DECOMPOSITION OF BARLEY STRAW IN A SUB-ARCTIC SOIL IN THE FIELD

The mass loss and N dynamics of barley stems and leaves, placed on the soil surface or buried, were examined over two summers. There was little difference in mass loss or N dynamics in straw placed 7.5 or 15 cm deep. However, the surface straw lost mass much more slowly and immobilized more N for a longer time than the buried straw. Filter paper had a slow rate of mass loss initially, but once started, lost mass much more rapidly than either the barley stems or leaves. Loss of mass was closely correlated with the cellulose loss in straw, whether buried or placed on the soil surface. The sustained rate of mass loss was 6.3 and 7.0% month-1, respectively, for surface and incorporated leaves compared with 3.5 and 4.3% month-1, for surface and incorporated stems. The greater loss sustained by the leaves was attributed to a lower lignin content rather than a higher N content, because the addition of N to the straw after 30 days in the field failed to increase CO2 evolution. Maximum net N immobilization occurred within 30 days for all the barley straw, except for the stems placed on the ground surface, which did not reach maximum N immobilization until the second summer. Immobilization and mineralization of N were estimated for a 3000 kg ha-1 grain crop. Surface straw immobilized 3.8 kg N ha-1 in the 1st year and 9 kg N ha-1 in the 2nd year, whereas incorporated straw immobilized 3.5 kg N ha-1 in the 1st year and mineralized 4.5 kg N ha-1 in the 2nd year. Thus, in Alaska, residue management does not affect N fertilizer requirements in the 1st year, but an additional 13.5 kg N ha-1 is required for surface residues in the 2nd year.