Measurement and variation of site-specific hardpans for silty upland soils in the Southeastern United States

Soil compaction in the form of a hardpan layer restricts root growth and reduces crop yield throughout the Southeastern United States. However, the depth of this compacted soil layer varies significantly over landscapes. A sampling procedure was developed and evaluated to determine the depth of the hardpan layer in upland soils of Grenada silt loam soil type in this region. Cone index profiles taken with a multiple-probe soil cone penetrometer in three fields were used to measure the hardpan depth and to predict their spatial variation. Continuous treatments of these fields for several years included conventional tillage, no-tillage, segregated traffic, and random traffic. Conventional tillage systems were found to bring the hardpan significantly closer to the soil surface as compared to no-till systems; in trafficked row middles by 0.144 m, directly beneath the rows by 0.165 m, and in no-trafficked row middles by 0.094 m. Little difference in depth of hardpan was found between a no-till field subjected to random traffic and a field where traffic was segregated. However, the effect of this random traffic was found to dramatically reduce the predicted range (which is a geo-statistical measure of field variability) from 43.2 m for the no-till field in the trafficked row middle as compared to 12.4 m for the randomly trafficked no-till field. This may indicate that the depth of the hardpan layer in these soils is brought uniformly closer to the soil surface by the effect of traffic, especially when annual tillage is not practiced which could alter this hardpan depth. This information about the variation of the hardpan layer will greatly assist researchers who are interested in developing site-specific tillage technologies to remedy this soil compaction condition.