Question

student edition
physical and chemical properties of soil cox lab 7
physical and chemical properties of soil lab 7 student edition
physical & chemical properties of soil
primary topic
topic 4.3
soil composition and properties
primary learning objective
ert-4.c
describe similarities and differences between properties of different soil types.
secondary topic
topic 8.3
the green revolution
secondary learning objective
bii-8.2c
describe changes in agricultural practices.
overview and purpose
in this lab investigation, you will perform a series of chemical and physical tests to discern the nutrient - and water - holding properties of soil, which are related to agricultural productivity and crop selection.

• you will learn to perform chemical and physical tests on soil samples.
• by the end of the lab, you will be able to use data to determine whether a type of soil is well - suited for growing different crops.

as you work through unit 4 of the course and this lab investigation, you will gain knowledge of how soil productivity is determined, to help foster a deeper understanding of crop yields and impacts of agriculture when these topics are discussed in unit 5. soil properties will also be important in the discussion of watersheds, sanitary landfills, and nutrient cycling.
pre - lab activity
researchers were interested in comparing the water - holding capacity of soils collected from various biomes. samples were collected from five biomes (tropical rainforest, taiga, temperate grassland, desert, and temperate deciduous forest). 50 - gram samples were collected at a depth of 6 inches from each of the various locations, and the percentage of water by mass was calculated and is shown in table 1.
table 1: water - holding capacity of various biome soils

biome

soil type

water - holding capacity

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---

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tropical rainforest

oxisol

17%

taiga

spodosol

11%

temperate grassland

mollisol

19%

desert

aridisol

10%

temperate deciduous forest

alfisol

21%

name gianna vadala date 11/13 per 6th cox

pre - lab questions
complete each of the lab questions in your lab notebook.

1. identify the independent and dependent variables in the investigation described.
2. identify one variable that the researchers should hold constant that was not mentioned in the description of their experimental design setup.
3. construct a graph comparing soil type to water - holding capacity. use data from table 1.
4. a researcher claims that aridisols have the highest clay content of these five soil types. provide reasoning to support or refute the researchers claim.
5. propose which type of soil might be most appropriate for growing crops that require large amounts of water, such as corn.

getting started
quickwrite
write down your answers to the following question in your lab notebook after you have been given an overview of the lab by your teacher.
considering the source of your soil sample (construction site, vegetable garden, wooded area, provided by your teacher), write a hypothesis about your soils ability to grow a food crop.
water - holding capacity:
the amount of water an area of soil can hold against the force of gravity. the water - holding capacity of a particular soil is related to its texture. the higher the clay content of a particular soil, the higher the water - holding capacity.
tip:
for the ap environmental science exam, you do not need to know the soil type names (e.g. oxisol, spodosol). you do need to know which biomes have fertile soils (grasslands, deciduous forests) and why (moderate temperatures, ample precipitation, etc.). you should also be familiar with which biomes have poor soil (tropical rainforests, tundra, boreal forests, deserts) and which characteristics of those biomes result in their poor soils.
your answers matter:
in order to be successful on the ap exam, your answers to the free - response questions need to be thorough and detailed. its important that your responses include complete thoughts and comprehensive answers. practicing this now will help you succeed on the ap exam.

Explanation:

1. Independent Variable: The independent variable is the factor that is changed or manipulated in an experiment. In this case, it is the type of soil (e.g., Oxisol, Spodosol, Mollisol, Aridisol, Alfisol) as different soil types are being compared.

Dependent Variable: The dependent variable is the factor that is measured. Here, it is the water - holding capacity of the soil, which is affected by the type of soil.

1. One variable that should be held constant could be the temperature at which the water - holding capacity is measured. Temperature can affect the rate of evaporation and thus the water - holding capacity measurement. If not controlled, it could introduce error in the experiment.
2. To construct the graph:

• On the x - axis, label the different soil types (Oxisol, Spodosol, Mollisol, Aridisol, Alfisol).
• On the y - axis, label the water - holding capacity (in percentage).
• Plot each soil type with its corresponding water - holding capacity value (e.g., Oxisol at 17%, Spodosol at 11%, etc.).

1. The researcher's claim that Aridisols have the highest clay content is refuted. The water - holding capacity of Aridisol is 10%, which is relatively low. Since water - holding capacity is related to clay content (higher clay content generally means higher water - holding capacity), and other soils like Alfisol (21% water - holding capacity) have higher water - holding capacity, Aridisol is likely to have a lower clay content.
2. Alfisol would be most appropriate for growing crops that require large amounts of water. It has the highest water - holding capacity (21%) among the given soil types, which means it can retain more water for the crops.

Answer:

1. Independent Variable: Type of soil; Dependent Variable: Water - holding capacity.
2. Temperature (or other relevant constant like soil sample size, method of water addition).
3. Graph with x - axis: Soil types; y - axis: Water - holding capacity (percentage), with points plotted for each soil - water holding pair.
4. Refuted. Low water - holding capacity (10%) of Aridisol suggests low clay content (since clay content is related to water - holding capacity).
5. Alfisol.