Soil tillage can originate compacted layers in the soil subsurface. This compaction reduces root growth, plant development and eventually soybean yields. This study examined the effects of subsurface compaction on soybean root growth and morphology as related to plant growth and mineral nutrition. Soybean plants cv. Primavera were grown up to 37 days from seedling emergence in pots where a compacted layer was set at the 15.0 to 18.5 cm depth. This layer was compacted to bulk densities of 1.03, 1.25, 1.48 and 1.72 g/cm³, corresponding to cone penetrometer resistances of 0.05, 3.0, 7.5 and 2.0 MPa, respectively. The soil was a Dark Red Latosol (Haplortox), sandy loam, with 80% of sand and 16% of clay. Soil subsurface compaction led to a higher concentration of roots in the surface layer of the pots, without significant effects on plant canopy growth and nutrition. In the presence of a compacted layer the roots were shorter, but nutrient absorption/cm of root was higher. There was some restriction to root growth in the bulk density of 1.25 g/cm³, but there was necessary a bulk density of 1.72 g/cm³ to inhibit completely the root growth. Soybean root growth was decreased by 50% when the penetrometer resistance reached 0.69 MPa.
Glycine max L. Merrill; penetrometer resistance; soil impedance; root growth