Soybean Root Distribution Related to Claypan Soil Properties and Apparent Soil Electrical Conductivity

Soybean [Glycine max (L.) Merr.] yield in claypan soils varies systematically with soil properties and landscape position. This is likely caused by soil interactions with soybean roots. Field observations of soybean root distribution are needed to reveal its effect on yield variability. This study examined profile distributions of soybean root length density (RLD) and average root diameter (ARD) as a function of landscape position, depth to claypan (DTC), apparent soil electrical conductivity (ECa), clay‐maximum translated depth (Dt), and other soil properties. A landscape of claypan soils was sampled postharvest at two sites near Centralia, MO, in 2001. Roots were washed from soil cores in 15‐cm layers (15–120 cm) and measured with image analysis. Root length density and ARD were significantly related to landscape position, DTC, Dt, and ECa Predictions of RLD and ARD were best from 15 to 60 cm, the depths with the greatest influence from claypan soil morphology. Soil profile distributions of base cations, P, and pH matched root density profiles. Soybean roots were inhibited in E horizons above the claypan and stimulated 20 to 40 cm below it. Soybean roots below the claypan had about 20 to 30% smaller diameter. We conclude that DTC and rapid estimators of claypan morphology, such as ECa, can be used to predict soybean root distribution in claypan soil landscapes.