NITROGEN-FERTILIZATION OF BARLEY WITH REGARD TO SOIL MINERAL NITROGEN AND CLAY CONTENT IN 2 AREAS OF SWEDEN

We conducted 21 nitrogen experiments in two different areas of Sweden between 1980 and 1982, one area in western Sweden and one in the east. Nine experiments were conducted on soils containing less than 15% clay, and 12 on soils containing more clay. Nitrogen rates were 0, 30, 60, 90, 120, 150, 180, and 240 kg/ha N as calcium ammonium nitrate (Nitrochalk, 28% N). Soil mineral N in the spring (NH4-N + NO3-N) was determined before fertilizer application. Sampling depth was 90 cm. Nitrogen fertilizer raised grain yields significantly. Grain yields were the highest in the western region. The difference equaled 600 kg/ha of grain. They were also the highest in the > 15% clay group. The latter difference may be a consequence of differences in soil mineral N between the soil groups, and the former mainly depends on precipitation differences. During the experimental period the precipitation totals from April until July in the western region were 10 to 99% above those in the eastern region. Mineral N in soil in the spring varied between 27.8 and 142.5 kg/ha in a 90-cm deep profile. The very high figure of 142.5 kg was due to application of farmyard manure the previous year. Mineral N was the lowest in the .ltoreq. 15% clay group, and it was lower in 1981 than in the other two years. The grain yield response to 90 kg/ha, N (y90) showed a negative relationship with soil mineral N. This was most clearly demonstrated in the western region, probably because of more favorable precipitation conditions there. The y90 decreased 11.8 to 81.9 kg/ha by a 1-kg/ha increase of soil mineral N. The greatest impacts of soil mineral N on the y90 were in the .ltoreq. 15% clay group.