Development of a model estimating root length density from root impacts on a soil profile in pearl millet (Pennisetum glaucum (L.) R. Br). Application to measure root system response to water stress in field conditions

Abstract

Pearl millet is able to withstand dry and hot conditions and plays an important role for food security in arid and semi-arid areas of Africa and India. However, low soil fertility and drought constrain pearl millet yield. One target to address these constraints through agricultural practices or breeding is root system architecture. In this study, in order to easily phenotype the root system in field conditions, we developed a model to predict root length density (RLD) of pearl millet plants from root intersection densities (RID) counted on a trench profile in field conditions. We identified root orientation as an important parameter to improve the relationship between RID and RLD. Root orientation was notably found to depend on soil depth and to differ between thick roots (more anisotropic with depth) and fine roots (isotropic at all depths). We used our model to study pearl millet root system response to drought and showed that pearl millet reorients its root growth toward deeper soil layers that retain more water in these conditions. Overall, this model opens ways for the characterization of the impact of environmental factors and management practices on pearl millet root system development.

A Deep Learning-Based Phenotypic Analysis of Rice Root Distribution from Field Images

“…In the traditional trench profile method, root length density is measured directly in the field or in the laboratory after collecting soil blocks from the field [ 12 , 22 , 23 ]. To the contrary, CNN-based image analysis requires only image data, meaning that all we need to do outdoors is to take pictures after flushing the trench profile wall.…”

“…The trench profile method is a technique to observe the vertical and horizontal root distribution of crops [ 10 ] by digging a vertical ditch beside the plant to quantify the distribution of roots present in the profile wall. The proportion of observable roots is the largest compared to the other field methods, and this technique is used for studying soil condition–root growth interactions [ 11 , 12 ] and for the basic characterization of crop root distribution [ 13 ]. The auger method is a sampling method primarily used to quantify vertical root distribution [ 10 ].…”

“…Typically, the trench is dug perpendicularly using a backhoe [ 11 , 22 ]. The distance between the trench and plant influences the root distribution on the profile wall [ 12 , 23 ]. Furthermore, the depth of the trench should be determined by the rooting characteristics of the target crops [ 12 , 13 , 22 ].…”

“…The distance between the trench and plant influences the root distribution on the profile wall [ 12 , 23 ]. Furthermore, the depth of the trench should be determined by the rooting characteristics of the target crops [ 12 , 13 , 22 ]. Root distribution on the profile wall is evaluated by sectioning the wall vertically and horizontally and measuring root density in each section.…”

“…Root distribution on the profile wall is evaluated by sectioning the wall vertically and horizontally and measuring root density in each section. For measuring root density, soil blocks [ 12 ] or core samples [ 22 ] were collected from each section, and root length was then measured. Otherwise, after removing a few centimeters of soil from the wall surface using a scraper, air pressure, or nebulizer for easy root observation and measurement [ 10 ], the root density in each block was estimated by root intersection counting based on their correlation relationship [ 23 ].…”