Critical Values of Soil Physical Quality Indicators Based on Vegetative Growth Characteristics of Spring Wheat (Triticum aestivum L.)

Abstract

This study was conducted to determine critical values of soil physical quality indicators according to vegetative growth of spring wheat in a range of degrees of soil compactness. A non-saline loam soil was used to produce a range of degrees of soil compactness in 10 mini-lysimeters. The mini-lysimeters were put outdoors and received similar amounts of water after sowing of spring wheat (Triticum aestivum L., cv. Pishtaz). Shoot dry weight (SDW) was measured, and relative SDW (RSDW) values of 0.9 and 0.8 were assumed to be the starting and end points of soil physical quality indicator limitation for wheat growth, respectively. Critical integral water capacity (IWC) values of 0.136 and 0.104 cm3 cm−3 were obtained for the start- and end-point limitations, respectively. This means that in the studied soil, the IWC values greater than 0.136 cm3 cm−3 represent good soil physical conditions for wheat growth. In the IWC range of 0.136–0.104 cm3 cm−3, there were slight physical limitations for wheat growth. In the IWC values smaller than 0.104 cm3 cm−3, unsuitable soil physical conditions (i.e., poor aeration and high mechanical impedance) strongly restricted the wheat growth. Start- and end-point limitations for Dexter’s index of soil physical quality (S) were found to be 0.051 and 0.038, respectively. Corresponding values for relative bulk density (RBD) were 0.805 and 0.846, respectively.