Take the soil sample from about 2-4" below the surface.
Place your soil sample into a clean container. Break the sample up with the trowel or spoon and allow it to dry out naturally. This is not essential, however it makes working with the sample easier. Remove any small stones, organic material such as grass, weeds or roots and hard particles of lime. Then crumble the sample finely and mix it thoroughly.
Set a small amount of soil aside after cleaning (about a spoonful) for the pH test. The rest will go into the Nitrogen, Phosphorus, and potassium (K) tests.
Testing your soil should be routine at the end of the growing season after harvest, again just before planting, and periodically during the growing season.
Soils are known as "sweet" if they are alkaline and "sour" if they are acid. Values of pH 7 indicate a neutral soil; above pH 7 is alkaline and below pH 7 is an acid soil. Most Soils are within a range of highly acidic pH 4 to alkaline at pH 7.5 to 8.
When pH is at the proper level, nourishment available in the soil is "unlocked", ready to give the plant the necessary vitality to produce, multiply, and resist disease. If the pH is too high or too low, this nourishment is locked out. Fertilizer applications are wasted. While some plants thrive on alkaline soils, others thrive on acidic soils. Most garden and field crops prefer the pH to be between 5.8 and 6.6, slightly acidic.
Phosphorus is a plant food lacking in soils after they have been under cultivation for a while. When the pH is high, above 7.8, phosphorus locks up (bonds) with calcium to form an insoluble calcium phosphate compound and becomes unavailable to the plants. When the pH drops below 7.8, phosphorus is again released in a soluble form.
Nitrogen has a special relation to pH. Nitrogen must be broken down by soil bacteria (cyanobacteria) before it can be absorbed by plants. These soil bacteria do their best work between a pH of 5.8 and 6.6. Therefore in highly acidic or alkaline soils there is very little breakdown of nitrogen. Plants can become starved for nitrogen under these conditions even with liberal quantities of fertilizer.
When the pH goes above 8.0 potash (potassium) becomes unavailable to plants.
If you wish to grow plants not suited to the pH of your soil, you can change the pH. You can make an acid soil more alkaline by adding lime. Slightly acid soils can be made more acid by adding peat, iron sulphate or flowers of sulfur. It is, however, more difficult to convert an alkaline, lime-rich soil into an acid soil.
pH affects the availability of plant foods - Nitrogen, Phosphorus and K (Potassium) - and prevents the spread of soil borne diseases. Check it regularly - at least twice a year - because nature tends towards the acid side.
Working with your soil - not against it - will help you achieve more successful results. Any changes in pH should be small scale - 1/2 to 1 pt at the maximum.
Altering pH does take time so do not expect an immediate change. After adding lime or iron sulfate to your soil, retest for pH in 40 to 60 days - If results are still significantly off, retreat your soil , not exceeding recommended application levels.
You can correct pH at any time of year but it is best (in temperate Northern hemisphere) to start in Fall and check progress in Spring. Allow one month to pass between adding lime and adding fertilizers.
To make soil more acid, dig in plenty of peat, compost and manure, and retest in a few months. For quick action use ammonia sulfate at the rate of 1 oz./sq. yd. or flowers of sulfur. But remember ammonia sulfate also adds Nitrogen (ammonia is NH3).
For established lawns, Nitrogen is the most essential nutrient to promote lush growth and deep, green color. Phosphorus and Potash, in lesser quantities, are all important for strong root formation and growth. Compound fertilizers will supply all 3 nutrients, or you select an individual fertilizer with a Nitrogen, such as our rapid feed Nitrogen with 44% Nitrogen.
There are at least six major plant foods which are essential to plant growth - carbon, hydrogen, oxygen, nitrogen, phosphorus and potash (potassium), the later three being expressed as N, P, and K. Carbon is obtained by plants from carbon dioxide in the air, hydrogen from water, and oxygen is produced by plants themselves from water. It is the later three that are not generally available and often have to be supplied by fertilizers.
NITROGEN (N) is essential to the proper functioning of plant metabolism. It increases the protein content of food crops and is needed by most leafy vegetables, foliage plants and grass. Nitrogen gives plants their dark green color (chlorophyll) and helps the growth of leaves and stems. Lawns, foliage plants and dahlias require a regular supply of nitrogen. Too much nitrogen can cause too rapid growth, leading to softened plant tissue and general weakness of the plant. At very high levels nitrogen can cause the leaves to "burn" and the plant to die. At flowering time too much nitrogen can cause the plant to return to leaf production prematurely.
PHOSPHORUS (P) is the most important nutrient in root formation, creating good fibrous root systems. It enables plants to get off to an early start and hastens maturity. Phosphorus encourages blooming and seed formation, helps plants' resistance to wintry weather and disease and increases the vitamin content of plants. Lettuce, potatoes, carrots, for example, require good reserves of phosphorus.
POTASH (K) is probably one of the better known foods because it stimulates flowering and makes fruit tastier through converting sunshine into starches and sugars. Tomatoes, strawberries, beans, peas and flowering plants require especially high levels of potash. Potash is also important in the formation and transportation of starch, sugar, and other carbohydrates in the plant. Plants with a proper supply of potash form stiff stalks and healthy, disease resistant tissue. Potash also promotes root growth. Too much potash can cause plants to take up too much water and become weak.
Plants also need sulfur and calcium, many general fertilizers supply these compounds. In addition plants often need micronutrients: trace amounts of metals such as magnesium, iron, copper, zinc, manganese, molybdenum, and the element boron. The environment often has sufficient quantities of these trace elements. Some plant foods also provide these elements. Some plants will flower only if fed the appropriate amount of a particular micronutrient. See page 145 of Botany for Gardeners for more information on micronutrients.
Plant food deficiencies can be corrected by adding nutrients in the form of fertilizers. Nutrient replacement can be approached in different ways:
A compound fertilizer is a mixture of all the essential foods a plant needs. Compounds are available in slow release (granular) and quick-acting (powder and liquid forms) and can be for general feeding or for specific plant needs.
If you prefer to use a compound fertilizer, which should normally be applied during early Spring (slow release) and during the growing season (quick-acting), use your soil test results to apply the fertilizer more efficiency You can thus avoid the possibility of over-feeding, which can be as detrimental as a lack of food.
If, for example, you find the levels for phosphorus and potash are both drastically low, you should increase the application rate of the compound by at least 100% and vice versa. Apply half of a soluble feed in dry form directly onto the soil and the other half as a liquid feed.
If, on the other hand, the levels are widely out of balance e.g. high in phosphorus and low in Potash you should not be using a compound fertilizer. This would not only be wasteful, but would increase the already high level to a potential excess.
Where both the pH needs correcting and fertilizer is required, divide the applications over several weeks. Do not, for example, add lime and fertilizer together. Add the lime first, then allow least a month to pass before applying fertilizer.
In the following tests be aware that the answer might also be "none present" or 0 parts per million.
Fill in the following table
| pH | Nitrogen /ppm | Phosphorus /ppm | Potassium /ppm | |
|---|---|---|---|---|
| Red clay near administration | 7.0 | Below detectable limits | Below detectable limits | Medium: 40 ppm |
| Soil from around hibiscus near classroom | 7.0 | Below detectable limits | Below detectable limits | Medium: 40 ppm |
| Muck from wet area across the road | 5.5 | Not tested | Below detectable limits | Medium: 40 ppm |
| Black soil from forest behind agriculture area | 4.5 | Below detectable limits | Below detectable limits | Not tested |
| Coralline sand | > 9.0 | Below detectable limits | Low: 4 ppm | Low: 20 ppm |
Dispose of test solutions by rinsing down the sink. Wash the comparators and caps in soapy water immediately after each use. Make sure any sediment or color staining is removed. Rinse well and dry.
The tablets are safe in normal domestic terms, but like all chemicals and pharmaceuticals, they should be put away and kept out of reach of children. Try to avoid touching the tablets. Always wash your hands thoroughly after making your tests. Do not eat, drink or smoke while using the soil test kit. Keep tablets away from food, drink and animal feed. If taken internally, drink copious amounts of water and seek medical advice.