Dairy farm roadway surface materials as a P-source within the nutrient transfer continuum framework

Abstract

Internal farm roadways are connectors within agricultural landscapes, which act as sub-components of the nutrient transfer continuum (NTC). On dairy farms, roadway surface runoff dissolved and particulate phosphorus (P) sources stem from a combination of cow excreta deposited at locations that impede animal flow, soil deposited from cow hooves or machinery tyres, run-on from up-gradient fields, public roadways or farmyards and incidental spill of organic/inorganic fertilizers. The present study investigates the storage and potential release of P from the underlying roadway material (i.e. composite of soil and stone aggregates) as this source component is not considered in the NTC framework or documented in the literature. Herein, farm roadway materials were sampled (to 1 cm depth) at 17 locations avoiding fresh cow excreta. Multiple location types were selected e.g. straight roadway sections, roadway junctions, before and adjacent standoff areas associated with cattle underpasses, with all locations varying in distance from the farmyard. Roadway samples were analysed for phosphorus (P) and metals (Al, B, Ca, Co, Cu, Fe, K, Mg, and Mn) content. Results showed that the soil component of roadway materials are significant P legacy sources and are in themselves a P-storage component that merits inclusion in the NTC framework. All sampled locations, when compared with fresh roadway stone aggregates or surrounding fields, had highly elevated P with plant available Morgans P > 8 mg L-1 (Index 4, ranging from 10 – 110 mg L-1). Sampling points within 100 m of the farmyard together with roadway junctions and underpasses beyond this distance had highest P concentrations. Critical source areas, where source, mobilisation and transport of P to waters coincided, formed at three locations. Possible mitigation measures are a) divert roadway runoff into fields using low-cost surface water breaks, b) disconnect cattle underpass tanks from receiving waters and c) change roadway infrastructure to improve cow flow and minimise source build-up. Future research should examine P loads in runoff from roadway sections across farm typologies and roadway material types.

Phosphorus in farm roadway substrates: contrasting spatial and temporal patterns in dairy and beef farms

“…Spatially on the Dairy Farm, the results from this study concur with those of Fenton et al (2022) and demonstrate that farm roadways on these farming systems have elevated P concentrations and are a subcomponent of the nutrient transfer continuum. However, the temporal data suggests that this source is available all year round to be lost in roadway runoff.…”

“…Samples of roadway material were collected as described by Fenton et al (2022) from farm roadways at 18 locations on each farm (Figure 2). It is important to note that the roadway material that was collected did not incorporate fresh faecal material, therefore contaminated areas with fresh excreta material from cows were avoided.…”

“…The source of nutrients in roadway materials is a combination of many factors on the farm. Fenton et al (2022) lists each of these contributing sources, which are dominated by fresh animal faeces and urine but also may include soil nutrients incorporated into surface materials from trafficking and animal hoofs originating from adjacent fields. The higher P concentration in these locations can be strongly linked with the impaired movement of the cows thus, giving them an opportunity to excrete a lot while standing (Fenton et al, 2021).…”

“…The nutrient content in the surface material is a product of the fertilised soil and animal deposits (dung pats and urine) that fall onto the roadway surface during animal movement to and from the milking parlour to grazing fields (Hubbard et al, 2004;Phillips et al, 2013). Fenton et al (2022) examined the spatial P distribution of farm roadway material on a dairy farm in the south-east of Ireland and measured concentrations, up to 14 times greater than the highest index four threshold of 8.0 mg Morgan's P L -1 (available P) for grassland soils. In Ireland, the P index system is used as guide to application of fertiliser P for grasslands and other crops and classifies soil available P from 'very low' (soil index 1, good crop response potential to P application) to 'sufficient/excess' (soil index 4, no crop response potential to P application) (Dunne et al, 2021).…”

“…In Ireland, the P index system is used as guide to application of fertiliser P for grasslands and other crops and classifies soil available P from 'very low' (soil index 1, good crop response potential to P application) to 'sufficient/excess' (soil index 4, no crop response potential to P application) (Dunne et al, 2021). On the dairy farm, Fenton et al (2022) showed direct connectivity between available P on the roadway surface and waters, identifying three distinct critical source areas (CSA).…”