Effects of Compost and Tillage On Soils and Nutrient Losses in a Simulated Residential Landscape.

Research has shown that soil management practices (e.g., organic amendments, tillage) can improve soil physical and chemical properties.  However, it is not known if these management practices can significantly improve soil conditions in urban settings, specifically new residential areas.  The objective of this study was to evaluate the effects of compost and tillage on selected soil properties and nutrient losses in leachate.  A secondary objective was to determine the effect of vegetative cover type (e.g., turf, ornamental plants) on nutrient losses in leachate.  Six soil management treatments (unamended soil, tillage only, aeration only, compost only, compost + tillage, and compost + aeration) were evaluated (four replications) in mixed landscape plots on compacted soils.  Composted dairy manure solids were applied at a rate of 508 m³ ha^-1 and soil was tilled to a depth of 10-15 cm.  Soil properties, and leachate volume, NO₃-N, NH₄-N and dissolved P were assessed periodically.  Results of our study suggest that the addition of compost to soils can improve soil properties in residential landscapes when fill soils are used.  Tillage and aeration had little effect on soil properties.  Compost applications reduced bulk density and pH and increased soil organic matter, electrical conductivity and concentrations of Mehlich 1 P, K, Ca, and Na.  Soil treatments and vegetative cover had no affect on P concentrations in leachate.  Leachate N concentrations and load were highest from compost amended soils and under mixed ornamental vegetation.  Losses of NO₃ + NO₂ were highest during the early weeks of the study, while NH₄ losses peaked during the summer when organic N began to mineralize.  Since the addition of compost increased the potential for nutrient losses in leachate, there are concerns that large volume one time applications of low C:N ratio organic amendments to soils may lead to significant N losses.