Winter Applied Slope Trial


To assess the environmental impact of land application of sludge without incorporation in terms of soil quality and surface water quality in areas with slopes >5%, and on frozen, and frozen and snow covered soils


The Winter Applied Slope Trial was initiated by SLP in 2000 at NE and SE 27-71-4-W5.  The trial included:

  • Operational plots which received sludge in non-frozen, frozen and frozen – snow covered conditions
  • 3 sludge application rates: 0, 30 or 60 t/ha. 
  • Extent of suckering, tree growth performance, and growth of understory cover were assessed
  • Aspen suckers were tagged and measured in each of the sludge amended and control areas in 2000
  • Measurements were obtained from 2001 to 2007 and in 2010.  

Results and Conclusions

  • Visual observations of the vegetation growth indicated that sludge application resulted in significant increases in vegetative cover. 
  • There was no indication of erosion or sludge loss after application as it was held on the soil surface by the vegetative cover.
  • The largest difference in volume between the control trees and treatment areas occurred in the 60 t/ha snow and frozen application area, mainly as a result of the large difference in diameters. 
  • All other treatments showed greater volumes than the control, however were similar to each other. 
  • Soil samples indicated that the increases in EC, sodium content, and SAR levels were similar for all of the sludge amended plots. 
    • The largest change occurred in the surface (0 to 15 cm depth) and the underlying 15 to 30 cm depth intervals. 
  • Some leaching of sodium was evident down to the 1 m depth based on the SAR values ranging from 3.5 in the 15 to 30 cm interval, to 1.7 in the 75 to 100 cm interval. 
  • No observed increase in NO3-N levels or evidence of any leaching resulted from the sludge application.
  • Surface water sampling conducted indicated that the applied sludge had no effect on surface water quality in the small temporary depressional areas downslope from the treated areas. 
  • The stream samples collected indicated that there was no impact on water quality below or downstream from the sludge treatment areas. 
Area Application Rate (t/ha) Age Shift Growth Multiplier
 Height Diam Height  Diam 
SLP Winter Applied
Slope Trial
Snow 30 -0.2 7.4 0.99 1.30
Snow 60 6.5 10.6 1.28 1.42
Frozen 30 1.9 10.1 1.08 1.40
Frozen 60 -0.6 8.3 0.97 1.33
Not Frozen 30 4.8 4.9 1.20 1.20
Not Frozen 60 -0.8 4.3 0.96 1.17