All a,b,c statements are correct and d is the answer none of these because in the statement of a,b,c all the right points has been mentioned that is found in organic manure.

Organic manure is a natural fertilizer that is obtained from various organic sources such as animal waste, crop residues, kitchen waste, etc. It is rich in essential plant nutrients and helps in improving soil health and fertility. However, the statement that is not true for organic manure is that "it has a balance of all plant nutrients". Let's understand this in detail.

Benefits of Organic Manure:

1. Enhances water holding capacity of soil:
Organic manure helps in improving the water holding capacity of the soil. It increases the porosity and permeability of the soil, which allows it to retain water for a longer period of time. This helps in reducing the frequency of irrigation and also prevents soil erosion.

2. Provides humus to the soil:
Organic manure is a rich source of humus, which is the decomposed organic matter in the soil. Humus helps in improving the soil structure, increases its fertility, and promotes the growth of beneficial microorganisms in the soil.

3. Improves texture of the soil:
Organic manure helps in improving the texture of the soil. It increases the soil's ability to hold nutrients and water, which promotes healthy plant growth. It also helps in reducing soil compaction, which allows roots to penetrate more easily.

Why Organic Manure Does Not Have a Balance of All Plant Nutrients?

Organic manure is a natural fertilizer that contains a wide range of plant nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, etc. However, the nutrient content of organic manure varies depending on the source of the manure and the method of preparation. Unlike chemical fertilizers, organic manure does not contain a balanced ratio of all plant nutrients.

For example, cow dung manure is rich in nitrogen but may be deficient in phosphorus and potassium. Similarly, poultry manure is rich in phosphorus and potassium but may be deficient in nitrogen. Therefore, it is important to use a combination of different types of organic manure to provide a balanced supply of plant nutrients to the soil.

Conclusion:
Organic manure is an important source of plant nutrients that helps in improving soil health and fertility. However, it does not have a balanced ratio of all plant nutrients and therefore, a combination of different types of organic manure should be used to provide a balanced supply of plant nutrients to the soil.