Open access publications in the SLU publication database

Abstract

Agricultural sources contribute significantly to the high phosphorus (P) loads in water, causing eutrophication in many of Europe’s water bodies. Consequently, priority has
been given to reducing P leakage from sources, including soils used for animal farming. Horse farms use about 4 % of the total agricultural land in the EU, but have not so far
been investigated thoroughly with regard to their impact on water quality. This study characterised the potential risk of P leaching losses from Swedish horse paddocks in a
three-stage investigation of the soil and water P status. The study began with an analysis of eight years of drainage P data from a small catchment, a so called – ‘observation field’, dominated by horse paddocks (Paper I). In the following study (Paper II), soil P status was examined in different parts of the horse paddocks (feeding, grazing and excretion areas) to identify potential hotspots for high P losses within the paddock. In the third experiment (Paper III), topsoil columns (0 - 20 cm) from different segments of the paddock (feeding, grazing, and excretion area) were isolated and potential leaching losses of P from the soil columns were measured during simulated rainfall in the laboratory. The studies showed that: i) horse paddocks can pose a potential threat to water quality via leaching of excess P, ii) feeding and excretion areas are potential hotspots for significantly high leaching losses, and iii) paddocks established on sandy soils are particularly vulnerable to high P losses.

Besides identifying P leaching problems, additional investigations were carried out to mitigate P losses from paddocks using organic bedding materials (e.g. wheat straw,
wood chips and peat) (Paper IV) and to determine an environmentally safe load of horse manure for arable soils (Paper V). The main findings of these studies were: iv) of
the three bedding materials, only wood chips could reduce P losses while the other two enhanced leaching losses, and v) the addition of composted horse manure up to 36 Mg ha-1 (22 kg P ha-1) did not increase P leaching from organic soil, but from the mineral soils, while 90 - 100 % of the added P from the compost was retained in the soils.

Finally, proposals for better paddock management were outlined and the need for national rules/regulations for horse paddocks were stressed to avoid nutrient build-up
and to reduce losses. In addition, to strengthen the understandings and conclusions, more field studies were suggested for future research.