Thresholds levels for cultivated crops
Focus
This activity provides opportunities for students to explore how scientific investigations can be used to provide data for decision making. Students develop skills in the use of salinity-monitoring equipment. The activity allows students to determine, through experimentation, the effect of salinity in irrigation water on the productivity of common agricultural crops, and to calculate the soil salinity threshhold levels for these crops.
Science
Science and Society
6.3 Students design and perform controlled investigations to produce believable evidence.
Materials
- Resource sheet 4 - Salinity threshold experiments (PDF, 55K)*
- Irrigation water quality fact sheet
Teaching considerations
This activity is designed to follow on from the activity ‘The effects of soil salinisation’, and is aimed at higher-level students.
During the experimental planning stage students may need assistance with working out:
- all of the variables involved
- how to use controls in their experimentation
- which variables are being tested and which need to be kept constant.
A framework of questions could be provided to assist students in structuring their experiments. For example, ‘What am I going to investigate?’, ‘What do I think will happen?’, ‘What happened?’, ‘Why’ and ‘What does this mean?’.
Ensure that students label all specimens and that records of germination and growth rates are taken at regular intervals.
Working scientifically
Time: 60 minutes + 10 minutes per recording interval
- Designing and performing experiments
- Identifying and controlling variables
- Measuring
- Interpreting data
Students are provided with a recipe-type experiment (see Resource sheet 4 (PDF, 55K)* ) where they are required to use an electrical conductivity meter to calculate the salt concentrations of various soil samples.
After familiarisation with the use of electrical conductivity meters, students then design their own experiments to test the amount of salt that can be tolerated by a number of different crop varieties.
Students conduct the experiments they have designed and record data over a number of weeks. These salt threshold tolerances may then be compared with the values given in the Irrigation water quality fact sheet for each crop variety tested.
Students reflect on the value of this test and the information it provides for future planning.
Additional learning
Students may perform electrical conductivity tests on soils in the local area and, using their threshold data, determine what crops could be grown in that area.
Gathering information about student learning
Sources of information could include:
- anecdotal records from observations and interviews with students during the planning and experimentation stages
- students’ salinity threshold data
- students’ reflections about the value of the information
* Requires Acrobat Reader
Last updated: 19 September 2008