Final answer:
Lime should be added to soil when it is too acidic for optimal plant growth. It generally takes several months for lime to fully adjust the soil's pH. This process involves neutralizing soil acidity through the addition of calcium from lime and monitoring with a pH meter.
Step-by-step explanation:
Lime should be added to the soil when the soil pH tests too acidic for the desired plant growth. To adjust the pH, materials such as slaked lime (calcium hydroxide) or limestone (calcium carbonate) are worked into the soil. Adjusting soil pH is a slow process and can take several months to fully change the pH level.
In terms of the mechanism, adding lime to the soil provides calcium which can neutralize the excess acidity, resulting in a higher, more alkaline pH. The effective rate of pH adjustment depends on several factors such as the starting pH of the soil, the texture and composition of the soil, and the amount and type of lime used.
Fertilizers can play a role in soil pH management too. By neutralizing acids such as sulfuric acid or nitric acid with ammonia gas, fertilizers contain salts that can be utilized in the soil. In addition, essential elements like calcium and magnesium found in lime can increase soil pH, whereas sulfur can decrease it.
Monitoring changes in soil pH requires accurate measurement, typically done with a pH meter that must be calibrated with standard buffers. Over time, this maintenance of pH helps ensure the proper growth environment for plants.