INTRODUCTION

On the Coastal Plain, deep tillage is usually necessary to fracture hardpan layers that form naturally and/or as a result of equipment compaction. We have shown that implements such as the ParaTill are effective in breaking up these compaction layers when crops are produced using narrow row/conservation tillage systems (please see Fall 1998 newsletter). However, deep tillage is an expensive practice. The magnitude of the yield response to deep tillage can depend on the crop grown, soil type, rainfall, method of deep tillage, and when deep tillage was last conducted. Because of the relatively high cost associated with deep tillage, it is important that methods be developed that would allow farmers to predict the economic return from deep tillage on a field by field basis.

OBJECTIVE

To quantify the relationship between soil compaction (soil strength) and crop yield for each of the major crops grown on the Coastal Plain

APPROACH

Soil strength (compaction) was measured in a series of experiments conducted to examine the interactive effects of surface tillage, deep tillage, crop rotation, and/or soil type on wheat, soybean, and corn yield when produced using narrow row culture. Soil strength was measured as cone indexes using a cone-tipped penetrometer as described by Busscher et al. (2000, 2001). Soil strength was measured to a soil depth of about 22 inches.

RESULTS

When the ParaTill was used as the deep-tillage implement, significant relationships were found between crop yield and soil strength (Fig. 1). These relationships were specific to each growing season. However, the relationships for each growing season had similar slopes, with yield decreases of 2.2 to 2.6 bushels per acre for wheat, 1.6 to 2.7 bushels per acre for soybean, and 0.8 to 3.8 bushels per acre for corn for each atmosphere increase in soil strength. We were able to adjust the seasonal curves to overlap one another (Fig. 2) by including in the analyses rainfall amounts during selected times of the growing season, such as silking in corn and grain fill in soybean.

CONCLUSIONS

A very good inverse relationship was found between crop yield and soil strength (compaction) for corn, wheat, and soybean. Because a close relationship was found, our next goal to see how natural factors (such as soil type) and other production practices affect these relationships. We hope to ultimately develop models that will allow growers to determine the economic return from deep tillage on a field by field basis, or even on a site specific basis.

REFERENCE

Busscher, W.J., J. R. Frederick, and P.J. Bauer. 2000. Timing effects of deep tillage on penetration resistance and wheat and soybean yield. Soil Sci. Soc. Amer. J. 64:999-1003.

Busscher, W.J., J. R. Frederick, and P.J. Bauer. 2001. Effect of penetration resistance and timing of rain on grain yield of narrow-row corn in a coastal plain loamy sand. Soil Tillage Research (in press).