LEACHING OF NITROGEN IN BARLEY, GRASS LEY AND FALLOW LYSIMETERS

The leaching of nitrogen from fallow, fertilized and unfertilized spri ng barley, and grass ley was studied in a 4-year lysimeter experiment carried out on clay, silt and sand soils, and Carex peat. The experime ntal factors included also irrigation and treatments where the nitroge n fertilizer was applied in the first year as N-15-labelled ammonium n itrate. During four years, 41-66% of the nitrogen applied in the first growing season was recovered in plants harvested. Most of it, 91-96%, was taken up in the year applied. Mostly, the water drainage was lowe st in silt and sand soils. The irrigation increased clearly the leachi ng of nitrogen almost in all treatments. Crops decreased the drainage of water through the lysimeters and the leaching of nitrogen, grass mo re than barley. The effects of plants and irrigation were similar in a ll soils, but most marked in sand. The largest amount of nitrogen was leached in irrigated, fallowed sand, 440 kg ha-1, during four years. T he majority of the leached nitrogen was nitrate. Only in peat soil a s ignificant amount of nitrogen was leached in some another form. The le aching of N-15-labelled fertilizer during four years was highest in sa nd, 2.3 kg ha-1 of N or 2.3% of the nitrogen applied in the first expe rimental year.