The question asks about the primary nutrients enriched in soil by green manure. Green manures are crops grown specifically to be incorporated into the soil while still green, improving soil fertility. Understanding the main functions of common green manure crops will help identify the key nutrients.
Correct Option: B) Nitrogen and Phosphorus. Green manure crops, especially legumes, are highly effective in fixing atmospheric nitrogen into the soil. When these crops are incorporated into the soil, their decomposition also releases phosphorus and other nutrients, but nitrogen and phosphorus are considered the two main nutrients significantly enriched.
The question asks to identify the most commonly mentioned green manure crops in NCERT textbooks. Green manure crops are specifically grown to be ploughed back into the soil to improve its fertility and structure. This requires knowledge of common agricultural practices and crops highlighted in NCERT for this purpose.
B) Sun hemp (\(Crotalaria \ juncea\)) and Guar (cluster beans) are widely recognized and mentioned in NCERT textbooks as effective green manure crops. They are legumes that enrich the soil with nitrogen and organic matter.
The question asks for the definition of biofertilizers as per NCERT Class 9. We need to identify the option that accurately describes biofertilizers as living organisms that enhance nutrient availability for plants.
D) Biofertilizers are living organisms (bacteria, fungi, cyanobacteria/blue-green algae) that help plants absorb nutrients from the soil by fixing atmospheric nitrogen or making phosphorus available. This is the correct definition of biofertilizers. Examples include Rhizobium (nitrogen fixation in legumes), Azotobacter (free-living nitrogen fixer), Mycorrhiza (fungi that help in phosphorus uptake), and blue-green algae (cyanobacteria) which fix nitrogen in paddy fields.
The question asks about the specific application of blue-green algae (Cyanobacteria) as biofertilisers. This requires knowledge of the ecological roles of Cyanobacteria, particularly their nitrogen-fixing capabilities, and the environmental conditions of different crop cultivations.
B) Paddy (rice) fields — they fix atmospheric nitrogen and improve soil fertility. This option correctly identifies the crop and the mechanism by which blue-green algae act as biofertilisers. The waterlogged conditions of paddy fields are ideal for the growth and nitrogen-fixing activity of Cyanobacteria, which enrich the soil with usable nitrogen compounds.
The question asks to identify the advantages of manure over chemical fertilisers. We need to evaluate each option based on the known properties and effects of manure and chemical fertilisers on soil and crops.
Manure offers several advantages over chemical fertilisers:
Therefore, option B accurately lists multiple significant advantages of manure.
The question asks to identify the disadvantages or limitations of manure when compared to chemical fertilisers. We need to evaluate each option based on the known characteristics of manure and chemical fertilisers in agricultural practices.
Correct Option: A) Manure is bulky and difficult to transport, less concentrated in specific nutrients, slow-acting (takes time for nutrients to become available), requires large quantities per hectare. These points accurately describe the disadvantages and limitations of manure compared to chemical fertilisers.