Soybean Growth and Yield as Affected by Surface and Suboil Compaction

Axle loads from wheel traffic on farmland ranges from less than 4.5 Mg axle⁻¹ to over 20 Mg axle⁻¹. Loads of <4.5 Mg axle⁻¹ generally cause compaction only in the upper 0.3 m of the soil (surface compaction), while higher loads have caused soil compaction below this surface layer (subsoil compaction). A replicated field study was conducted on a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquoll) in southern Minnesota and on two Ves clay loams (fine-loamy, mixed, mesic Udic Haplustoll) in southwestern Minnesota to assess the effect of surface and subsoil compaction on the growth and yield of soybean (Glycine max L. Merr.). Surface compaction treatments consisted of no interrow traffic on either side of the row at any time during the experiment and annually applied interrow wheel traffic on both sides of the row from an axle load <4.5 Mg. Subsoil compaction treatments consisted of control (no subsoil compaction), 9 and 18 Mg axle⁻¹ loads applied once at the beginning of the experiment. Surface compaction, when averaged over years on both Ves sites, decreased yield by 15% overall and up to 27% in a single year. Yield response to surface compaction on the Webster site was climate dependent, in general, decreasing yield during a wet year but increasing yield during a dry year. Subsoil compaction from the 18 Mg axle⁻¹ treatment reduced plant height and integrated leaf area index on the Webster site each year of the experiment, and tended to decrease yield. The response to the 18 Mg axle⁻¹ load on the Ves was inconsistent. Yield was increased significantly in 5 out of 14 location-years by the 9 Mg axle⁻¹ treatment when compared with the control treatment. Soybean growth parameters and yield were affected more by annual surface compaction than by a one-time application of subsoil compaction. A decrease in vegetative growth did not necessarily result in a comparable decrease in seed yield. Joint contribution to the USDA-ARS-MWA and the Minnesota Exp. Stn. Scientific article no. 17 110.