INFLUENCE OF PRIMARY TILLAGE ON DENSITY, PORE VOLUME AND PORE-SIZE DISTRIBUTION OF AN ARABLE FARMING SOIL IN THE CENTER OF UPPER AUSTRIA .3.

In this contribution the results are presented of the influence of dif ferent primary tillage methods on soil density, pore volume and pore s ize. The type of soil under investigation was a deep medium-heavy calc ium-free loose-sedimentary brown earth in semihumid climate. After ten years of customary tillage in a four-course rotation significant effe cts were registrated on all three factors mentioned above for the root ed top soil fraction. Under natural conditions the mean soil density i ncreases with increasing soil depth from 1.48 for the top soil to 1.56 g/cm3 for the compacted horizon below the tillage zone. After tillage , the density of the A(p) horizon ranged from 1.51 after ploughing to 1.59 g/cm3 in the rotary tiller variant. During the vegetation period (after sowing up to the next soil preparation) the soil density steadi ly increases to a small extent. The results of the total pore volume s how the same tendency as described for the soil density, but in the op posite direction. During the vegetation period the highest value of 44 .20 % was detected after ploughing, 40.40 % in the cultivator variant and 37.70 % with the rotary tiller. The largest differences were found in the subsoil. The decrease in total pore volume was mainly caused b y the reduction of the fraction of large pores, the fraction of small and fine pores remained nearly constant. At the above mentioned locati on a yearly alternation of ploughing and of reduced cultivation within crop rotation could prevent the negative side effects of soil compact ing and concomitant yield reduction.