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Prevention of soil compaction

Sept. 6, 2012 | 0 comments


Soil compaction is an important issue on state farms, especially as equipment gets larger and manure spreading windows get tighter.

Francisco Arriaga, a new soil scientist with the University of Wisconsin, gave farmers and crop consultants information on the topic during the annual Agronomy and Soils Field Day, Aug. 29 at the UW’s Arlington Agriculture Research Station just north of Madison.

Arriaga joined the staff of the soil science department in July, filling some of the research and education roles of the recently retired Dick Wolkowski.

A Puerto Rican native, Arriaga previously did graduate work at the UW-Madison and earned a Masters at Auburn University. His specialty is in soil and water management and the physical properties of soil.

Soil compaction is difficult to see with the naked eye, he said, but it can negatively impact crop production since it restricts the growth of plants’ roots and as such it is something growers need to pay attention to.

In a year like this, when many growers have experienced drought, soil compaction is a concern because when water hits a compacted soil layer, Arriaga said, it can’t penetrate. Water above that compacted layer will tend to run off more as a result of the previous compaction.

The causes of soil compaction include traffic at the wrong time when the soil is too wet, heavy equipment that has gotten bigger and bigger over time as growers work more land. Another cause is repeated traffic in the same spot.

Excessive tillage can also contribute to soil compaction, creating "plow layers" and affecting the organic matter in the soil.

"It is critical to prevent soil compaction from occurring in the first place since eliminating compaction once it has occurred can be difficult."

Arriaga said that the effect of sub-soiling doesn’t last because compaction changes the structure of the soil, which impedes plant growth by reducing root development.

"Steps to reduce soil compaction are ok but it takes a lot of horsepower and the costs to remediate it are high. Prevention of compaction is the key."



Incorrect tire pressure can also contribute to soil compaction, he said. Tires that are over-inflated will experience more slippage with the ground and cause more compaction versus properly inflated tires.

A recent research trial compared properly inflated tires to over-inflated tires and proved the point, he said.

One of the methods being used in some places to control the amount of tire traffic on fields is axle extenders, he said. They are used to match the tire spacing on all implements and tractors. "When the width matches it reduced the potential for compaction."

The soil’s structure, whether it is sand, silt or clay, is very tough to change. The secondary structural components of soil, like organic matter, can be affected though.

Various crops have different kinds of penetration force in their root systems, he said, and can help remediate soil compaction problems. Harsh winters with their freezing and thawing cycles can also help reduce the effects of compaction.

Arriaga demonstrated several kinds of penetrometers that can be used to measure the amount of soil compaction present in a given spot.



The 2,000-acre Arlington Agriculture Research Station includes some land that has been operated in an organic system for several years and is certified organic.

Erin Silva, an organic researcher in the UW Agronomy Department, has been conducting research into a system of no-till soybeans and corn grown in a variety of killed cover crop.

It is a system that even farmers operating their ground with conventional methods have expressed interest in, she said. Silva focused on soybeans no-tilled into a cover crop of rye that was killed with a mower-crimper.

Unfortunately, this wasn’t a very good year to showcase the practice, she told visitors to the plot last week. The cover crop had taken moisture that was in short supply this year and the soybeans germinated poorly.

"In organic systems farmers’ primary tool for weed control is cultivation. They may go over a field four, five, six times with tine weeders and rotary hoes. All that tillage burns up organic matter and leaves it susceptible to erosion.

"The holy grail of organic crop production is no-till but we have also seen some interest from farmers with conventional systems," she said.

Her plots looked at hairy vetch as a cover crop as well as rye. The rye, she noted, had effectively prevented weeds from establishing throughout the season with almost complete elimination of weeds in these plots.

That same degree of weed suppression was not seen in the other small grain cover crop treatments or in the hairy vetch cover crop plots, she added.

When using the rye, the cover crop is seeded in the fall and then it is killed the following spring with the mower-crimper or with a sickle-bar mower. That same day, in May or June, the cash crop is seeded into the mulch.

Silva said the cash crop will emerge after a couple of weeks and no further operations are needed. "This is a great improvement in weed management for organic growers, specifically with the rye."

Using this system reduces the need for labor and the ecosystem benefits as well, from improvements to runoff and trapping of excess nitrogen.

"There is significantly less soil loss potential with no-till and we have predicted an increase in organic matter," she said, although the trade-off has been an increase in some perennial weeds like dandelions and quackgrass.

Problems with the system include potential cover crop establishment glitches, incomplete kill of the mulch, inadequate weed control, competitiveness of the cover crop – as in this year when it stole moisture away from the cash crop – and timing.

The correct cover crop seeding rate and planting date are important and when using rye, it can be planted no later than the end of September, she has found. Timing for the spring termination of that cover crop is also important.

Silva said the system produces cash crop yields that are typically 25 percent lower than "traditional" organic systems, but yields are pretty close together in fields that follow alfalfa.

For her control plots, to compare "traditional" organic systems to the cover crop plot, Silva said weed control practices included flex-tine weeding, rotary hoeing and inter-row for a total of four operations until the canopy of the soybean crop closed in July.

The data she talked about came from the 2010-11 test plots for this project.

While soybeans have fared pretty well in this kind of system, corn has been more problematic because of delayed emergence.

In some test plots she found that the system increased microbial biomass carbon.


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