Differential Genotypic and Root Type Penetration of Compacted Soil Layers

Abstract

Total number of root penetrations of compacted subsoil layers have been commonly used to assess plant tolerance to subsoil compaction. Root‐type specific responses to compacted subsoil layers have not been investigated despite the documentation that plant root types are physiologically and genetically different. A set of maize (Zea mays L.) and soybean (Glycine max L. Merr.) cultivars were grown in growth chambers in containers with compacted middle layers (1.2 and 1.65 Mg m−3) of Howard soil (loamy skeletal, mixed, mesic Glossoboric Hapludalf) with 17% clay content. The containers were exposed to a neutron beam to determine the relative root lengths (RRL) of taproot (RTRL) and basal root (RBRL), the numbers of lateral roots in the compacted layer, and lengths of lateral roots above the compacted layer. The resulting neutron radiographic images revealed that maize ‘SA‐3’ and soybean ‘PI 416937’ taproots penetrated the compacted layer and maintained >90% RTRL in the subsoil, but their basal roots hardly penetrated the compacted layer. In contrast, maize ‘La Posta’ and soybean ‘Weber’ taproots were severely restricted by the compacted layer, but their basal roots penetrated the layer and had >70% RBRL in the subsoil. Maize ‘TS‐6’ taproots were also restricted by the compacted layer, but TS‐6 basal roots had a moderate penetration that produced a 38% RBRL in the subsoil. On the other hand, soybean ‘Perry’ had a moderate penetration and RRLs in the subsoil with both tap and basal roots. This variation in root type response to subsoil compaction among cultivars stresses the importance of considering different root types as distinct entities in studies on plant tolerance to compacted subsoil conditions.