The correct option is (a).
Explanation
Organic manure is a natural substance obtained through the decomposition of plant residues and animal waste. It plays a critical role in sustainable agriculture by modifying the physical and biological properties of the soil to support plant growth.
Statement-wise Analysis:
- Statement 1 is Correct: Organic manure adds humus to the soil, which improves soil structure. This addition significantly enhances the water-holding capacity of the soil, allowing it to retain moisture effectively for crop use.
- Statement 2 is Incorrect: Organic manure does not make the soil compact; rather, it makes the soil porous. This porosity is essential as it facilitates the easy exchange of gases (aeration), ensuring that plant roots receive adequate oxygen.
- Statement 3 is Incorrect: Organic matter serves as a nutrient source for soil organisms. Therefore, the application of manure increases the number of friendly microbes (such as decomposers and nitrogen-fixing bacteria), which improves soil fertility and texture.
Key Takeaway: Organic manure improves soil texture, increases water retention and aeration (porosity), and boosts the population of beneficial soil microbes, unlike chemical fertilizers which may degrade soil biology over time.