Denitrification and immobilisation in flood-irrigated alkaline grey clays as affected by nitrification inhibitors, wheat straw, and soil texture

Published field studies have shown that etridiazole and other nitrification inhibitors may significantly improve N fertiliser recovery in alkaline grey clays. Laboratory experiments were conducted to examine the extent to which nitrification inhibitors could suppress denitrification directly in waterlogged soil, and determine whether this may contribute significantly to the conservation of N fertiliser in the field. Etridiazole reduced the loss of added nitrate-N from waterlogged soil in the short term (days) only. All other nitrification inhibitors failed to suppress N loss. Little nitrate-N was lost from soil maintained at field capacity, whereas 15-85% of applied nitrate was lost from soil that was waterlogged for 10 days. The addition of milled wheat straw encouraged both denitrification and biological N immobilisation to similar extents, although both processes were probably restricted by C availability. Where no straw was added, little N was immobilised and denitrification was halved. Soil texture (clay content) also had a profound influence on N fertiliser recovery (N loss). The laboratory experiments indicated that a component of the responses to etridiazole observed in published field experiments conducted on these soils could be attributed to direct suppression of denitrification by etridiazole.