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Topic 2 of 7 · Form 5

Crop physiology and production

Land preparation (conventional tillage versus conservation agriculture), seed selection (certified hybrids, open-pollinated varieties), plant population and spacing, planting date, fertilisation, weed control, irrigation and harvesting.

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  1. PDFCrop physiology and production – Agriculture notes (ZIMSEC A Level)47.8 KB

Crop physiology

  • Photosynthesis: C3 crops (wheat, soya beans, groundnuts) and C4 crops (maize, sorghum, sugar cane) – C4 crops are more efficient at high temperature and light intensity.
  • Transpiration and water use efficiency; stomatal control.
  • Growth stages of maize: emergence, vegetative (V stages), tasselling, silking, grain filling, physiological maturity (black layer). Moisture stress at tasselling and silking reduces yield most.
  • Plant hormones: auxins, gibberellins, cytokinins, ethylene and abscisic acid.

Crop production practices

Land preparation (conventional tillage versus conservation agriculture), seed selection (certified hybrids, open-pollinated varieties), plant population and spacing, planting date, fertilisation, weed control, irrigation and harvesting.

Worked example: Maize is planted at 90 cm between rows and 30 cm in the row, one seed per station. Find the plant population per hectare.

Area per plant = 0.9 × 0.3 = 0.27 m²; 10 000 ÷ 0.27 = 37 037 plants/ha

Crop improvement

Selection, hybridisation (hybrid vigour/heterosis), mutation breeding, tissue culture and genetic modification. Breeding goals: yield, drought tolerance, disease resistance and quality.

Cropping systems

Monocropping, intercropping (maize and legumes), crop rotation, relay cropping and agroforestry.

Post-harvest handling

Drying to safe moisture (about 12.5% for maize grain), grading, storage hygiene, hermetic bags and grain protectants to control weevils and the larger grain borer.

Exam tip: Link each management practice to the crop's physiological stage – e.g. top dressing before rapid vegetative growth.

Check yourself

  1. Why are C4 crops suited to hot climates?
  2. At which growth stage is maize most sensitive to drought?
  3. What is heterosis?
Show answers
  1. They concentrate CO₂ around rubisco, reducing photorespiration and using water efficiently.
  2. Tasselling and silking (flowering).
  3. Hybrid vigour – greater performance of hybrids compared with their parents.
Next topicCrop protection and integrated pest management

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