Strukturkalkning på lerjordar

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. Soil structure can be stabilised by different kinds of binding agents that armour the bond s between particles and micro aggregates. Calcium (Ca) is a binding agent which can be added to the soil with lime and stabilises the aggregates by cat ion exchange processes, concrete reactions and formation of mortar. The purpose of this work is to examine how different forms of lime can affect the soil structure and aggregate stability and to measure the effect on yield. The investigation included four field experiments with five treatments: a. no treatment b. slaked lime (Ca(OH2), 3 t/ha c. limestone meal (CaC03), 4 t/ha d. "sugar factory lime" (mostly CaC03), 8 t/ha E. slaked lime (Ca(OH2), 9 t/ha The water content of the top soil, before spring operations, showed that slaked lime improved drying of the soil in the layer 0-10 cm, and the largest effect was obtained by the higher amount (9 t/ha). At the time of sowing, the seedbed was examined. Aggregate size distribution, tilling properties and water content were examined, but no significant differences between the treatments were found. Aggregate stability was examined in the laboratory. The aggregates were subjected to an increasing intensity of disaggregation, both mechanically and chemically. In the two mechanical steps of degradation, mild and heavy, there were in some cases beneficial effects of lime on the aggregate stability. The amount of dispersible day, that is the amount of day detached from the aggregates, showed some decrease in limed plots. Furthermore, the percentage of stable micro aggregates (20-200 µm) increased in the surface layer. More stable soil aggregates will increase the ability of the soil to retain its structure under the action of e.g. water and heavy machinery. The harvest of sugar beets in the field experiments showed a considerable increase in sugar yield in limed plots. In plots with large amounts of slaked lime the increase was 10% compared to the plots with no lime. The increase in sugar yield was between 2 and 5% in the other treatments. There is no doubt that lime has influence on the soil structure or that liming can give rise to considerable increases in yield. Further investigation should concentrate on the liming effects in combination with early sowing. There are reasons to believe that the beneficial effects of liming on soil structure are greater at early sowing