March 12, 2020
Soil compaction hurts yields. Using information from compaction testing, however, will help producers plan cover crop and tillage programs to help eliminate compaction, so plants can thrive throughout the growing season.
Speakers at the recent Louisiana Agricultural Technology and Management Conference (LATMC) discussed soil compaction's effects on root growth and nutrient availability.
Lisa Fultz, soil microbiologist, LSU AgCenter, and Dan Fromme, LSU AgCenter agronomist and state specialist for cotton, corn, and grain sorghum, discussed soil health, cover crops, and compaction testing.
Soil health, cover crops
Fultz looks at how different management practices — such as reduced tillage, conservation tillage, irrigation methods, cover crops, and crop rotation — influence soil microbial communities and soil health.
"These management practices increase organic matter and maintain cover on the soil, so when you do have events such as a large amount of pressure from rainfall or irrigation, there is a buffer between that and the soil," she said. "One of my favorite illustrations to show my classes is of a raindrop hitting bare soil, and it looks like a bomb goes off and leaves behind a little crater. That's what happens every time a raindrop hits bare soil."
If you have a standing cover such as biomass from the previous year's crop, it can act as a buffer to help dissipate pressure from forces like rain irrigation.
"Two methods to get rid of impenetrable layers of soil is subsoiling or growing something that has rooting characteristics like cover crops, grasses, or radishes," Fultz said.
Radishes aren't a quick fix to open up the claypan or hardpan.
"It's an investment, and it might not be the right option, depending on the farm," she said. "They will work great in some environments, but radishes are not great for some of the soils in Louisiana. Grasses might be a better choice because the smaller root systems infiltrate deeper into the soil and leave behind organic matter. Everyone's farm is different, so it's important to test your soil to know what will work best for you."
Testing soil compaction
Compaction problems are particularly an issue in Louisiana where rainfall can be excessive.
"We usually have to get in the field when it's wet; we don't want to, but it's unavoidable far too often," Fromme said. "In addition, we have had a lot of reduced, minimum tillage for several years now, and while it's a good practice that saves you time and labor, you're going to have compaction after a while."
Issues from soil compaction include yield reduction and nutrient deficiencies such as potassium and nitrogen.
"Compaction can also become an issue in a dry year if you don't have irrigation," he said. "Be aware of compaction issues, especially if you don't till on a regular basis, and check your fields using a penetrometer, which costs around $200. You don't even have to have a penetrometer. You can make one with a steel rod with a point on it and cut another board to weld on top of it to make a T shape."
A penetrometer includes 3-inch marks. You go down until you hit resistance and check the dial. The best time to test a field is about 24 hours after a soaking rain.
"If you hit resistance, say greater than 300, you're going to have some serious problems," Fromme said. "I think soil compaction tests should be done every year. Test several different spots within a field to get an accurate estimate of your soil compaction. If there are less than 30 places that show compaction in a field, you might wait and till next year. The one rule of thumb was every three years you should till, but it really depends on your soil and the weather that year."
Fromme suggests paratill.
"My experience with breaking a compaction layer is that paratilling works well," he said. "In one field, we needed to paratill badly. The second year after paratilling we had the best corn crop yield ever.
"Compaction limits how much nutrients a plant can get further down in the soil, ultimately affecting yields."
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