Using 1-m Rooting Columns to Better Simulate Field Soil Water Profile and Soybean [Glycine max (L.) Merr.] Growth Response Under Controlled Environment Conditions.

Soybean is the number one field crop grown in Ontario. Drought stress significantly limits Ontario’s soybean yield in most growing seasons with demonstrated losses ranging from 8-24%. The pattern of soil water availability in frequently watered small pots is different from field environments. In small pots, volumetric soil water content (VSWC) is relatively high throughout the rooting zone due to lack of suction to remove water from large and midsize capillaries.  This necessitates the use of growing media with large pore space to avoid anaerobic conditions and so prohibits the use of field soil in small pots. However, in 1-m rooting columns, the 0.01-MPa gravitational potential difference between top and bottom may permit the use of lightly-amended field soil as a growing medium and provide for realistic soil water profile variation with depth. This study aimed at developing a controlled environment culture system that permits realistic rooting depths and the establishment of soil water profile gradients that mimic field conditions, and selecting the best growth medium based on rooting depth, soil water distribution, and biomass accumulation. The soybean cultivar OAC Bayfield was grown in a field soil (FS) amended with different volumes of granitic sand and peat-based potting mix in polyvinyl chloride tubes having an inside diameter of 10 cm and length of 100 cm.  We tested 3 soil mixtures (0, 50, and 67% FS mix), watered to 75 and 100% tube capacity. VSWC was calculated from time-domain reflectometry (TDR) measurements. The 67% FS mix watered to 100% tube capacity resulted in a uniform field-like VSWC with depth, and the highest biomass accumulation. Watering to 75% tube capacity of the 67% FS mix significantly reduced shoot, root, and whole-plant biomass by 27, 20, and 26%, respectively. These results suggest the 67% FS mix as the best growth medium for subsequent studies.