Scientific Practices and Experimental Skills in Agricultural Science
Domain focus
Scientific practices and experimental skills is the domain that tests whether you can turn an agricultural question into a fair, safe investigation and interpret the evidence. Expect questions on hypotheses, variables, controls, sampling, measurement, data presentation and evaluation of reliability and validity.
Core rules
- State a testable hypothesis and identify the independent variable, dependent variable and at least two controlled variables.
- Include a control treatment where it answers the question, and use replication and randomisation to reduce bias.
- Measure with appropriate instruments and units; distinguish accuracy (closeness to true value) from precision (repeatability).
- Record raw data, calculate means and ranges, and choose a graph that matches the data type.
- Evaluate sources of error, including sampling error, measurement error and confounding factors.
Worked example
A student compares 0, 50 and 100 kg N/ha on grass yield. Nitrogen rate is the independent variable; dry-matter yield is the dependent variable. Controlled variables include grass variety, soil type, plot size, cutting height and cutting date. Each rate is replicated in randomised plots, with the 0 kg rate acting as the control. Yield is measured as kg dry matter per plot and converted to t/ha. Means are plotted with range bars. The conclusion is cautious: under these conditions, increasing N increased yield, but the result may not apply to another soil or season.
Traps
Do not call a controlled variable a control treatment. Do not treat repeated measurements on one plot as true replication. Avoid changing several variables at once, mixing units, or claiming proof from one trial.