2.4: Soil Pit Field Trips
Learning Objectives
- Describe a soil profile using a soil profile description sheet.
- Delineate soil profile horizons.
- Interpret a soil profile using the five soil forming factors.
- Identify the impacts of management on soil properties.
One of the fundamental skills of a soil scientist is to accurately describe a soil profile. To do so, soil scientists need to have a thorough understanding of many concepts that have already been covered in this course, including soil color, texture, structure, taxonomic classification, soil development processes, and the five soil forming factors. Using those soil science concepts, you will be working with your classmates in groups to fill out a soil profile description sheet at two different sites over the course of two field trips. One site has been used for row crop agriculture, while the other is managed range land. Through these two land uses we can compare how two different management systems impacted these two particular soil profiles. We will also discuss the soil mapping process, and appropriate interpretation and use of data from the Web Soil Survey.
Materials
- Cultivated and Prairie Soil Comparison Problem Set
- Trowels
- Shovels
- Muffin tins
- Munsell Soil Color Charts
- Clinometers
- Water squirt bottles
- Hydrochloric acid, 10%
- Soil profile measuring tape and a nail
- Profile horizon markers
Recommended Reading & Viewing
- Eye on Agriculture Today: Soil Texture by Feel (KSREVideos, 2010)
- Soil Profiling: Color (KSREVideos, 2011a)
- Soil Profiling: Structure (KSREVideos, 2011b)
- Soil Profiling: The Proper Tools (KSREVideos, 2011c)
- Illustrated Guide to Soil Taxonomy (Soil Survey Staff, 2015)
Prelab Assignment
Using the recommended reading and viewing resources and the materials for the Soil Formation, Soil Classification and Mapping, and Soil Texture and Structure labs, consider the questions listed below.
- Define epipedon, and name one example.
- Define subsurface diagnostic horizon, and name one example.
- What is the difference between consociations, complexes, and associations?
- List the landscape positions on a hillslope from top to bottom. Which position is the most stable?
- When labeling soil profile horizons, how does a number to the left of the master horizon (example: 2Bt) differ from a number to the right of the master horizon (example: Bt2)?
-
In a few words for each, identify the soil profile feature indicated by each subordinate horizons.
- g:
- k:
- n:
- p:
- t:
- ss:
Appropriate Clothing
We recommend wearing long pants, sturdy shoes or boots, and socks that extend past your ankles on this field trip. Sunscreen and bug spray may also be needed.
Physical Ability
This field trip may require 5 to 10 minute hikes over uneven terrain. It may also entail climbing eight foot tall fences. If you cannot perform these tasks, contact your instructor ASAP. An alternative laboratory and/or field trip activity will be organized for you.
Assignment: Problem Set
A problem set will be handed out at the start of this lab. The questions in the problem set focus the soil pit field trip(s).
Subsequent Lab Setup
To examine the influence of texture and density on water holding capacity and pore size distribution, the moisture status of different soil materials will be monitored through a drying cycle. Each lab group will be responsible for two soils and one treatment (Air Dry, AD; Wilting Point, WP; Field Capacity, FC; and Saturated, S). Your laboratory instructor will assign the treatment. You will complete the experiment on both soils.
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Label an empty cup as follows:
- Lab Section
- Soil Type: Sandy or Clayey
- Treatment:AD (air dry)
- WP (wilting point)
- FC (field capacity)
- S (saturated)
- Punch eight small holes in the bottom of the cup.
- Weigh the empty cup and record the value on the data sheet.
- Cut a small piece of paper towel and place in the bottom of the cup to prevent soil from falling through the holes.
- Place a cup on the balance, tare out the weight of the cup, and add exactly 50g of soil and gently tap the cup on the lab bench to settle the soil.
- We need to know the volume of soil in the cups so we can calculate bulk density. Fill another cup (without holes!) with water to the same level as the soil in the cups. Pour the water into a graduated cylinder and record the value on the data sheet. (assume 1 ml = 1 cm 3 )
- Get the data for the other soil from the lab groups with the other soil.
- Calculate and record the bulk density.
- Carefully and slowly place the WP, FC, and S cups in the water in the dishpans provided so the soil can become saturated from the bottom to the top. Your lab instructor will remove WP cups tomorrow and allow them to dry for 6 days. The FC cups will be removed in 6 days and allowed to drain for 1 day. The S cups will remain in the water all week.
- Place the AD cup in the dishpan without water.