Strip-tilling alleviated compaction but reduced residue below the 30% threshold for conservation tillage, according to a Penn State University study.

This University of Delaware photo shows drowned-out areas in a field caused by compaction issues.

Penn State University professor Sjoerd Duiker led the study in 2002 and 2003 at the university's Dairy Farm Operations in State College, Penn.

The study was conducted to determine the effects of soil compaction in no-till, the benefits of flotation tires vs. truck tires, and the effects of shallow and deep in-row tillage to alleviate soil compaction.

The site of the experiment was in no-till for more than 10 years before the study was established. There were nine compaction treatments in the study.

The plots were 250 feet long by 30 feet wide, with four replications for each treatment, for a total of 36 plots.

Effects On Residue Cover

The residue cover in 2003 showed significant differences among treatments. The no-till treatment showed the greatest residue cover at 48%.

Zone-till reduced crop residue cover by 15% to 33%, and strip-till reduced residue by another 11% to 21%.

The residue cover that remained was enough to categorize it as conservation tillage (less than 30% residue) with zone-till, but not with strip-till. The zone-builder set up had two coulters behind and besides each shank, which created too much soil and residue disturbance to meet conservation tillage standards.

Compaction Issues

Plant population was reduced due to truck-tire compaction. When the soil was strip-tilled first, and then compacted with truck tires the results were no better.

Strip-till after compaction, however, alleviated the reduction in plant population. Also, soil that has been strip-tilled exhibits much more rutting when compacted than a no-till soil that has not been strip-tilled.

The irregularity in the field contributes to less precise seed placement. Zone-till and flotation tires helped to reduce the plant population reduction due to compaction in 2002, but not as much as post-compaction strip-till. In 2003 there was no significant plant population improvement due to these treatments.

Penetration Resistance

Root penetration has been shown to be optimal if penetration resistance is approximately 100 psi. At 200 psi, roots start to experience detrimental resistance, whereas at 300 psi root penetration is minimal.

Because penetration resistance is lowest in wet soils, measurements are taken when the soil is at field capacity (24 hours after soaking rain). This represents a best-case scenario, because penetration resistance will only increase with additional soil drying. The measurements were taken in the row in the spring of 2003.

Penetration resistance was significantly increased due to compaction with truck tires to a depth of 4 inches only compared to control. This suggests that despite the high axle load, compaction did not penetrate into the subsoil.

Zone-tillage significantly decreased penetration resistance to a depth of approximately 4 inches, and post-compaction strip-till reduced penetration resistance to the depth of tillage 17 inches.

Flotation Tires Cut Yield Loss

Annual compaction with truck tires reduced yields 31 bushels in 2002, and 18 bushels in 2003. The year in 2002 was dry, whereas 2003 was a wet year. The results suggest higher yield losses can be expected when the crop experiences drought stress in the summer.

Flotation tires helped to cut the yield loss roughly in half in both years. Benefits of flotation tires are therefore greatest if the crop experiences drought stress. Strip-till to alleviate compaction was quite effective, although yields were still depressed in 2002 compared to no-till without compaction.

In 2003, strip-till after compaction completely eliminated the yield loss due to compaction. Shallow zone-till after compaction was somewhat effective in 2002, but did not increase yields compared to doing no tillage after compaction in 2003. Traffic after strip-tillage completely destroyed the yield gain obtained by the strip-till operation.

Conclusion: Avoid Compaction

The results show that compaction can have significant negative effects for soil properties and crop yield in continuous no-tillage systems.

Penetration resistance was not significantly increased below 4 inches depth with 10-ton axle load. This suggests that subsoil compaction may be less of a threat in long-term no-till. An alternative explanation may be that the subsoil was already compacted due to heavy field traffic preceding the experiment.

Yield reductions due to annual compaction of the whole field surface ranged from 15% to 25% in the 2 years of this study. Using flotation tires instead of truck tires to avoid compaction reduced the yield loss by approximately 50%.

In-row strip-till to a depth of 17 inches improved soil physical properties and eliminated much of the yield loss due to compaction. However, traffic after strip-tillage completely destroyed all its benefits. Zone-till to a depth of 4 inches was somewhat effective to alleviate the yield reduction in one year, but not in the other year. It appears zone-till is not aggressive enough to reduce the effects of compaction.

Although strip-tillage was effective to alleviate compaction, it reduced residue cover below 30%, which is unacceptable for erosion control. In addition, we know every tillage operation does damage to soil structure.

Strip-till should therefore be used only occasionally, when substantial compaction was caused that merits a remedial treatment.

"We suspect that if a farmer monitors soil moisture conditions for traffic, and uses flotation tires in continuous no-tillage, sub-soiling operations will only be marginally economical," the Penn State scientists say.