SOIL AND SLUDGE

What is Soil testing?

It is the farmland analysis for multiple parameters like chemical content, toxicity, pH level, salinity, earth-dwelling biota, etc. Such tests also provide information on chemical contamination, humic or organic content, electric conductivity, cation exchange capacity, and other physical and chemical properties.

Type of Soil tests

The analysis type depends on the explored components or properties of the field ground that may beneficially or adversely impact crop development. The most frequently-used types analyze and measure:

• Mineral content
• pH level
• Soil moisture
• Salinity
• Pesticides and chemical contamination
• Structure and texture, etc.

Soil Nutrient Testing

Valuable information on nutrients content allows accurate fertilization to support plant needs within precision agriculture implementations. This is why the chemical test for soil nutrients is the most common.

Primarily, soil tests report on the content of nitrogen (N), phosphorus (P), and potassium (K), which are the most important nutrients for crops. Secondary nutrients to examine are calcium (Ca), sulfur (S), and magnesium (Mg). An extended test also includes minor elements like iron (Fe), manganese (Mg), boron (B), molybdenum (Mo), and others.

Soil Acidity Test(pH)

Proper pH in the field is essential for plant productivity, and either too high or too low pH will adversely affect crop growth. Testing pH of soil, one calculates its hydrogen ions. pH values may range from 0 to 14. The neutral value is 7, lower levels are for acidity, and higher than 7 mean alkalinities. Acidic or alkaline fields are treated correspondingly. For example, pH can be raised with lime, and an accurate pH test helps determine its required quantity.

Soil Salinity Test

In saline fields, plants suffer from osmotic stresses due to poor water absorption. Soil salinity testing helps understand the suitability of lands for agricultural activities. Field salinity can be analyzed through:

• evaporation of total soluble salts (TSS) from the ground-water extract;
• measuring the electric conductivity (EC) of a saturated paste extract or a distilled water-earth dilution.

Testing Soil for Pesticides and Contaminations

Pesticides help control any non-beneficial organisms that destroy crops. Chemicals effectively suppress weeds, manage crop diseases, or combat pests. At the same time, such substances poison non-target organisms and pollute nature. Highly aggressive substances leach into groundwater, remain in the land for many years, and harm humans and animals, accumulating in food.

Physical Soil Testing for Texture and Structure

Apart from the chemical content, agricultural soil testing also analyzes the soil type and its physical properties like texture, structure, and moisture.

The main components are clay, sand, and silt, and their proportions define the ground texture and its ability to retain nutrients with moisture. For example, sandy fields dry faster than clay ones, so a soil texture test helps in precision irrigation and fertigation planning.

Soil structure describes the size of its parts and pore spaces, which affect the flow of water and air in the earth. Clay fields are finer, and their pore spaces are small. Therefore, they are prone to compaction and require regular aeration.

Soil Moisture Testing

Water is essential for plant growth, and vegetation cannot develop properly under a lack of ground moisture. When the field’s surface is dry, it can be noticed visually; yet accurate water rates are measured with soil moisture sensors or in the laboratory. A soil moisture content test reports water availability for plants or their dehydration. High-temperature moisture evaporation from samples is the typical soil moisture test. The calculation of moisture rates in the samples is based on measuring their masses before and after evaporation.

Chloride Content:

At the time of Soil Testing, the effect of chloride concentration in soil on corrosion of reinforcing steel was evaluated by measuring corrosion potentials and corrosion current density. Concrete in contact with soil bearing high levels of chloride could suffer from early ingress of this chloride, leading to corrosion of any embedded reinforcement. Measures of chloride levels in soils are often taken to check whether the soil will be suitable to be used adjacent to concrete.
Test Method: BS 1377

Electrical Resistivity:

Electrical resistivity of the soil can be considered as a proxy for the spatial and temporal variability of many other soil physical properties (i.e. structure, water content, or fluid composition). Because the method is non-destructive and very sensitive, it offers a very attractive tool for describing the subsurface properties without digging.
Test Method: ASTM  G 1857

Linear Shrinkage:

This test is used to measure the percentage decrease in dimension of a fine fraction of a soil when it is dried after having been moulded in a wet condition approximately at its liquid limit.
Test Method: ASTM D 4943

Modified Proctor Compaction Test:

The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density.
Test Method: ASTM D 1557

Organic Matter Content:

Organic matter is stable in the soil. It has been decomposed until it is resistant to further decomposition. Usually, only about 5 percent of it mineralizes yearly. That rate increases if temperature, oxygen, and moisture conditions become favorable for decomposition, which often occurs with excessive tillage. It is the stable organic matter that is analyzed in the soil test.
Test Method: BS 1377

Particle Size Distribution by Sieve Analysis:

The objective of this test is to determine the relative proportions of different granular sizes as they are passing through certain sieve sizes. Thus, the percentage of sand, gravel, silt and clay can be obtained from the sieve analysis test.
The sieve analysis (grain size analysis) is widely used in classification of soils. The data obtained from grain size distribution curves is used in the design of filters for earth dams and to determine suitability of soil for road/highway construction, embankment fill of dam, airport runway/taxiway, etc.
Test Method: ASTM D 6973

Particle Size Distribution by Hydrometer:

Hydrometer test is the procedure generally adopted for determining the particle-size distribution in the soil for the fraction for that is finer than sieve size 0.075 mm. The lower limit of the particle size determined by this procedure is about 0.001 mm.
Test Method: ASTM D 7928

Plasticity Index:

The Plasticity Index is simply the numerical difference between the liquid limit and the plastic limit for a particular material and indicates the magnitude of the range of moisture content over which the soil remains plastic.  It is a measure of the cohesive qualities of the binder resulting from the clay content.  Also, it gives some indication of the amount of swelling and shrinkage that will result in the wetting and drying of that fraction tested.
Test Method: ASTM D 4221

Sulphate Content:

This method determines the soluble sulfate content of soil by using turbidimetric techniques.  The results are used to determine whether chemical stabilization (with lime, fly ash, cement kiln dust, etc.) of the tested soil is appropriate.
Test Method: BS 1377

SOIL TESTING-CONTAMINATION:

As the requirement for land for housing, retail, office and industrial development continues to grow, there is a real need for developers to use sites previously used for industrial purposes (Brownfield sites). These sites may not have been subject to the rigorous environmental legislation that applies today, resulting in the possibility of various levels of contamination. It is necessary, therefore, to conduct a contaminated land survey for these types of site. 

SOIL GEO TECHNICAL INVESTIGATION

Load Bearing Capacity: This test helps in determining the maximum load the soil can withstand.
Test Method: Shear Strength: This test helps in determining the magnitude of the shear stress that a soil can sustain. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts.
Test Method: ASTM D3080 / BS 1377

Dynamic Core Penetration Test: This test helps in determining the compactness of the sub soil layer without making a bore hole. The data obtained by the test provides a continuous record of soil resistance. This is an in-situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil.
Test Method: BS EN ISO 22476-3 / ASTM D1586 / AS 1289.6.3.1

Triaxial Compression Test: This test helps in determining the shear testing of soils.
Test Method: ASTM D4767 – 11 / D2850

Plate Bearing: In the design of shallow foundation or traffic surface, design engineers need to know the bearing capacity of soil underneath. Plate bearing test is carried out in the field to serve this purpose. Results from the test can be used as design parameter or used to confirm the design assumption.

Test Method: BS 1377 Part 9: 1990 Standards.

Sludge

Sludge is a mud-like mixture consisting of solid materials and water, commonly found in natural and industrial processes. Sludge is a semi-solid slurry that can be produced from a range of industrial processes, from water treatment, wastewater treatment or on-site sanitation systems. It can be produced as a settled suspension obtained from conventional drinking water treatment, as sewage sludge from wastewater treatment processes or as fecal sludge from pit latrines and septic tanks. 

Industrial sludge tends to form by sedimentation and settling of biological or heavy metal impurities and waste from other processes. It can have different water content depending on the original process that led to it and there are several stages of its formation, treatment, and eventual reprocessing.