Ökologisch-meteorologische untersuchungen an windschutzstreifen im nassen sommer 1968

Abstract

Shelterbelts show apart from positive effects (reduction of the soil erosion, improvement of the microclimate) also negative effects (shadowing). The relation between both is largely determined by the weather. Thus the loss of sensible heat out of the plant cover to the free atmosphere is reduced by wind shelter especially on clear days with strong radiation. A stress of the water balance of the plants, which frequently leads to a partial or complete closure of the stomata at such weather, is avoided by the simultaneously diminished transport of water vapour and by the hereby reduced evaporation. The measurements in the area of Düren/Rhineland in the wet growing year 1968 were firstly made to study the extent of the shelter effects on wind speed as a function of the lay-out and the composition of several mature shelterbelts. It could be shown, that the shelter effect of parallel rows of belts is markedly worse than that of a network of parallel and perpendicular rows with distances of 20 to 25 times the height of the belts. Relatively narrow belts consisting of one row of poplar trees with two to three filling rows of shrubs gave sufficient shelter effect. The microclimatological measurements showed an enormous loss of global radiation of the plants growing close to the shelterbelts. The soil moisture is not influenced by the shelterbelts at least in wet years. On the other hand, the daytime temperature of the air and the soil is higher in sheltered areas than in the open. The measurements were extended to determine the temperature of leaves, the water potential of the cell sap, the transpiration of leaves as well as the refractometer values of the root bodies of sugar beets. Evidence was obtained that the wind exerts a stress on the water balance of sugarbeets and, therefore, contributes to a reduction of the gas exchange. The results of the plant-ecological measurements were mutually supporting. These measurements may not only be a contribution to the methods of such investigations, they are also indispensable to understand the relations between the microclimate and the response of plant yield. Finally the measurements of the total yield as well as of some qualities of the harvested sugar beets showed that the positive effects of shelterbelts exceed the negative effects caused by shadowing even in a wet and cool year.