Thinking Ahead to Spring: Plants, Soil & Water

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By Chris Mahony, NRCS Soil Conservationist & GGWC Board Member

Water, plants and soil—we all have them and we all use them, whether in our crop fields, gardens, or lawns.  Considering a plant’s water needs and root structure and the soil type can help you plant in a way that’s smart for the watershed.

Plants: Different plant species have drastically different water requirements. For instance, during the hottest and driest weeks of the Gallatin Valley summer, alfalfa plants need 1/3-inch of water daily while a native plant species may need only 1/10-inch of water each day.

Roots: A plant’s root growth and structure also play an important role in how it uses water. The roots of an alfalfa plant are able to access water to a depth of 5 feet, while Kentucky bluegrass can typically only access water that is less than 1 foot underground.

The effective rooting depth of a plant is impacted by management. Plants that have been grazed or cut below 50 percent show drastic declines in root biomass and as a result are more prone to drought.

Root DepthsSoils: The water-holding capacity of soil is largely determined by the size of the soil particles and by the organic matter content. Sandy soils have a less organic matter and larger soil particles than silty soils. As a result, sandy soils can’t hold as much water as silty soils. Additionally, management practices can have a large effect on the ability of water to infiltrate a soil.

Knowing the effective rooting depth and the daily water requirements of the plant species you are managing for and the water-holding capacity of the soil will allow for more effective and efficient water use on your property.

For additional information please contact Chris Mahony or Marvin Hansen, USDA; Natural Resources Conservation Service, 406-522-4012