Soil water holding capacity is a term that all farms should know to optimize crop production. Simply defined soil water holding capacity is the amount of water that a given soil can hold for crop use. Field capacity is the point where the soil water holding capacity has reached its maximum for the entire field. The goal for agricultural producers is to maintain the field at or near capacity. When there is a deficit in the amount water in the soil, the soil profile needs to be replenished by precipitation or irrigation. The key is for farmers to understand the nuances of soil water holding capacity and how to manage it so that the farm does not need to irrigate or suffer from a drought.
Soil texture and organic matter are the key components that determine soil water holding capacity. In terms of soil texture, those made up of smaller particle sizes, such as in the case of silt and clay, have larger surface area. The larger the surface area the easier it is for the soil to hold onto water so it has a higher water holding capacity. Sand in contrast has large particle sizes which results in smaller surface area. The water holding capacity for sand is low.
Soil organic matter (SOM) is another factor that can help increase water holding capacity. Soil organic matter has a natural magnetism to water. If the farm increases the percentage of soil organic matter, the soil water holding capacity will increase. SOM is decayed material that originated from a living organism. SOM can be increased by adding plant or animal material.
The question that farmers should ask themselves is, “What can I do to increase the soil water holding capacity on my farm?” Unfortunately changing the soil texture of the field is not a viable option. Soil texture can be changed naturally by erosion, but that usually changes soil texture in a negative way. The best option for a farm is to increase their soil organic matter. Here are some basic ways that a farm can increase their SOM:
- Use cover crops
- Change to conservation tillage practices, for example no-till or minimal tillage
- Add manure
- Add compost