Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/1996
Publication Date: N/A
Interpretive Summary: Surface placement of crop residue with conservation tillage can improve soil physical, chemical, and biological properties compared with incorporation of residues with conventional tillage, resulting in significant reductions in wind and water erosion. Specific mechanisms that lead to increases in soil organic matter due to surface placement are not well understood. Whether surface-placed residues become more chemically resistant to decomposition needs to be investigated in order to better understand nutrient cycling under conservation tillage systems. Canola residue decomposition was greater when buried than when surface-placed, despite having a greater fraction of total N as lignin-bound N in residue remaining throughout the decomposition period. Our working hypothesis that surface-placed residue undergoes compositional changes leading to more microbially resistant residue remained unsubstantiated. At least for canola residue with low N quality, surface placement appears to spare residues from decomposition due to reduced contact with soil and more intensive drywing-wetting, rather than causing significant alterations in residue composition during decomposition.
Technical Abstract: Surface-placed crop residues protect agricultural soils from the destructive forces of wind and water erosion. We determined the compositional changes in C and N components of buried and surface-placed canola (Brassica campestris L.) residue 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 21.3 kg N/ha applied as canola residue, 7.9 kg N/ha was initially present as lignin-bound N and an additional 2.1 and 1.5 kg N/ha was sequestered as lignin-N when buried and surface-placed, respectively. In situ mineralization from total residue N was 87 and 82% of non-lignin-bound N in buried and surface-placement, respectively. These features of crop residues under conservation tillage systems are important for protecting soil from erosion and improving water infiltration and utilization by crops.