Ginny:

The calculator got it right. 16% of 20 lbs is 3.2 lbs nitrogen. I'm with you, 10 lbs is a lot more than I have ever put on a tree in one year. So why not try one lb or so 3-4 times a year and see how things go.

If you can fertilize based on what your tree is telling you rather than some formula, you and the tree will be better off. If your tree is growing nicely and producing good fruit it doesn't need any fertilizer. If your tree isn't growing enough, apply some. If your other tree responded well to fertilizer, then add some. Any set rule will be wrong most of the time.

Ginny:
The problem here is tree size is not factored in.
Try this:
http://aggie-horticulture.tamu.edu/citrus/nutrition/L2288htm

Dr. Julian Sauls only gives age but you can see the ammount needed for an acre is only 50 lb for 4 yr old trees. Assuming 120 trees/ acre is only 0.42 lb N per year per tree. Then 0.42 lb-N/(0.16 lb-N / lb fert) = 2.6 lb total fert per tree per yr (16-12-16).

Fruitnut is right 10 lbs. fert is way too much.
I'm still looking for lb-N / in. of diameter data I have but not with me now. Anyone with Bob Randal's book pls post a reply.

I just get a good brand of citrus fertilizer and follow the instructions on the package for application rates and timings - each brand has a different schedule and amount. I have not gone wrong so far and I have been growing citrus for 15 years following this philosophy. I suggest that you eliminate the guesswork out of feeding the plants and just buy a citrus specific fertilizer.

After thinking way too much about how much fertilizer to apply I put down a complete fertilizer without trace elements!! It was not a "citrus" fertilizer. I realized that of course, after it was down and watered in. What a dummie I can be!!

Now I'm reading about how to apply those trace elements my trees need. I feel sure they will need them as the tangerine especially, has pale leaves.

Last spring I did put down a layer of composted horse manure and a little of my own compost and I read that helps.

Any suggestions for how to apply those trace elements would be appreciated.

Thanks!!

Ginny

I'm going to throw in with ashleysf for the most part and recommend that you do your homework, select a brand of fertilizer and stick with it rather than calculate actual N percentages. Follow the directions and keep a close eye on your tree(s). Bear in mind that this will be more art than science. I would also add that citrus likes an acid pH, so don't overlook that aspect. I began feeding my small trees with Miracle Grow for Azaleas and can report awesome results. It has been like flipping on a light switch. I picked up this recommendation from Four Winds Growsers when I bought one of their trees -- note that MG for Azaleas has replaced Miracid.

Here is a link that might be useful: Miracle-Gro® Water Soluble Azalea, Camellia, Rhododendron Plant Food

I would suggest that you get a soil sample. That way you will know exactly what nutrients are available or lacking and not waste money nor cause environmental damage by adding unnecessary nutrients.
Your local extension office can point you in the right direction.

That is probably a good idea, but the OP most likely won't see your suggestion. This is a 4 year old thread. Thread necromancy, lol!

Geekygranny,

Soil sample... good idea; but off the mark. A soil sample only tells you what is in the soil; not what the tree needs, or what is in the tree, or what the tree has absorbed or can.
A leaf analysis is what you need; it tells you what the tree has and what it needs. Soil sampling is a common myth that leads to more fertilizer being applied than needed and/or the things the tree really needs not being applied. I doubt any serious commercial citrus grower would use soil analysis, at least not after the trees are planted.