Option 1: Lime is not primarily used to maintain the water content in the soil. It is used for other purposes related to soil fertility and pH level.

Option 2: The correct answer. Lime is used to decrease the acidity of the soil. It neutralizes the acidity by releasing calcium and raising the pH level. This is important because acidic soil can hinder plant growth and nutrient absorption. By reducing soil acidity, lime creates a more favorable environment for plants to thrive.

Option 3: This option is incorrect. Lime does not decrease the basicity of soil, as it is not used to neutralize alkaline soils. Lime is specifically used to combat acidity.

Option 4: Lime concentration in the soil does not need to be high for plant growth. The appropriate amount of lime required depends on the pH level of the soil. It is important to apply lime in the correct quantity as too much lime can negatively affect plant growth.

In conclusion, farmers mix lime with soil primarily to decrease the acidity of the soil, creating a more suitable environment for plant growth.