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Early season corn considerations

By Harold Watters, Ohio State University Extension agronomist

OK, I finished replanting my corn last week, only about three weeks ahead of last year. Oh, and for my planting window, now I have had four periods of about 24 hours each. And for this last planting opportunity, conditions were finally fit to actually plant well. One of my farmer cooperator buddies told me this year he has never used so much technology to plant so poorly.

Poor stands – Compaction and Pythium

The two most common seedling challenges this year were compaction and Pythium. We overworked the soil, this spring and last year both. Poor soil structure leads to soil compaction and crusting. I often quote Sjoerd Duiker, agronomist at Penn State University. This time I’ll just give you his link: https://extension.psu.edu/soil-crusting. Pythium is another problem — our seed treatments only work for so long. This year with cold soils, crusting and excessive rains at the wrong time created a great opportunity for this disease. See Anne Dorrance’s article in a recent C.O.R.N. newsletter for some thoughts on seedling disease: https://agcrops.osu.edu/newsletter/corn-newsletter/2020-17/corn-and-soybean-seedling-blights. I’d like to give you all some advice with this column, this time I’ll quote a co-worker, “We should have left the seed in the bag until conditions were right to plant.”

Do we have a sulfur problem?

Everyone talks about the reduction in use of high-sulfur coal, and how power plants have cleaned up their emissions. We even use low-sulfur fuel in our farm machinery now. So we must need to add sulfur for plant growth, right? It is one of the secondary elements in plant production after the biggies we may add — like nitrogen, phosphorus and potassium. But typically in Ohio with our reasonable organic matter levels and medium- to fine-textured soils we don’t need to add it yet. We do however need to keep watch, and we also watch to our west to see if major sulfur deficiencies show up there first.

Results from our work:

Table 1. Yield response to added sulfur by crop and year.
YearCropOM%w/o Sulfurwith SulfurLSD 0.10Significant?
2016Corn1.8208.2202.59.6NSD
2017Corn2.3233.2230.919.7NSD
2018Corn1.8224.5229.09.9NSD
2019Corn2.4199.2220.117.8Significant
2016Soybean2.363.663.28.9NSD
2017Soybean1.856.758.13.3NSD
2018Soybean2.368.170.13.5NSD
2019Soybean2.765.870.86.9NSD
2019Soybean2.759.968.78.2NSD

NSD means there were no significant differences. There was the one trial in corn for 2019 that showed up as a yield increase with added sulfur.

  • If you suspect S deficiency do some diagnostic work. It will appear sporadically in the field at first. Pull leaf samples from the “good” and the “bad” areas. Compare those after a lab test.
  • Or do a strip test on your farm. Before planting, or even shortly after planting, put a strip of sulfur as sulfate — such as gypsum (CaSO4) or ammonium sulfate — across the field. Compare appearance in-season and yield at harvest.

What about a zero?

I was looking through the Agronomic Crops Team’s On-Farm research reports (https://agcrops.osu.edu/on-farm-research) for some ideas on nitrogen management. And I found that many trials start with 100 or more pounds of nitrogen as the starting point. What about a zero rate in these trials? We (I hope) all know that every year is different especially for nitrogen management, so by using a zero rate as the base we get a feel for what kind of season we had for comparison. In my trials I have made 60 bushels per acre up to 160 bushels per acre in yield with no nitrogen on the same farm but in different years. The year we hit 160 was the year we had a 160-bushel per acre state corn yield average.

I know we need nitrogen to grow corn, and our current recommendation tool relies on economics to set that rate. Our current best guess for a corn N rate is about 175 pounds of N per acre (http://cnrc.agron.iastate.edu) on average, in average years. Is this year average? By doing a zero strip in your field you can get an idea of what your field can do to mineralize nitrogen. And until we get those results over several years, it will be difficult to know what to recommend for a variable rate.

The other factor we need is crop removal. Several trials of late in Ohio show we are somewhere between 0.65- and 0.75-pound N removed per bushel of corn. Let’s say 0.7 pound of N per bushel. If you make 100 bushels per acre of corn from your zero N strip then your soil mineralized 70 pounds of N per acre. The 60 to 160 bushels per acre I have had on my trial field made 42 to 112 pounds of N per acre, depending on the year. In the year we made the 42 pounds of N, we needed more nitrogen to maximize our yield and in the year we made 112, we needed less.

The problem is I didn’t know this until the year was over. This is where some of the forecast tools come into play — the satellite services, the soil tests, and the crop sensors. Try one or all and get familiar with them, then start to build your understanding of your farm, nitrogen management and weather impacts. This will save you money and benefit the environment.

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