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

Abstract

The yield of sugar beet is often reduced by drought stress and it has previously been shown that water uptake, especially from deeper layers of the soil profile, may be limited by inadequate total root length. Experiments were conducted to assess root growth at different depths in response to specific watering regimes. Sugar beet plants were grown in wooden boxes (2.16 m 2 x 1.2 m) in a polytunnel in two consecutive years. Minirhizotrons allowed regular monitoring of root growth at five different depths. Only when water in the upper soil layers had been depleted, did roots start proliferating in deeper soil layers. This development of the root system architecture, together with a lag between roots arriving at depth and actively taking up water, led to a delay in water being extracted from those deeper layers. During the period when roots were proliferating at depth, stomatal conductance reduced, indicating that the plants were suffering from water stress despite there still being water available. Even though new soil layers with high water availability were explored the stomatal conductance did not recover.

Water use efficiency responses to fluctuating soil water availability in contrasting commercial sugar beet varieties

“…Increased WUE i under water deficit, as evident in our results, has been shown previously in sugar beet ( Bloch et al., 2006 ; Rinaldi and Vonella, 2006 ; Fitters et al., 2018 ). As the water deficit increased the stomata began to close to conserve water and g s declined with the reduction in transpiration causing an increased canopy temperature ( Baker et al., 2007 ).…”

“…The increase in chlorophyll content was opposite to that typically observed under drought for many species such as maize ( Din et al., 2011 ) and rice ( Pirdashti et al., 2009 ) and there was no change in the ratio of chlorophyll a and b which is also sometimes observed ( Saeidi and Zabihi-e-Mahmoodabad, 2009 ). However, an increase in chlorophyll content has previously been reported in sugar beet exposed to drought ( Hussein et al., 2008 ) and increased SPAD values (a proxy for chlorophyll content) were observed in sugar beet exposed to high level water deficits by Fitters et al (2018) , although these differences were no longer present after re-watering and were attributed to a dilution effect. No such dilution effect is evident in this study as leaf water content was measured at the same time as collection of leaf discs for chlorophyll extraction.…”

Water use efficiency of sugar beet genotypes: A relationship between growth rates and water consumption

“…Under drought stress conditions in the field, fibrous root growth can exploit water resources in deeper soil layers (Morillo‐Velarde & Ober, 2006; Scott & Jaggard, 1993). However, Fitters et al (2017), Fitters et al (2018) observed a duration of up to 16 days for new roots to exploit water resources in deeper soil layers. During this time, yield restrictions due to drought should have already occurred, so that drought stress cannot be completely avoided by a deeper root system (Hoffmann et al, 2020).…”

Cover crop effects on soil structure and early sugar beet growth

“…Colombi et al (2017) furthermore found that crop roots actively grow towards artificial macropores in compacted soil, enhancing crop productivity. At the early stage of sugar beet growth, at which sampling took place in our study, sugar beet roots in the plough pan may be developed only to a small extent (Fitters et al, 2018; Windt & Märländer, 1994). However, as a result of the high water uptake rate by sugar beet roots (Windt & Märländer, 1994), slight advantages in root growth at this stage of development might be sufficient for considerable gains in crop growth.…”