Biologisk alvluckring

Soil structure can be defined as the arrangement of particles in soils. Size of particles, type of minerals and organic matter is of great importance for the development of soil structure and its stability. A good soil structure also has pores of different sizes and consequently a good infiltration of water and air which is very important for plantgrowth and for a good harvest. The purpose of this work is to examine how much one year of ley of either red clover (Trifolium pratense) and meadow fescue (Festuca pratensis) or alfalfa (Medicago sativa) and meadow fescue (Festuca pratensis) compared to winter wheat affects soil structure and in the end the harvest of the following sugar beets. The mean sugar yield at the experimental sites was high with a relatively big variation between the experimental sites. There were overall no significant differences in sugar yield depending on the preceeding crop. However, the number of sugarbeet plants was significantly lower after winter wheat than after alfalfa as preceding crop. At one experimental site the winter wheat as preceding crop gave significantly higher sugar yield compared to alfalfa. The other experimental sites showed no significant differences in sugar yield. Measurements of infiltration rate in the topsoil showed that the infiltration rate generally was much higher after red clover and alfalfa than after winter wheat. The infiltration rate in the subsoil showed no significant differences between treatments but the tendency was the same as in the topsoil. The infiltration rate showed no correlation with the yield of sugar beets, however in same plots at one experimental site there were both lower infiltration rates and lower yield of sugar beets compared to other plots. The number of earthworms in the topsoil was generally many times larger after red clover and alfalfa than after winter wheat. The number of roots and wormholes at different depth in a profile were correlated. The amount of organic material in the soil showed no difference between the treatments. The amount of organic material and the water stability of soil aggregates did not affect the yield of sugar beets. Measurements of pH in water in the topsoil showed that low pH could have affected the sugar yield in a few plots at one of the experimental sites. Comparison with other measured parameters showed that the same plots with low infiltration rate in the subsoil also had low pH and lower yield of sugarbeets than other plots. The reason why the two leys as preeeding crops to sugarbeets did not have a more positive effect on the soil than the winter wheat, can depend on the time the ley was grown. One year of ley might affect the soil structure as much as winter cereals e.g. winter wheat. Longer time (more than one year) could have a stronger effect on the amount of organic material in the soil and the effects could prevail for a longer time. Also a better pore size distribution could be achieved