Sugar beet growth is often impaired by cold and compacted soil. The aim of the study was to determine the effect of soil temperature and soil compaction on the growth and function of sugar beet roots. For this purpose a pot experiment with sugar beet (Beta vulgaris) was conducted in a growth chamber, in which the soil temperature was kept constant either at 10°C or 20 °C and the air temperature at 20 °C. The soil was uncompacted (1.30 g cm-3) or compacted to a bulk density of 1.65 g cm-3. In order to find out whether the growth restriction was caused by insufficient P supply of the plants the experiment was run without and with P application (300 mg per kg soil).Root growth was much smaller at 10°C compared to 20 °C, whereas root/shoot ratio was not affected by soil temperature. Hence, root and shoot growth was inhibited to the same extend. P content of the plants was not reduced, neither by cold nor by compacted soil, although parameters of acquisition such as root length and morphological root properties were altered. Soil temperature strongly affected P influx, whereas compaction did not. The calculation with a simulation model showed that at 10 °C soil temperature the predicted P uptake of the plants agreed with the measured P uptake irrespective of compaction and P application. However, at 20 °C the model underestimated the P influx at low soil P availability even if allowance was made for root hairs. It is concluded that under conditions of high shoot P demand and low P availability in soil P has been mobilized by mechanisms not taken into account by the model.