Texture: 

  • Definition: The texture of a soil describes the relative percentages of sand, silt, and clay in the soil. Sand grains are larger than silt; silt grains are larger than clay. Texture is an inherent property of soil, meaning it cannot be changed by management practices.
  • This soil is a silt loam: Sand: 15%,  Silt: 67%,  Clay: 18%.

Aggregate Stability

  • Definition: Aggregate stability is a measure of how well soil aggregates (soil clumps) hold together under intense rainfall or irrigation and is an indication of the biological and physical health of soil. Aggregate stability is influenced by microbial activite. Soil aggregates are held together by microbial colonies and plant exudates (sticky substances).
  • Significance: High aggregate stability prevents crusting (when soils crust. they resist absorption of water), runoff, and erosion and facilitates aeration, infiltration, water storage capacity.
  • This soil had a reading of 17%. This means that when exposed to water stress, only 17% of soil aggregates resisted disintegration. This indicator is almost in the “constraining column!” This low value suggests that microbial activity is also low and poor aeration of soil will negatively impact microbial communities. This also reflects a low water storage capacity. The risk of poor infiltration is higher runoff and erosion.
  • Verified by experiements by Lafayette students:
    • A slake test demonstrates the stability of soil aggregates in water. By placing a sample of topsoil into water, the water is drawn into the soil and displaces air. If pores in the soil are stable, water can move into the soil without causing aggregates to break apart. If pores in the soil are instable, as water moves into the soil, it will cause aggregates to break apart. The image below compares a sample from LaFarm (Lafayette College Farm) to a sample from the Conventional farm (the soil that is being analyzed in this independent study).

Left: Conventional …………. Right: LaFarm

Predicted Available Water Capacity

  • Definition: Available water capacity (AWC) is a measure of the amount of plant-available water in a soil. Soils that have low aggregate stability typically have low avaiable water capacity.
  • This soil had a very high rating relative to soils with similar texture. This does not add up, considering the soil had a very poor aggregate stability. We can verify the poor aggregate stability rating from the slake tests that have been done. This leads me to believe that the AWC is not as good as the analysis says.

Organic Matter

  • Definition: Organic matter is any substance that was once part of a living organism (crop residues, leaves, insects, earthworms, fungi).
  • Significance: Soil organic matter attracts and holds many soluble plant available nutrients so they are retained by the soil and are available to the plant.
  • This soil ranks as being in the high range. There are two nutrients measured for this indicator: carbon and nitrogen. The organic matter percentage which totaled to 1.89: Total Carbon = 1.74 and Total Nitrogen= 0.15.
  • I was skeptical of the high rating based on the land use practices (which are not conducive to high amounts of organic matter) and did some additional research:
    • Numerous scientists have asserted that soils with less than 2% SOC should be considered unstable for soil aggregates and not sustainable into the future. {NoTillFarmer}
    • A case study done on soils in the United States and Canada showed significant decline in structural stability if soil organic carbon (SOC) less than 2%.
    • Crop yields might suffer due to reduction in the soil’s capacity to cycle nutrients. This will, in turn, lead to reduction in the return of organic matter to the soil via crop residues, causing a cycle of intensified deterioration. {ScienceDirect}
    • A note about nitrogen:
      • Nitrogen is the most limiting nutrient in agriculture. After all, it was the Haber-Bosch process that caused the “Green Revolution.” This process found a way to transform diatomic nitrogen (a form that is inaccessible to plants) from the air and converted it into a form (ammonia) that was bioavailable to plants. This is a way to synthetically fix nitrogen, however, legumes and nitrogen-fixing soil bacteria can do this naturally. If there are no (or few) microorganisms, the organic nitrogen remains unavailable to plants. {me}

Predicted Soil Protein

  • Definition: Soil protein is the fraction of the soil organic matter that is present as protein or protein-like substances.
  • Significance: Soil protein influences the ability of the soil to make N available by mineralization. It is associated with soil aggregation and water movement.
  • This soil scored very low which adds up to other indicators (poor aggregate stability, therefore poor infiltration and water storage capacity).

 

Soil Respiration

  • Definition: Soil respiration is a measure of the metabolic activity of the soil microbial community. Just like us, microbes metabolize nutrients! Respiration (breathing) is critical to effective metabolization.
  • Significance: Soil respiration is an indication of the biological status, abundance and activity level, of microbes which perform key functions including nutrient cycling and aggregate formation.
  • This soil has a low soil respiration value, meaning the soil microbes are struggling to “breathe” and metabolize.

 

Active Carbon

  • Definition: Active carbon is the portion of organic matter that can serve as a food source for soil microbes and is an indicator of soil biological health.
  • This soil had a measure of active carbon in the medium range. Not bad but not great.

 

Soil pH

  • Definition: pH is a measure of how acidic or basic a soil is. The lower the pH, the higher the acidity. The ideal range is 6.2 – 6.8 for most crops.
  • This soil had a pH of 6.2. This reading is on the lowest end of the spectrum, meaning the soil is on the verge of being too acidic. Soils can tolerate lower pH values if there is high organic matter. However, the organic matter for this soil is not ideal, as explained previously, meaning the soil is at risk of becoming too acidic for plants to tolerate.

 

Extractable Phosphorus, Potassium, and additional nutrients 

  • This soil scored 100 … a perfect score for all nutrients. Something I have learned throughout my farming journey so far is that more is not always better. Excessive nutrients can leech out of soil into marine environments and cause toxic algal blooms. Additionally, if there is an overabundance of one nutrient, it can inhibit the plant from taking up other critical nutrients.
  • I looked into how Cornell assigns scores for each micronutrient. Potassium is scored on a “more is better” scale; however, excess of potassium can inhibit plants from uptaking other nutrients, like calcium. Phosphorus is measured within an optimal range.
  • Another soil assessment would be necessary to determine the specific values for each nutrient in the soil. 

I did not do further testing (and interpretation), however the takeaway message of this analysis of the soil analysis is to always be thinking critically about the information presented before you. Does it add up with what you understand? If not, why might that be the case? Was your prior understanding flawed or is it the new information?