15 Soil Infiltration
15 Soil Infiltration
15 Soil Infiltration
***Content and lab derived from the USDA-NRCS Guides for Educators. Please see the Guides for
additional helpful pictures and diagrams.***
Objectives
By the end of the lesson, students will know or be able to:
Define: infiltration rate, restrictive layers, soil aggregates, soil porosity, steady-state
infiltration
List and describe inherent factors that affect soil infiltration
Describe soil infiltration management practices
Explain soil infiltration problems and how they affect soil function
Measure soil infiltration and interpret results
Pour an equal amount of water into each of the cups and encourage students to monitor the two
rates.
Inform students that during this lesson, the class will explore soil infiltration rates, what affects,
problems that exist and management of it.
Direct students to search the room for note cards with key terms and definitions on them for this
lesson.
Review the terms and definitions using the accompanying PowerPoint or the information found
here:
Infiltration Rate: a measure of how fast water enters the soil, typically expressed in inches per hour
but recorded in minutes for each inch of water applied to the soil surface
Restrictive Layers: compacted layers and layers of dense clay, bedrock or other restrictive features
than limit infiltration below the surface of the soil.
Soil Aggregates: soil particles held together by organic matter and related substances. Well
aggregated soils have higher infiltration rates and are less prone to erosion.
Soil Porosity: Amount of pore space in the soil. Soils with higher porosity have more pore space and
higher infiltration rates than those with lower porosity.
Steady-State Infiltration: The infiltration rate is steady and does not increase or decrease as more
water is added. It typically occurs when the soil is nearly saturated.
Instruct students to discuss with someone near them how each of the terms might affect plant
growth in soils.
Soils with a sandy texture has large pores and water moves through it quickly, like the marbles.
Soils with a clayey texture has small pores and water moves through it slowly, like the Play-Doh.
Soil texture, as discovered in the previous labs, is an inherent factor, meaning it cannot be changed.
Ask students to predict what type of soil they believe exists around the school, in their yard, in their
fields, etc. Elicit responses.
Surface crusting
Compaction
Soil Organic Matter
Ask students to discuss how surface crusting, compaction and soil organic matter might affect
infiltration rates.
Share the following information with the students and encourage them to add it to their guided
notes:
Soil crusting
o Soils dry out, causing pore space to increase as cracks form
o Water fills the cracks quickly, wetting the soil
o As water becomes wetter, the infiltration rate slows because of restrictive layers
Compaction
o Results from equipment and tillage practices
o Minimizes pore space
o Slows water movement through the soil profile
Soil Organic Matter
o Bare soil is more drastically affected by erosion by rain drops
o Dislodged soil particles fill in and block surface pores
o OM binds soil particles together, forming aggregates; aggregates increase porosity
and infiltration rates
o OM encourages a living environment for organisms such as earthworms; organisms
move about in the soil and increase pore space
Improve Infiltration Rates by
o Avoiding soil disturbance and equipment operation when soils are wet
o Using designated field roads or rows for equipment traffic
o Reducing the number of trips across the space
o Sub-soiling to break up existing compacted layers
o Using continuous no-till
o Adding solid manure or other organic materials
o Using rotations with high-residue crops, such as corn and small grain and perennial
crops, such as grass or alfalfa
o Planting cover crops and green manure crops
o Farming on the contour
o Establishing terraces to minimize run-off and erosion
Instruct students to identify something their family does (in their fields, garden or yard) or
something another individual in the community does to minimize soil compaction. Also consider
challenging students to identify something they could do.
Divide students into five small groups and provide each group with one of the following soil
infiltration problems. Instruct each groups to discuss and be prepared to present what the problem
could cause and potential solutions.
Instruct small groups to share their thoughts on the results of the problem and their possible
solutions.
Discuss with students how a farmer is economically affected by poor soil infiltration and how
consumers are economically affected as well.
Provide the Experience – Measuring and Interpreting Soil Infiltration – Approximately
3 minutes
Review the laboratory scenario with students. Students can find the scenario in their guided notes.
A local farmer recently purchased some recreational ground and plans to turn the space into farm
ground. One concern the farmer has is regarding the amount of vehicular traffic that has occurred
on the former recreational ground. The worry is that the transportation has negatively affected the
ground’s ability to infiltrate water.
Review and identify each of the supplies from the soil testing kit that will be used during the lab
activity.
3-inch-diameter ring
Plastic driver (mallet)
Small block of wood
Plastic wrap
Plastic bottle marked at 107 mL (for 1 inch of water) or graduated cylinder
Distilled water or rainwater
Stopwatch or timer
Review the steps of the laboratory activity and provide any instructions specific to your classroom
expectations and time.
See the attached laboratory guided notes for the steps to complete the laboratory. Review the results
and analysis steps of the lab
Review the Content – Approximately 4 minutes
Review the process students used to test the soil infiltration rates. Discuss how soil infiltration
relates to each of the other lab topics covered during the unit.
Congratulate students on their discovery of infiltration rates and their understanding of how
infiltration rates relate to other lab topics.
Guided Notes: Soil Infiltration
Vocabulary Matching
Infiltration Rate
Restrictive Layers
Soil Aggregates
Soil Porosity
Steady-State Infiltration
Compaction
A local farmer recently purchased some recreational ground and plans to turn the space into farm
ground. One concern the farmer has is regarding the amount of vehicular traffic that has occurred
on the former recreational ground. The worry is that the transportation has negatively affected the
ground’s ability to infiltrate water.
Laboratory Supplies
3-inch-diameter ring
Plastic driver (mallet)
Small block of wood
Plastic wrap
Plastic bottle marked at 107 mL (for 1 inch of water) or graduated cylinder
Distilled water or rainwater
Stopwatch or timer
Laboratory Steps
Select a test site that provides at least two areas that are under different management. (As an
example, in a row crop field, the two areas would be a wheel traffic row and a row without wheel
traffic.) If possible, measure the bulk density of each location prior to doing this lab.
Plan to conduct multiple ring measurements since a single ring measurement is only an estimate.
Conduct the test during a time when the surface soil is not unusually dry. Add water to the surface if
necessary and allow enough time for the water to soak in prior to conducting the test or conduct the
test after rain or irrigation.
Infiltration Test
Was a steady-state infiltration rate achieved? How do you know? Do you need to add a third inch of
water?