Skip to main content
SLU publication database (SLUpub)
Research article - Peer-reviewed, 2011

Impact of horse grazing and feeding on phosphorus concentrations in soil and drainage water

Parvage, Masud; Kirchmann, Holger; Kynkäänniemi, Pia; Ulen, Barbro

Abstract

The number of horses in Sweden has increased, from 77 300 in 1970 to 283 000 in 2003 (ca. 250%). These horses are kept on 300 000 ha, which represents 10% of total agricultural land in Sweden. Maximum recommended livestock density in Sweden is 2.5 units/ha for grazed pasture, but no limits have yet been set for outdoor keeping and feeding areas (paddocks) for horses. This study characterized the potential risk of phosphorus (P) losses from a horse paddock established on a heavy clay soil with a stocking rate of 3.75 livestock units/ha compared with nearby arable land. The horse paddock received 15 kg P/ha/yr and 75 kg N/ha/yr through horse excreta, while annual input of P and N to the adjacent arable land was 13 and 112 kg/ha, respectively. There was no significant difference in water-soluble P (WSP) in fresh and dried soil samples between the horse paddock (mean values: 0.62 and 0.43 mg/100 g soil; n = 15) and the arable field (mean values: 0.52 and 0.37 mg/100 g soil; n = 5). In contrast, phosphorus extractable in ammonium acetate lactate (extractable P) in the topsoil of the horse paddock (mean: 15 mg/100 g soil) was significantly higher (P = 0.03; n = 15) than in the arable land, whereas total P extracted with nitric acid (total P) showed no statistically significant differences. Furthermore, there was no significant difference in lactate-extractable iron and aluminium (extractable Fe and Al), organic carbon (C), total nitrogen (N) or phosphorus sorption index between the two parcels of land. However, the degree of P saturation in soil was significantly higher (P = 0.02; n = 15) in the horse paddock. Extractable Al and Fe were highly correlated to extractable P (P < 0.001; n = 69), the correlation being negative for Al. No relationship was found with calcium, but soil C content was found to be correlated with extractable P (P < 0.001; n = 69). Over the past 8 yr, high P concentrations (up to 1.5 mg/L), mainly in dissolved reactive form, have been recorded in drainage water from the grazed catchment. We concluded that horse grazing at high stocking rates (> 2.5 livestock units/ha) may pose a risk of high P losses to nearby water bodies.

Keywords

Phosphorus (P) losses; higher risk; horse paddock; livestock; arable land; drainage

Published in

Soil Use and Management
2011, Volume: 27, number: 3, pages: 367-375
Publisher: WILEY-BLACKWELL