Assessing water uptake in sugar beet (Beta vulgaris) under different watering regimes

Sugar beet yield worldwide is substantially reduced as a result of drought stress. Water uptake may be limited by the plant (e.g. low root density) or by soil physical constraints. An experiment was conducted to assess the ability of sugar beet to produce roots and take up water throughout the soil profile under contrasting water regimes. Sugar beet was grown in columns, 15 cm in diameter and 1 m height in a glasshouse. In situ soil moisture was monitored hourly, and stomatal conductance was measured weekly. Root length and diameter at different depths were assessed destructively at 78 and 94 DAS. Greater water availability resulted in a higher root length and lower water use efficiency. Water uptake was initially from the upper soil layers but, as demand for water increased, there was a strong increase in root length density at depth. However, it was a further 16 days, after roots reached the deep layers, before significant water was taken up. A possible reason for the delay, between presence of roots and water uptake by roots, was the absence of secondary xylem early on, which was supported by a second root anatomy study. Sugar beet can grow roots up to 1 m deep and take up water from depth, however this did not happen until the late stages of drought stress and thus storage root dry weight had already been severely reduced, indicating that prevention of drought is necessary, early on, to minimise yield losses.