NCERT Solutions For Class 8 Science Chapter 1
Crop Production and Management

Continuous plantation of crops in a field causes depletion of certain nutrients like phosphorus, nitrogen and potassium etc. Plants are depended on these nutrients for their proper growth and functioning. Depletion of these nutrients from the soil would directly affect the yield of the crops sown in the depleted soil.

If wheat is sown in the kharif season (from June to October), it has to face adverse climatic conditions and the entire wheat crop might get destroyed. Wheat is a rabi crop. Therefore, it requires low temperature, less humidity, less water and moderate sunshine. But if it is sown in kharif season, it would receive lot of water, excess temperature, and humidity. These climatic conditions would not favour the growth of the crop.

(a) Two examples of Kharif crop are paddy and maize.
(b) Two examples of Rabi crop are wheat and gram.

(a) Crop
(b) preparation
(c) float
(d) water, nutrients

The undesirable plants that grow naturally along with the main crop are called weeds. These weeds compete with the main crop plant for water, nutrients, sunshine and space. Weeds can be controlled by weeding. Weeding is the removal of weeds from the field.

Weeding can be done by:

Tilling: In this method, the weeds are either manually uprooted or cut from soil. The uprooted and cut weeds are then left in the field so that they would decay and act as the manure.

Using Weedicides: In this method, certain chemicals called weedicides such as 2, 4-D are sprayed over the fields to kill the weeds. Weedicides are used during the vegetative growth of weeds.

Irrigation is a process by which water is supplied to crops. The time and frequency of irrigation depends on the seasons, crops and soil types.

Two methods of irrigation that help in conservation of water are:

• Sprinkler system: In this system, perpendicular pipes with rotating nozzles on top are joined to the main pipe at regular intervals. With the help of a pump, water is allowed to flow through main pipe under high pressure. From the main pipes, the water escapes outside through the rotating nozzles. This system works efficiently in sandy soil where sufficient water is not available.
• Drip irrigation: In this system, water is dropped at the root of the plants, drop by drop. Water is not wasted in this type of irrigation and this method is used for watering fruit plants and gardens.

(a) Preparation of soil: Before growing a crop, a farmer first prepares the soil of the field. During preparation, he turns the soil with the help of a plough or a cultivator and loosens it. Loosening of soil allows the new germinating roots of the plants to penetrate deep into the soil. The loose soil also facilitates easy breathing to the roots even when they go deep into the soil. The loosened soil helps in the growth of earthworms and microbes present in the soil which further turn and loosen the soil and add humus to it. Turning and loosening of soil brings the nutrient-rich soil to the top so that plants can use these nutrients.

(b) Sowing: After soil preparation, the farmer’s next job is to sow the seeds. First, good quality and high yielding seeds are selected. Seeds are sown with the help of a tool called seed drill. This tool facilitates the sowing of seeds uniformly at proper distances and depths and saves time and labour. It ensures that seeds get covered by the soil after sowing. This prevents damage caused by birds.

(c) Weeding: The undesirable plants that grow naturally along with the main crop planted are called weeds. These weeds compete with the main crop plant for water, nutrients, sunshine and space. Weeds can be controlled by weeding. Weeding is the removal of weeds from the field. Weeding can be done by tilling and by using weedicides. Some weeds interfere even in harvesting and may be poisonous for animals and human beings.

(d) Threshing: After harvesting a crop, its grain seeds need to be separated from the chaff. This process of separation of grain seeds from chaff is called threshing. This is done with the help of a machine called combine which is in fact a combined harvester and a thresher.