Alterations in canola residue composition during decomposition

Surface-placed crop residues protect agricultural soils from the destructive forces of wind and water erosion. Knowledge of changes in residue composition during decomposition of differentially placed crop residue is important in understanding the potential effects of conservation tillage systems on soil quality properties, including C and N conservation and soil tilth. Compositional changes in C and N components of buried and surface-placed canola (Brassica campestris L.) residue were determined during decomposition in a cold, semiarid climate. Decomposition during the period of 23 March to 24 August 1995 was 57 and 30% for total mass, 53 and 25% for acid-detergent fiber, 46 and 46% for total N and 17 and 17% for lignin components when residue was buried and surface-placed, respectively. Of the 2.13 g N m−2 applied as canola residue, 0.79 g N m−2 was initially present as lignin-bound N and an additional 0.21 and 0.15 g N m−2 was sequestered as lignin-N when buried and surface-placed, respectively. In situ mineralization from total residue N was 87 and 82% of non-ligin-bound N in buried and surface-placement, respectively. Surface-placed canola residue had greater mass remaining and lower total and lignin N concentration than buried residue. These features of crop residues under conservation tillage systems are important for protecting soil from erosion and improving water infiltration and utilization by crops.