Maize and Soybean Tap, Basal, and Lateral Root Responses to a Stratified Acid, Aluminum‐Toxic Soil

Abstract

Although crop seedling root systems are made up of several types of root (e.g., tap, basal, and lateral roots) there has been little attempt to determine their respective sensitivity to abiotic stresses. Most acidic agricultural fields are treated so that they are only slightly or non-Al-toxic in the topsoil with Al-toxicity in the subsoil—effectively stratifying the soil profile relative to Al-toxicity. To determine if there is differential root type sensitivity to Al-toxic soils, several maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] cultivars reported to be Al-tolerant, or sensitive, were grown in containers with a stratified soil. This assembled soil consisted of a non-Al-toxic, 100-ramdeep top layer and a 200-mm-deep Al-toxic bottom layer of Porter soil, a coarse-loamy, mixed, mesic Umbric Dystrochrepts, pH 4.5 and 92% AI saturation. Containers, backed with X-ray film, were exposed to a neutron beam to determine tap, basal, and lateral root lengths in both layers. Root lengths, relative to a limed control for each cultivar, in the Al-toxic bottom layer suggest that the tap, basal, and lateral roots of maize cv. CMS-36 are each Al-tolerant. The other “tolerant” maize and soybean cultivars had only one or two root types tolerant with the remaining root type(s), and all root types the sensitive cultivars, showing no growth in the Al-toxic bottom layer. Only two cultivars, maize cv. SA-6 and soybean cv. Perry, increased lateral root production in the non-toxic top layer, a classic avoidance response. This variation in root type response to an Al-toxic bottom layer observed among the previously identified Al-tolerant cultivars emphasizes the importance of considering different root types as distinct entities in studies of root function.