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.