It's been said somewhere here that containerized citruses take NPK in a ratio in 5+1+3. Does that mean if I'm using a 6+4+6 fertilizer, and I use 250 ppm Nitrogen every watering the other nutrients (P and K) will be taken up in the 5+1+3 ratio in relation to N, despite that I'm using a 6+4+6 fertilizer, not a 5+1+3?

By the way, what US university tested and confirmed that 5+1+3 is the best ratio for containerized citrus? I've been telling some people about this and they didn't believe me and they would like some proof.

It is true, there is much on this forum that says 5.1.3. is the correct ratio for citrus(and not specifically containerized) However, not all of us are so sure, myself included. There are too many factor to address for there to really be a "one size fits all" ratio. Tree type, size, health, climate, soil type, nutrient uptake, container, in ground, organic/synthetic, are a few of the many factors that effect nutrient uptake. I truly doubt there is any research to support 5.1.3.

I believe the point of 5.1.3. is more directional advise for people that have no idea where to start. Its an average or standard in the commercial citrus field as well.

Evaldus, your questions have been answered on this forum before, the last time a week or so ago. Use the search function on this forum. - Millet (884-)

read here:
link

Evaldss, The exact research on the 5-1-3 nutrient uptake ratio by citrus that I have previously posted, was carried out by the Italian University of Messina's Dr. Giovanni Dugo.. You can read his findings plus the entire technical literature in his published work "Citrus -The Genus Citrus". If your interested in additional readings by Dr. Dugo pertaining to citrus, he has also published the absolutely astonishing book" Citrus Oils, Composition, Advanced Analytical Techniques, Contaminants, & Biologal Activity". You can also find a lot of additional work by Dr. Dugo on Anthocyanins. Dr.Dugo, co-partners were Dr. Angelo Di Giacomo at with the Experimental Station for Citrus, at Agrumi Italy, and Prof. Calabrese at the Institute of Fruit Crops, Faculty of Agriculture University of Palermo.

I'm sure if you would just spend a little amount of time, doing your own research on the Internet, you will find many other resources, including research done by other universities and experiment stations, both in the US and other citrus producing countries. In just 7 or 8 minutes I found the following list recommending 5-1-3 as the perfect fertilizer ratio for citrus.

eHow
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Piece of Marin Garden Forum
Permaculture Passion
Aloha Fellow Citrus Growers
All experts. COM
Wiki

Evaldas, feel free to either accept or not the work of The University of Messina's Dr. Dugo and the Italian Citrus Experimental Station's Dr. Di Giacomo. Personally it certainly will not bother me one way or the other, it is your tree, care for it as you wish.. Take care, and the very best to you and to your tree. - Millet (884-)

Thank you telling me the source.

But I still don't understand: if I'm using 6+4+6 fertilizer will my trees be still taking the nutrients in 5+1+3 ratio?

Yes, that is the uptake ratio--so when you apply 6-4-6, you will have excess P and K. In a container, that can result in a build up of salts unless the container is flushed several times a yr--my containers are outside most of the yr and get flushed frequently by mother nature--that is why slow release fertilizers work best for me.

Even for inground trees, excess P can build up in soil resulting in mineral binding problems and or environmental contamination. Excess N and K are washed away easily. That is one reason I use a bag of composted cow manure on each of my inground trees every yr--just keep it away from the trunk to help prevent root rot.

Then I have one question for you...

If 5.1.3. is the "perfect ratio" then why are there many citrus specific fertilizers that are not in fact 5.1.3.?

Examples all found on Google:

High Yield Citrus Fertilizer 16.8.6.
Espoma Citrus Tone 5.2.6.
Sunniland" Citrus 6.4.6. - Formulation used by Florida growers
NutriStar 12.10.10. Citrus & Avocado Food
Jobe’s Organic Granular Fertilizer for Fruit & Citrus 3.5.5.

Not a single 5.1.3. - Wonder why?

Research done in Italy would tell you what ratio is perfect for Italian trees grown in Italian soil in an Italian climate in that Italian region you mention. Which can all vary GREATLY from region to region. The truth is 5.1.3. is not "perfect" in all situations, soils,climates, ect and I think you know that Millet.

RyanL, the study is for CONTAINERIZED CITRUSES.

There are many citrus fertilizers that don't have this perfect ratio because the manufacturers don't care, they just want to sell it, that's why they call it a "Citrus Fertilizer".

What is your problem anyway? Seems like you just want to argue here, you have a problem with everyone using CHC, you don't like the suggested fertilizer ratio.

Evaldas, stop getting emotional look into the facts. If a Moderator of this forum told you to jump off a cliff, would you?. Point is, Don't believe anything just because the name moderator is beside there name.

I also forgot Gro Power used by Grow quest Cali, 9.3.9. - looking for some real citrus experience, check out Grow Quest of California - these guys are true professionals. - You know the guys that grow citrus for a living. And Evaldas, dont tell me some forum moderator knows more about citrus then them, And no, they dont use CHC as a medium.

Evaldas, Its not that I just like to argue, I just call BS when I see it.

Apparently they are only professional at growing, not customer service. However, back to the point, the tree quality is simply the best and they don't use 5.1.3.