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Lesson 2 Overview Biological and agricultural concepts Leaving the Leftovers Investigating how crop residue can affect soils' ability to absorb water Crop residue, such as plant stems and roots, left after a crop is har- vested, is an important consideration in the care and maintenance of soil, and thus plays a role in the production of food. In this activity, students will gain an understanding of what crop residue is, and learn about the benefits, as well as the disadvantages, of using crop residue in crop production programs. Specifically, students will use bottle constructions to illustrate the effects of crop residue on soils' ability to absorb water. Using soil and simulating crop residue, students will also look at the effects of rainfall on soil surfaces. Soil science Soil ecology Water cycle Percolation Crop residue management Crop Residue I 2-1
Transcript

Lesson 2

Overview

Biological and agricultural concepts

Leaving the Leftovers Investigating how crop residue can affect soils' ability to absorb water

Crop residue, such as plant stems and roots, left after a crop is har­vested, is an important consideration in the care and maintenance of soil, and thus plays a role in the production of food. In this activity, students will gain an understanding of what crop residue is, and learn about the benefits, as well as the disadvantages, of using crop residue in crop production programs.

Specifically, students will use bottle constructions to illustrate the effects of crop residue on soils' ability to absorb water. Using soil and simulating crop residue, students will also look at the effects of rainfall on soil surfaces.

Soil science Soil ecology Water cycle Percolation Crop residue management

Crop Residue I 2-1

Lesson 2

The teachable moment

Background

2-2 1 Crop Residue

Teacher material

Biology and agriculture teachers can use this experiment to illustrate aspects of the water cycle, namely how water, falling as raindrops onto soil, moves through the soil eventually meeting groundwater.

In addition, percolation, or water movement through soil, can be stud­ied along with soil science, plant physiology, groundwater issues (such as purification and contamination), and crop residue management.

"As long as roots of plants prosper in the soil beneath our feet, there will be green plants on the face of the land and our lives and those of many creatures will be possible." (Francis D. Hole 1991) Because soil is critical to our existence, thoughtful care and management of soil is important.

When farmers harvest crops, they need to make a decision what to do with the residual parts of the plant, called crop residue, that are not harvested. They can leave the residue (leaves, stems, or roots) in the field, remove the residue from the field for use as animal bedding, or till the residue under the soil. Leaving crop residue in the field is very important for soil management and conservation. In fact, crop residue requirements are now part of many farm conservation laws, and farm legislation.

There are many benefits in leaving crop residue on the field surface rather than tilling them under or using as bedding for animals. They include the following (from Our Soils and Their Management, by Donahue, Pollet and Tulloch):

• less erosion by water and wind • greater water-holding capacity in the soil surface • more water available to plants • more snow captured by adhering to residue • lower soil temperature in summer and higher in winter • more soil humus from decomposed residue • vital nutrients, such as nitrogen, phosphorus, and potassium,

added to soil from decomposing residue • less crusting of the soil surface • friendlier environment for songbirds and migratory ducks • more beneficial animal life, such as earthworms, encouraged

lesson 2 Teacher material

Disadvantages of using crop residue in the field can include:

• poorer drainage for many north-temperate, already poorly drained, soils

• more insects, diseases, weeds, and rodents • slower seed germination due to more moisture and lower

temperatures at the soil surface on north-facing slopes • increased use of herbicides (chemicals used to eliminate

unwanted plants or weeds that grow in the presence of residue)

• slow seed germination of some crops caused by residues from plants such as sweet clover, corn, wheat, and oats

• special farm equipment may be necessary to work a field left with residue

As crop residue decomposes, nutrients necessary for plant growth are released. Organic acids are formed, which may enhance the availabil­ity of certain plant nutrients and aid in the breakdown of minerals in the soil.

Organic matter helps soil retain water by providing increased surface area for water to adhere to and more pore spaces for water to fill. Water infiltration, movement of water into the surface of the soil, often increases with additional organic matter as a result of changes in soil structure, or improved soil aggregation (or dumping).

Soil temperature, an important factor for seed germination, may also tend to be slightly higher when residue is present. Increased organic matter generally causes soil to be darker in color, which absorbs and retains more heat from the sun.

As mentioned above, crop residue can have some detrimental effects. It may harbor insect pests and disease-causing fungi and bacteria that can be harmful to the next year's crop. Residue can also harbor weed seed that may germinate in the future. Also, if the residue is low in nitrogen, which is normally the case with crops like com and wheat, temporary nitrogen shortages may occur for the next growing season, because the residue may hold and actually use available nitrogen from the soil in its decomposition process.

Crop Residue I 2-3

Lesson 2

Teacher management

Teacher material

Preparation time One hour for collection of materials

Activity time Initial bottle construction-one class period (50 minutes) Experiment-one class period (50 minutes)

Materials • local soil samples (you can also use commercial soil mixes)

Tips and safety

Key terms

2-4 I Crop Residue

• assorted types of residue such as grass clippings, leaves, corn stalks, hay, wheat stubble, etc.

• six 1-liter bottles per student/group (you can substitute 20-oz) • water measurement containers (graduated cylinders or graduated

1-liter bottles) • ruler • markers • black electrical tape • hole punches, pins, or needles • scissors

1. Avoid compacting soils tightly in the soil columns as this may negatively affect how much water can move through the column. Try to keep the soil in as "natural" a state as possible by trying to leave the soil in the state in which it was collected.

2. The "clouds," which are the original base of the soil column bottles, are used to simulate rainfall on the soil. When constructing these "clouds," a student can vary the number, size and location of the holes in the base. Note that when poking holes in the "cloud," the direction in which the holes are poked affects how the water will drop through. Holes can be made with a pin or a needle.

Channelling: pathways into the soil made by residue

Erosion: the process by which topsoil is washed, blown, or otherwise moved by natural agents from one place on the landscape to another

Groundwater: water beneath the earth's surface in saturated soil or porous rock

Herbicides: chemicals used to eliminate unwanted plants or weeds

Lesson 2

References

Teacher material

Infiltration: the downward entry of water into soil

Mulch: a layer of material spread over the soil surface to protect it and plant roots from erosion, crusting, freezing, and drying

Percolation: the movement of liquids in the soil

Residue: organic matter left on or in the soil and/ or incorporated into the soil upon completion of a life cycle or harvesting of the plant

Saturation: the condition of a soil when all pores are filled with water

Milo I. Harpstead, Francis D. Hole, William F. Bennett. Soil Science Simplified.

Fundamentals of AgriScience, Delmar Publishers: Albany, N.Y.

Donahue, Follett and Tulloch. Our Soils and Their Management, Increas­ing Production Through Environmental Soil and Water Conservation . Interstate Publishers, Inc.: Danville, Illinois.

Crop Residue 1 2-5

Lesson 2

Introduction

2-6 I Crop Residue

Student material

Leaving the Leftovers Investigating how crop residue can affect soils' ability to absorb water

"As long as roots of plants prosper in the soil beneath our feet, there will be green plants on the face of the land and our lives, and those of many creatures will be possible." (Francis Hole 1991). Soil is impor­tant- supporting life, food production, buildings, roads, and many other things. Because soil is so critical to our existence, the way we care for and manage soil is everyone's concern.

When farmers harvest crops, they need to make a decision what to do with the residual parts of the plant, called crop residue, that are not harvested. They can leave the residue (leaves, stems, or roots) in the field, remove the residue from the field for use as animal bedding, or till the residue under the soil. Leaving crop residue in the field is very important for soil management and conservation. In fact, crop residue requirements are now part of many farm conservation laws and farm legislation. Examples of residue includes cornstalks, bean stalks, wheat stubble, straw, tree leaves and grass clippings.

Benefits from leaving crop residue in the field, rather than tilling it under or using it as bedding for animals, include the following:

• less erosion by water and wind • greater water-holding capacity in the soil surface • more water available to plants • more snow captured by adhering to residue • lower soil temperature in summer and higher in winter • more soil humus from decomposed residue • vital nutrients, such as nitrogen, phosphorus, and potassium,

added to soil from decomposing residue • less crusting of the soil surface • friendlier environment for songbirds and migratory ducks • more beneficial animal life, such as earthworms, encouraged

Lesson 2

Procedure

Student material

Disadvantages of using crop residue in the field may include:

• poorer drainage for many north-temperate, already poorly drained, soils

• more insects, diseases, weeds and rodents • slower seed germination due to more moisture and

lower temperatures at the soil surface on north-facing slopes • increased use of herbicides (chemicals used to eliminate

unwanted plants or weeds) • slowed seed germination of some crops caused by residues

from plants, such as sweet clover, com, wheat, and oats • special equipment may be necessary to work a field left with

residue

Water infiltration, movement of water into the surface of the soil, often increases with additional organic matter as a result of changes in soil structure, or improved soil aggregation (or clumping).

Soil temperature, an important factor for seed germination, may also tend to be slightly higher when residue is present. Increased organic matter generally causes soil to be darker in color, which absorbs and retains more heat from the sun.

Water is critical to every ecosystem and essential to all life. It aids in plant growth and development, residue decomposition, and is a part of the water cycle. The rate at which soil absorbs water is an important factor in determining if plants will have water in the future. This absorption rate will vary with different soil types and with the amount and kind of residue on the surface of, or mixed in, soils.

Through this experiment you will be determining the different effects of soil residue on the soil sample as it relates to water absorption. You will compare soil without residue, soil with residue on the surface only and soil with residue mixed in it.

Constructing the bottle columns: For information and tips on making bottle constructions, see Bottle Biology Basics (section ii).

1. Remove the labels from six 1-liter bottles.

2. Cut three bottles 1 em below the shoulder. These will be your reservoirs. You can cut part of the base off for easier viewing.

3. Cut three bottles just above the base of the bottle to create the soil column. The base from each of these will be your "clouds."

Crop Residue 1 2-7

Lesson 2

2-8 I Crop Residue

Student material

4. Punch an identical pattern of several holes in three bottle caps. This will allow water to move out of the soil column into the reservoir.

5. Create the "clouds" by making small holes with a needle in the bases you removed from the soil column bottles. Tape over any large base holes with electrical tape.

II C..L-OIA.."D "

"A"

tiLt\ C.AN

11 LI...OU..D"

(lop V' fiW)

"C.1...ou..D" (SI'r:>E" VIEW)

Filling the columns and beginning experiment:

1. Collect 1500 ml of soil from a single site or source.

2. Consider the types of residue available-com stalk pieces from a field, grass clippings from a yard, leaves from a forest floor or weeds from a garden. Collect 600 ml of residue and cut it into 1 em or smaller pieces. A scissors may work best for this.

3. Number soil columns as #1, #2 and #3. Fill all three columns with 500 mls of soil.

4. Measure two equal 300 ml portions of the residue.

5. Place one of the residue portions on the surface of column #2.

Lesson 2 Student material

6. Dump the soil from column #3 into a separate container and mix the second portion of residue with the soil. Place the soil/residue mixture back into the column.

7. Press a film can over the cap of each column. This will keep the water from draining out while you saturate the column.

8. Place the rain cloud on each soil column and pour 100 m1 of water into each cloud.

9. When the water has moved out of the cloud, add an additional 100 ml of water until you have poured 400 m1 into each column.

10. Five minutes after the last portion of water has been added, take the film cans off the columns and allow the water to drip through.

Observations:

1. After each addition of 100 ml, watch the water as it moves through the soil.

2. Record your observations on page 2 of the data sheet.

3. After adding all400 ml of water and when no more water drains through the soil column, measure the amount of water in the reservoir in ml. Record the amount of water that moved through the soil column into the reservoir. (Be careful not to squeeze the column as this will cause more water to run through.) Make certain that all water has moved through. This may take a while.

4. Record your results on page 1 of the data sheet.

Crop Residue I 2-9

Lesson 2 Data Sheet

Student name: _________ _

Directions: Record water movement data

Column #1- without residue Measured Total Added Percentage

Water drained into = ml I 400 ml x 100 = % reservoir

Water in the soil = ___ ml I 400mlx 100 = ___ %

Totals = ___ ml ___ %

Column #2- surface residue

Measured Total Added Percentage

Water drained into = ml I 400 ml x 100 = % reservoir

Water in the soil = ___ ml I 400mlx 100 = ___ %

Totals = ml % --- ---

Column #3- residue mixed in

Measured Total Added Percentage

Water drained into = ml I 400 ml x 100 = % reservoir

Water in the soil = ___ ml I 400 ml x 100 = %

Totals = ml % ---

2-10 I Crop Residue

Lesson 2 Data sheet

Recording observations: Indicate at least five observations you made during this experi­ment and create a hypothesis as to why this occurred.

1. Observation:

Hypothesis:

2 Observation:

Hypothesis:

3. Observation:

Hypothesis:

4. Observation:

Hypothesis:

5. Observation:

Hypothesis:

Additional Observations:

Crop Residue 1 2-11

Lesson 2

Results and discussion

Extensions

2-12 1 Crop Residue

Student material

1. What are the variables in this experiment?

2. If the amount of residue in the soil or on the surface were changed, what results might be expected?

3. Why would soil contract or expand in the presence of water?

4. Why is the subsoil moisture important to plant life?

5. Are there some agricultural soils that would benefit more than others from residue? Can you guess what they might be? Why?

6. How could you measure the available water-holding capacity of these soils and quantify the effects of residue management choices?

1. What would happen if the soil columns were of different lengths?

2. What effects would various soil types have on water infiltration?

3. What would happen if different soils were layered in the soil column?

4. If you changed the rate of water falling from the clouds, would it affect infiltration, percolation, or both?

5. Will water percolate up when soil is drying?

6. Will the soil return to its original level after drying back to its original moisture amount?

7. If earthworms were added would it affect the movement of water? How?

8. If you used distilled water would there be microorganisms in the groundwater?

9. If you grew plants in the column, harvested them to stalks and left the roots, would infiltration be affected?

10. Will the degree of coarseness or fineness of residue affect the water infiltration?

Lesson 2 Student material

11. Would the degree of dryness or wetness of the residue affect the water infiltration?

12. Plot the data from all of the students/ groups. Compare results for different types of residue and soil.

13. What happens if the amounts of soil residue are changed in the same soil type?

14. What would happen if you used fresh green residue?

15. How would adding sand or gravel to the soil affect the water-holding capacity of the soil?

16. How does residue left on the soil affect water movement in compacted soils? Compaction can be caused by equipment, livestock, people, etc., and is a significant problem for row crop farmers.

Crop Residue I 2-13


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