CBSE Class 10 Biology Food Production Notes Set 05

From Hunting to Farming

Early humans lived by hunting and gathering. About 10,000 years ago they began to grow crops in river valleys, settled in one place and built the first cities. Present-day cereals were once weeds that were improved by selection. The discovery of hybridisation and plant breeding greatly raised the food output. Norman Borlaug's work with high-yielding wheat started the Green Revolution and earned him the Nobel Prize in 1970.

Plant Breeding

Plant breeding is the science of improving the heredity of crop plants. The aims are higher yield, better quality, resistance to diseases and pests, a change in the time of ripening and in growth habit, and the ability to grow in different conditions.
1. Introduction and acclimatisation: a plant from one region is brought to another and made to adapt (sunflower, chilli and tobacco are examples).
2. Selection: choosing the best plants. Mass selection picks plants by their looks; pure-line selection separates genetically pure lines (many wheat, cotton and jowar varieties); clonal selection uses plants grown from one parent by vegetative propagation, so every plant is identical (potato).
3. Hybridisation: crossing two genetically different plants and selecting the best offspring. The cross may be within a variety, between varieties, between species or between genera.
4. Polyploidy: plants with more than two sets of chromosomes. Colchicine induces it. Plants with an odd number of sets (3n, 5n) are sterile and give seedless fruit.
5. Tissue culture: cells or tissue grown in a sterile nutrient medium. They form a callus. The right balance of auxin and cytokinin makes the callus form roots and shoots. It gives disease-free plants quickly.
6. Induced mutation and genetic engineering are modern methods.

Kinds of Crop Plants

Maize is called pampered corn because it depends wholly on humans for propagation. High-yielding varieties include IR 8 and Jaya (paddy), Kalyan Sona (wheat) and Ganga 101 (maize).

Steps in Crop Production

1. Soil preparation: the soil should be firm enough to hold roots, aerated, rich in nutrients and able to hold water. It is ploughed, levelled and tested; manure or fertiliser is added if needed.
2. Sowing: by hand (broadcasting) or with a seed drill, which places seeds at the right depth and gap. Seeds are treated with fungicides. Paddy is sown thickly in a nursery and the seedlings are transplanted into water-logged fields.
3. Irrigation: water from wells, tanks, rivers, canals or rain at the right time. Drip irrigation saves water.
4. Manure and fertilisers: farm manure and bio-fertilisers such as the blue-green algae Anabaena and Nostoc improve the soil. Chemical fertilisers are easy to use, but when washed into lakes their nitrates and phosphates cause eutrophication and algal bloom that kills other life.
5. Weeding: weeds rob crops of food and water. They are removed by hand, by weedicides such as 2,4-D, or by biological control.
6. Crop protection: insecticides and fungicides must be used little, because they enter the food chain and become more concentrated at each level (biomagnification). DDT kills useful insects as well as pests. Biological control is safer.
7. Harvesting: with a sickle or a harvesting machine, followed by threshing and winnowing.
8. Storage: dry grain in rodent-proof and insect-proof bins; fumigate with gas such as methyl bromide; neem leaves keep pests away.

Crop Rotation

Growing the same crop again and again drains the soil of nutrients. After a cereal crop, a pulse crop is grown. Rhizobium bacteria in the root nodules of pulses fix atmospheric nitrogen, and ploughing back the roots enriches the soil. A third crop can then be grown. Rotation also keeps pests under control.

Food Production in India

The area under cultivation has crossed 185 million hectares and the yield per hectare has risen because of new irrigation, better varieties and fertilisers. From a food importer in the 1950s India became nearly self-sufficient in food grains, but the growing population needs a continuing rise in output.