The average acre foot of soil weighs in at 4 million pounds. This is a lot of material in the top 12 inches of your soil! Remember it is a lot easier to purchase farm land the way you want it (in soil constituents) than to try to modify it later. If you have clay soil, then you need to learn to garden in clay soil. It is impractical to consider adding enough sand or loam to significantly change the soil in a large area. Note, take care even in small plots, as sand mixed with clay could form a product very similar to concrete. We can amend the soil to the proper nutrient levels, and that will be our focus on this article.
The chemical nutrients desired can be measured in parts per million. This is how your soil analysis will be measured from the lab. If your objective is 40 ppm and you have 4 million lbs of soil (in 12" of soil over an acre) then you would ideally have 160 lbs of that specific nutrient. (40 ppm x 4 m lbs = 160 lbs). If your lab test identifies you have 37 ppm in the soil, then you could calculate your field has 148 lbs of the nutrient present. (37 ppm x 4 m lbs = 148 lbs). The difference between the goal of 160 lbs and what you have as 148 lbs would be 12 lbs of that nutrient should be applied and mixed into the soil at a depth of 12 inches to reach the optimal nutrient density in the soil.
So, lets review some of the quantities suggested for soil nutrients. Table 1 represents the suggested totals from Bob Gregory, a farmer with extensive agriculture experience. Table 2 is the best I have found from various sources to note deficiency. This table is hard to nail down, as different plants need different levels of the nutrients, but it is an interesting point to compare with. The 3rd table has notes and toxicity levels of the nutrient. And again, toxicity is per crop and hard to nail down.
Table 1: Desired nutrient levels
N 40
P 40
K 220
Mg 180
Ca 2000
S 20
Zn 10
Mn 40
Fe 20
Cu 2
B 2
pH 6.5-7.0
Organic 3-5%
Table 2: Deficient nutrient levels
N
P 10
K 30
Mg 30
Ca 400
S 10
Zn 2
Mn 10
Fe
Cu 0.5
B
pH
Organic
Table 3: Notes
N
P
K
Mg
Ca Ca : Mg = 6:1 to 7:1
S N : S = 10:1 to 15:1
Zn
Mn
Fe
Cu Toxic above 40 ppm
B Toxic above 4 ppm
pH
Organic
Remember that additions are not 100% of the active element. You have to calculate the weight of the calcium in a bag of calcium carbonate, and use that percentage of the bag weight to calculate how many pounds of material you should evenly apply.
Table 4: Common nutrient amendments and the constituent nutrient %
Ammonium nitrate 34% N
Ammonium Sulfate 21-0-0-24S 21% N + 24% S
Urea 46-0-0 46% N
Soft rock phosphate 15 - 25% P + 30% Ca
Single super phosphate 18 - 20% P + 12% S
Tripple super phosphate 0-45-0 45% P
Potassium Sulfate 0-0-52 52% K + 18% S
Magnesium Sulfate (epson salt) 24% Mg + 4% S
Calcium Carbonate 38% Ca
Hydrated Lime 54% Ca
Dolomite 22% Ca + 11 Mg
Calcium Sulfate (gypsom) 79% Ca + 12% S - does not alter pH
Elemental Sulfur 90 - 100% S - lowers pH via biological reaction
Zinc Sulfate 36% Zn + 16% S
Manganese Sulfate 24% Mn + 15% S
Iron Sulfate 36% Fe + 11% S
Copper Sulfate 25% Cu + 11% S
20 Mule Team Borax 11 - 14% B
Finally remember that the rates of application that we calculated where based on an acre field. If you have more or less, then you will need to adjust the total needed by this ratio. 1 acre of land is 43,560 square feet. This is about 208 ' x 208 '. Take your garden size in square feet and divide this by 43,560 to get your % of an acre.
When applying amendments, make sure you mix the minerals in well. A turn over plow is suggested. Apply 1/2 of the amendment to the soil, and plow to 6 inches and then add the remaining 1/2 of the nutrient, and then turn over the entire 12 inches with second pass. If you use a disc or chisel plow, the effective mixing will be 1/2 of the plow depth.
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