Soil moisture is the water stored in the soil and is affected by precipitation, temperature, soil characteristics, and more. These same factors help determine the type of biome present, and the suitability of land for growing crops. The health of our crops relies upon an adequate supply of moisture and soil nutrients, among other things. As moisture availability declines, the normal function and growth of plants are disrupted, and crop yields are reduced. And, as our climate changes, moisture availability is becoming more variable.
Where is the water in soil? Solids, liquids, and gasses, the three phases of matter, are always present in soil. Small mineral and organic particles comprise the solid fraction, and there are spaces (pores) between the solid particles. Some pores are large, and others are very small. Air and water, the gas and liquid phases, exist in the pores. The size of the soil particles and pores affects how much water a soil can hold, and how that water moves through the soil.
Calling all student scientists! Soil scientists and agronomists use gravimetric methods and in-situ instrumentation to monitor soil moisture at the field scale in cropped lands. Other scientists look at a bigger picture, using Earth-observing satellites to survey the planet for soil moisture changes. These data will assist soil scientists, hydrologists, and climatologists in forecasting potential changes in moisture availability. NASA recently launched a satellite called Soil Moisture Active Passive (SMAP) to monitor the water in the top 5 cm of soil. (http://smap.jpl.nasa.gov/) The SMAP mission team needs help and is partnering with GLOBE to get students involved in collecting ground truth measurements. These student-provided measurements will help scientists calibrate satellite information and interpret the data.
- Visit www.soils4teachers.org/esw for complete details and instructions for this activity. This set of activities introduces students to the basic properties and measurements of soil water, and how the global distribution of soil moisture is monitored.
- Younger students will use sponges and soil materials to learn how and where soils hold water, how they release it, and the concepts of gravimetric and volumetric water content.
- Older students will collect data using the GLOBE Gravimetric & Volumetric Soil Moisture Protocols to collect ground-truthing (in-situ) data for the SMAP program. They will assist scientists by collecting data at a small/local scale in order to validate the SMAP satellite data. Learn more about participating at www.globe.gov/web/smap/overview.
- Sponges with different pore sizes
- Dry soil materials: sand (play sand or sand from a beach or dune), topsoil (from a lawn or garden), cat litter
- Trays or baking dishes to hold water and wet sponges
- 250-ml clear containers (Use graduated beakers, if available.)
- Balance (0.1 g sensitivity, at least 400 g capacity)
- Ruler (SI units)
- Computer with internet access