# Potential of short‐term heat‐treated horse manure as a recycled growing media

## TL;DR

Horse manure can be safely reused as plant-growing media after pasteurization, reducing waste and supporting sustainable agriculture.

## Contribution

A farm-scale heat treatment process is shown to effectively sanitize horse manure for use in plant cultivation.

## Key findings

- Pasteurization reduces Escherichia coli to safe levels and eliminates seed germination.
- Phytotoxic effects occur at high concentrations of pasteurized manure.
- Pasteurized manure with peat bedding shows limited nitrogen availability for plants.

## Abstract

This study evaluated the effectiveness of a farm‐scale manure pasteurizer in transforming horse manure into growing media for plants within a circular economy framework. Horse manures with wood or peat beddings were homogenized in a controlled short‐term heat treatment process lasting a total of 1–2 days, including a 1 h pasteurization phase. The elimination of harmful microorganisms and seed viability were studied prior to and after sanitation. The phytotoxicity and fertilization effect of the treated manures were evaluated. This study indicated a substantial reduction in Escherichia coli, from over 5.2 × 104 colony‐forming unit (CFU) g−1 in untreated manure to below 173 CFU g−1​ in pasteurized manure, and complete loss of germination in four cereal seeds and a weed seed mixture tested. In a phytotoxicity test conducted using cress (Lepidium sativum L.), 20% of pasteurized horse manure with bedding was well tolerated, whereas phytotoxic symptoms were detected in treatments containing 50% of untreated horse manure or pasteurized horse manure (PHM) with wood or peat bedding and in the treatment with 20% PHM with wood bedding. In the growing experiment with Chinese cabbage [Brassica rapa L. subsp. pekinensis (Lour.) Hanelt], a fertilization effect was indicated despite the low rate of nitrogen efficiency. The promising application of the short‐term heat treatment process highlights its potential to improve sustainable farming, in line with the principles of the circular economy, by recycling horse manure into a growing media.

Horse manure can be reused as a growing media after pasteurization.Pasteurization effectively eliminates microbes and reduces the viability of seeds existing in horse manure.Phytotoxic symptoms may occur with high concentrations of pasteurized horse manure.The nitrogen in pasteurized horse manure with peat bedding is not readily bioavailable in short‐term cultivation.

Horse manure can be reused as a growing media after pasteurization.

Pasteurization effectively eliminates microbes and reduces the viability of seeds existing in horse manure.

Phytotoxic symptoms may occur with high concentrations of pasteurized horse manure.

The nitrogen in pasteurized horse manure with peat bedding is not readily bioavailable in short‐term cultivation.

Nowadays, horse stables are often located near cities, making manure circulation to fields challenging. We evaluated pasteurization as a method for manure treatment and the suitability of sanitized manure mixed with peat for plant cultivation. Pasteurization effectively sanitizes manure, making it suitable for plant cultivation at low concentrations. Pasteurized horse manure can partially replace peat in growing media, promoting sustainability goals in agriculture and conserving natural resources.