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A print-friendly version of this newsletter is available to download here: SW MN IPM Stuff 2020-04
Rainfall, air and soil temperatures, degree-days, soil moistures, and other current and historical weather data for the University of Minnesota Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN, can be found at SWROC Weather.
The Easter snow storm and subsequent statewide cold snap put planting on a temporary hold. I expect there will be much more field activity by next week. Where fields are fit, planters should start rolling. It would be good if we could get an easier spring planting season for a change. Just a reminder to watching your planting depth settings this spring. It’s a chronic problem so I attached a reworked 1999 IPM Stuff article.
For the most part, it looks like alfalfa and winter cereals did OK through the cold snap but I am waiting for plants to put on some regrowth and will reevaluate early next week.
Corn Planting Depth
Searching for Nirvana
In order to save some agony later this spring, it is wise to do a good job of placing corn seed within the soil. Planting will pay big dividends if done correctly but can create heartache and unhappy bankers if done poorly. The benefits of early planting into a good seedbed should be well known by now. Having to replant a poor stand at a later than optimum date or having to watch a non-vigorous stand struggle through the season are activities best avoided.
The most common planting mistake that I encounter is poor seed placement with respect to depth. Some operators seem to be intent on planting at a magical 1 ½ -inch depth. Some are even quite good at hitting it, at least temporarily. Even with the recent advances in planter and monitor technology, it is extremely difficult to plant a field uniformly at 1 ½ - inches. Loose, fluffy seedbeds (You know... the ones where the field has never worked up this nice before!) can easily settle 1/2 inch or more. Seed depth that started out at 1 ½ - inches can easily be an inch or less after a good rain. Adjusting down pressure can help or can make things worse. Often, an attempt at 1 ½ - inches creates a good chance (probably greater than 50 %) of ending up too shallow. Even with the new high speed planters, there is a speed limit for accurate planting and it’s well before your head starts bouncing off the cab’s ceiling.
So what's the big deal?
There are several problems with shallow planted corn. The potential for poor root development is increased. Soil near the surface is prone to dry out and is exposed to greater fluctuations in temperature than soil at a greater depth. This means that root development is at risk from dry, hot, or cold conditions. Stressed root systems can develop symptoms that look like herbicide or nematode injury (stunted, stubby and swollen). Nodal roots develop closer to the surface when corn is planted shallow and their development can be aborted if hot, dry conditions occur where roots are developing. These problems are not a big deal as long - as the corn plant doesn't need water, nutrients or help standing up.
Injury from some herbicides can increased in shallow planted corn. A combination of shallow planting and urea in contact with the seed can also produce some impressive symptoms.
An individual, late-emerging, corn plant is unable to compete well with earlier emerging neighbors and may function like a weed rather than a productive plant. There is strong evidence poor stands and weeds reduce corn yields. One might think that shallow planting, where soils are warmer during the day, would speed your corn’s emergence. It does for some seeds. Unfortunately, the environment is a lot more variable near the surface. Some seeds will be exposed to adverse cold or dry conditions and be slower to germinate/emerge. They may sit there a long time if the spring turns dry. Because temperatures are more consistent than at the surface, corn planted at 2-inches will likely emerge more uniformly than shallower planted corn.
Some final thoughts
Planting is one of the most important steps in obtaining good corn yields. It takes time and seed costs are substantial. You only get one chance to do this right. Set your planter to plant at 2-inches and check your setting in each field. If your planter starts to run a bit shallower, you will be ok for depth. If you get a bit deeper you will still be ok. When checking planting depth in very mellow soil, you might want to step on top of the row to firm the topsoil before you measure depth. I have never calibrated this technique but it probably works well for people between 150 and 300 lbs. and size 9 to 14 shoes. Check seed depth at more than one row. In spite of modern advances in engineering, and manufacturing, and how well you made the previous adjustments, rows can vary in depth, particularly on outside rows.
There seems to be an aversion to planting corn deep but no problem in planting soybeans to soil moisture, even when the first moisture occurs at 4-inches. Soybeans planted too deep can have issues emerging. With appropriate conditions, soybeans can be planted much shallower than corn with good results. You can reset your planter shallower to match soil type, moisture, residue conditions when you switch to soybeans. Some soybean herbicides have minimum planting depth restrictions; remember to check the label. Based on soil moisture and weather forecast, you may want seed at an inch or more deep to avoid germinated seed from drying out. However, 2-inches is probably close to a maximum depth, even when soils are dry. Soybeans can compensate for uneven emergence better than corn and cotyledon stage soybeans are reasonably frost tolerant. Perhaps even more so than corn, soybean yields respond to early planting, emergence and vegetative growth.
Why would someone working in integrated pest management care about a fundamental agronomic issue like planting depth? Symptoms of shallow planting are often blamed on herbicide injury and carryover, insect damage, disease problems and poor quality seed. Secondly, when a corn field is already afflicted with reduced yield potential due to shallow planting caused complications, managing pests becomes a lot less interesting and profitable.
Spend some time adjusting your planting depth this spring! It only takes a few minutes. Check more than one row. Once you have it set, don’t assume it is all good for the season. Check your planting depth often and adjust for changing conditions within and between fields.
University of Minnesota Southwest Research & Outreach Center
23669 130th Street
Lamberton, MN 56152