DECOMPOSITION AND NITROGEN MINERALIZATION FROM LEGUME AND NON-LEGUME CROP RESIDUES IN A SUB-ARCTIC AGRICULTURAL SOIL

An understanding of the C and N dynamics of crop residues is important for efficient nutrient management. The present experiment was conduct ed to determine the rate of mass and N loss from alfalfa, faba bean, b arley, and rape crop residues in a subarctic agricultural soil. Mass, C, and N losses were measured from residues contained in mesh bags and placed on the soil surface or buried 15 cm below the surface. The mas s loss from October, 1988, to May, 1989, was the same for surface and buried alfalfa, barley, and rape residues, averaging 40, 20, and 61%, respectively, while surface and buried faba bean residue sustained 30 and 40% mass loss, respectively. The mass loss of the buried residues continued over the summer but not of those placed on the soil surface, resulting in an average 23% greater mass loss of the buried materials after 1 year. The N loss from October to May was similar from the sur face and from the buried placements for the alfalfa, faba bean, and ra pe residues, averaging 11.3, 10.3 and 38.4 g N kg-1 residue, respectiv ely, while the surface and buried barley lost 2.9 and 4.2 g N kg-1, re spectively. The C:N ratio of all of the residues increased during the winter. These data indicate that the rate of decomposition and N miner alization from crop residues in subarctic environments can equal that measured in temperate climates. Furthermore, the concurrent loss of ma ss and N combined with an increase in the C:N ratio of the residues su ggests that physical rather than biological processes were functioning during the winter. Most of the mass and N loss from these residues oc curred during the winter, out of phase with crop demand, thereby creat ing the potential for N loss from the system and inefficient use of cr op residue N.