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BUILDING A GOOD TOPSOIL

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AGRO-METEOROLOGY FOR FARMING BENEFIT

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BUILDING A GOOD TOPSOIL
EXCELENT TOPSOIL SPECIFICATION

General - Topsoil shall be free of roots, clods, stones larger than 1-inch in the greatest dimension, pockets of coarse sand, noxious weeds, sticks, lumber, brush and other litter. It shall not be infested with nematodes or other undesirable disease-causing organisms such as insects and plant pathogens.

 

Topsoil shall be friable and have sufficient structure in order to give good tilth and aeration to the soil.

 

Gradation limits - soil shall be a sandy loam, loam, or clay loam. The definition of soil texture shall be the USDA classification scheme. Gravel over 2 millimeters in diameter shall be less than 20% by weight.

 

Permeability / Infiltration Rate - Hydraulic conductivity rate shall be not less than one inch per hour nor more than 10 inches per hour when tested in accordance with the USDA Handbook Number 60 method 34b or other approved methods.

 

Fertility - The range of the essential elemental concentration in soil shall be as follows:

 

Ammonium Bicarbonate/DTPA Extraction

        parts per million (mg/kilogram)

                     dry weight basis 

 phosphorus   10 - 40 ppm 
 potassium  100 - 220 ppm
 iron  5 - 35 ppm
 manganese  0.6 - 6 ppm
 zinc   1 - 8 ppm
 copper  0.3 - 5 ppm
 boron  0.2 - 1 ppm
 magnesium  50 - 150 ppm
 sodium   0 - 100 ppm
 sulfur  25 - 500 ppm
 molybdenum  0.1 - 2 ppm

 

Acidity - The soil pH range measured in the saturation extract (Method 21a, USDA Handbook Number 60) shall be 6.0 - 7.9.

 

Salinity - The salinity range measured in the saturation extract (Method 3a, USDA Handbook Number 60) shall be 0.5 - 2.5 dS/m.

 

Chloride - The maximum concentration of soluble chloride in the saturation extract (Method 3a, USDA Handbook Number 60) shall be 150 mg/l (parts per million).

 

Boron - The maximum concentration of soluble boron in the saturation extract (Method 3a, USDA Handbook Number 60) shall be 1 mg/l (parts per million).

 

Sodium Adsorption Ratio (SAR) - The maximum SAR shall be 3 measured per Method 20b, USDA Handbook Number 60.

 

Aluminum – Available aluminum measured with the Ammonium Bicarbonate/DTPA Extraction shall be less than 3 parts per million.

 

Soil Organic Matter Content - Sufficient soil organic matter shall be present to impart good physical soil properties but not be excessive to cause toxicity or cause excessive reduction in the volume of soil due to decomposition of organic matter. The desirable range is 3% to 6%. The carbon:nitrogen ratio should be about 10. A high carbon:nitrogen ratio can indicate the presence of hydrocarbons or non-humified organic matter.

 

Calcium Carbonate Content - Free calcium carbonate (limestone) shall not be present for acid-loving plants.

 

Heavy Metals - The maximum permissible elemental concentration in the soil shall not exceed the following concentrations:

 

Ammonium Bicarbonate/DTPA Extraction

        parts per million (mg/kilogram)

                   dry weight basis

arsenic 1 ppm
cadmium 1 ppm
chromium 10 ppm
cobalt 2 ppm
lead 30 ppm
mercury 1 ppm
nickel 5 ppm
selenium 3 ppm
silver 0.5 ppm
vanadium 3 ppm

If the soil pH is between 6 and 7, the maximum permissible elemental concentration shall be reduced 50%.

If the soil pH is less than 6.0, the maximum permissible elemental concentration shall be reduced 75%.

No more than three metals shall be present at 50% or more of the above values.

 

Phytotoxic constituent, herbicides, hydrocarbons etc. - Germination and growth of monocots and dicots shall not be restricted more than 10% compared to the reference soil.

Total petroleum hydrocarbons shall not exceed 50 mg/kg dry soil measured per the modified EPA Method No. 8015.

Total aromatic volatile organic hydrocarbons (benzene, toluene, xylene and ethylbenzene) shall not exceed 0.5 mg/kg dry soil measured per EPA Methods No. 8020.

 

Source:

Garn Wallace

 

Download full copy of USDA Handbook No. 60


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