# Soil organic carbon stocks after ten years of reduced tillage, compost and mulch application in temperate organic agriculture

## TL;DR

This study shows that reduced tillage and compost application over ten years increased topsoil carbon in organic farming, but subsoil carbon remained unchanged.

## Contribution

The study demonstrates that combining reduced tillage and compost application boosts topsoil organic carbon stocks in organic agriculture.

## Key findings

- Reduced tillage and compost application increased topsoil SOC stocks by 16% compared to conventional practices.
- Crop biomass was the main carbon input source over ten years.
- Mulch application had no significant effect on SOC stocks.

## Abstract

Increasing soil organic carbon (SOC) aims to increase and maintain soil quality for sustainable crop production and to achieve carbon removal targets. Agronomic practices are therefore needed to reduce carbon losses and increase SOC stocks, especially in deep soil layers, which promote long-term storage. Regenerative agriculture is an approach aimed at increasing soil quality for sustainable production and therefore should be suitable for achieving the required goals under organic farming conditions. We analysed SOC content down to a depth of 1 m and calculated the SOC stock based on bulk density after ten years of regenerative farming practices, i.e., reduced tillage, dead organic mulch, and high-quality yard waste compost application, in two organic field trials set up one year apart in Central Germany and we calculated the carbon (C) and nitrogen (N) input to the soil from organic amendments and from main crops and cover crops by applying C allocation factors for crop residues, roots, and rhizodeposition. C derived from crops was the main carbon input source over ten years. Increasing C input promoted an increase in the cumulative SOC stock down to 1 m. We observed greater SOC stocks dominated by topsoil changes with reduced tillage and compost application and with the combination of all practices (+ 16%) than in the control with conventional ploughing and no external carbon input while none of the farming practices affected the subsoil SOC stock. Mulch application had no effect at all on SOC stocks. Crop biomass contributed most C input. Farming practices, especially the combination of reduced tillage and compost application, enhanced topsoil SOC stocks and N but not subsoil C storage. Other farming practices and crop rotation adjustments must be identified to increase crop production as well as subsoil SOC stocks and promoting long-term C storage, e.g., by fostering deep-rooting crops and cover crops.

The online version contains supplementary material available at 10.1038/s41598-026-42050-9.