**Field Capacity**

The moisture content of the soil, after free drainage has removed most of the gravity water, is known as field capacity. It represents the amount of water retained in the soil after excess water has drained away due to gravity.

**Explanation:**

1. **Soil Moisture**:
- Soil moisture refers to the water content present in the soil.
- It is essential for plant growth and plays a crucial role in various soil processes.
- The moisture content in the soil is influenced by factors such as precipitation, evaporation, transpiration, and drainage.

2. **Gravity Water**:
- Gravity water is the water that is held in the soil due to the force of gravity.
- When the soil is saturated, excess water drains away due to gravity.
- This drainage process continues until the amount of water retained in the soil reaches the field capacity.

3. **Field Capacity**:
- Field capacity is defined as the moisture content of the soil after free drainage has removed most of the gravity water.
- It represents the amount of water held by the soil against the force of gravity.
- At field capacity, the soil is considered to be well-drained, and excess water has drained away.

4. **Measurement of Field Capacity**:
- Field capacity is determined by conducting a field or laboratory experiment.
- In the field, it can be measured by collecting soil samples from the desired depth and determining the moisture content using various methods such as the gravimetric method or the use of soil moisture sensors.
- In the laboratory, soil samples are collected and subjected to controlled conditions to allow for drainage and measurement of the moisture content at field capacity.

5. **Importance**:
- Field capacity is an important parameter in agriculture and civil engineering.
- In agriculture, it helps determine the amount of water available to plants and aids in irrigation scheduling.
- In civil engineering, it is used in the design of drainage systems and the calculation of soil water balance.

In conclusion, the moisture content of the soil after free drainage has removed most of the gravity water is known as field capacity. It represents the amount of water held by the soil against gravity and is an important parameter in agriculture and civil engineering.