Leaching continues until there is not enough water to saturate all of the pore space. At this point pores contain some air and thin films of moisture. The water films within the pores are held by the surface tension of soil colloids, thus water stops leaching. After leaching stops, and excess water has drained from the soil, the soil is described as being at field capacity. Soil at field capacity has pores that are partially filled with air, surrounded by films of moisture.
Soil at field capacity is optimal for plant growth and aerobic soil microorganisms, since both air and water are available. In contrast, saturated soil, where all pores are filled with water, will create an anaerobic environment that can kill plants and suppress aerobic soil microbes. The mass of moist soil consists of the mass of the dry soil particles, plus the mass of the water within the soil.
The dry mass of the soil particles is fixed, whereas the amount of water within moist soil can vary. Therefore, moisture content is calculated on a dry basis, rather than a total mass basis, to ensure consistency. The moisture content of soil is described as the ratio of the mass of water held in the soil to the dry soil. The mass of water is determined by the difference before and after drying the soil.
The following experiment will demonstrate how to measure soil moisture content in the laboratory using these principles. To begin, collect soil samples and transfer them into the laboratory. Samples of soil can be collected in the field using a soil auger, or a trowel. Use of a soil auger allows for the soil to be sampled to specific depths. Transfer them into the laboratory. Weigh two aluminum dishes, and accurately record the weight of each dish. Aliquot approximately 20 g of the moist soil into each aluminum dish, then reweigh the dish.
Subtract the weight of the empty dish from the full dish to acquire the moist soil weight. On the next day, carefully remove the soil samples from the oven using tongs. Place the soil samples on the bench top to cool. When the dry soil samples are cool, reweigh them and record the total weight. Subtract the weight of the aluminum dish, and record the dry soil weight. Calculate the moisture content of the soil by subtracting the weight of the dry soil from the weight of the moist soil, and then dividing by the weight of the dry soil.
Although the measurement is simple, it is important to determine soil moisture content in order to better understand soil characteristics. Soil moisture content plays a large roll in environmental concerns, especially when considering soil runoff that may contain fertilizers and pesticides. In this example, soil runoff was analyzed using a simulated rainfall study in order to determine the retention of a compound in moist soil. Soil, containing urea, was packed into soil boxes and assembled under a rainfall simulator.
Soil runoff was collected, and the concentration of urea in the runoff water calculated. The amount of urea in the soil runoff was higher for soils that had higher moisture content, indicating that urea is better absorbed in drier soil, than in moist. The fate of chemicals in soil can also be analyzed by direct pore water sampling, using a lysimeter, as shown in this example.
In this experiment, lysimeters, or long metal tubing, were installed in soil with turf grass to analyze pore water in vegetative soil. The pore water sampler was then installed, and water pumped from the lysimeter after applying chemicals to the soil.
The collected water was then analyzed, and the concentration of applied chemicals correlated to soil depth and moisture content. The results demonstrated that the concentration of the herbicide monosodium methyl arsenate, or MSMA, was the highest in the top 2 cm of soil.
You've just watched JoVE's introduction to soil moisture content. You should now understand how to accurately measure soil moisture content in the laboratory. Thanks for watching! The color with the hex code 3c83e8 identifies:. The color with the hex code identifies:. The color with the hex code e identifies:. The color with the hex code fed37f identifies:. The color with the hex code fefe00 identifies:.
The color with the hex code aaf identifies:. The color with the hex code 4ce identifies:. The color with the hex code 38a identifies:. The color with the hex code a00 identifies:. Source s : NASA. Source s : NationalSoilMoisture. Learn more about these data. Download screenshot of this panel. Data and Map Gallery. CPC Soil Moisture. Period of Record. File Format. Groundwater and soil moisture drought indicators based on terrestrial water storage observations derived from GRACE satellite data and integrated with other observations, produced each week by NASA.
The research-based website NationalSoilMoisture. The Soil Climate Analysis Network SCAN provides soil and climate data to support natural resource assessments and conservation activities, focusing on agricultural areas of the U.
Related Content. By Sector Agriculture. Explore the Page. Research and Learn. Learn More. Soil Moisture Research and Resources. Peer-Reviewed Publications. June 8, Vadose Zone Journal. This refers to the energy concept in moisture retention relationships. The force with which water is held is also termed as suction. At the end of the wave guides, the pulse is reflected back to its source. The resulting transit time and dielectric constant are dependent on the moisture content of the material.
This highly complex but extremely easy to use technology should not be confused with capacitance or FDR techniques which, although acceptable for general relative measurements cannot be used for serious research. In particular accuracies can be seriously compromised in clay rich or very organic soils. This is….
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