Water withdrawal by plant roots

Abstract

As part of a study dealing with the influence of some environmental conditions on plant growth, water withdrawal patterns of Red Cabbage ( Brassica oleracea L., c.v. Rode Herfst) grown on a sticky clay soil are analyzed. An analysis of the transport resistance for liquid flow in the plant as well as an investigation on the geometry factor of the root system for red cabbage is presented. The variation of these factors with depth is described, and root extraction rates at different depths are calculated and compared with data obtained from water balance studies. The plant resistance data are in reasonable agreement with existing literature. Because of a non-homogeneous and poor root development in the early stages of growth, the geometry data of the initial growing stages differ a factor ten from data found in literature. With root development increasing with depth, geometry data decrease to values also reported for other crops. From calculations it is shown that at increasing drying out of the soil the geometry factor is slightly affected, but the plant resistance increases considerably. The latter resistance, however, decreases when the evaporation flux from the plant increases. This phenomenon is mainly caused by the root distribution in the soil with depth, resulting in a relatively higher water uptake from the top layers, as compared with the deeper layers, when the evaporation flux increases. The obtained results may at least partly explain the apparent non-Darcian behaviour of the flux of water through the plants, sometimes reported in literature.