Ncert Books Class 9 Science Chapter 15 Free Download

This is a very important question. Here's how to structure the answer:
Fertilisers are commercially produced, inorganic compounds that supply specific nutrients like Nitrogen, Phosphorus, and Potassium (NPK). They are nutrient-specific and fast-acting but can degrade soil structure over time.
Manures are organic substances obtained from the decomposition of animal and plant waste. They are less nutrient-rich but improve soil in several ways:

• They add humus to the soil, improving its texture and water-holding capacity.
• They provide a wide range of nutrients in small quantities.
• They promote the growth of beneficial soil microbes.

Hybridisation is the process of cross-breeding between two genetically dissimilar plants to obtain a new variety (hybrid) that has the desired characteristics of both parents. For instance, a high-yielding but disease-prone variety can be crossed with a low-yielding but disease-resistant variety.

It is a crucial technique because it allows us to combine multiple desirable traits into a single variety. These traits can include:

• Higher yield
• Improved quality (e.g., protein content in pulses)
• Resistance to biotic stresses (diseases, insects) and abiotic stresses (drought, salinity)
• Shorter maturation duration
• Wider adaptability to different environmental conditions

Both are methods of growing two or more crops simultaneously on the same piece of land, but they differ slightly. These patterns are important from an exam perspective.

• Mixed Cropping: In this, two or more crops are grown together, but seeds are mixed before sowing. Example: Wheat + Gram. The main aim is to minimise the risk of total crop failure due to unfavourable weather. If one crop fails, the other might survive.
• Inter-cropping: This involves growing two or more crops in a definite row pattern. Example: Soybean + Maize. This method ensures that the nutrient demands of different crops are met, as they don't compete for the same nutrients. It also helps in controlling pests and diseases from spreading throughout the field.

The primary objective of improving food resources is to ensure the availability and accessibility of nutritious food for a growing population. It is not just about increasing the quantity of food but also enhancing its quality and ensuring its production is sustainable.

This chapter is critical because it addresses real-world challenges like food security and environmental sustainability. For a country like India, with its vast population and dependence on agriculture, understanding scientific methods to improve crop yield, manage livestock, and protect our natural resources is of national importance.

Biotic and abiotic factors are major sources of stress that can significantly reduce crop yields. It's a common topic for short-answer questions.

• Biotic Factors: These are the living components of an ecosystem that harm crops. They include weeds (which compete for nutrients, e.g., Xanthium), pests (insects that damage parts of the plant, e.g., locusts), and pathogens (disease-causing organisms like bacteria, fungi, and viruses).
• Abiotic Factors: These are non-living environmental factors. Examples include drought (lack of water), salinity (excess salt in soil), water-logging (excess water), extreme temperatures (heat or cold), and frost.

Animal husbandry is the branch of agriculture concerned with the scientific management of livestock. This includes feeding, breeding, and disease control for farm animals.

For dairy animals like cows and buffaloes, the key management practices for high milk yield include:

• Shelter: Clean, well-ventilated sheds to protect animals from harsh weather and provide a comfortable resting place.
• Feeding: A balanced diet consisting of roughage (fibre-rich fodder) and concentrates (protein and nutrient-rich grains). Proper quantities of clean water are also essential.
• Health Care: Regular vaccination against common diseases, and timely identification and treatment of sick animals to prevent the spread of infections.
• Breeding: Selective breeding, often through artificial insemination, to produce offspring with higher milk production and better disease resistance.

This is a classic comparison question that tests detailed understanding of poultry farming.

• Purpose: Broilers are raised specifically for meat production and have a short life cycle of 6-8 weeks. Layers are raised for egg production and are managed for a longer period.
• Dietary Needs: Broilers require a diet rich in protein and fat for rapid growth and muscle development. Their feed is designed to achieve maximum body weight quickly. Layers, on the other hand, require a diet rich in vitamins, minerals (especially calcium for eggshells), and a balanced amount of energy to sustain egg production over a long period.

Weeds are unwanted plants in a cultivated field. Eradicating them is difficult because they are highly competitive and resilient. They multiply and spread rapidly through seeds or vegetative parts and can survive in adverse conditions.

Weeds are harmful primarily because of competition. They compete with the main crop for essential resources such as:

• Nutrients from the soil.
• Sunlight for photosynthesis.
• Water for growth.