How Do Different Amounts of Water Affect the Soil's Temperature?

Soil Texture

• Depending on a soil's texture, it can hold different amounts of water. Soil texture is determined by its percentage of different-sized particles. The amount of sand, silt and clay will classify the soil as sandy, loamy or clayey. A very sandy soil soaks up a lot of water, but the water also quickly drains through it. These types of soil have a low water-holding capacity. When wet, they will be cooler; but, since sand grains have a low-surface-area soil, water can easily evaporate, leaving the soil warmer. A soil with lots of clay has particles with a much greater surface area. These soils can hold and retain much more water than a sandy soil. With the increased amount of water, these soils remain cooler for longer periods of time, even when exposed to the same amount of water as a sandy soil.

Water-Holding Capacity

• There are four different levels of soil water-holding capacity. Soil saturation occurs when all of the air pockets and gaps between soil particles are filled with water. The field capacity of a soil is the amount of water left in the soil when all of the free water has drained out. Free water is water drained from the soil by the force of gravity. The water in the soil between saturation and field capacity is called gravitational water. Wilting point is the amount of soil water that is still present but is unavailable to plants. There is still water left in seemingly very dry soil, because it is held by the capillary forces between soil particles. This amount of water is measured by drying soil in an oven and comparing the amount of weight lost. A soil is coolest when it is at saturation. The drier it gets, the closer it gets to the air temperature. Dry soil can even get hotter than the air temperature if it is in direct sunlight.

Organic Matter

• Increasing the organic matter in soil allows more water to be held in it. Organic matter comes from decayed materials from plants and animals. Adding leaves, grass clippings and food scraps to the soil increases organic matter. As these materials break down, they create organic compounds that can absorb tremendous amounts of water per volume of dry matter. Soils with lots of organic matter retain more water and are cooler.

Ideal Soil Temperature

• If you are growing a garden or lawn, it is important to provide sufficient water for the plants to grow. Keeping enough water in the soil for plant growth will keep the soil cool enough. If plants begin to wilt, the soil is getting too dry and may also be heating up due to decreased amounts of water. It is okay to saturate the soil of your lawn or garden if you have good draining soil. Allow the soil to get fairly dry between watering, but not so much that plants wilt. If water pools on the surface of your soil for more than 24 hours, you may need to add sand and organic matter to your soil. Even though saturated soil will be cooler, it will suffocate plants.