A Sample Garden Soil Test

General Information

Plants need carbon [C], hydrogen [H], oxygen [O], nitrogen [N], phosphorus [P], potassium [K], sulfur [S], calcium [Ca], iron [Fe], and magnesium [Mg]. The first three elements are supplied by the atmosphere and water. The rest are supplied largely by the soil, provided that the pH is right. The pH is the measure of the relative acidity or alkalinity of the soil. A pH of 7 is neutral, lower than 7 is acidic, and higher than 7 is alkaline. 

Nitrogen is an important constituent of protein. Proper balance of this element in your soil will provide dark green foliage and active growth. Nitrogen is especially essential for vegetables in which leaves, stalks, or stems are the important end products. 

Deficiency of this nutrient results in a sickly yellow-green coloration, distinctly slow and dwarfed growth, or drying ("firing") of leaves, starting at the bottom of the plant. In corn, grains, grasses, and the like, firing starts at the tip of the bottom leaves and proceeds down the center or along the midrib. 

Excessive nitrogen causes too rapid growth, resulting in soft tissues and general weakness of the plant. Too much nitrogen at flowering time causes the plant to continue active vegetative growth, retarding flower and seed formation. 

Phosphorus (also known as phosphate) stimulates early root formation and growth. It's responsible for a rapid and vigorous growth start, and it stimulates blooming and seed formation. Proper phosphorus levels in the soil also help to hasten maturity and give winter hardiness to fall-seeded hay and grain crops. 

Deficiency of this element produces purplish leaves, stems, and branches. Other symptoms include slow growth and failure to reach maturity in a timely manner. In corn, phosphorus deficiency causes small stalks to form, and in grains it promotes lack of stooling. Low yields of grain, fruit, and seed are typical symptoms of phosphorus deficiency. 

Potassium (also known as potash) is important for the formation and transfer of starches, sugar, and other carbohydrates within a plant. It imparts increased vigor and disease resistance to plants, and aids in the production of strong, stiff stalks. Potash is very important to root, tuberous, and bulb plants. For large mealy potatoes, juicy carrots and beets, and healthy dahlias, be sure there's adequate potash in the soil. 

Lack of potassium results in mottling, spotting, streaking, or curling of leaves, beginning on the lower levels of the plant. These lower leaves will appear to be scorched or burned on the margins and tips. The dead areas eventually fall out, leaving ragged edges. This results in a premature loss of leaves and, in plants like corn, a tendency to fall down because of poor root development. In corn, grain, and grasses, potash-deficient firing starts at the tip of the leaf and proceeds down the edge, usually leaving the midrib green. 

Excessive potassium in the soil causes plants to retain water, resulting in high susceptibility to both drought and frost injury.

Sample Garden Soil Test Results 

Item Tested Ideal Level Soil's Level Fertilizer Rating Required
nitrogen 25 ppm 12.1 ppm 5.3%
phosphorus 5 ppm 3.0 ppm 7.1%
potassium 20 ppm 18.0 ppm 4.1%
pH 7.0     6.1 +1.0 (change required)

To put these results another way, the soil's pH level is mildly acid, the level of nitrogen is fair, the phosphorus level is good, and the potassium level is good. In light of these results, our recommendation is to raise the pH by 1, raise the nitrogen with 5.3% nitrogen fertilizer, raise the phosphorus with 7.1% phosphorus fertilizer, and raise the potassium with an appropriate fertilizer rated at 4.1%. 

Because almost every gardener's fertilizer needs are unique, your local nurseries and fertilizer supply houses take great care to stock a wide variety of soil amendments. Usually one of the combination fertilizers listed below (in order of preference) will meet your needs. 

Popular Nonorganic Combination Fertilizers 

Number Type Lb./Acre Lb./100 Sq. Ft.
1 23-19-17 757 1.5
2 15-30-15 783 1.6
3 22-34-11 751 1.5
4 6-10-4 2,381 5.0
5 6-10-10 1,799 4.3
6 5-4-3 3,773 8.4
7 5-15-10 1,758 4.1
8 8-4-4 3,086 7.2
9 15-5-10 1,919 4.9
10 25-3-3 3,503 8.1
11 6-0-0 2,417 5.1
12 21-0-0 691 1.2

As an alternative, you can mix your own fertilizer from "basic ingredients" so that it closely matches your individual requirements. This is often very economical, since the ingredients are more concentrated than typical combination fertilizers. Sudbury makes the commonly available formulations Unit X (44%-0-0), Unit Y (0-44%-0) and Unit Z (0-0-44%). If you find this method more desirable than using a combination fertilizer from the above table, the amounts you should apply are as follows:

  Lb./Acre Lb./100 Sq. Ft.
unit X 330 0.6
unit Y 412 0.9
unit Z 265 0.3

To make the pH adjustments for your soil, estimate your general soil type, then choose one of the following modifiers. (For soils low in organic matter, reduce the amounts by 25%. For soils high in organic matter, increase them by 100%.)

pH Adjustment Recommendations (Amount in Lb./Acre and Lb./100 Sq. Ft.)

Type Light, Sandy Sandy Loams Loams Silt and Clay Loams
ground limestone, marl, or oyster shells

2,050.1

4.5

2,590.1

5.9

3,000.1

6.8

3,300.1

7.2

burnt lime

1,250.1

2.8

1,540.1

3.1

1,960.1

4.0

2,340.1

5.8

hydrated lime

1,530.1

3.1

2,030.1

4.4

2,790.1

6.9

3,200.1

7.7

Organic Fertilization   

Organic fertilizers not only supplement soil with needed primary nutriments such as nitrogen, phosphorus, and potassium, but also supply crucial trace elements. And organic supplements tend to be "timed release" in action and generally are more gentle, consistent fertilizers than "chemical" feeders are. 

Because the sample soil is deficient in nitrogen, add two of these supplements: 

Organic Nitrogen Fertilizers 

Type Lb./Acre Lb./100 Sq. Ft. Characteristics
cottonseed meal 1,450.1 3.7 lasts 4 to 6 months, acidifies the soil slightly
blood meal 604.0 1.8 lasts 3 to 4 months, is quick-acting, good in compost pile
fish meal     725.0 1.4 lasts 6 to 8 months
hoof and horn meal 604.0 1.8 lasts 1 year, has slow release, acts in 4 to 6 weeks

To raise the phosphorus content of the sample soil, add one of the following supplements:

Organic Phosphorus Fertilizers 

Type Lb./Acre Lb./100 Sq. Ft. Characteristics
bone meal     648.0 1.0 lasts 6 to 12 months, is great for roses and fruit trees
rock phosphate 549.0 1.6 lasts 3 to 5 years, has very slow release
soft phosphate     1,007.0 2.7 lasts 2 to 3 years

Since the sample soil is deficient in potassium, you'll need to add two of these supplements:

Organic Potassium Fertilizers 

Type Lb./Acre Lb./100 Sq. Ft. Characteristics
kelp meal     486.0 1.3 lasts 6 to 12 months, is rich in trace elements
crushed granite 1,457.1 3.7 lasts 8 to 10 years, is slow to release, and rich in trace elements
greensand     833.0 1.9 lasts 8 to 10 years, is slow to release, and rich in trace elements  

Calculating Fertilizer Amounts 

In the event that you'd like to use some nutrients not given in this analysis, you can figure out the amount of fertilizer you'll need by using this formula: 

Amount needed (lb./acre) = % needed divided by % in fertilizer X 2,000 

Example: If you're using steer manure [.7%N/.3%P/.4%K] and from your soil analysis results you read that the "fertilizer rating required" is 2.2% for nitrogen, 0.6% for phosphorus, and 1.1% for potassium, you can calculate the amount of manure needed in this way: 

To meet the N requirement: 2.2/0.7 X 2,000 = 6,282 lb./acre
To meet the P requirement: 0.6/0.3 X 2,000 = 4,000 lb./acre 
To meet the K requirement: 1.1/0.4 X 2,000 = 5,500 lb./acre

This doesn't mean that you must apply 6,286 + 4,000 + 5,500 pounds per acre, but it means that if you apply 5,500, you will be supplying enough potassium, a little more phosphorus than is needed, but not quite enough nitrogen. So in this case, you might want to compromise a bit and apply 6,000 pounds per acre. 

To convert the above figures to pounds per 100 square feet, divide them by 435.6. In other words, [lb./100 sq. ft.] = [lb./acre/435.6]. For the example above, you'd apply 13.8 (6,000/435.6) pounds of steer manure per 100 square feet.

For information on starting a soil testing business, see Make Money Through Soil Testing.


EDITOR'S NOTE: The nonorganic fertilizers recommended here are those most commonly available in author Terry Nelson's locality. That part of the program, then, should be revised—simple, if you know BASIC computer languageto apply to areas where other formulations are more widely stocked. You might also note that bulk fertilizer elements in 100-pound bags, bought cooperatively with neighbors, are a less expensive alternative to commercial customizing preparations that come in small quantities. 

Not all soil experts or gardeners agree on data interpretation and appropriate action. Many suggest a mildly acid (6.5 pH) soil rather than a neutral one. Nutrient levels, fertilizer formulations, and application rates are all open to debate, so you might modify the author's program or create your own to reflect your horticultural philosophy and expertise. 

An excellent source of information on soil health, analysis, and balanced fertilizer formulations for a variety of purposes and plants is The Bio-Dynamic Gardener's Bible by Lee Fryer (to whom, not incidentally, we express our gratitude right here and now for the invaluable advice given us in the preparation of this article).  





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