A study of the tensile force required to pull wheat roots from soil

Abstract

SummaryExperiments were carried out to determine the tensile properties of mature wheat roots and the force necessary to pull roots from undisturbed soils at a range of moisture contents using an Instron materials testing rig. Roots decreased in cross sectional area from 1.5 to 0.1 mm2and in tensile strength from 7.0 to 2.3 Newtons (N) along the first 12 cm of their length. Breaking strain was constant along the root but the breaking stress increased. Increased seeding rate decreased root diameter and tensile strength but plant growth regulators and fertiliser nitrogen level did not affect the tensile properties. Roots were pulled from mesh tubes of soil (25 mm ± 75 mm) into which they had grown. The peak loads for sandy clay loam and sandy loam soils were 4.8 and 3.9 N respectively and increasing the soil moisture from 17% to 26% reduced the peak load from 5.2 N to 3.5 N. With the drier soil the inner stele pulled free leaving the outer periderm in the soil in a higher proportion of the roots indicating a stronger root/soil bond than in the wetter soil. The load us displacement relationship when pulling roots from soil resembled that for a fibre reinforced composite material. The presence of branch roots resulted in an uneven trace in which there were a number of sub‐peaks as branch roots gave way. It is suggested that soil wetting could contribute to lodging of wheat by reducing the resistance of roots to slippage and breaking.

The Supporting Roots of Trees and Woody Plants: Form, Function and Physiology

“…We obtained the inverse phenomenon, when the soil is wet. These two observations support the findings of Easson et al (1995) during the study of the tensile properties of wheat roots.…”

Influence of root characteristics and soil variables on the uprooting mechanics of Avena sativa and Medicago sativa seedlings

“…Furthermore, root breaking occurred more frequently with decreasing moisture content. Several authors related drops in the force–displacement curves to root breaking (Blackwell et al ., ; Ennos, ; Easson et al ., ; Bailey et al ., ; Mickovski et al ., ). In our case, they result from root loosening, as described by Gregory ().…”

Material stiffness, branching pattern and soil matric potential affect the pullout resistance of model root systems

“…Previous model and experimental studies on root resistance to pullout have not considered the effects of soil pore water suction in detail, although it has been shown that increased soil water content decreases root resistance to uprooting (Ennos, 1990; Easson et al , 1995). Soil water content is related to soil matric potential and, hence, to effective stress.…”