What types of substrate influence water potential?
The substrate (layer under your soil) could be compacted clay, rock, coarse sand, or the bottom of the container. Root crops require moderately good drainage. Moist, but not wet, makes good conditions for potatoes and carrots, so a permeable substrate is preferred. Water potential? Not sure what you mean. An impermeable substrate prevents water from draining: bad for root crops. Show in your experiment a substrate of clay, one of sand, one of rock, and one of wood or plastic at the same depths with similar soil, or show variations of depth, but make make one series for each variation in depth. Grow the vegetable to show different stages (sprout, mature plant, root/tuber production) and effects of the varying substrate. Potatoes don’t have a “taproot” so they will grow well in a minimum of about eight inches of soil. A good experiment on potatoes would be to show varying depths of soil starting with four inches to twelve inches. Carrots, however, will limit length depending primarily on
