Rotating the crop planting will help.Rotate planting legumes and corn.Next time plant the legumes in the area where you have been planting corn.Legumes leave behind Nitrogen nodules in the soil which will provide Nitrogen to corn.This works more efficiently than providing Nitrogen thru fertilizer.

get a soil test done. do you irrigate?

I have never seen 12 feet corn. Even 8 feet sounds huge. I don't know how I would keep up 12 feet corn in my windy neighborhood. One thing that I use is alot of home made compost. Usually my compost is still not fully broken down so when my corn is about 2 feet high I use alot of compost around the corn stalks for added support. I prepare the beds before seeding with a fertilizer then add more fertilizer as the planting season goes on. Corn is a very hungry plant to grow. Soil test is very important to see what type of soil you have.

I'm not a corn expert, since I just grew my first last summer, but I second (third?) the soil test suggestion. You could have a deficency of some other nutrient besides N that is causing less growth. I'm also curious what you mean when you say you're adding "pure N". Nitrogen in certain forms gets used up by soil life or just plain escapes into the atmosphere and water real quick. Maybe you need to switch fertilizing methods? Anyway, soil test will help you decide. I had mine done and it was easy, cheap, and oh-so useful. Cheers!

hobbiest, How are the ears? Are they still of decent size? Are the stalks stocky? 12 foot corn isn't normal for normal varieties of corn so I discount trying to maintain 12 foot corn. Uh, are you bragging a bit here?

If stalk height is the primary shortfall then you likely need the nitrogen applied later, after plants are about 2 ft. high. Soil tests are good but few labs will include a nitrogen test unless you specifically ask for it since this element leaches quickly in wet springs. More labs are doing the corn leaf test to determine N supplementation needs. In your case urea would be a good fertilizer since anhydrous ammonia should be chiseled into the soil.

The N topdress will lead to better yield as well as long as you get some rain after it is applied. Some other things to consider would be root worms or nematodes, especially if you continue planting corn in the same area.

Always plant with a higher Phosphorus starter fertilizer, regardless of what a soil test might indicate. Something like 5-10-5 in proximity, but not touching the seed will give plants a good start.

I 2nd the 2nd N boost once the stalks are knee high. Corn is the only crop I'll use store bought fert on. After trying several sources of N I've settled on grass/lawn fert such as a 30-5-5 or similar numbers with preferably a urea source, but it has to be fert only, no weed killers, pesticides, etc. Plus plant spacing 8-10" depending on variety.
And I agree with Wayne, it's the ear size that matters more so than stalk height.

Went back and looked at the photos I took of the first year I put a garden in by the house. I agree myself with some of the doubts of the 12 ft. high stalks! Hehehe! Most of the stalk heights were around 10 ft. or so with some being less. Was late when I put this topic up and seemed to me that the stalk heights were much higher than what they really were. Time has a way of playing tricks on the mind I think! LOL! Sorry for that. :)

Someone mentioned urea in the soil. The previous owner before I moved in, had a dog kennel with wood chips as bedding, where the garden now resides. I think that may have had a good effect on the first year or two garden results. The plants then, looked better than they do now. Each year I usually add dead leaves and other yard waste to the soil in the Fall. A few years ago, I did add a few hundred pounds of processed cow manure into the soil which seemed to help that years crop. I do remember the beans that were growing in the same patch of soil as the corn was, really had a nice rich green color to the leaves.

The nitrogen fertilizer I use is 38-0-0. I also try to keep the plants watered about every 5 or 6 days. I usually just dig a small hole in the ground near the plants and see how dry the soil is to let me know if the soil is really dried out or still moist under the surface.

The ear sizes the first year or two were nice looking and long. Seems like each year the majority of the ears that I get are getting shorter. Sounds like to me that it may be related to a soil nutrient deficiency. I have been toying with the idea of using a good amount of compost and seeing what kind of results I can get.

I am definitely sold on the soil test idea. Would be interesting to see what it looks like now. I had one done around 4 years ago.

Thanks folks for the help and suggestions. It is really appreciated. :)

I do use alot of finished compost that still has a lot of heavy materials in it to mound up around the stalks to keep them up. But you really need to use a good fertilizer to feed the corn for quality corn. Also are you growing different varieties. That could account for different size corn stalks and cob. The plus to using alot of compost is that the next year I can grow anything in that spot and seem to get good results.

Hobbiest, you mention adding dead leaves to the soil each year, they are great for adding organic material to the soil but as I understand it they use up nitrogen when breaking down. As for the composted cow manure, if it's store bought the N levels may be too low for corn. Just some rambling thoughts on spring...

...and as an experiment, if you're adding leaves this fall I'd sprinkle on blood meal heavy in one area. BM takes time to break down and should still be N high by spring. Then plant as usual with a little 38% soil boost 2 weeks prior to sowing, and side dress lightly again when knee high....more rambling...

I used fresh chicken manure/bedding straight from my brooder last year. I was raising some meat chicks and they do make some poop.I spread it right on the corn, straight from the brooder box about every 4-5 days for a few weeks. I also spread my coffee grounds on the corn and the corn was growing in a raised bed filled with pure, composted horse manure. ( no bedding material of any kind)
I was growing Texas Honey Sweet and although I didn't get large ears, from what I understand, this is normal for this variety. The cornstalks were 10-13 feet tall with the shorter end being the side not getting as much sun, the whole bed did get afternoon shade.
I should have watered more and I also planted much too late, this was my first time planting corn in AZ. But, overall, I think it went quite well. I do know not to plant such a tall variety. I had a lot of trouble with it falling over when the monsoon season started, which unfortunately coincided with the ears filling out. I think the ears would have been much larger if the stalks weren't laying halfway down from being blown over.
Anyway, my point is that corn can take a lot of nitrogen and seems to need it. Before I started to add the chicken manure I saw some minor signs of nitrogen deficiency. When I added the manure it cleared right up.

Here are my soil test results for 2007. I am not sure what nutrients get eaten up over time growing corn. Maybe someone can tell me.

Water PH: 7.2
Buffer value:7.6
Phosphorus: 120
Potassium:320+
Calcium:1280+
Magnesium:64+
Zinc:24+
Copper:0
Iron:7
Manganese:68
Boron:3.4
Sodium:23
Organic matter %:3.4

All of these values were obtained by Mehlich 1 Soil Test Results and Ratings and are Pounds Per Acre.

Off to the Co-op tomorrow to get a soil sample test kit.
I really want to see what has changed over the last 4 years.

BTW,
John, I am not using different varieties of corn year to year. However, this year I did try some Hickory King corn in an area unoccupied by the Silver Queen. Man! Those suckers really did do 12 feet in height! Only downside to growing them was that I didn`t quite get the ears picked quickly enough when they were coming in. Wound up with some ears that were about to get hard and starting to have kernels that were shriveling. I made a mental note to pick them earlier next year. Reason for growing them? Those rascals are "Jack and the Beanstalk" size when they are maturing! Hehehe! :) Also, the ears & kernels are very large from what I had seen a friends Dad grow.

Your previous soil test shows that you are phosphorus deficient and need to add some boron. Get a new test done and see if the ph has dropped. Corn grows best at about 6.5 though it is pretty tolerant of anything from 5.5 up to 7.5. If you need to adjust the ph, use some basic slag and some dolomite lime. This will boost the micro-nutrients.

Buy a box of 20 mule team borax in the laundry dept of most grocery stores. Apply 1 level tablespoon per 100 ft of corn row. This will supply all the boron you need for a year. Don't overdo it, boron is a vital micro-nutrient but is also HIGHLY toxic to plants if concentrated!

The other mineral required by corn that southeastern soils are commonly low on is zinc, but your soil showed to be slightly high on the last test. Verify in the current test if it is needed and if so add some zinc sulphate.

If your test shows needing phosphorus, you can do a quick fix with a bag of super phosphate. It would be best to use the soil test recommendation since phosphorus can be really mucked up if you apply too much.

Here is a link to an article that was written 60+ years ago but is still very applicable.
Phosphate

DarJones

Wow 6 to 12 feet hickory king corn. I have been growing the mirai corn super sweets. It is so sweet and tender you eat it right off the stalk raw.The neighborhood kids come over and love it raw. I don't think your taste buds are like mine. I enjoy the new sweeter corns out there now.

12 foot corn? Crickey. Mine are say....5-7 foot and even the smaller ones have 3 ears nearly full out. A few have 4. Blood and bone, organic compost dug in, heavy compost mulch.....and that's it. Everyone seems super scientific. Maybe I was blessed with a green thumb or something.

Well, have 2 soil test sample kits sitting here for 2 patches I grow veggies in. As soon as the soil dries out from the rain we have been getting, I am going to send the samples in to see what has changed.

Fusion Power,
My soil test result in the phosphorous area was stated from the lab as a "V", meaning very high. I am a little confused here. You say it is low but they say it is high. Can you elaborate? The Boron level I will agree with you on.

Thank you for the link you posted! Was helpful! :)

John,
I like sweet corn also. I think I may have to try some of what you are growing. I have only tried the Silver Queen and Hickory King variety. Sounds like what you are growing is good stuff!

Urban,
I have had a few of the Silver Queen plants make 3 or 4 ears but I usually get only maybe 2 ears that are usable. Always one ear is long and nicely filled out. The other 1 or 2 are runts and aren`t even worth putting away for eating. "Blood and bone, organic compost dug in, heavy compost mulch.....and that's it." I think you may have some good soil that you are growing things in. I really do need to try the compost idea that others have mentioned. I haven`t done the multi-fertilizer" thing yet. Just trying to stay all natural if possible. Maybe I am missing something here.