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

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.