Novel Topological-Architectural Parameters of Root Growth in Soybean (Glycine max (L.) Merrill) to Determine the Presence of Soil Mechanical Impedance

Abstract

Objectives: Mechanical impedance causes structural changes in roots. Nevertheless, little is known about the changes in soybean root systems grown under compacted soils (mechanical impedance). The aim of this work was to understand the morphological and topological-architectural changes occurred in plants root system of soybean grown under soil compaction. Methods/Analysis: Three experiments were carried out and three mechanical impedance levels were tested. Silt loam soil passed through a 2-mm-mesh sieve (Typic Argiudol Esperanza series) was used. Three soil compaction levels were determined: 1.1 g.cm-3, null mechanical resistance (NR); 1.3 g.cm-3, low mechanical resistance (LR); and 1.5 g.cm-3, corresponding to high mechanical resistance (HR). Three soil resistances were consequent determine: < 0.1 MPA, 0.5 MPa and 3.5 MPa, respectively. Morphological, geometrical and topological-architectural roots parameters were measured. Findings: Plants grown in HR conditions had a root system confined to the first centimeters of the ground and showed shorter total root length, less number of lateral roots, higher diameter and low specific length. Growth form of root systems was sensitive to soil mechanical impedance even at resistance levels lower than 1 MPa. As soil impedance increases, lateral root growth occurs via the principal root rather than via the secondary roots and there were higher numbers of lateral roots on the principal root in the area from the proximal zone to the stem base. Novelty/Improvement: The main differences among NR, LR and HR plants were due to changes in the characteristics of the root system rather than in the shoot system, particularly in the root growth zone. As a conclusion, the present research demonstrates that there are morphological parameters that can be used to determine if crops have been exposed to soil compaction. Keywords: Architectural Parameters, Compacted Soil, Glycine Max, Morphological Parameters, Root Growth, Root System, Topological Parameters