CBSE Class 9 Science Chapter 15: Improvement in Food Resources NCERT Solutions

From various food sources, we obtain essential nutrients vital for our health and energy:

1. Cereals: These are a primary source of carbohydrates, which provide the body with energy needed for daily activities.
2. Pulses: Pulses are an excellent source of proteins, crucial for growth, repair, and building body tissues.
3. Fruits and Vegetables: These are rich in vitamins and minerals, which are essential for various bodily functions, immunity, and overall well-being. They may also contain small amounts of proteins, carbohydrates, and fats.

Both living organisms (biotic factors) and non-living environmental conditions (abiotic factors) significantly influence crop production:

Biotic Factors: These include pests, nematodes, and diseases that can damage crops, leading to reduced yield. For instance, pests like the boll weevil feed on cotton crops, diminishing their output. Weeds also compete with the main crop for essential resources like nutrients, sunlight, and space, thereby lowering productivity.

Abiotic Factors: These encompass environmental conditions such as soil salinity and temperature. Natural calamities like droughts and floods, which are unpredictable, can also devastate entire crops, severely impacting agricultural output.

Desirable agronomic characteristics are specific traits that breeders aim to develop in crops to enhance productivity and suitability. For crop improvement, these include:

1. Tallness and profuse branching: This is particularly desirable in fodder crops to increase the yield of green fodder.
2. Dwarfness: In cereals like wheat and rice, dwarf varieties are preferred as they allow for higher plant density and reduce lodging (falling over), leading to increased grain production.

These characteristics help in maximizing the output from the available resources.

Macro-nutrients are essential mineral elements that plants require in relatively large amounts for their healthy growth and development. They are called macro-nutrients simply because the quantity needed by the plants is substantial compared to other essential elements.

There are six macro-nutrients that plants primarily obtain from the soil and other environmental sources: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulphur (S).

Plants obtain the sixteen essential nutrients required for their growth and development from three primary sources: air, water, and soil. While carbon, oxygen, and hydrogen are obtained from air and water, the majority of other essential nutrients are absorbed from the soil through their roots. Soil serves as the main reservoir for these vital mineral nutrients.

Both manure and fertilizers are used to replenish nutrients in the soil, but they differ significantly in their composition and effect on soil fertility:

Manure:

Manure is prepared from the decomposition of organic materials like animal excreta and plant waste.

It enriches the soil with organic matter, which improves soil structure, water-holding capacity, and aeration.

It also adds essential nutrients to the soil, promoting long-term fertility and supporting beneficial soil micro-organisms.

Fertilizers:

Fertilizers are typically inorganic compounds, either natural or synthetic, that are rich in specific plant nutrients like nitrogen, phosphorus, and potassium.

While they provide nutrients quickly and can boost crop yield in the short term, their excessive use can be detrimental.

Overuse of fertilizers can harm the beneficial symbiotic micro-organisms in the soil, disrupt the soil's natural nutrient balance, and potentially lead to a decrease in soil fertility over extended periods.

In summary, manure is generally preferred for sustainable soil health and long-term fertility, whereas fertilizers offer a quick nutrient boost but require careful management to avoid negative environmental impacts.