Epsilon Archive for Student Projects

Abstract

The number of horses in Sweden has increased in recent decades, reaching over 300,000 in 2009. The horses are kept on 300,000 ha representing 10% of total agricultural land in Sweden. This study characterised the potential risk of phosphorus (P) losses from a heavy clay soil used for horse grazing and feeding (paddock) and compared the losses with nearby arable land managed conventionally and losses from ungrazed pasture. Water-soluble phosphorus (WSP) concentration in surface soil (0-10 cm) from the paddock areas (mean 0.62 mg 100 g-1 soil) did not differ significantly from that in arable land, but differed very significantly (p<0.001) from reference areas with ungrazed pasture. Phosphorus extracted in acid lactate (P-AL value) in the topsoil of paddock (mean 14.7 mg 100 g-1 soil) differed significantly both from arable land and ungrazed pasture (p=0.031 and 0.033, respectively). Total phosphorus extracted with nitric acid (P-HNO3) in topsoil of paddock areas (mean 117.3 mg 100 g-1 soil) did not differ significantly from arable land (p=0.08) but was significantly higher (p<0.001) than in ungrazed pasture. Paddock soils with high levels of different P forms, thus, pose a high risk of P losses. Aluminium and iron content in acid extract (Al-AL and Fe-AL) were found to be highly correlated to P-AL (r=0.76, p<0.001; r=0.75, p<0.001, respectively), indicating no significant difference for the dominance of Al over Fe for P availability in the fields studied. No good correlation was found with Ca (r=0.26, p=0.03) but soil C content was found to be correlated with P-AL (r=0.46, p<0.001). In the past 8 years, high P concentrations (up to 1.5 mg L-1), mainly in dissolved reactive form, have been recorded in drainage water from the catchment (30 ha). Therefore, we concluded that horse grazing at high stocking rates (>2.5 livestock units ha-1) may pose a risk of high P losses to nearby water bodies.