Describing Soil Profiles

Summary

The video script provides an in-depth guide to describing soil profiles, emphasizing the importance of understanding the geology and parent materials before analysis. Set in central Pennsylvania's Ridge and Valley Province, the tutorial demonstrates how to 'face off' a soil profile dug by a backhoe to reveal accurate soil horizons. It identifies the presence of A, B, and R horizons, explains the absence of an E horizon due to plowing, and details the depth and characteristics of each horizon. The script also covers the use of the Munsell color system for soil color identification and discusses various soil structures like granular and blocky, highlighting the significance of earthworm activity and animal burrows as indicators of soil health.

Takeaways

• 🗺️ The script describes a soil profile in Central Pennsylvania's Ridge and Valley Province, emphasizing the importance of understanding the geology and geomorphology of the area.
• 🏔 The soil profile is developed from Limestone Bedrock, indicating it's a residual soil that has formed over thousands of years.
• 🔍 To accurately describe a soil profile, one must 'face off' the profile to remove smears caused by digging, ensuring a clear view of the soil horizons.
• 🏗 The six master horizons in a soil profile may not all be present, and the script highlights the presence of A, B, and R horizons in the described profile.
• 🌱 The absence of an E horizon in the profile is noted, likely due to plowing which mixed the material into the AP horizon.
• 📏 The depth of the soil profile is measured from the surface (0) down to the Bedrock, which is 28 inches deep in this case.
• 🟥 The soil color is described using the Munsell color system, with the script illustrating how to compare soil color to color chips.
• 🧱 The soil structure is a key aspect of soil profile description, with the script mentioning granular and blocky structures as examples found in the profile.
• 🐛 The script points out natural soil features like animal burrows and earthworm channels, which can affect soil homogeneity and are indicators of soil health.
• 🌿 The presence of earthworm channels is a good sign of well-drained soils and overall soil health.

Q & A

What is the importance of understanding geology and geomorphology before describing a soil profile?

Understanding geology and geomorphology is crucial as it provides a background that helps predict what might be observed in the soil profile. It sets the context for the parent materials and the development of soil horizons.

What is a soil profile and why is it important to 'face off' the profile?

A soil profile is a vertical section through the soil to the parent material or bedrock, revealing the soil horizons. 'Facing off' the profile, which means breaking off smeared areas, is important to get an accurate representation of the soil horizons, as tools like shovels or backhoes can distort the natural layers.

How many master horizons are there in a soil profile, and which ones were identified in the described profile?

There are six master horizons in a soil profile. In the described profile, the A, B, and R horizons were identified, with no E horizon due to plowing that mixed the material into an AP horizon.

What does 'AP Horizon' signify in the context of soil profiles?

The 'AP Horizon' signifies the plowed layer at the surface of the soil profile, where 'A' indicates the topsoil and 'P' indicates that it has been plowed.

Why is the E horizon sometimes not visible or described in soil profiles?

The E horizon is an eluvial horizon where materials are leached out. If it is mixed with other horizons due to activities like plowing, or if it is too thin (less than 2 inches), it may not be described separately in a soil profile.

What is the significance of the B horizon and its suffixes in soil science?

The B horizon is a subsoil layer that often shows evidence of clay accumulation (Bt). The suffixes like Bt1 and Bt2 indicate different stages or characteristics within the B horizon, such as color, texture, or structure.

How is soil color used in soil profile description, and what system is commonly used?

Soil color is an important property that can indicate organic matter content, mineral composition, and soil development. The Munsell color system is commonly used, with specific notations like '10R' to describe the color precisely.

What are the different types of soil structures mentioned in the script, and what do they indicate?

The script mentions granular and blocky soil structures. Granular structure is common under grasses, indicating good soil conditions, while blocky structure indicates more developed soil with natural clumps or pads.

What are the implications of finding earthworm channels in a soil profile?

Earthworm channels, or middens, indicate good soil health and drainage. Earthworms homogenize and mix the soil, which is beneficial for aeration and nutrient cycling.

Why are old animal burrows significant in soil profiles?

Old animal burrows can provide insights into the biological activity in the soil and can affect soil structure and properties. They can also be indicators of past land use or natural processes.