Calculating corn: The corn math

It doesn't seem like something that you need to put much thought in when you grow a vegetable.  Most people have grown something - tomatoes are popular - and some folks have even put in a garden and tended it over the season.

When I grow corn there's a lot of choices to be made; what ground, how much, what seed, plant and row spacing, fertilizer and other amendments, and cultivation/weed control.  

My corn is grown for my own operations - that is, my intention is to feed it to my own animals, so I've got a captive market for it - read I don't have to sell it to anyone else, no marketing costs - and to be economically viable I have to compete against my other source of corn - feed mills, which sell pretty expensive corn.  a bushel of corn that a farmer might sell for $4 in Iowa comes to me as hog feed at $0.20/lb - or roughly $11 a bushel.   Of course hog feed has ingredients other than corn, but it's mostly corn, and since that's relatively easy me for me grow, I'll grow it myself. 

Corn requires a certain amount of heat per year to grow - growing days.  This is the number of days where the temperature exceeds 50 degrees.  In this area, western Washington, from April 1st to October 31st there's about 2,450 heat units available.  That is, the number of hours that the temperature exceeds 50 degrees.     

Link to the full page for this seed

These heat units are part of how I make the decision on which seed I choose.  In this case variety P7213r has less heat units than I'm likely to have in the year, which means that there's a good chance that it will fully mature in the growing season that I have available to me.  The tradeoff between an "early" - read short growing season - variety and a longer growing season variety is yield.  This particular corn will theoretically produce less grain than longer-maturing corn, and I have to fight the urge to be an optimist and plant slower varieties because if it doesn't work out I don't get much of anything.  So I'll look through the varieties available for corn that has a heat unit requirement that is about what I'd expect from an average year.  If you'd like more information on CRM and GDD (growing degree days) check here.

To figure out what I had for growing degree days I have a weather station that I installed when I purchased the farm, and I use that data, and I refer to the WSU agricultural extension and to the weather underground.   My local climate is a bit warmer than is reported by the weather sites based on the readings of my weather station.  

Note on the weather station:  I've gone through a bunch of them over the years and this is the one that has lasted the longest of the bunch.  I want a consistent reading and I don't want to have to fiddle with the weather station, and this one has done the job.

 Note:  I have no connection with Pioneer, I'll just note that it is a very popular choice with the local farmers and seems to do well in this area.  

Speaking of that, copying what other farmers are doing in the area is something that I will do, too.  If you're using the same sort of seed you'll find it at local supply sources, too.  No need to ship it in from somewhere, and supporting the local businesses is generally good policy for me.

  Farmers tend to pick what works for them, and in the area they are.  So I'll watch carefully at local farms and note when they're tilling, when they're planting, when they're weeding and when they're cultivating.  I've got a guy who leases ground across the street from me and he is provided me with a heads up whenever there's haying weather.  When I see his mower arrive I break mine out :)

Having selected the seed, density plays a role.  If I were planting sweet corn I'd be going for large ears - that's what the consumer wants.  for grain corn I want the maximum number of corn kernels per acre, which for modern corn seed means planting very close together.  Each seed provider has a recommended seed spacing, and row spacing.  Most corn is planted in 30" rows, and most corn is planted between 5 and 9 inches apart in the row.    

At 5.5" apart and 30" rows, you'll be talking about 37,600 seeds per acre.  at 9" apart it's 23,000 plants per acre.  So why wouldn't you just plant them close together?   

Plants per acre, 30" rows

Depends on the seed, and the goal.  for big ears you want them farther apart.  for maximum kernels, you'll probably want them closer.  Not every seed will germinate, and not every corn plant will make it to maturity.  So I'll plant a little closer to make up for the losses, and I'll accept the smaller ears for more ears and more grain overall.  

My first year planting corn I had some ravens that thought it was great fun to pull my little corn plants out by the roots.  And they pulled thousands of them out over a two  month span.  I couldn't figure out what was doing it - I kept coming out and finding corn plants drying on the ground, pulled out like green onions.  I finally staked out the field and found them doing it one day.   It stopped when the corn got big enough, but I lost the better part of an acre to the pesky birds.  

Corn seed comes in bags that contain about 80,000 corn kernels per bag - roughly 50lbs, but it varies.

So 1 bag of corn seed at $220 will plant about 2.3 acres - so I'll be spending roughly $4,000 for corn seed.  Add to that the cost of any soil amendments like lime, fertilizer and then the costs of tillage - fuel, repairs, labor and wear-and-tear, and , and the total bill gets pretty big pretty quick.  It wouldn't be too far off to guess that it might cost me $250/acre to get it all done.  

For a list of commonly performed soil preparation and what people pay for that work hired out in iowa, click here.   I can't really hire it out here because I cannot trust the local guys to do it.   If I want corn I have to do it myself.

So in return for the $250/acre, I'll get between 100 and 150 bushels of corn at harvest - 5600 to 8400 lbs, or between  2.25 and 4.2 tons of corn.   At the low end the corn is costing me $111 a ton.  At the high end it's costing me $59 a ton.  

So if the harvest works out, and the weather cooperates, and there's not a big drought, and plagues of insects don't appear, and the cows stay out of the corn and so on, I'll have feed at about 1/3rd the cost of what I'd normally be paying, which will add about $30k to the bottom line of my farm, which isn't bad pay for a part-time job.   

And that's the corn math.