A field experiment was conducted at Fort Vermilion in northwestern Alberta, Canada, during 1998-99 and 1999-2000 to determine the amount of potassium (K) released from crop residues of four different crop rotations that included red clover [ Trifolium pratense] green manure, field pea, canola [rape] and spring wheat, under conventional and no-till seeding systems. Crops were grown on soils that had soil test levels of 150 ppm K (0.5M NaHCO 3-extractable), and no fertilizer K was added. Crop residues dry matter returned to the soil by the different crops were considerably higher in 1999-2000 relative to 1998-1999, reflecting the higher crop production during the 1999 growing season. Crop residue yield showed a large difference between the two study periods in the amount of total K being returned to the field. The results illustrate that all crop residues considered released more than 90% of their accumulated K in the 52-week period. The tillage system had no effect on the release of K from the crop residues.
