Published August 5, 2019 | By Mike Petersen
Sidewall compaction due to wet soil conditions Courtesy Anderson
After attending the National Strip Till Conference (NSTC) in Peoria, IL the week of August 1-2, 2019; I got to thinking that more information to you all seems imperative from what we saw as negative impacts with the wet spring. Growers that tried to do some tillage then planting when it was wet would want some clues of what we and you are noticing across the countryside. Using the spring coulter system with the 1tRIPr in near saturated soils did induce some shallow compaction this spring at about 3 to 4 inches down as did planters with more than 100-150 lbs of downforce. One of my co-workers and I measured some of those ill effects in the Platte River Valley of Central Nebraska. We also measured where sidewall compaction was induced with planters and created the “mohawk” root system, not a good deal for the plants. Where am I going with this? See the image on left.
In sandy clay loams, silty clay loams and clay loams – in a wet spring like this one the conditions were ripe for compressing the soils both downward and off to the side or laterally. In the first 3 to 4 weeks of the corn plants life the root system develops out from the seed placement and down at a 25 degree angle parallel of the soil surface. Squished and pressed wet soils deform out at a 25 to 40 degree angle from the tires or tracks. When a farmer is running on dual wheeled setups and too high of pressure in the tires this will more than likely cause “pinch compaction” at depths of 3 to 7 inches deep. With the rotating of the tires and the pinch-squeeze the soil presses out any air and crushed pores, channels, any kind of a gap and tiny early roots just cannot get through or down; ending up with serious concerns for water/nutrient uptake and stand-ability later in the season.
We have seen quite a number of fields across the Corn Belt with those symptoms. Before the corn got to tassel time it did not seem to be an issue, now if storms come thru with big winds, folks could be in for problems. University Extension folks have told me that in Minnesota and Northern Iowa they may be looking at 25% reduction in yields with compromised root systems due to compaction.
Another key point that farmers visited with me about at NSTC in Peoria, IL; what kind of information is out in the soils world did I have about root pits, root growth, compaction did I have that was new. I have been digging (what else does a soil scientist do?) into the research and finding more information that details the amount of force a corn root can exert at its root tip to penetrate either wet compacted soils or soils that are dense and drying out. Researchers in Scotland back a few years (2011) back wrote after work evaluating early growth in corn that corn feels the negative effects of soil resistance/compaction from 0.8MPa and at ~2.0MPa root extension stops. At 2.0MPa (megapascals) corn plants at V2-V5 will curl up their toes significantly. This amount of soil resistance of 2.0MPa is equal to~280 pounds per square inch (psi). When corn plants get further into the season V8-VT the amount of turgid pressure at the root tip increases to give ‘push’ at the root tips at a force of up to 2.85MPa or 408psi. A co-worker of mine and I looked at the very moist to nearly saturated conditions this spring when corn was V2-V4 and measured soil resistance in the seed-zone [1-5 inches] in silty clay loam soils in conventional till to be >250psi. You can guess what we found, yes sir – blunted off roots, trying to make right turns and kinked. The first two nodal root sets were blunted or just did not come out on the side where the soil was so dense, but the soil was wet to soggy. Plants were short, first leaves were purple tinged – strong evidence of compaction when we dug around. Unfortunately in the long term No-Till fields we observed this also and then with follow up field visits the corn is spindly, shortened, fewer leaves and when shaking a plant it is wobbly and not well anchored in the ground. I am suggesting to folks take a good look at their corn fields and dig up a few of these kinds of plants and see what your root system looks like. Small root systems with an appearance of being one sided or like the picture above, compaction either by pinch or smearing is an issue. Freeze-thaw is not going to remedy this over time folks, other measures will have to be considered.
Looking ahead into the next few weeks; come to Husker Harvest Days [September 10-12, 2019] near Grand Island, Nebraska and visit us at the Orthman Manufacturing stand/booth for we are going to be presenting great information about our spring findings of 8 different soil types in Strip-Till fields, Conventional till fields and No-Till fields as to what two forms of soil compaction is happening in wet soil conditions. Our guys will be happy to explain what we saw, what values are trouble and what is not a problem. You bet I will be there ready to visit with you all any of the three days. This data is not being done by University folks which is unfortunate, so we at Orthman want to bring you finding straight from the field and talk about what are options for pre-plant tillage. After the show we will be publishing the results here on Precision Tillage.com.