Seasonal persistence of faecal indicator organisms in soil following dairy slurry application to land by surface broadcasting and shallow injection

Christopher J Hodgson,David M Oliver,Robert D Fish,Nicholas M Bulmer,A Louise Heathwaite,Michael Winter,David R Chadwick

doi:10.1016/j.jenvman.2016.08.047

Abstract

Dairy farming generates large volumes of liquid manure (slurry), which is ultimately recycled to agricultural land as a valuable source of plant nutrients. Different methods of slurry application to land exist; some spread the slurry to the sward surface whereas others deliver the slurry under the sward and into the soil, thus helping to reduce greenhouse gas (GHG) emissions from agriculture. The aim of this study was to investigate the impact of two slurry application methods (surface broadcast versus shallow injection) on the survival of faecal indicator organisms (FIOs) delivered via dairy slurry to replicated grassland plots across contrasting seasons. A significant increase in FIO persistence (measured by the half-life of E. coli and intestinal enterococci) was observed when slurry was applied to grassland via shallow injection, and FIO decay rates were significantly higher for FIOs applied to grassland in spring relative to summer and autumn. Significant differences in the behaviour of E. coli and intestinal enterococci over time were also observed, with E. coli half-lives influenced more strongly by season of application relative to the intestinal enterococci population. While shallow injection of slurry can reduce agricultural GHG emissions to air it can also prolong the persistence of FIOs in soil, potentially increasing the risk of their subsequent transfer to water. Awareness of (and evidence for) the potential for ‘pollution-swapping’ is critical in order to guard against unintended environmental impacts of agricultural management decisions.

Highlights

Water used for recreation, drinking or food production is routinely screened for faecal indicator organisms (FIOs) by regulators to track compliance with health related standards and associated legislation (Pachepsky et al, 2016; Clements et al, 2015)
A steady decline in concentration of both E. coli and intestinal enterococci (IE) was evident from the shallow injection plots (Fig. 1a & b)
A two-log decline in viable E. coli concentration in the slurry taken from the intermediate bulk container (IBC) was observed for the 51 days for May

Summary

Introduction

Water used for recreation, drinking or food production (including shell fisheries) is routinely screened for faecal indicator organisms (FIOs) by regulators to track compliance with health related standards and associated legislation (Pachepsky et al, 2016; Clements et al, 2015). 65% of the dairy cattle housing systems are slurry-based systems (Anon, 2006), where the slurry is a mixture of faeces, urine and water. The FIO concentrations contained within animal manures are highly variable depending on shedding rates, manure type (liquid or solid manure) and storage conditions Their rate of decline after manure application to land has been shown to be dependent on environmental factors, such as UV exposure, temperature, soil type and desiccation (Park et al, 2016; Stocker et al, 2015). The risk of microbial loss from land to water will vary across contrasting seasons and according to different methods of manure application, and this warrants further investigation

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