NO3N vs N?

I have a potting media test report from the local agent which shows everything in mg/L rather than percent. Can someone tell me the conversion factor? Also, instead of N the report shows NO3N. What is the conversion factor for NO3N to just plain elemental N?

Thanks

PS - the density of the bone-dry media is 72 ounces per gallon which, by my quick calculation, is about 540 grams per liter. So would, say, the 171 mg per liter P lab measurement be the same as 0.171 grams P / 540 gram media = 0.003 or 0.03 percent P? Or did I get that wrong? If that is right I still can't figure out what percent of N is in the NO3N. Too many senior moments lately...

What is causing you to believe these numbers are important?

Al

I'm trying to make an organic potting mix from local sources so I'd like to know what my most nutrient-rich base media has (in NPKCM) before I add anything non-local like colloidal phosphate, greensand, nitrogen containing meals, etc. Also, I have some food waste products which can be added in small amounts but if there is sufficient nutrient in the base material I don't want to add any more than necessary since those things tend to clog up the media. The pine bark fines I get I consider essential devoid of nutrients but I have a source of wood chip "compost" that clearly has some nutrient value. I don't intend to add liquid or other fertilizer after the original mix is constructed since it is mostly for short term growth of vegetales (perhaps a kelp or alfalfa meal top dressing mid season). The spent material will be reused in other places so as not to waste any residual rock powder nutrients. I may also try using it for a longer term media if I can get a good balance of slow release and quick release nutrients. At any rate, I'm also just plain curious as to the nutrient values of organic materials I might use for the mix and the nutrient analysis is cheap enough to have done, even though it only gives the readily soluble nutrients rather than the long term availability it is a start. The test report only gives a high, medium, and low range for the values and while that is probably good enough I'd like to know how that compares with materials that have percent values published (all the NPK charts for everything from coffee grounds to citrus peel) since that would guide me a bit on what the overall mix should be. Most of the time up to now I have just thrown in something for each of the NPK nutrient based on published values with some dolomite just in case and it works well enough - but I'd like to be a little more precise.

Hmm - I'm not sure I was real clear there. Let me try again with some specifics. I am thinking to balance the organic mix according to your optimum average NPK ratios posted in another thread (12-4-8) so I am not over fertilizing in any one nutrient but still minimizing expensive and non-local materials. I know the available nutrients will change over time in the medium as the plants grow but it seems a good start. Among other things I have readily available an infinite supply of aged coffee grounds, locally mined colloidal phosphate, expensive non-local greensand, an almost local, but still expensive alfalfa meal, local pine bark fines by the yard, and a local wood chip compost that drains rather well for "compost." From published NPK values and bag values I can get a decent enough estimate on blending a 12-4-8 fertilizer from most of that but since some of the materials I want to use for the substrate (especially the wood chip compost) do have some nutrients I could lower some of the added materials, at least at the early part of the season. That should keep drainage higher since all of those added things tend to decrease drainage. For example, I've been told that wood chips should have enough potash that I should be able to eliminate the expensive and non-local greensand (not sure I believe that but that is what a person who should know has told me). Anyhow, I haven't yet gotten the analysis for the wood chip compost but I have one for another substrate I was previously using and I found it less than useful since I am having trouble figuring out the percent N in NO3N and the "percent" associated with mg/l. If I can get all my data in either percent NPK or everything in mg/l I can likely blend a ratio along the lines of 12-4-8. Then I just need to figure out how much to use in the starting mix and, by experience, or a mid season test, determine if I need to add anything as a top dressing. But, while I know I'm missing something obvious, I keep messing up the attempt to get everything in the same units so I can put together a decent ratio. Anyhow, that was why I asked if anyone could help with that.

Elemental N is a gas & won't be found in significant amounts in soils. It will only be found in other molecules. Nitrate and sometimes nitrite are the forms of N measured, but it will do you little good unless you know which salts are present. What if your sample contained a significant portion of NaNO3?

Mg/l is the same as ppm, so to find the % you would multiply mg/l x 0.0001. E.g - 4,000/ppm = 4,000 mg/l.
4,000 mg/l x .0001 = .4%

I don't understand how you can use these figures unless your intent was to determine how to custom blend your fertilizer in order that you might bring a fast (nursery) crop to sale using the least amount of fertilizer possible while maintaining a specific EC or TDS level. The variables are so many that it would be a major challenge, even to professional growers with sophisticated equipment.

I don't mean for this to sound insulting - there is non of that in what I'm saying. I would love to be able to help you, but I think there is reason to be concerned that you could easily do yourself more harm than good. E.g. - Did you know that a 12-4-8 fertilizer does not contain 4% phosphorous (P)? Fertilizer formulas report P as P2O5, not actual P, and potassium (K) is reported as K2O, not actual K. To convert P2O5 to P, you need to multiply the P2O5 value by 0.43, and to convert K2O to actual K, multiply the K2O value by 0.83.

For example, using the equation above, the P2O5 and K2O values supplied by 12-4-8 at 200 ppm N would be 67 ppm and 133 ppm. This converts to an actual P concentration of 29 ppm P, and an actual K concentration of 57 ppm K. Do you see what I mean about how easily calculations can bring problems unless there is an awareness of these and other significant factors that may not be as you might expect?

Plants will pretty much 'take what they need and leave the rest'. As long as you supply all the essential nutrients in adequate amounts, and keep EC/TDS below problem levels, you cannot go wrong. That is how the phrase 'weakly weekly' came to be. Nutrient levels and pH in containers can change radically with each irrigation or fertilization. For all intents and purposes, I consider soils to be devoid of all nutrients. I lime to get pH close to a favorable range and provide Ca/Mg, then depend on only what I provide as the planting's source of nutrients. This high degree of control has served me very well over the years.

A couple of notes I noticed I'd like to share as I read through your later posts: Unfinished compost has some nutrients, but make sure you take into consideration its tendency to break down quickly and immobilize N in the soil. Finished compost is more stable structurally, but adds very little in the form of nutrients - including micronutrients. It's my opinion that it's (compost) much more trouble than it's worth in containers and it's small particle size makes it preclusive for my purposes.

All the technical info is nice to know - primarily for technical problem resolution when you've exhausted the obvious, but it really doesn't have to be any where near that complicated. If we needed to know every intricacy of how an automobile worked before we could drive, we'd all be borne on shank's mare. Container culture has comparable parallels.

Take good care, Dan. Best of luck.

Al

This message was edited Dec 30, 2008 6:12 PM

Thanks Al,

The potting mix test report doesn't really tell me which type of N I have in the tested mix. It just says NO3N in the table and lists that as "Nitrate-N". I was hoping there is some way of reading that which tells me just the fraction of N in what is reported. I tried counting the molecular weight of two Ns and 3Os but have no idea if that is what "NO3N" actually means. So that seems less than usable to me and I've been struggling to get my head around it so to speak. I'm still not sure what to do about that other than just ignore it and not count on any N from that portion of the mix. Since, as you noted, there is some tie-up of N in decomposition of other medium components my approach to nitrogen has been "just add extra to offset any tie-up and calculate what the plants might need from the other additives (high N things like coffee grounds, fertilizer, etc.). That seems a bit loose to me but I suspect it will do for now. When I get the next batch tested I'm going to grill the guy as to how much elemental N that means (if, in the next media additive it shows any NO3N worth speaking of).

On the P2O5 and K2O issue I actually already knew about that but I *assumed* the test report and all the published NPK data are using the same terminology so I figured I could set up an NPKCM ratio using consistent terminology. One more thing to grill the lab guy about - is the listed reading in P205 and K2O or the elemental values.

On the calculation for mg/l to percent. I think, after reading your post, a few neurons were jogged loose and I abandoned the attempt to get everything in percentages. All I really need is a ratio of mass to mass (or weight to weight) of the various nutrients to get a consistent ratio. And that is more happily done using units I actually mix with. So I'm going to convert anything that is mixed by the bucket full (the proposed compost for one, as well as coffee grounds, etc.) into ounces of nutrient per bucket and the ones I add by the cup full (greensand, colloidal phosphate, etc) into ounces per cup full. Once I do that I can get an accurate ratio of nutrients by setting up a spreadsheet that adds them all up - or more likely just use a quick back of the envelope calculation. Or, to restate that, I will simply ask myself for example how many cups and buckets are needed to get 12 ounces of N, 4 ounces of P and 8 ounces of K into the mix. Then all I will need to do is weigh the largest bulk material (the pine bark fines) and add it to get whatever starting nutrient levels I need - presuming I can figure out what that level is.

Which brings up your comments on why I am doing this anyhow. That is a bit more of a sticky wicket and requires a bit of historical data on what I've done so far and where I might take it. Basically I have been container gardening for about three years now since I retired. Love it. I am a tinkerer and a gardener and container gardening is a recreational activity for me - mostly. But previously I have made my soil mixes sort of haphazardly by throwing together bulk materials, some organic additives like rock powders, Ozmocote at half the manufacturer's recommended rate, and a light sprinkling of either 10-10-10, ammonium nitrate, or urea when the mix has a lot of woody material which could tie up nitrogen. I haven't been at all concerned about the ratio of fertilizer salts and not much concerned about drainage structure of the media. So far it all works. Peculiarly, even when I end up with what looks like a mucky poorly draining medium by mid season the veggies seem to grow fine and, when I dig up the roots immediately after harvesting they all seem to be healthy and white with no visible dead roots. I do always make sure there is plenty of water flowing through the containers when they are drip irrigated four times a day so I suspect plenty of oxygen is being carried in my the irrigation water and more oxygen gets in when the plants suck up and transpire all the perched water on hot days between waterings. And usually the medium does not get too mucky since after each growing season (or occasionally two growing seasons since we have three a year here in Florida) the medium is replaced and the old stuff used in a conventional raised bed to recycle any rock powder nutrients that may be left. So I'm far less concerned about long term mix structure and nutrient levels in the medium than others who have to worry about multi-year growth of containerized shrubs and such.

However, I have been concerned that I am flushing nutrient through the containers with all the irrigation water so I want to reduce that to about a10% flow through. That, I expect, might make having the right amount of nutrients more important since (from reading your post on fertilization) I might end up with one or more excessive nutrients causing the ozmotic pressure problems you noted. I can always measure the EC with a soil meter and adjust the irrigation flow rate to keep it low but then again I am probably flushing usefull nutrient - and, though I direct the effluent and excess nutrient to a conventional garden area to reuse it, I still *might* be flushing too much nutrient and that then into the ground water. I'm not too concerned about the actual cost of the lost nutrients, if I worried about the cost of growing veggies in containers I'd be buying them at the grocery store instead. :-)

The second issue I'm working on involves a volunteer group I work with. At that group we pot up edible plant shrubs and trees and sell them cheaply at the local farmer's market to encourage local food self-sufficiency. The group is all volunteer and all those idealistic young volunteers are seriously committed to organic only potting mix. Plus our nursery area is leased from an organic farm and we cannot mess with their certification by bringing any chemicals onto the site. The potting mix we use there is, well, less than optimal to my mind. The trouble is it has to be nearly free to sell the plants (and sometimes just give them away) at the rates our idealistic young enthusiasts want to sell them at. So, it is based on stable cleanings (free), about 10% pine bark fines (not free but not too expensive and "local", coffee ground (free), perlite (expensive and not local), colloidal phosphate (not free but local and relatively cheap) and New Jersey Greensand (neither cheap nor local). We definately do not have the budget to buy top dressing orgainc additives like blood meal (and our vegans would shout about that) or similar soluble nutrients. Fortunately, we seldom have plants in those pots for more than a year. We propagate in the fall and winter in a greenhouse and sell out most everything by the next winter warning all the buyers to plant it out as soon as possible or report into bigger pots with their best potting mix. Seems to work well enough but I would like to come up with a cheaper, better, and all organic mix. There are some apparent nutritional issues with some of the touchier plants and who knows what unseen nutritional deficiencies are possibly stunting the plants. Probably all that saves us is we focus on food plants that are easy to grow and survive sometimes extreme neglect but still snap back and provide food when the growing conditions improve. Which leads me to why I want to try out a local, inexpensive, all organic, season-long potting mix in my container veggies. When I get something that works for veggies I should (hope to) be able to work with that and craft something a bit better for the group. The cheap, local, wood chip compost is one of my hopes to replace some of those very non-draining weed infested stable cleanings in the potting mix. Anyhow, I suspect I can do at least a bit better for the group if I can quantify some optimum additives rather than just two buckets stable manure, half a bucket of pine bark, a cup of this and a cup of that. But maybe not. Doesn't hurt to try.

Along with all that there is just plain interest on my part in experimenting. I have three rows of container vegetable gardens I just started. One is my traditional mix I've come to by trial and error (which, by the way is rather similar to yours in proportions except, instead of the peat, I add some wood chip compost, coffee grounds, colloidial phosphate, and greensand, leave out the micronutrients and use half the recommended CRF). The second row increases the pine bark, leaves out the perlite, and adds more of the compost and coffee grounds - CRF stays the same. The third row is going to be the most interesting. It includes no CRF or other chemical fertilizer, more pine bark, no perlite, all the other additives as row two and, for a touch of micronutrients, and some alfalfa meal that is grown and processed not too far north of here (semi-local). I sort of expect I will have to top dress it with something along the way but maybe I'll give it a shot with nothing but what is in it. Next season, if I can figure out an optimal mix other than my trial and error one (which I suspect is in the overkill range for some on the rock powders, especially the expensive greensand) I'll adjust for minimal use of additives.

Thanks for all your carefully presented info, both here and in your other posts.

Dan

OK, you made my brain hurt.
Lisa

Me too - and I wrote it. :-)

Dan