Visual Estimation of Root Density and Depth in Maize Using Perforated Cylinders and a Video Recording Device Equipped with a Long Borescope.

Our objective was to develop a method for studying roots that would be less expensive and simpler than existing methods, yet provide valid data on treatment effects on rooting patterns. In the first year of method development 20, 30-cm-long perforated cylinders were placed vertically in the soil at the V2 leaf stage, offset 13 and 25 cm on both sides of the maize row. Treatments were liquid starter fertilizer (53 kg N and 21 kg P ha^-1) 5 cm below and 5 cm to the side of the seed and a no starter fertilizer control; each treatment was replicated 3 times. Cylinders were inspected every other day until each contained a root. Starter fertilizer did not affect the timing of root movement to 13 cm, but did delay root movement to 25 cm on the row side containing starter fertilizer. On the row side without starter fertilizer, root arrival at 25 cm was similar to that with the control. We modified the method in hopes of developing an alternative to the soil core/root extraction method for quantifying root length density. In two neighboring fields (corn-soybean rotation & continuous corn), 10 30-cm-long perforated cylinders were placed on both sides of the row at 13 and 25 cm. In each field, two treatments consisting of liquid starter fertilizer (50 kg N ha^-1) and a no starter fertilizer control were replicated 5 times in a randomized block design. Cylinders were inspected at V3, V7, V13, and R2 using a video recording device equipped with a borescope. Total number of roots penetrating the cylinder void were counted at their respective depths using the video images. At each observation time, 10 30-cm-long soil cores were extracted and measured for root length density at the same cylinder distances from the row. Root length density measured from the soil cores was compared to the number of roots found in the cylinders at each observation time, treatment, row side, and depth.