Crop Production and Management — Class 8 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 8 Science, Biology — Chapter 21. How food is grown — from ploughing to storage.
1. About this chapter
This chapter covers types of crops (kharif and rabi), the steps of crop production, manure vs fertilizer, irrigation methods, and crop rotation.
2. Types of crops
- Kharif crops are sown in the rainy/monsoon season (June–October), e.g. paddy (rice), maize, cotton.
- Rabi crops are sown in winter (October–March), e.g. wheat, gram, mustard.
3. Steps of crop production
- Ploughing / tillage — loosening and turning the soil so air and nutrients reach the root zone (done with a plough or cultivator).
- Sowing — placing seeds in the soil, by hand or with a seed drill.
- Adding manure and fertilizers (manuring) — to replace soil nutrients.
- Irrigation — supplying water to the crop.
- Weeding — removing unwanted plants (weeds) that compete with the crop.
- Harvesting — cutting the mature crop.
- Threshing — separating grain from the chaff.
- Storage — keeping grain safe from moisture and pests.
4. Manure vs fertilizer
| Manure | Fertilizer |
|---|---|
| Natural (from cow dung, plant waste) | Man-made chemical |
| Adds humus, improves soil texture | Rich in specific nutrients (N, P, K) |
| Slow-acting | Fast-acting |
5. Irrigation and crop rotation
- Methods of irrigation: surface (flow) irrigation, sprinkler and drip irrigation (drip saves the most water).
- Crop rotation is growing different crops in the same field in turn (e.g. a legume after a cereal) to keep the soil fertile — legumes restore nitrogen.
6. Worked examples
Example 1. Name two kharif crops. Paddy and maize (also cotton).
Example 2. What is threshing? Separating the grain from the chaff after harvesting.
Example 3. Why is crop rotation done? To maintain soil fertility (a legume restores nitrogen).
7. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- Paddy is a — (a) kharif / (b) rabi crop. Ans: (a) kharif.
- Loosening and turning the soil is called — (a) sowing / (b) ploughing (tillage). Ans: (b) ploughing.
- Separating grain from the chaff is — (a) harvesting / (b) threshing. Ans: (b) threshing.
- The irrigation method that saves the most water is — (a) drip / (b) flow irrigation. Ans: (a) drip.
- Growing different crops in turn in the same field is — (a) crop rotation / (b) weeding. Ans: (a) crop rotation.
II. Fill in the blanks 6. Seeds are sown in rows using a seed drill. 7. Unwanted plants in a field are called weeds. 8. A natural nutrient added to soil from cow dung is called manure.
III. Answer briefly 9. Differentiate manure and fertilizer. 10. Name the steps of crop production in order.
8. Common mistakes
- Mistake: Saying wheat is a kharif crop. Fix: Wheat is a rabi (winter) crop; paddy is kharif.
- Mistake: Treating manure and fertilizer as the same. Fix: Manure is natural and adds humus; fertilizer is a man-made chemical rich in nutrients.
- Mistake: Confusing harvesting and threshing. Fix: Harvesting = cutting the crop; threshing = separating grain from chaff.
9. Quick revision
- Biology Ch 21 · crops and farming.
- Kharif (rainy: paddy, maize) vs rabi (winter: wheat, gram).
- Steps: ploughing → sowing → manuring → irrigation → weeding → harvesting → threshing → storage.
- Manure = natural (humus); fertilizer = chemical (N, P, K).
- Irrigation: surface, sprinkler, drip (drip saves most water).
- Crop rotation keeps soil fertile (legumes restore nitrogen).
