For good crop emergence, the seed should be placed at a depth where good conditions concerning oxygen, temperature and water are provided. To place the seed in the soil, some type of see d coulter is used. Väderstad-Verkens Rapid is a seed drill that places the seed at a certain depth in relation to a wheel running on the ground. This can lead to a to shallow seed placement. On fields with clayey soils and spring sown cereals a to shallow seed placement can lead to poor emergence, especially if there is no rainfall after seeding. To improve the ability of the Rapid drill to place the seed in moist soil, Väderstad-Verken has developed a spring-loaded coulter. This coulter, like the ordinary Rapid coulter, is placed beside a disc but it can move up and down approximately 15 mm. The idea is to make a coulter which is adjusted to follow the soil mechanical resistance and place the seed in an environment favorable for germination. The aim of this thesis was to compare the performance of the new spring-loaded coulter with the ordinary Rapid coulter. A field experiment was carried out to investigate seed placement and germination. Oats were sown in the spring with three different coulters, one ordinary Rapid coulter and two spring-loaded coulters with different spring-forces, at three different sowing depths. In another experiment the go al was to study how the spring-loaded coulters were moving during sowing. Two linear position sensors were used to measure the movement, one on a coulter with high spring-force and one on a coulter with low spring-force. Three different working speeds and four different sowing depths were used during the test. Compared with the ordinary Rapid coulter the spring-loaded coulters placed a higher proportion of the seeds at a correct depth. Also the plant emergence was better for the spring-loaded coulter. There was little difference in seed placement and plant emergence between the high and low spring-force coulter. The coulter with high spring-force worked deeper and with less standard deviation than the coulter with low spring-force. Both coulters worked more shallow in relation to the disc when the sowing depth or working speed was increased. The standard deviation of the coulter movements was only slightly affected by the sowing depth. The coulter movements were compared with the relief of the seedbed bottom, as measured by a laser. There was no significant relation between the coulter movements and the shape of the seedbed bottom. The advantage of the spring-loaded coulter was that it manages to work deeper than the ordinary Rapid coulter. To make the spring-loaded coulter more able to follow the uneven bottom under the harrowed layer some changes in the design might be necessary. The coulter must be able to move more, especially downwards. The coulter should have longer pivot arm with a low pivot axis and less friction in the suspension joint. Furthermore the spring force should be adjustable. To conclude which is the best design more experiments on different prototypes are necessary.
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