Soil compaction and soybean seedling emergence

Soil compaction can cause nonuniform emergence and poor field stands. The effect of soil compaction on soybean [Glycine max (L.) Merr.] seedling emergence in controlled (greenhouse or growth chamber) environments was evaluated using seed lots from six cultivars with high standard germination but variable seed vigor (accelerated aging test). Soil compaction treatments providing a range of compactive efforts (CE) were imposed after planting in near-cylindrical containers. As compaction increased from low (4.6 kJ m^-3 CE) to high (22.9 kJ m^-3 CE), emergence declined; however, high-vigor seed consistently emerged better than low-vigor seed. Emergence of high-vigor seed lots remained >80% until compaction increased to 13.7 kJ m^-3 CE, while low-vigor seed lots had low emergence (<50%) even at the lowest compaction (4.6 kJ m^-3 CE) level. Three seeds per container (spaced 3.81 cm apart) had consistently higher seedling emergence in compacted soil than one seed; however, seed size had no effect on emergence at any level of compaction. Seeds that did not emerge either germinated but remained under the soil crust or were dead (occurred more frequently in low-vigor seed lots). Seedling emergence at 15 or 20°C in the growth chamber was less than at 25°C, and the effect of compaction was enhanced at lower temperatures. Seed lots with high vigor provided adequate seedling emergence following moderate levels of soil compaction (4.6 and 9.2 kJ m^-3 CE). Thus, planting high-vigor seed would be advantageous on soils that are susceptible to compaction.