ANS:B - 7-8

Maintaining soil pH within the range of 7 to 8 is beneficial for optimum growth and health of most plants. Here's an explanation of why this pH range is preferred:

1. Nutrient Availability: The pH of soil influences the availability of essential nutrients to plants. In slightly acidic to neutral soils (pH 6 to 7), nutrients such as phosphorus, potassium, calcium, and magnesium are generally more readily available for plant uptake. At pH levels above 7, these nutrients may become less soluble and less available to plants, leading to potential nutrient deficiencies. Therefore, maintaining soil pH within the slightly acidic to neutral range (pH 6 to 7) ensures optimal nutrient availability for plant growth.
2. Microbial Activity: Soil pH also affects the activity of soil microorganisms, including beneficial bacteria and fungi that play crucial roles in nutrient cycling, decomposition of organic matter, and plant health. Many soil microorganisms thrive in slightly acidic to neutral conditions (pH 6 to 7), and maintaining soil pH within this range promotes a healthy and diverse soil microbial community.
3. Ion Exchange Capacity: Soil pH influences the ion exchange capacity of soil particles, which affects the retention and release of nutrients. In soils with pH levels between 7 and 8, the ion exchange capacity is generally optimal, allowing for efficient nutrient retention and exchange between soil particles and plant roots.
4. Aluminum Toxicity: In soils with pH levels below 5.5, aluminum toxicity can become a problem for plants, particularly sensitive crops like legumes. Maintaining soil pH within the range of 7 to 8 helps to mitigate the risk of aluminum toxicity and other adverse effects associated with highly acidic soils.

Overall, maintaining soil pH within the range of 7 to 8 provides an optimal environment for plant growth by ensuring adequate nutrient availability, promoting beneficial microbial activity, optimizing ion exchange capacity, and reducing the risk of aluminum toxicity. However, it's important to note that the preferred pH range may vary depending on the specific requirements of different plant species and soil types.