As we know, NPK is nitrogen, phosphorus and potassium. Depending on what you are growing, is how you want to use the numbers. Basically, nitrogen is the first major element responsible for vegetative growth of plants above ground. With a good supply, plants grow sturdy and mature rapidly, with good, dark green foliage. Phosphorus is the second major element, essential for healthy growth, strong roots, fruit and flower developement and greater resistance to diseases. Potassium is the third element needed for the development of strong plants. It helps plants resist diseases, protects from the cold and during dry weather by preventing excessive water loss. If the soil is in good shape, compost and the like, you may not need much. For the lawn, you want more nitrogen, as you want more 'foliage' that's dark green. If too much nitrogen goes to the flowers, you will get more foliage but less blooms. Therefore, the need for the other two elements.

You'll find more info on this over on the Soil & Compost forum but basically "Composted Manure" is 80%+ manure (usually from feeder lots) that has been stockpiled and aged for 30-60 days. Manured Compost is approx. 80% composted organic materials such as straw, leaves, paper, grass clippings, paper, cardboard, wood chips, etc. to which some aged manure has been added. Given the greater availability of organic materials to make compost out of it is usually cheaper. And, I contend, usually better given the diversity of materials and nutrients it contains. Mushroom compost is also not as readily available given it is from mushroom growing operations only and yes it is the lowest nutrient value of the 3. What is best? That all depends on the quality of the stuff to begin with - there is good and bad out there. And it depends on what your primary goal is - soil tilth and drainage improvement or nutrients? All 3 or any of the 3 are beneficial to a garden. Composted manure is usually the highest in N-P-K but does little to improve soil. While manured compost usually contains good levels of N-P-K plus many of the micro-nutrients and minerals and provides excellent soil improvement. Mush compost is lowest in nutrients but an excellent soil conditioner. There are exceptions to this of course and in general farm or homemade will be better than any of the bagged stuff but if the bags are all that are available and I had to choose just 1 of them then I'd go with the Manured Compost. Hope this helps. Dave

I agree with gardengal 48 and Jolj. And so do most university agriculture experts, extension offices, and documented and verifiable scientific studies. I am taking a course on this now. Oh, and to the comments about you can't have too much compost...well, that is inaccurate. One contributor said it is balance. I agree, but to know what the balance is or what is needed to maintain that balance requires testing. Most of us can't afford a complete soil test (it isn't just about NPK), so we guess as best we can. Sure, there are some NPK and other nutritional elements to compost, but compost is still considered an amendment, not a fertilizer. Part of it is WHEN or HOW do those nutrients become available to the plants. Anyway, this is several years after the original post, so I hope the poster is still gardening and is successful. :)

Thanks for the response, Sey. I would love to see some reports, any reports, from universities or any qualified source that actually have a specific answer as to how much, in grams, a given tomato plant uptakes for each of the six elemental macronutrients over its life time. My overall goal is to develop a recipe for a potting mix and supplied specific quantities and forms of nutrient fertilizers that consistently result in good, consistent, repeatable yields of tomatoes in the smallest container possible at the lowest cost possible. I have read so many posts by people that get great yields from their container tomato growing efforts, but they all have thrown the issue of cost out the window. When you spend tons of money for Pro Mix Bx potting mix, liquid and granule brand name ferts, mychorrizae fungus, all in 15 to 25 gallon containers for a single plant, of course you are going to get a good yield, generally speaking. There is neither efficient use of science nor great challenge in that. From an economic stand point, that makes no sense to me. I mean, I wouldn't buy a Ferrari for basic transportation to take the kids to school, nor do I need a Gucci watch to tell time. But, if one combines good, objective quantitative and empirically established science with the practicality of sound, common sense economics, I intuit that success is not only quite possible, but quite probable. For container tomato growing, unlike growing in soil, the control of the chemical and physical grow media environment is completely in the hands of the grower The grow media is what the grower makes it. Things like the different migration and leaching properties (or the lack thereof) for each of the nutrients needs to be taken into consideration for determining the grow media potting soil recipe (e.g., quality of air retention, water retention and pass through capacities, electrical properties of the mix to hold onto nutrients [cation exchange capacity], etc.). Another controllable variable is whether to use a Self Watering Container (SWC) approach or a container approach where water is required to drain through the grow media; each of which requires different grow media properties and therefore different mix recipes. The choice of container type also influences the type of fertilizer properties and application since nutrient is allowed to wash through on one container but not in the SWC. Also for consideration are the physical and chemical forms of the nutrient fertilizers; periodic feeding with liquid ferts that contain immediately available macronutrients in dissolved ionic forms, or slow release dry ferts that are either compacted or coated chemicals that retard release over time, and/or macronutrients that are in a chemical form that requires that microbes pass the nutrient through their gut in order to transform the nutrient into the right ionic form that the plant can then uptake. Optimal plant growth and yield are achieved when the plant gets all the nutrients it needs when it needs it. That implies the "right" balance of the "right" grow media and the "right" balance of the "right" nutrients. This balance is, in part, an unstable equilibrium in that an imbalance causes the plant to not perform its best. Too much of one nutrient can crowd out the other nutrient and cause a plant nutrient deficiency in the nutrient that was crowded out. Not putting enough of one or more nutrients will produce a deficiency or deficiencies itself, obviously. There is plenty of sufficient information out there on grow media physics and chemistry. That is not a problem at all. Where there is a great deficiency and gaping insufficiency of information is on the issue of detailed actual uptake of macro nutrients on a per gram per plant basis. And that, my friends, is the all important answer to fertilization, period. It's just not out there; and it should be. I do not buy the response that there are just "too many variables" to deal with. Science deals with much, much more complicated issues than this, every day, all the time, always has, and at a very detailed level. I strongly suspect that the answer is in existence; that there are those that do, in fact, know how much, to the gram, a given cultivar, on the average, under certain specific known circumstances and conditions, uptakes of each macronutrient. Scientifically, it is not a difficult question; it is a simple scientific question, comparatively speaking. I think the answer is not out there "at our level" because we, the tomato growing enthusiasts, haven't asked the precise question yet. We haven't asked each other that question. We, as a group, have all tacitly accepted the approach of "trial and error" much too readily when it comes to fertilizing our plants. When most all people in this forum and all the other forums post how they fertilize their plants, their posts are much, much too general and lack the all important detail with specificity. For example, whenever someone says "I use Tomato-tone when I plant the seedling, then I periodically feed with fish emulsion". That is a near useless post. He/she should indicate exactly how many tablespoons or fluid ounces or cups of Tomato-Tone "per plant" at planting time in exactly how much grow media (if in a container), and exactly how many teaspoons or tablespoons (not capfuls) of what specific brand of fish emulsion and exactly how often it is fed to "each plant"; on a per plant basis. As a result of this information deficit, we have and are spending too much money on growing tomatoes and, in many cases (if not all cases) missing the mark and therefore not getting the results that we should be getting.