Stem nitrate nitrogen and yield of wheat in a permanent rotation experiment

Abstract

The growth of wheat on the permanent rotation experiment at the Waite Agricultural Research Institute was examined over two seasons. Measurements of stem nitrate nitrogen concentration were used to assess the effect of nitrogen on yield for treatments which can also affect the availability of water and the severity of pests and diseases. High nitrate nitrogen was positively correlated with yield in a wet year, but its importance changed between years and was determined by rotation and environmental conditions. On average the sequence oats-oats for grazing-fallow-wheat had the highest nitrate nitrogen and the highest long-term mean yield, even though it had no apparent nitrogen input. Rotations which included grass-clover phases can be more severely infested by pests and diseases, and the wheat less able to respond to favourable nitrogen supply than rotations which included fallow or a non-host crop.