Nutrient leaching from manure-amended topsoils (Cambisols and Histosols) in Sweden

Due to rapid growth of the horse industry in the EU, manure production from horse farms has become substantial. Horse manure is a valuable resource in terms of plant nutrients that should be utilised primarily as a fertiliser and soil conditioner on agricultural soils, but in an environmentally friendly manner. This study estimated potential retention and leaching losses of phosphorus (P), nitrogen (N) and carbon (C) from two mineral (Nåntuna loamy sand and Wiad loam) and one organic (Hidinge peat) agricultural topsoil amended with two levels of composted horse manure, 18 and 36 megagram (Mg) ha− 1, compared with non-amended control soil. Soil columns (20 cm long, 18.8 cm diameter) were exposed to three consecutive simulated rainfall events with an intensity of 8 mm h− 1 and a pore volume of 100 mm each time, which resulted in about 280 mm total discharge. Results showed that the background losses from Hidinge peat were several-fold higher (8 kg P, 122 kg N, 235 kg C ha− 1) than from Nåntuna loamy sand (0.05 kg P, 2 kg N, 12 kg C ha− 1) or Wiad loam (1.6 kg P, 24 kg N, 19 kg C ha− 1). On applying composted horse manure the leachate concentrations of P, N and C significantly increased for the mineral soils, but only at the high application rate of 36 Mg ha− 1. Unexpectedly, P, N and C concentrations in leachate from organic soil decreased after manure addition, indicating greater potential for retention than leaching. The increased amounts of P, N and C lost from Nåntuna loamy sand and Wiad loam corresponded to less than 10% of the amount added via composted manure, indicating high potential for retention. We concluded that composted horse manure can improve soil nutrient status, as potential nutrient retention was higher than leaching from manure-amended soils, and that information on background nutrient content in soil may be more important than data on nutrient load applied through amendments when assessing retention and/or leaching potential in manure-amended soil.