A Detrimental Interaction of Subsoil Aluminum and Drought Stress on the Leaf Water Status of Soybean

Drought and subsoil A1 are major concerns which face soybean [Glycine max (L.) Merr.] producers in the southeastern USA. However, the interaction of these two factors is not clearly understood. This study was designed to characterize the combined effect of these two stress factors on soybean water status. A greenhouse experiment was conducted, with two levels of subsoil A1 saturation (6 and 71%), and two levels of drought stress (watered and unwatered). A split plot experimental design with three replications was employed. Soil treatments were applied via a soil layering technique using topsoil of a Goldsboro sandy loam (fine-loamy, siliceous, thermic, Aquic Paleudult). The top layer in all pots consisted of the unamended topsoil. In the lower layer, highly contrasting A1 saturation levels were obtained by amending one half of the pots with A1₂(SO₄)₃. Data were collected during a 14-d moisture stress treatment imposed at podfilling (R3). Traits measured were leaf water potential, relative water content, transpiration, and diffusive resistance. A detrimental interaction between subsoil AI and drought was observed in all traits measured. Plants grown in the presence of both stress factors had lower levels of leaf relative water content and water potential, and a lower transpiration rate than predicted additively by independent stress factors. In general, subsoil AI had much greater effects on leaf water status in drought-stressed soybean plants than in the wellwatered plants. These results suggest that hindered root growth in highly AI-saturated subsoils may have limited the ability of the plant to withstand drought. Soybean producers in regions characterized by drought and subsoil AI should consider the incorporation of Altolerant germplasm into management systems. Field studies including water stress as a variable should be interpreted with regard to this interaction, if soil A1 is present. Joint contribution of the USDA-ARS and North Carolina Agnc. Res. Serv. Paper no. 11413 of the journal series of the North Carolina Agric. Res. Serv., Raleigh, NC 27695-7601.