Wheat straw decomposition in subtropical Australia .II. Effect of straw placement on decomposition and recovery of added 15N urea

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Abstract
Decomposition of 14C-labelled wheat straw and its effect on fertilizer 15N transformations was studied in a subtropical environment over a 2 year period. The effect of straw management was also studied. Wheat straw incorporated in topsoil initially decomposed at a faster rate than wheat straw placed on the soil surface. This was due to the greater positional availability of straw carbon to soil organisms in incorporated straw. Later decomposition rates were similar. After 1.5 months, 44% of applied 15N-urea was recovered from incorporated straw treatments and 55% from surface-retained straw treatments. Losses were attributed to biological denitrification. The greater loss in incorporated straw treatments was suggested to be due to a greater availability of carbon to the denitrifying population compared with treatments where straw was retained on the surface. After 2 years, the recovery of 15N decreased to between 12 and 15% of that applied.