Particle Size and Textural Analysis Importance in a Soil Test Report

Particle Size and Textural Analysis Importance in a Soil Test Report

Professor DeBacco


Soil Texture
Soil texture is a classification instrument used both in the field and laboratory to determine soil classes based on their physical texture.
A soil textural analysis determines the relative proportions of sand, silt and clay in a sample.
The textural class is based on the USDA’s textural triangle classification where there are 12 different textural classes.
Soil texture can be determined using qualitative methods such as texture by feel, and quantitative methods such as the hydrometer method.
Knowing a soils texture can help gauge the required inputs and potential productivity of a soil for crops.



Soil Triangle
This triangle is used to determine the classification of a soil based on the percentage clay, slit, and sand.
Notice how the percentage of clay has a large impact on the soils classification.
This is due to the small particle size and resulting high surface area to volume ratio.



Sand – Silt - Clay
Loam is often the classification given to a soil that is not predominantly sand, silty or clay.



Sandy Soil
Sand has the largest sized particles
Sandy soils may have good aeration and drainage but limited ability to retain water and nutrients.
The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz.



Silt
Mid sized particles and offers properties in-between sand and clay.
Silt has a moderate surface area with a typically non-sticky, plastic feel.
Silt usually has a floury feel when dry, and a slippery feel when wet.
Silt can be visually observed with a hand lens, exhibiting a sparkly appearance.



Loam
Loam By weight, its mineral composition is about 40–40–20% concentration of sand–silt–clay, respectively.
These proportions can vary to a degree, however, and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam.
Note that the primary definition of loam in most dictionaries is soil with humus (organic content) and no mention of particle size texture, and this definition is used by many gardeners.
In the United States Department of Agriculture, textural classification triangle, the only soil that is not predominantly sand, silt, or clay is called "loam". Loam soils generally contain more nutrients, moisture, and humus than sandy soils, have better drainage and infiltration of water and air than silt and clay-rich soils, and are easier to till than clay soils.



Clay
Smallest sized particles and has the greatest impact on soil properties
The high surface area allow it to hold nutrients well which reduces the chance of leaching.
However, this soil can also hold water which can result in plants to be more likely water logged.
Also, when clay soil dries out it will crack and be more difficult than other types to rehydrate.



Ribbon Test- Determining Texture by Feel


Soil Texture Favorable for Growing
Loam (silt loam)
By weight, its mineral composition is generally about
40% sand
40% silt
20% clay
Variance in these proportions result in the different types of loams…
sandy loam
silty loam
clay loam
sandy clay loam
silty clay loam
loam



Soil Texture Long Term
Assuming no major modifications to the soil the textural class should remain fairly consistent so it is not necessarily needed with each soil test a grower takes.


However, when initially performing a soil test for a new or prospective area this is a good test to include.




Link to Lecture Slides: https://drive.google.com/file/d/19qcf...

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