Nitrogen: Corn’s Most Intense Nutrient

Nitrogen Cycle - Cornell

Some call nitrogen the most important nutrient, but any nutrient in short supply will limit yield.  I like to call nitrogen the most intense nutrient because having the right supply at the right time can be difficult.  Here is why:

  • Soil nitrogen tests can be extremely variable across a field at any given time
  • Soil nitrogen tests are expensive
  • Nitrogen leaches (it moves rapidly down through the soil profile with water)
  • Nitrogen volitilizes (it becomes a gas and is released into the atmosphere when hot/dry)
  • Denitrification is loss to bacteria in anerobic environments (wet soils)
  • Immobilization of nitrogen occurs when soil microbes use the mineral to digest dead plant matter (paying the carbon penalty)
  • Mineralization is when those soil microbes reach the end of their life cycle and die, releasing the nitrogen back for plant availability

v5 corn close

Nitrogen management in corn is a big subject and much can be said, but for my purposes here I only want to highlight a few important management practices that I use to deal with minimizing nitrogen waste while maximizing yield.  Ken Ferrie’s Corn College is where I learned some of how to calculate and study to develop my particular nitrogen needs, plans, and emergency options.

  • Carefully calculate how much nitrogen a crop will need based on yield history, accounting for known variables and considering the costs and benefits of the risk involved in having too much or too little.
  • Take some nitrogen tests in a few fields under different conditions to learn how to guess the rest of the acres by management zones.
  • Estimate the amount of plant matter in each field from the previous crop and pre-season weeds to assess the “carbon penalty” that needs to be paid at planting. A previous crop of corn will leave more residue, requiring 40-70 pounds of pre-plant nitrogen to be applied.  This penalty will be credited back to the crop gradually over the next few weeks as the microbes die.
  • Divide the crop’s estimated nitrogen needs into multiple applications to avoid leaching.  Apply most nitrogen just before the crop’s demand begins to soar at V5 (when plants have 5 leaf collars and are usually 18-24″ tall).
  • Use nitrogen stabilization products to inhibit denitrification by the urease enzyme with products such as N-Fixx or Agrotain.
  • Re-calculate the costs and benefits of when to apply nitrogen and in what forms.
  • Consider the cost and benefits to variable rate nitrogen by zones developed from either soil types, historic yield maps, or satellite imagery.
  • Utilize irrigation pivots to apply as much of the crop’s nitrogen needs as is feasible.
  • Utilize late-season aerial applications of dry nitrogen sources in years where moisture is adequate and yield potential justifies the cost.
  • Every year in a field or two have two or three blocks for testing the effectiveness of using more or less nitrogen than the rate estimated as most efficient to prove guesswork and provide knowledge for years to come.
  • Watch for visual and tissue sampled nitrogen deficiencies during the crop year and investigate to find the cause.
  • Test fields for compaction with a steel probe through the winter and watch for problems to develop in fields in the V2-V4 stage of corn.  I have come to call this the “ugly chick” stage of corn because in no-till conditions it sometimes reminds me of that awkward stage where chicks are just getting their feathers.  Don’t worry, it will look better soon.  Maybe this ugly unevenness can be avoided with a planter-applied starter fertilizer.  I will find out.v6 corn Anson standing

Between the Rows

Ideal corn stage, no-till residue, and plant spacing
Ideal corn stage, no-till residue, and plant spacing

Yield is the top priority of every row-crop farmer.  Many decisions are made based on how much yield increase a practise may provide.  However, other considerations are also important.

For fifteen years my farm has planted corn in rows 20 inches apart, instead of the typical 30 inches for most of the US.  This does not necessarily result in higher yield, but it is a more efficient use of fertilizer because there is less open space between the rows, allowing roots from plants in the row to access nutrients in the center 33% sooner.  (In 30″ rows plants are 15″ from the center.  In 20″ rows plants are 10″ from the center.)  This advantage pairs well with my nitrogen plan of side dressing with 28% UAN (urea ammonium nitrate) applied when the corn is 6 to 14″ tall and has 3 to 6 leaf collars.  Planned mid-season nitrogen applications give the crop this key nutrient just in time for when the plants need it the most and by not applying it all before planting we prevent early, excess nitrogen from running off in big rains, leaching into the subsoil, volatilizing into the air, and being converted by the urease enzyme.

My method of application is to spray this liquid nitrogen in streams between the corn rows.  The sprayer makes quick work of this at 100 feet wide and 8 miles per hour; but it is tedious work keeping a big machine with 16.5″ wide tires between 20″ rows.  Jonathan does a good job of it and puts in long hours in the peak season.

Sprayer tires keeping between narrow rows
Sprayer tires keeping between narrow rows

Every acre of every crop get sprayed with herbicide before planting.  Corn gets sprayed again at about 6 weeks after planting and side-dressed at about the same time.  Another big advantage of 20″ rows is that the corn plants will canopy much more quickly; that is, the leaves will entirely shade the middles between the rows, inhibiting the growth of weeds from lack of sunlight.

There is a window of about 4 weeks in which we can most efficiently apply both side-dressed nitrogen and post-emergence herbicide. Most herbicides work best in warmer temperatures and can even damage corn in cool, wet weather.  This year we have been able to stay right on schedule with the number of acres that need to be covered, even though the cool weather has caused us to apply nitrogen instead of herbicide first.

It takes about 5 big days to spray herbicide on all our fields in 16 gallons per acre of water. But nitrogen takes longer because we apply 40-45 gallons per acre, depending on the quality of the soil, requiring us to travel more slowly and refill more often.  At this point we are about half finished with each and the corn is not too tall, so we are in good time and are thankful to be this far along before yesterday’s 1″ rain.

Gentle rains are better for not washing away fertilizer, herbicide, and soil.  So we pray for gentle, timely rains, all season long.

Make Hay While the Sun Shines

Zach puts in a late night

One of the consequences to waiting until field conditions are ideal before bringing the heavy equipment in is the long days into the nights that we work to get it all done in a short window of days. Springtime often brings frequent rains, which gives us precious few good days to run in a stretch before being put out again for maintenance and jobs of secondary importance.

I like to make time to stop and eat, and always make time to hug my children and teach them a lesson or two, but 14-16 hour work days in the spring and fall are common. Planting, spraying, and harvesting are my bread and butter, so fishing and playing usually have to wait for a rainy day.

The benefit of cramming all of that work into long days is top yields from a well timed, placed, and cared for crop. Waiting until conditions are dry enough also saves our fields from compaction problems and uneven emergence.

Let me also remember that my dear wife works long days taking care of the children and teaching them diligently while I am away.

Sunrise under pecan trees on the farm
Sunrise under pecan trees on the farm


How to Fix Ditches in Fields

sunset ditch fixing

It used to be standard procedure each spring to hook up a big tractor to a disk and smooth out ditches that formed in the field over the past year to prepare for planting, even no-till planting. But, “smoothing out ditches” actually amounts to destroying the soil structure and integrity of the field around the ditch in order to make it look smooth. The final result is a natural drainage area being given a loose-dirt bottom that will be blown out even deeper with the next big rain, compounding the original problem. Reflecting on this makes me wonder how much the topography of these fields has changed over the past 200 years of this tillage practice.

sunset farm ditch fixed

Today we fix ditches smarter with a 12 yard dirt-moving scraper (or dirt pan, as we call it). The earth is for mining as well as farming, so we find a place in the edge of a field or other under-utilized land to scrape off topsoil, then lay it in the ditch, mounding it up, driving over it to pack it in, and flattening it out as we finish. The result is a structurally sound, water-dispersing, natural drainage area that will resist washing out through the next big rains. If the area gathers too much water for crop roots to hold, we set aside the drainage area from planting and spraying, sow it with fescue which grows a thick mat of roots and ground cover, and call it a grassed waterway.

Tennessee Corn Planting is Well Underway

Warm temperatures in March had a lot of planters rolling early this year.  But, on my farm, we waited, because although soil temperature was adequate, it was not ideal and there was still a chance of frost and areas of excess field moisture. So I decided to hold off and hope for more ideal conditions. By the time those conditions came it was April 13th; and a couple days later, when I had 200 acres done, some farmers had 1,000+ acres behind them and were finished.

Planting end-rows where leaving a wide grass field border on a slope
Planting end-rows where leaving a wide grass field border on a slope

But I am happy with the way it has worked out. As of this hour, we have 400 acres planted, which puts us at 37%. If Zach gets as big of a day in the planter as he did yesterday we could be at 57% by the time rain comes tonight.

When planting is done at the ideal soil temperature of +60 degrees, seedlings germinate and emerge quickly and evenly, leading to a better stand and higher yields. Last year I learned a hard lesson by planting some ground that was too wet just to get 40 acres done the day before a rain. Those acres ended up with a poor stand, and yield dragged 30 bushels behind what I had hoped for. It also created compaction which had to be relieved by ripping 15 inches deep before planting a crop of canola.

In the picture below you can see unevenness in the stand of canola from ripping at diagonal lines.

canola shop bin top ripping marks
Picture taken from the top of a grain bin showing ripper lines at a diagonal

Sowing Grass Along a Creek

kids seeding creek bank

Trees were cut along the bank of a big creek on the edge of a field I rent near Cottage Grove a year ago. Having the trees gone is good for production along the borders, because trees compete with my crops for moisture, nutrients, and sunlight up to 60 feet into the field. The outside pass with my combine around a tree-lined field border always yields below my cost of production, unless I leave a field buffer strip 40 feet from the tree trunks. Then someone must bear the cost of so much underutilized land.

Here is provided a great opportunity to sow the creek bank with fescue seed for a good, thick stand of grass to prevent erosion. Trees prevent erosion on steep banks only about as well as their mat of fallen leaves can stick to the ground and turn off water. But grasses have a dense network of root hairs which prevent erosion like nothing else.

Notice, in the picture above, the exposed earth on the opposite side of the creek. It is that way up and down both sides of this creek ditch, which is 15 feet deep and 30 feet wide. Last year, trees were cut on both sides, so the chance to sow fescue and stop erosion is a fresh opportunity.

These trees undoubtedly grew here naturally. Natural, in this case, means untended, uncontrolled, and chaos; like hard storms and erosion are natural. Hopefully, our grass seed will take root and maintain the current creek boundaries to preserve this farmland for the next generation.

Children enjoy work