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

Abstract

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 3 severely reduced, indicating that prevention of drought is necessary, early on, to minimise yield losses.

Sugar beet root growth under different watering regimes: A minirhizotron study

“…In some layers a delay was observed between roots reaching a certain depth and water uptake from that depth. A possible explanation for this could be that the xylem had yet to mature before optimum water uptake could take place (Mapfumo et al 1993;Fitters et al 2017). In 2017, this delay between roots reaching a depth and there being water uptake was more pronounced.…”

“…This could eventually be translated into recommendations depending on soil type and average weather patterns for a certain region. As well as looking at root architectural traits breeders could look for varietal differences in the rate of xylem maturation which has been found to limit water uptake for a few weeks after new roots have formed (Fitters et al 2017).…”

“…Compaction results in poor root growth, often at depth, and this, in turn, results in reduced water uptake from compacted soil layers (Kirkegaard and Lilley 2007). Root tissue development can be limiting when new roots are initially formed and the xylem tissue has not matured for optimum water uptake, as reported in grapevine and sugar beet (Mapfumo et al 1993;Fitters et al 2017).…”

“…During periods of drought, roots proliferate in soil layers with higher water availability (Li et al 2002;Padilla et al 2013). In sugar beet, roots can grow to over one metre deep and take up water from that depth if there are no soil constraints (Fitters et al 2017). However, when there is compaction, sugar beet hardly show any root proliferation in deeper layers before mild to severe drought occurs (Romano et al 2012).…”

“…However, when there is compaction, sugar beet hardly show any root proliferation in deeper layers before mild to severe drought occurs (Romano et al 2012). Once drought occurs root proliferation at depth starts (Koevoets et al 2016), but delays in root tissue development at that time can prevent immediate water uptake (Fitters et al 2017).…”