Microorganisms such as fungi may “tie up” nitrogen as they feed on the wood, potentially leaching nitrogen from the soil. However, if sufficient topsoil, greens, and mulch are provided, this is rarely ever a problem. Plant roots also take time to reach the decomposing wood layer, so the nitrogen will be freed up by then. Planting with nitrogen-fixing plants such as legumes during the first year may also help with this issue.