As tractors, combines and other farm equipment have become larger and heavier, Iowa farmers' concerns about soil compaction and its impacts on crop yields have increased as well, according to the 2013 Iowa Farm and Rural Life Poll.
Combine and grain cart axle loads are some of the heaviest on row crop land, with axle loads for larger grain carts easily exceeding 75,000 pounds, says Mark Hanna, an Extension agricultural engineer at Iowa State University. "The 2013 Iowa Farm and Rural Life Poll results show that many farmers are concerned about soil compaction impacts of heavy equipment traffic. As farmers start to plan fieldwork for this spring, they should consider strategies such as controlled traffic lanes to mitigate potential compaction," Hanna says.
ISU Extension and Outreach sociologists J. Gordon Arbuckle Jr. and Paul Lasley co-direct the annual poll. The 2013 poll included a series of questions examining farmers' experience with soil compaction, their concerns about the issue and their perspectives on common compaction management techniques. The questions were developed in partnership with the ISU Department of Ag and Biosystems Engineering. These questions were asked only of farmers who had planted corn, soybeans or other row crops in 2012, says Arbuckle.
"About 71% of farmers indicated they were concerned about soil compaction on the land they farm," Arbuckle notes. "About 75% agreed that they were concerned about the impact of heavy machinery on soil health. Half of the farmers agreed or strongly agreed that they consider the weight of equipment when making purchasing decisions."
Impact of soil compaction on crop yields
"Compaction is variable depending on soil conditions and wheel loads," says Hanna. "Some research suggests that yields may be depressed 2 to 5 bushels per acre or more in seasons with wetter soil, and we wanted to know if farmers are noticing yield losses."
Respondents were asked to consider all of the land that they farm and estimate the average annual impact of soil compaction on corn yield over the past five years. Arbuckle says 16% reported they do not have soil compaction, while another 33% indicated they have soil compaction issues, but with negligible effect on yields. However, more than half of farmers estimated that soil compaction has had an impact on yields: 25% estimated that those losses were 2 bushels or less per year; 20% reported yield losses of between 2 and 5 bushels an acre; 6% estimated loss of five to 10 bushels; and, 2% reported annual losses greater than 10 bushels per acre.
Best management practices to reduce compaction
Arbuckle says 91% of farmers indicated they attempt to avoid compaction by taking soil moisture content, a major mediating factor, into account as they plan fieldwork. And 65% agreed that wheel traffic pattern control, a best management practice, is an effective means of reducing soil compaction.
"Compaction can be significantly reduced by aligning combine, grain cart, tractor and other wheel tracks into a controlled traffic pattern," says Hanna. "Using the same wheel tracks helps minimize the amount of land damaged. Farmers also should carefully evaluate wheel tread patterns when acquiring machinery."
Other practices were also seen as effective. Of the farmers surveyed, 60% agreed that removing crop residue can lead to increased soil compaction, and 57% agreed that no-till is an effective way to reduce compaction. Also, 55% indicated fall tillage is an important compaction management strategy for their operation; 47% indicated that winter freeze-and-thaw and summer shrink-and-swell are sufficient to address soil compaction on the land they farm.
Information available on managing compaction
Seventy-five percent of farmers reported they use "simple observation" to determine whether soil compaction is an issue. Fifty-nine percent use evaluation of plant growth, 24% dig the root system, and 21% use a penetrometer or other metal rod to measure soil resistance.
"Digging and inspecting old root masses to look for compaction is a good practice before investing in deep tillage operations," adds Hanna. "Excessive tillage can destroy natural soil structure that helps prevent compaction."