Practical Skills and Laboratory/Field Work: Sampling, Testing and Calibration
Field and laboratory routines
Soil sampling: move in a zigzag over the plot, take 10–15 cores at 0–15 cm for cultivated land, mix thoroughly, quarter down to about 500 g, air-dry in shade and label with date, depth and plot. Seed testing: purity analysis first, then germination - 100 seeds on moist filter paper, count normal seedlings at seven days; moisture by oven method. Record book: date, plot, treatment, observation, and signature, written at the time and not afterwards.
Worked example - sprayer calibration
One nozzle delivers 1.2 litres per minute; walking speed 1 m/s; effective swath 0.5 m. Area per minute = 1 m/s × 60 s × 0.5 m = 30 m². Output = 1.2 L ÷ 30 m² = 0.04 L/m² = 400 L/ha. If the label specifies 250 L/ha, the sprayer is over-applying by 60 per cent - increase walking speed or reduce pressure, then recalibrate. The reasoning step is what matters: calibration converts nozzle output into a field rate.
A companion check: if 100 seeds are sown and 82 normal seedlings, 3 hard seeds and 15 dead seeds are counted, germination is 82 per cent.
Traps that cost marks
- Collecting soil from the surface only, or from a single spot.
- Reading the meniscus incorrectly in a measuring cylinder.
- Calibrating with water but spraying a denser formulation.
- Recording observations from memory instead of in the field.
- Quoting a germination figure without stating the number of seeds tested.