Plant Science and Crop Production
The Plant Science and Crop Production domain tests whether you can link crop physiology to agronomic decisions: how photosynthesis, partitioning and phenology translate into yield components you can actually count in a field.
Core rules
- C4 crops (maize, sugarcane, sorghum) have a lower CO₂ compensation point, a higher temperature optimum (about 30–35 °C) and better water-use efficiency than C3 crops (rice, wheat, potato).
- Yield is built from components that compensate: panicles or pods per unit area × grains per panicle × filled-grain % × grain weight. Raising plant density pushes the first component up but depresses the others.
- Harvest index = economic yield ÷ biological yield; it separates total dry matter production from the share that is harvested.
- Critical periods: water deficit at flowering and grain filling in rice, and at tasselling/silking in maize, causes the largest yield loss per unit of stress.
Worked example
Estimate paddy yield from components. Established hills 250 per m², 1.2 panicles per hill, 100 filled grains per panicle, grain weight 25 mg. Yield = 250 × 1.2 × 100 × 0.025 g = 750 g/m². Multiply by 10 000 m²/ha and divide by 1000 → 7.5 t/ha. Check: only filled grains should be counted; if 20 % are unfilled, the estimate drops to 6.0 t/ha.
Traps that cost marks
Confusing biological with economic yield; assuming maximum plant density maximises yield; quoting one optimum temperature for all crops; ignoring compensatory tillering when a density recommendation is questioned.