Practical Work and Field Application
Practical work and field application tests measurement, calculation, and correct field procedure. Questions ask you to interpret a seed test, calculate a seed rate or yield, take a soil sample, or prepare a spray safely.
Core rules
- Seed testing: purity % = pure seed weight ÷ sample weight × 100; germination % = normal seedlings ÷ seeds tested × 100. Pure live seed (PLS) = purity × germination ÷ 100. Only normal seedlings count; abnormal, dead, and hard seeds are excluded.
- Soil sampling: take a composite sample from several spots at plough depth (0–15 cm for cultivated fields), mix, quarter, and send a representative sample. Avoid bunds, manure heaps, and wet spots.
- Yield estimation: cut a quadrat of known area, thresh and weigh grain, then convert to kg/ha. 1 m² sample weight in g × 10 = kg/ha.
- Spray preparation: calculate active ingredient required, then formulation; calibrate sprayer; measure volume; wear PPE; observe PHI.
- Field layout: randomisation and replication reduce bias; border rows and guard rows protect trials. Record dates, doses, and observations.
- Instruments: pH meter, EC meter, moisture meter, seed germinator, quadrat, measuring tape, weighing balance.
Worked example
A seed lot has 95% purity and 80% germination. PLS = 95 × 80 ÷ 100 = 76%. If the recommendation is 100 kg pure live seed/ha, bulk seed needed = 100 ÷ 0.76 = 131.6 kg/ha. Reasoning: PLS adjusts for inert matter and dead seeds; dividing by 0.76 gives more bulk seed, not less.
Traps
Counting abnormal seedlings as germinated; adding purity and germination instead of multiplying; sampling only one spot; converting g/m² to kg/ha incorrectly (multiply by 10, not 100); using formulation instead of a.i. in spray calculations; ignoring border effects in field trials.