Submitted to: Soil Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/1999
Publication Date: N/A
Interpretive Summary: Among the soybean varieties that are currently available, some penetrate hard soil layers better than others. Better root penetration aids growers by improving growth, reducing tillage, and lowering production costs. In this experiment, we developed and used a test to single out soybean varieties with roots that can grow better in compacted soils. In the test we grew different soybean varieties in variably and uniformly compacted soil columns. In variably compacted columns, soil strength increased with depth. In uniformly compacted columns, soil strength was low and uniform throughout the column. Two soybean varieties (one established and one experimental) were grown in variably and uniformly compacted soil columns. Columns were not watered. Plants were allowed to grow until they died. As expected, plants grew better and lived longer in soils with lower strengths. Roots of the established variety grew appreciably better in lower-strength, uniformly compacted columns than in higher-strength, 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 reduced by compaction as much as it was for the established variety - the experimental variety produced about the same total root growth in both the lower- and higher-strength columns. Results from this and other tests can help plant breeders find varieties with the potential to improve growth in compacted soils.
Technical Abstract: In terms of time, energy, and equipment, reducing soil compaction by deep tillage is expensive. Tillage can be reduced by developing or selecting genotypes with better penetrability. Two soybean genotypes were compared for their tolerance to soil compaction. A single-grained Ap horizon of Norfolk loamy sand was compacted into 2.5-cm-deep, 7.5-cm-diameter cylindrical cores at bulk densities of 1.40, 1.55, 1.65, and 1.75 g/cc. One set of cores was used to measure compaction as penetration resistance (PR) of a 3-mm-diameter cone-tipped penetrometer. Another set was used to build columns. Columns had 4.5-cm-deep loose soil on the top and cores of increasing bulk density with depth. Check columns were also included with all cores compacted at 1.4 g/cc. To maintain high PR, columns were not watered throughout the study. Two soybean genotypes (Essex and PI416937) were grown in the columns until they died. Both grew better and lived longer in soils with lower bulk density and PR. Root growth was more abundant for Essex than PI416937. However, root growth of PI416937 was not reduced by compaction as much as it was for Essex. PI416937 is potentially better adapted to compacted soil. This comparison was possible because we contrasted growth in columns with and without increasing bulk density. A single-compacted-layer test would not have been able to do this. Further use of the test can help screen other genotypes for their tolerance to soil compaction.