Question
There is nothing more rewarding than a healthy plant full of blooms. My passion is to grow annuals in my home garden on a serious scale ( half an acre of flower beds and hundreds of pots). (N-P-K) I always thought phosphorus is good for healthy root system and potassium is necessary for good blooms and nitrogen looks after the foliage. Today i read otherwise while browsing, i.e excessive Nitrogen can arrest growth. Phosphorus is essential for blooms and potassium is good for roots. What is the truth? Please also guide me as to where to look for reliable and detailed info on the art of fertilizing annuals species wise. I grow plants from seeds. I also use effective micro organisms (EM) for preparing compost and cow manure. I also use growmore, Shultz, urea and foliar sprays. Most of this is based on hearsay and has produced excellent results while scorching my plants at other times. I never really know what paid off or what caused the damage as i tend to use a variety of fertilizers during a growing season. A response and guidance will be highly appreciated.

Answer
The NPK Story is an unfinished book -- we have much to learn.  But thinking ahead, with what we now know from research only a decade old now, I can make a few points about fertilizer that will clear up your questions pretty well.

First, you should understand that ANNUALS do not respond to fertilizer the same as PERENNIALS or BULBS.  This is just theory right now, but I'm pretty sold on the idea that Annuals are sensitive to the ratio of nutrients on a level that other plants aren't.  Annuals are genetically programmed to make Seeds asap!  Much more than other plants.  Because they only get one season to do that.  They don't have the luxury of time.  Flowering must be done asap, Seed-making must be done asap, germination can't take too long.  There is no time to second-guess any early decisions.  They get one shot.

Consider, too, that leaves are where a plant's energy comes from.  Not fertilizer.  So if a plant has a lot of leaves, it is going to have a LOT of energy, and that is going to be very useful when it comes to making flowers and Seeds.

Annuals, it seems to me, respond to excessive Nitrogen levels by making a whole lot of leaves.  Makes sense.  You can make more Seeds and Flowers that way.  Unfortunately, by processing all that Nitrogen, they get in the way of processing any Phosphorus.  Perennials seem to respond in a similar way, just not as pronounced.  And Bulbs are a whole other story, involving plant pathogens that consume certain kinds of Nitrogen fertilizer and use it to generate a population explosion of disease-causing organisms that end up killing your Bulb.

It sounds like you are doing one of those 'hybrid' horticultural approaches.  You are building up your Soil, making it nutrient rich, raising the quality of tilth, doing terrific things.  But you are at the same time 'feeding' your plants with fertilizers.  This is somewhat counter-productive.  Why?  Because the natural system you are using on one hand is building a good, solid farm of highly beneficial bacteria and other microbes that are feeding the plants like a well oiled machine.  And on the other hand, the concentrated chemical fertilizers you are using is killing many of those beneficial bacteria, adding Salt to the soil (which may already be high in salts due to your use of Cow Manure), perhaps overdoing some of the fertilizer parts and burning roots and leaves.

You need a Soil Test, my friend.

You have probably seen my rant about Soil Testing, so I'll spare you that.  But there is nothing to be gained by compulsively adding chemical fertilizers to awesome Soil.  Which you probably have.

You should understand that all Nitrogen is not the same.  Ammonium N is a lot less effective than you would think, compared to Nitrate forms of N, which carries a negative charge.  Ammonium N is the preferred form of N for all Fungi, as well as the disease causing bacteria; it is positively charged.  These charges determine how much will leach out and how much will be available for use by your flowers.

Also consider that a plant is pre-programmed, genetically, to perform a certain way.  The flowers, under the most ideal conditions, cannot be any bigger than 'x'.  They will not be brighter than 'y'.  The plant will not grow taller than 'z'.  No matter what you feed it with.  Now of course if you have access to various hormones, then you can do all kinds of mad scientist tricks of the trade, but in a normal situation, with normal tools, no plant can do the impossible just because you fed it a lot of Phosphorus.  Am I clear?  It's easy to miss this.  No fertilizer company wants you to think in those terms.  It is however the unwavering truth.  No exceptions.

Get a Soil test.  Find out what is in your Soil, and what is not.  For the monocultures you are raising, you want to keep a healthy level of nutrition in your Soil.  This is the best advice I can give anyone, and I'm still doing it: Get a Soil Test!

My answer is getting a bit long, but I still have much to say on this matter, so: Your followups invited.  Thanks for writing.