Effects of solid manure particle fractionation on transport, retention, and release of Escherichia coli

Abstract

Understanding the effect of manure particle fractionation on transport, retention, and release of bacteria plays a critical role in manure management and environmental policies that address soil and water bacterial pollution. Compared to soil particle size, there is less understanding of the importance of solid manure particle size and fractionation on bacterial fate and transport in soils. Four different cow manure particle sizes (0.25, 0.5, 1, and 2 mm) were used to investigate Escherichia coli fate in a saturated loamy sand soil. Leaching experiments were performed for up to 20 pore volumes. Preferential transport of chloride mitigated as manure particle size increased. The larger manure fractions (1 and 2 mm) showed greater heterogeneity in bacteria transport and release; smaller manure fractions (0.25 and 0.5 mm) had a greater bacteria retention with retarded release. Bacteria release was associated with transport and re-entrainment of manure particles through soil columns. The results highlighted the contribution of fine and transported particles as of primary importance for retention near the surface and transporting bacteria in soil. Similar retention shapes (i.e., exponential) for different fractions illustrated the similarity of manure source, where greater retention was observed at 0−3 cm depth for the smallest (0.25 mm) and largest (2 mm) manure fractions. The findings also highlighted the dependency of bacteria transport, retention, and release on manure physical fractionation, which should be considered in managing soil and manure practices in the field. © 2021 The Authors