Class 8 Science
Seeds are sown in the field after ploughing. A farmer needs to separate damaged seeds from good seeds. The seeds should be sown at proper gaps and at proper depth. Proper gap between seeds and proper depth in soil ensures adequate sunlight, moisture, air and nutrients to the growing plants. Seeds can be shown by any of the following methods:
Broadcasting: This is a traditional method of sowing seeds. In this method, seeds are sprayed on the field manually, i.e. by hand. Broadcasting is only effective on plots of small size.
Traditional Seed Drill: A seed drill is composed of a funnel which has a long and pointed neck. The seed drill is attached to the plough-shaft. When seeds are kept in the funnel they drop gradually through the neck; when the field is being ploughed. The pointed end of the neck of seed drill pierces the soil and thus seeds go deep into the soil. Seed drill helps in saving time when the farmer needs to sow a farm of large size.
Modern Seed Drill: The design of modern seed drill has evolved from the traditional seed drill. It contains many hollow and pointed tubes which are fitted on a huge frame of iron. All the tubes are connected to a huge container at top. Seeds are kept in the container so that seeds can drop through the hollow tubes. Tractor-driven seed drills helps in sowing seeds on large farms in less time.
Adding Manure and Fertilisers
We know that plants take nutrients from soil and thus exhaust the soil of most of the nutrients with passage of time. Manures and fertilizers need to be added to soil to replenish plant nutrients.
Manure is prepared by decomposition of plant and animal waste. Farm waste is dumped in the field and is left to decompose. Sometimes, the farm waste may be covered with a layer of soil to hasten the process of decomposition. Sometimes, help of earthworm is also taken to hasten the process. Farmers also make compost pits to prepare manure.
Advantages of Manure:
- Manure increases nutrients in soil.
- It improves soil texture.
- It improves water retaining capacity of soil.
- It is free of any toxic material and thus is environment friendly.
Fertilizers are chemicals which contain a specific plant nutrient. Fertilizers are made in factories and a pack of fertilizer may contain any one nutrient or a mixture of more than one nutrient. Urea, ammonium sulphate, super phosphate, potash and NPK (Nitrogen, Phosphorus and Potassium) are examples of fertilizers.
Advantages of Fertilisers:
- Fertilizers give faster results compared to manure.
- Use of fertilizers helps farmers in significantly improving farm yield.
Disadvantages of Fertilisers:
- Excessive use of fertilizers can make the soil unfertile.
- Harmful chemicals in fertilizers pollute the soil and groundwater.
Some other methods of replenishing soil nutrients:
Fallow Field: When the field is left uncultivated for a season, it is called fallow land. Leaving the field fallow allows the soil to recuperate nutrients through natural processes.
Crop Rotation: This is time tested method and has been used by farmers since a long time. This involves growing a legume crop between two successive cereal crops. Rhizobium bacteria live in the root nodules of legume plants. These bacteria help in nitrogen fixation in soil. Thus, legume plant facilitates replenishment of nutrients in soil.