Soil Testing for Home Gardeners
|Agdex #: 543|
|Author:Soil and Feed Testing Laboratory|
Your soil test report includes four important sets of information:
Further explanation of the soil test values and soil ratings can be found in the pamphlet "How to Interpret your Soil Test Report."
The suggested applications of fertilizer have been determined from the actual soil test values and the soil ratings. The suggested applications of fertilizer are based on Atlantic Canada soil fertility research and should provide adequate plant nutrition for good plant growth most years. However, remember that soil test results can be no better than the samples taken and can only represent the samples taken.
Suggested applications of fertilizer
Your soil test report indicates the suggested applications of plant nutrients to achieve good plant growth. This information is shown on the soil test report as the amounts of the plant nutrients Nitrogen (N), Phosphate (P2O5 )and Potash (K2O), in the units kg/ha.
The rates of fertilizer mixes required to supply those plant nutrients still needs to be calculated and depends on your choice of fertilizer mix. Fertilizer mix is also known as fertilizer "grade" or 'analysis'. It describes the content of the fertilizer mix. For example, a 10-10-10 fertilizer has 10 percent Nitrogen, 10 percent phosphate and 10 percent potash in it, or a 6-12-12 fertilizer would have 6 percent Nitrogen, 12 percent phosphate and 12 percent potash in it.
Calculated examples of rates of fertilizer mixes (ie: 10-10-10) that would supply the suggested applications of plant nutrients are on the sheets "Additional Soil Test Information" and "Actual Fertilizer Application (Options)" attached to your soil test report.
How much fertilizer or limestone should I apply?
The suggested application rates of fertilizer mixes listed on your "Actual Fertilizer Application (Options)" sheets are in the units kg/ha. Alternatively, suggested application rates of fertilizer mixes may be found in the "remarks" on the bottom of your soil test report, in the units lb/1000 square feet. These units are fairly large. For smaller areas, such as home gardens, lawns and shrubs, smaller units can be used.
The following conversions are useful for home garden, lawn and shrub fertilization rates:
Choice of fertilizers for home gardens
The fertilizer application rate and mix suggested on your report should supply adequate plant nutrition for your home vegetable or flower garden.
Typical fertilizer mixes sold for home garden use are 10-10-10, 6-12-12, 17-17-17 and 12-24-24. Several other fertilizer mixes are available commercially as well. These mixes differ in their fertilizer content and in their ratio .
The ratio of a fertilizer mix is it's Nitrogen, Phosphate and Potash content reduced to its simplest terms. For example, a 10-10-10 fertilizer mix has a ratio of 1:1:1 and a 12-24-24 fertilizer has a ratio of 1:2:2.
For home garden use, fertilizers mixes of a 1:1:1 ratio or a 1:2:2 ratio do a good job matching garden plant requirements for all three of the plant nutrients, Nitrogen, Phosphate and Potash supplied in the fertilizer mix.
Leafy vegetables require substantial amounts of Nitrogen, while root, tuber and other vegetables have a fairly high requirement for Phosphorus and Potash. Consequently, desirable fertilizer ratios are typically 1:1:1 for leafy vegetables , 1:2:2, for tuber and root vegetables and 1:2:1 for other vegetables.
Some flowers may require a fertilizer with a lower Nitrogen content, hence fertilizers of a ratio of 1:2:2, such as 6-12-12 or 12-24-24 are good fertilizers for flowers in home gardens.
If you are uncertain of the fertilizer requirements for your garden, you should contact a horticultural specialist or the Prince Edward Island Soil & Feed Testing Lab for advice on the nutrient requirements of your garden plants.
Choice of fertilizers for lawns
The fertilizer application rate and mix suggested on your report should supply adequate plant nutrition for your lawn.
Typical fertilizer mixes sold for home lawn use are 21-7-7, 24-4- 8 and 10-6-4 for spring application, while 6-8-14 and 4-8-12 are sold for fall application. Several other fertilizer mixes are available commercially as well. These mixes differ in their fertilizer content and in their ratio.
The ratio of a fertilizer mix is it's Nitrogen, Phosphate and Potash content reduced to its simplest terms. For example, a 21-7-7 fertilizer mix has a ratio of 3:1:1, a 24-4-8 fertilizer has a ratio of 6:1:2, and a 4-8-12 fertilizer has a ratio of 1:2:3.
Home lawns should be fertilized in the spring and in the fall. More intensively used turfgrasses, such as playing fields and greens, are often fertilized more frequently.
Good lush green growth in a lawn in the spring can be achieved with a fertilizer that is high in Nitrogen. Fertilizers mixes of a 3:1:1 ratio or a 6:1:2 ratio have a high Nitrogen content. These ratios do a good job matching lawn requirements in the spring for all three of the plant nutrients, Nitrogen, Phosphate and Potash supplied in the fertilizer mix.
Lawns require more Potash in the fall and need less Nitrogen. Good fall growth and overwintering can be achieved with a fertilizer mix that has a ratio such as 1:2:3 which is lower in Nitrogen and higher in Potash.
Some fertilizers (10-6-4 "Weed and Feed" mixes and others) contain sulphur coated urea (SCU) . Use of a slow release Nitrogen fertilizer in the spring, such as SCU, may have additional benefit to your lawn.
If you are uncertain of the fertilizer requirements of your lawn, you should contact a horticultural or turfgrass specialist or the Prince Edward Island Soil & Feed Testing Lab for advice.
Choice of fertilizers for shrubs and trees
The fertilizer application rate and mix suggested on your report should supply adequate plant nutrition for your shrubs and trees.
Typical fertilizer mixes sold for home use on shrubs and trees are 28-14-14, 30-10-10 and 10-4-8. Several other fertilizer mixes are available commercially as well. These mixes differ in their fertilizer content and in their ratio .
The ratio of a fertilizer mix is it's Nitrogen, Phosphate and Potash content reduced to its simplest terms. For example, a 28-14-14 fertilizer mix has a ratio of 2:1:1, a 30-10-10 fertilizer mix has a ratio of 3:1:1 and a 10-4-8 fertilizer mix has a ratio of 2.5:1:2.
A fertilizer mix with a ratio close to 3:1:2 is generally appropriate for most trees and shrubs. Hence, 10-4-8 is a good all-purpose tree and shrub fertilizer. However, flowering shrubs, evergreens, conifers and some trees differ in their nutrient requirements substantially. A fertilizer with a higher Nitrogen content, such as 30-10-10, may be better for evergreens. A fertilizer with a lower Nitrogen content, such as 28-14-14 may be better for roses and flowering shrubs and some trees.
Fertilizer for established trees and shrubs can be applied in the spring and in the fall. For trees and shrubs, fertilizer may be very effective if applied to the soil along the leaf canopy "drip line". That is often where the younger "feeder" roots that take up the fertilizer will be in the soil. Trees and shrubs that are relatively young, but not new plantings, would probably benefit from additional applications of fertilizer in late May and again in Late June.
For new plantings of trees and shrubs, small quantities of fertilizer should be mixed into in the soil near the roots of the plant when it is planted. Newly planted trees and shrubs have a substantial requirement for Phosphorus to promote new root growth, require Nitrogen to promote new leaf and shoot growth and require Potash for general vigour. A 15-30-15 fertilizer or other high Phosphate containing fertilizer would be useful for this purpose, but only reduced quantities can be placed in close proximity to the roots to lessen the risk of fertilizer burn. Specially formulated fertilizer mixes of appropriate ratios are also commercially available for this purpose.
You should contact a nursery or horticultural specialist to determine the specific seasonal nutrient requirements for your particular plants.
Choice and use of limestone
In Prince Edward Island most soils are in the acidic pH range. A soil pH of 7.0 is considered neutral. A soil pH of less than 7.0 is considered acidic and a soil pH of less than 5.0 is considered very acidic. The availbility of plant nutrients in the soil is reduced at low soil pH's.
If your soil pH is low there will be suggested applications of limestone on your soil test report for your soil. There may be three possible suggested applications given on your soil test report. There is one suggested application each, for the amounts limestone required to achieve a soil pH of either 5.5, 6.0 or 6.5 . You must choose the soil pH you wish to achieve in order to select your suggested limestone application from these three choices.
The final pH you wish to achieve will depend on your home use of the limestone. For example, Blueberries and few types of flowers grow well at acid soil pH's (5.5 or less), a soil pH range of 5.5 to 6.0 would be best for potatoes, depending on the scab resistance of the potatoe variety you wish to grow, whereas for most other flowers, garden vegetables, shrubs, trees and lawns, growth would be best at soil pH's over 6.0 or 6.5.
You also have a choice between calcitic limestone and dolomitic limestone. Dolomitic limestone is a good source of Magnesium (Mg). If your soil test report indicated that your soil was low in available amounts of the plant nutrient Magnesium, then use of a dolomitic limestone will provide the required Magnesium at that same time as it corrects the soil pH.