Tx_Crinum

As a new member I have been randomly selecting posts and reading them rather than just asking questions. I came across Richard's post on fertilizer. I found it to be a very interesting post but I thought I could add something in the way of number crunching. If you're only buying a bag of fert a year, this won't make much difference overall but if you're loading up with say 10 or more bags of fert for your bananas alone, this might ease some strain on your wallet. I have copied a portion of Richard's post that I wish to use and have in italics below.

For fruiting bananas in non-tropical regions, the proportion of 1 part nitrogen (N) to 1.5 parts potash (K) is an excellent ratio. The following fertilizers can all provide it: Alfalfa Meal (2-0-3), Geritz Garden Mix (10-5-15), Scotts Miracle-Gro For Fruits (16-8-24), Grow More 20-5-30.

I don't use organics but I will address them to the point that pound for pound in available nutrients, unless you're getting it for free, organic fert is the most expensive plant fert in the world. Weather it is better or worse is not part of the debate.

I have no idea what these cost but for the sake of argument I've assigned costs. For this example these three all have the same percentage of minors and micros. We know that isn't true but for the example it is. You walk into the a store selling all three side by side. Geritz is $10.00; Scotts is $14.80 and Grow More is $19.00. Which should you buy for the best deal?

The answer is Scotts. The cost of N in Scotts is $1.85/lb. Geritz is a whopping $2.00/lb and Grow More in this hypothetical example is $1.90/lb of N.

The numbers as Richard stated represents a percentage of active ingredient (AI). Scotts contains 16% N. .16N (X) 50lb = 8lbs of N per 50lb bag of fert.
$14.80/8lbsN = $1.85/lb of N.

Most of my work has been with turf applying 1lb of N per 1000sft per application. So if I were to use these ferts for turf application to get that 1lb down on 1000sft of turf, I would have to apply 10lbs of Geritz, 6.25lbs of Scotts and 5lbs of Grow More.

Not only do the numbers tell you how much nutrient you are getting and how much actual product you need to use; the numbers also can lead you to purchasing a more expensive bag of fertilizer that is cheaper to use.

Just be careful and check the weight of your bags. Many companies are now packing 40lbs of fert in a bag rather than the traditional 50lbs we all are accustomed to.

Richard

Yea! Now of course, your calculation is based on the nitrogen component. Now make the same computation for the Potash component (for bananas) and see what you think!

I can add some local reality:
5 lbs Alfalfa Meal (2-0-3) ~ $4.00
20 lbs Geritz Garden Mix (10-5-15) ~ $35.00
20 lbs Scotts Miracle-Gro For Fruits (16-8-24) ~ $36.00
25 lbs Grow More 20-5-30 ~ $39.00

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stumpy4700

But I have a question. Would you have to use more of the Alfalfa Meal to equal the nutrient value say of the Grow more? I guess what I'm asking is would I use more to equal the amount that the banana would need?

sbl

It would take 10 times as much Alfalfa meal to equal grow more. In other words, it would take 250 pounds of alfalfa meal and a cost of $200 to equal 1--25 pound bag of Grow More.

Tx_Crinum

Calculating fertilizer based on anything other than N is a mute point. N is and has always been the most expensive component of a balanced fertilizer. See link table 7.

ERS/USDA Data - U.S. Fertilizer Use and Price

Since 1974, N (NHSO4) has cost from 30-50% more than K (KCL) During that time frame the only report of K exceeding N was 2008 so I'm not ready to concede K is more expensive than N until a few more years worth of data is recorded. If that becomes the new trend, then fertilizer cost will be calculated on percent AI of K. However based on the volatility and purported decreasing supply of and increasing demand of propane and the federal mandates to increase ethanol production, I don't see N becoming one of the cheaper components of fertilizer.

Tx_Crinum

Per Richards request. sbl has already clearly addressed the economics of the alfalfa meal. Sorry it took so long, had to check, reheck and re-recheck the numbers because there is always a spring butt in the audience looking for a typographical error to pounce on.

...........................cost of 1lb N...................cost of 1lb K

Geritz.......................17.50.............................. 11.67
Scotts......................11.25............................... 7.50
Grow More*.................7.80...............................5.20
*Prorated at 31.20 for a 20lb bag.

Sorry about the dots, it doesn't recognize my tabs and squished it

Once again with Richard's real world numbers, calculating the cost of a balanced fertilizer with anything other than N as the cost index is a mute point as shown by his example. I will say though that is some HIGH dollar fert.

Now compare that with a 50lb bag of 10-20-10 I purchased at 13.00 at the local ag feed store.

Ag Grade......................2.60..............................2.6 0

I'm not worried about the missing minors and micros in ag grade fert. The cation exchange capability of clay soil is so great that most micros and all minors are immediately unavailable to the plant so I go with foliar apps only for that.

Richard

Tx, thanks for starting this thread. Just fabulous for people to learn about.

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