosts soil microbes and decomposition in sugarcane fields but increases nitrate leaching, risking water quality.

## Contribution

This study reveals that vermicompost increases nitrate leaching in tropical sugarcane soils despite enhancing microbial activity.

## Key findings

- Vermicompost increased bacterial diversity less than control soils during wet-season recovery.
- Vermicompost accelerated decomposition and shifted bacterial community composition.
- Nitrate leaching increased with vermicompost through direct effects, not microbial pathways.

## Abstract

Agricultural intensification has elevated nitrogen losses that threaten water quality and farm efficiency. Organic amendments such as vermicompost are promoted as tools to enhance soil health and reduce fertiliser demand, yet their effects under tropical field conditions remain uncertain. A six‐week field trial in Australian sugarcane soil tested factorial combinations of vermicompost and nitrogen fertiliser. Metabarcoding, trait‐based analysis and structural equation modelling were used to assess soil biodiversity, decomposition and nitrate leaching. Bacterial genera diversity increased in the control soils during early wet‐season recovery but rose less in vermicompost‐amended soils. Vermicompost also shifted bacterial community composition and accelerated decomposition, while fungal and nematode responses were small over the short timeframe. Despite these microbial shifts, vermicompost increased nitrate leaching through a strong direct effect, with indirect pathways via fungi and decomposition remaining weak and uncertain. These findings show that vermicompost can stimulate microbial activity yet still exacerbate nitrogen losses in clay soils with moderate nutrient retention during high rainfall. Management strategies that align organic amendments with crop uptake or combine them with stabilising materials may help capture microbial benefits while reducing off‐site impacts.

A six‐week field trial in Australian sugarcane soil used metabarcoding, trait‐based analysis and structural equation modelling to test how vermicompost affects soil biodiversity, decomposition and nitrate leaching under tropical conditions. Vermicompost shifted bacterial community composition and accelerated decomposition, yet increased nitrate leaching through strong direct effects rather than microbial pathways. These findings show that vermicompost can stimulate microbial activity while still exacerbating nitrogen losses in clay soils during high rainfall, suggesting management strategies should align organic amendments with crop uptake timing.