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San Diego, Ca.

This may seem like a simple question but I want to be sure.
Say you have your soil tested and the lab sends back soil fertility guidelines saying you should add 3 pounds of nitrogen.
Now lets say you decide to use calcium nitrate (15.5-0-0).
Would this be the correct formula for finding out how much calcium nitrate you should use?
1 divided by .155 = 6.45 ( 6.45 pounds calcium nitrate is equal to 1 pound nitrogen).
Since 3 pounds is needed, 3 lbs x 6.45 lbs = 19.35 lbs
So to add the 3 lbs of nitrogen needed, you would need to add 19.35 lbs of calcium nitrate to your patch? Right?

12/11/2004 1:03:05 AM

Garden State Pumpkins

That's it!

12/11/2004 6:53:38 AM

Puyallup, WA

That's a mighty small patch, Jim!!

12/11/2004 8:38:32 AM

Mill Bay, British Columbia

That calculation works too....I found this calculation that I used this year.

Turning Test Reports into Results:

Soil test reports recommend how many pounds of each major nutrient to apply per 100 or 1000 square feet. A simple way to figure how much fertilizer is needed to get one pound of nutrient is to divide the percentage of the nutrient contained in the fertilizer into 100. For example:

Recommendation: Apply 2 pounds of nitrogen per 1,000 square feet.

Fertilizer: Whitney Farms Blood Meal.

Nutrient Content: 13% Nitrogen.

Calculate: 100/13=7.7 pounds of Blood Meal needed to supply 1 pound of nitrogen. 7.7 X 2=15.5 pounds of Blood Meal per 1,000 square feet.

12/11/2004 11:28:19 AM

Ctpumpkin@optonline.net

That math is cortrect.

But keep something in mind. Most labs will recommend nutrients on a seasonal basis. So if they recommend 3 pounds of potassium (potash), the gut instinct might be to run out & till 5 lbs of 0-0-60 into the rootzone.

This will place a lot of available potash into the next few weeks of growing. But we want more of our potash to come later in the season. Especially since too much early can cause early fruit maturation.

So we also need to factor in *WHEN* the optimum time to apply is based on the report & our goals.

There's also the fertilizer efficiency factor but that's fodder for another thread.

12/12/2004 10:23:03 AM

San Diego, Ca.

Good point Steve. I did not know the recommendations were for the entire season. (I learned something)
Now you have my curiosity up about "fertilizer efficiency factors". Are you going to elaberate? I'd like to learn more.

12/13/2004 8:27:09 PM

Ctpumpkin@optonline.net

We (growers) see the numbers on a soil test report expressed in either Parts Per Million (PPM) or Pounds Per Acre (PPA) PPM times 2 = PPA at plough depth (about 9 inches).

Now lets assume we just got our hypothetical test report back & the lab is reporting that Potash is 1000PPM or 2000PPA.

The lab is also recommending we appy 3lbs of elemental Potash per 1000 sq ft (Equal to 5 lbs of 0-0-60). This is logically equal to 132 lbs of potash per acre.

Well if we started at 2000PPA then we obviously end up at 2132PPA right? Wrong. The efficiency factor is around 30% depending on the soil. So at best we end up at 2040PPA.

So why did we do it if the application we made does so little for our soil?

The lab had us apply the approximate amount of potash that our targeted crop (Pumpkins) is likely to use in a single growing season. So they helped prevent us from drafting the soil potash down below where we started.

This is all looking at one single cation nutrient. Things get really ugly if we're trying to correct a micronutrient deficincy. Soils that are deficient in Iron, Manganese, etc & are found to be the correct pH are almost impossible to correct because the condition that causes the deficiency usually causes the soil to lock the micronutrient out of plant availability again almost immediately. Thus the need for chelated foliar fertilizers.

I especially dislike granular oxide forms of micro-fertilizers that sometimes show up on soil tests after application but the crop still demonstrates a deficiency by tissue analysis due to poor solubility. Yet if the applied element really was soluble, the soil would lock it up anyway. Go figure.

12/13/2004 9:49:06 PM