Root length density and water uptake in cereals and grain legumes: how well are they correlated

Abstract

Total root length per unit ground area (La) is often considered to be directly related to the amount and rate of water uptake. Experiments were conducted to compare the water use of spring wheat, barley, lupin (L. angustifolius) and field pea on four differing soil types in drought-stressed conditions. The La values of cereals were consistently five to ten times as large as those of grain legumes, whereas the aboveground biomass was sim~iar and never greater than twice that of the grain legumes. Growing-season water loss (WL) from the soil profile was very similar for wheat and lupins, despite this big difference in root length. Soil evaporation may have been greater under lupins, but when crop water uptake was compared for the period when leaf area was greatest, rates of change in soil water content within the root zone were still similar and were not well correlated with La. Specific root water uptake (Ur) was consistently greater for lupin than wheat. Maximum rooting depth was better correlated with WL than was La in all cases. Higher Ur values in lupin and pea may be related to their large and abundant metaxylem vessels, which give much lower axial resistance than in cereals. These results provide strong evidence for genotypic variation in root morphology, density and root extension between dicotyledenous and monocotyledenous species. They also indicate that La is not necessarily the root morphological characteristic most responsible for efficiency of water uptake in drought-stressed environments.

Mechanisms of drought resistance in grain: II Stomatal regulation and root growth

“…Besides root density and depth, root hydraulic resistance (the radial resistance from soil to root xylem) may have played a decisive role in water uptake of chickpea plants, so as to cover luxurious water demand. Likewise, root length density of wheat was substantially greater than that of lupines, while water uptake per root surface was higher in lupines (Hamblin and Tennant, 1987). Similar results were also reported for chick pea and barley, whereby chick pea plants were found to have lower root length density than barley, but absorbed water more efficiently than barley plants ( Thomas et al, 1995).…”

“…Similar results were also reported for chick pea and barley, whereby chick pea plants were found to have lower root length density than barley, but absorbed water more efficiently than barley plants ( Thomas et al, 1995). The difference in water use between these species was a function of root hydraulic conductivity, which is governed by the diameter and distribution of the meta-xylem vessels (Hamblin and Tennant, 1987), rather than by root density.…”

Ecological principles underlying the increase of productivity achieved by cereal-grain legume intercrops in organic farming. A review

“…These increasing concerns about environmental impacts and reduction of inputs require a transformation of current cropping systems for improved efficiency and sustainability (Cox and Atkins 1979;Jackson and Piper 1989;Vandermeer et al 1998;Griffon 2006). Organic farming is thus regarded as one prototype to enhance the sustainability of present agriculture and cereal-rich cropping systems because organic farming does not allow the use of chemicals and is also in general assumed to rely on higher crop diversity than its conventional counterpart.…”

“…Organic farming is thus regarded as one prototype to enhance the sustainability of present agriculture and cereal-rich cropping systems because organic farming does not allow the use of chemicals and is also in general assumed to rely on higher crop diversity than its conventional counterpart. Indeed, diversification of farming systems by increasing the number of cultivated species and including a larger proportion of legumes was proposed as a global response to the challenges of future agriculture (Vandermeer 1995;Vandermeer et al 1998;Altieri 1999;Griffon 2006;Malézieux et al 2009). Instead of using synthetic nitrogen fertilizers to increase farmland productivity in the short term and the overall farm production like for the Green Revolution, new systems could be designed based on symbiotic N 2 fixation by legumes.…”

Improving Drought-Avoidance Root Traits in Chickpea (Cicer arietinumL.) -Current Status of Research at ICRISAT

“…Root length density of chickpea has been shown to be substantially lower than that of barley but, absorbed water more efficiently than barley plants (Thomas et al, 1995). The difference in water use between these species was a function of root hydraulic conductivity, which is governed by the diameter and the distribution of the meta-xylem vessels (Hamblin and Tennant, 1987). Chickpeas have the ability to change their root distribution across soil depths depending on the soil moisture availability.…”