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.

Uneven application of Nitrogen cost me $16k last year!

Covington WRDVI Corn 8-24-16

This February, as I was reviewing last year’s field records in the office on cold winter days, I discovered curious lines in my fields on the WDRVI satellite imagery provided by a service which I started using last year.  FarmLogs is a cutting edge farm technology company that provides several unique services that I find valuable.  I took my family to Florida in December to attend a two day conference they hosted where I learned about the use of this imagery in discovering problems just like this, so I had an eye out for it.

After studying these lines and developing a preliminary conclusion, I called for a discussion with the FarmLogs agronomist, Tracy Blackmer.  The company produced a well documented story about helping me find the equipment problem that caused streaks in my fields last year that is very interesting. Read it on their company blog here.

List of Fertilizer Conservation Practices

fertilizer loading anson

Fertilizer is where most of our crop input money is spent each year.  It is easier to waste money and damage the streams by over fertilizing than anything else we do, so it only make sense that I spend more time planning fertilizer rates than anything other input.

  • Soil samples are taken according to soil type maps.
  • Fertilizer prescriptions are made according to recommended rates for reasonable yield goals.
  • Dry fertilizer is applied in late winter or spring rather than fall.
  • Enviromental stabilizers and availability aids, like Helena’s Hydra Hume, are used to maximize usage.
  • Nitrogen is applied in readily available forms in multiple applications to avoid leaching, denitrification, runoff, and over-application.
  • Nitrogen is applied with proper directed nozzles on a sprayer to utilize technology minimizing overlaps.
  • Nitrogen is added to irrigated fields through fertigation in 3-6 applications using an Agri-Inject system to minimize leaching while optimizing yield.
  • Crushed limestone is applied as-needed to maintain balanced pH levels which minimized the need for high rates of fertilizer.