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HOME / LABORATORY SERVICES / SOIL, FEED AND WATER CHEMISTRY TESTING LABORATORY / SOIL TESTING /

How To Interpret Your Soil Test Report

Introduction

Your soil test report includes four important sets of information:

1. The actual soil test values of the available amounts of plant nutrients in the soil.
2. The soil ratings of the available amounts of plant nutrients.
3. The suggested applications of fertilizer and limestone.
4. Auxiliary soil test information on soil cation exchange capacity (CEC), % Base saturation and suggested adjustments in fertilizer requirements for management factors such as manure applications and sod plowed down.

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 to produce good economic yields most years. However, remember that soil test results can be no better than the samples taken and can only represent the samples taken.

The following is a brief explanation of the actual soil test values, soil ratings, and the suggested limestone and fertilizer applications, in the order that they appear on the Soil Analysis Report Form.

Organic Matter: This is the amount of organic matter in your soil sample on a percent basis. Soil Organic Matter plays an important role in maintaining plant nutrients in the soil and soil structure. Soil Organic Matter improves soil aggregation, drainage, aeration, CEC and influences pesticide activity in the soil.

pH: This is the actual soil pH as determined using a soil/distilled water mixture in the lab. 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. In PEI, most soils are in the acidic pH range. Potatoes grow well at a soil pH range of 5.5 to 6.0, depending on the scab resistance of the potatoe variety. Growth of field crops grown in rotation with potatoes may be better at a pH greater than 5.7.

Phosphate, Potash, Calcium and Magnesium: These are the actual soil test values. These show the available amounts of plant nutrient phosphate, potash, calcium and magnesium in your soil sample in units ppm P₂O ₅, ppm K₂O, ppm Ca and ppm Mg. Beside each value are the soil ratings. The soil ratings show how the actual soil test values of your soil sample compare to a highly fertile soil. The range of soil ratings used to indicate high, medium and low fertility are: H+, H, M+, M, L and L-. At any particular soil test value, the soil rating may differ between crops because different crops have different ranges of nutrient demands.

Boron, Copper, Zinc, Sulphur, Manganese and Iron: These are the actual soil test values. These show the available amounts of plant nutrient Boron, Copper, Zinc, Sulphur, Manganese and Iron in your soil sample in units ppm B, ppm Cu, ppm Zn, ppm S, ppm Mn and ppm Fe. The range of soil ratings used to indicate high, medium and low fertility are: H+, H, M+, M, L and L-.

Sodium: This is the actual soil test value. This shows the amount of sodium in your soil sample in units ppm Na. Sodium is not usually considered an element that is essential as a plant nutrient nor is it necessary for normal plant growth. The sodium analysis of your soil sample is used as part of the calculation of the % Base Saturation value shown in the bottom section of your soil test report.

Lime Index: The Lime Index value together with the soil pH are used to determine the lime requirement of your soil. The Lime Index is determined in the laboratory by mixing an SMP buffer solution with your soil and then measuring the pH. The Lime Index value is sometimes also known as the 'buffer pH' value. The suggested applications of lime for your soil are listed in the next section of your soil test report.

Conductivity: This is a measure of the salinity of the soil in your soil sample in the units mS/cm. Germination of seeds may be delayed or prevented, plant growth may be poor or plants may be killed in a soil with a high salt content. A salt value of 0.0 to 0.45 is tolerated by most plants as long as excessive amounts of fertilizer are not used. Salt values of 0.46 to 1.0 may reduce seed emergence or cause damage to plants. Salt values over 1.0 are likely to cause damage to most plants.

Suggested applications of limestone: There are three suggested applications of limestone for your soil given in the units T/ha. There is one suggested application each, for the amount of 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 cropping program. For example, Potatoes grow well at a soil pH range of 5.5 to 6.0, depending on the scab resistance of the potatoe variety. Growth of field crops grown in rotation with potatoes may be better at a pH greater than 5.7. Most other crops would benefit from a soil pH over 6.2.

'Pure calcite' (CaCO₃ or calcitic limestone) is 40% Ca, a good source of Ca for plant nutrition and neutralizes soil acidity. 'Pure dolomite' (CaMg(CO₃)₂ or dolomitic limestone) is 21.7% Ca and 13.1% Mg with a Ca:Mg ratio of 2:1. It is a good source of both Caand Mg for plant nutrition and neutralizes soil acidity. More generally, the term 'calcitic limestone' is used to mean a limestone with very little Mg. The terms 'dolomitic limestone' or 'Mg limestone' are used to mean a limestone that can vary in Mg content from 13.1% Mg to 0.6% Mg. 'High Mg limestone' contains 5% Mg and 31% Ca, making it a good source of both Ca and Mg for plant nutrition and it has a good neutralizing value. 'Gypsum' (CaSO₄) is also sold, with varying purity and %Ca and %S contents. It is a good source of Ca and S for plant nutrition, but has little or no neutralizing value and does not affect soil pH. 'Hydra-lime' is a mix of 10%

Suggested applications of fertilizer: Your soil test report indicates the suggested applications of plant nutrients for a successful crop yield. This information is shown on the soil test report as the amounts of the plant nutrients Nitrogen (N), Phosphate (P₂O₅) and Potash (K₂O) suggested, 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. Calculated examples of the rates of suggestedfertilizer mixes (ie: 10-20-20) that would supply these plant nutrients are on the sheets "Additional Soil Test Information" and "Actual Fertilizer Application (Options)" attached to your soil test report. If you need help in calculating specific fertilizer rates and mixes based on the suggested fertilizer applications, please contact your District Agricultural Office, the Soil and Feed Testing Lab, a crop specialist or an ag An explanation of the auxiliary information on your soil test report

Cation exchange capacity (CEC): This is a measure of the ability of a soil to hold and exchange plant nutrient cations. It is expressed in the units meq/100 g. Many plant nutrients occur in the soil as positively charged cations. The ability of a soil to hold these plant nutrient cations from being leached and lost from the soil is important to maintaining soil fertility. Clay or organic matter in the soil are negatively charged and contribute to the soil's ability to hold these nutrient cations. Soils with high clay or organic matter contents tend to have higher CEC, be more fertile and require more lime to correct pH. Sandy soils tend to have lower CEC. Ranges of CEC associated with soil textures are presented in Table One. While there is no such thing as "an ideal soil nutrient level", these ranges serve as an example of the influence of CEC and soil texture on nutrient cation content in the soil.

%K, %Mg, %Ca, %H, %Na: These are the actual amounts of exchangeable cations in your soil, expressed in percent (%). K, Mg, and Ca are plant nutrient cations. H and Na are other cations normally present in the soil. These are used to calculate the % Base Saturation of your soil (see below).

% Base Saturation: This is a measure of the proportion of the total CEC in your soil that is occupied by Na and the "basic" nutrient cations K, Ca, Mg, expressed in percent (%). Table Two shows the % Base Saturation values for PEI soils. While there is no such thing as an "ideal % Base Saturation", % Base Saturation values are sometimes used to make recommendations for Potash, Calcium or Magnesium amendments to soils. However, typically this approach fails to consider the cost and economics of such an application nor does it take into account excessively high levels of cations.

Adjustments in Fertilizer requirements for Management factors: Any kind of manure applied to the soil adds plant nutrients. The nutrient value of any manure application you may have indicated on your sample submission form has been accounted for by the computer when calculating your fertilizer application rates by making an appropriate reduction in your fertilizer rates. This will reduce your fertilizer costs, maximize your returns from your farm operation and help prevent nitrate and phosphate leaching and runoff into streams and groundwater. If you did not provide the lab with manure information on your sample submission form, then Table Three will give you the appropriate amount of nitrogen (N), phosphate, (P₂O₅), and potash (K₂O) to be substracted from the suggested application listed on your test form. Notice that the amounts of nitrogen to subtract are higher for spring applied manure than fall applied manure. Rapid incorporation of the one day of application) increases the amount of nitrogen available to plants and therefore lessensthe amount of the suggested applications. Any sod containing a legume that is plowed down adds nitrogen to the soil. The nitrogen value of any sod plowdown you may have indicated on your sample submission form will also have been accounted for by the computer when calculating your fertilizer application rates by making an appropriate reduction in your fertilizer rates. If you did not provide the lab with sod information, then Table Three will also give you the appropriate amounts of nitrogen to be subtracted from the suggested application listed on your soil test report.