EFFECT OF NITROGEN-FERTILIZER RATE ON SOIL NITRATE NITROGEN-CONTENT AFTER HARVESTING WINTER-WHEAT

The nitrate nitrogen content of the soil (0–90 cm) was measured immediately after the harvest of winter wheat at eight sites in central and eastern England in 1987 and 1988. On average, 50% of the total nitrate detected was in the 0–30 cm, 30 % in the 30–60 cm and 20 % in the 60–90 cm soil horizon. Although soil nitrate N increased with the amount of N fertilizer applied, it was not a linear relationship. There were small nonsignificant increases in soil nitrate up to the ojtlimum fertilizer rate for yield but, once the ojtlimum was reached, further addition of fertilizer increased nitrate contents significantly. Therefore, applying the correct quantity of N for high grain yield did not significantly increase soil nitrate residues after harvest compared with the no-fertilizer treatment. This emphasizes the importance of applying the appropriate rate of N for each crop, because applying too much is not only uneconomic but also significantly increases the amount of mineral N which could be subsequently leached over the winter. © 1990, Cambridge University Press. All rights reserved.