Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 2, 1997
Publication Date: N/A
Interpretive Summary: In the southeastern Coastal Plain, naturally compacted soil layers are common. Roots of some soybean varieties penetrate these layers better than others. Better root penetration reduces tillage, which in turn lowers grower costs. We distinguished soybean varieties with roots tolerant or intolerant of compaction using a test that grew plants in variably and uniformly compacted soil columns. Variably compacted soil columns increased in soil strength with depth. Uniformly compacted soil columns had a lower uniform strength throughout the column. Two varieties of soybean (one established and one experimental) were grown in the columns until they died. As expected, plants grew better and lived longer in soils that had lower strength. Roots of the established variety grew better in the uniformly compacted columns than in the variably compacted columns. Total root growth of the established variety was greater than it was for the experimental variety. However, root growth of the experimental variety was not as affected by compaction as the established variety - the experimental variety produced about the same total root growth in both the uniformly and variably compacted columns. Results from tests such as this can help breeders find plants that have the potential to improve growth in compacted soils.
Technical Abstract: Some cultivars penetrate compacted soil layers better than others. Better penetration reduces tillage, and thus lowers grower costs. We developed a test to distinguish compaction-tolerant from compaction-intolerant cultivars. The test was performed using a Norfolk soil in sets of 2.5-cm deep 7.5-cm-diameter cylindrical cores. Cores were compacted to bulk densities of 1.4, 1.55, 1.65, and 1.75 g/cm3. One set of cores was probed with a 3-mm-diameter cone-tipped penetrometer to measure penetration resistance (PR). Another set was used to build columns with 4.5-cm-deep loose soil at the top and increasing core bulk densities with depth. We also included check columns where all cores were compacted uniformly at 1.4 g/cm3. Columns were not watered throughout the study because watering would reduce PR. Two soybean cultivars (Glycine max. L. cultivars Essex and PI416937) were grown in the columns until they died. Both cultivars grew better and lived longer in soils with lower bulk density and PR. Roots of Essex grew better in uniform than in variable columns. Essex grew more roots than PI416937. However, root growth of PI416937 was not reduced by compaction as much as it was for Essex. This comparison was possible because we contrasted growth in the column that had bulk density increasing with depth to the column that was less compacted. A single compacted-layer test would not have been able to do this. This test can help screen plants for potential breeding resistance to soil compaction.