# Enhancing Ecological Functions in Chinese Yellow Earth: Metagenomic Evidence of Microbial and Nitrogen Cycle Reassembly by Organic Amendments

## TL;DR

Adding organic materials with less nitrogen improves soil health and corn yield in Chinese Yellow Earth by changing microbes and nitrogen cycles.

## Contribution

The study shows how organic amendments with reduced nitrogen reshape soil microbes and nitrogen processes in Chinese Yellow Earth.

## Key findings

- Organic amendments with reduced nitrogen increased soil pH, nitrogen, and organic matter, boosting maize yield by 4.41–8.97%.
- Metagenomics found beneficial microbes like Sphingomonas and Bradyrhizobium linked to improved soil conditions.
- Nitrate nitrogen was the main driver of microbial community changes, with Lysobacter and Reyranella linked to higher yields.

## Abstract

Background: Chinese Yellow Earth is a key subtropical agricultural resource in southwestern China; however, its productivity is limited by acidity and poor nutrient retention. This study examined how reduced nitrogen plus organic amendments affect its soil microbial structure and maize yield. Methods: A field experiment with four treatments evaluated reduced nitrogen fertilization amended with rice husk plus rapeseed cake (RS) or RS with biochar (BC). Soil properties (pH, nitrogen, organic matter) and maize yield were analyzed. Metagenomic analysis (NR database) characterized microbial communities, and correlation analysis with Mantel tests identified key relationships. Results: Combined organic amendments under reduced N significantly increased soil pH, nitrogen components, and organic matter, increasing maize yield by 4.41–8.97%. Metagenomics revealed enriched beneficial genera including Sphingomonas and Bradyrhizobium. Yield positively correlated with nitrate nitrogen and a beneficial microbial cluster containing Lysobacter and Reyranella, whereas Steroidobacter negatively correlated with key fertility indicators. Mantel tests revealed nitrate nitrogen as the primary correlate of functional gene community succession. Conclusions: This study reveals that reduced nitrogen with organic amendments promotes soil improvement and microbial modulation, demonstrating potential as a sustainable practice to maintain crop productivity in Chinese Yellow Earth. The observed trend toward yield improvement underscores its promise and warrants further validation through additional trials. Overall, the findings highlight the beneficial effects of these amendments on soil health and their role in supporting sustainable subtropical agriculture under reduced nitrogen input.