Contenido

La humedad puede estar presente como humedad adsorbida en las superficies internas y como agua condensada capilarmente en los poros pequeños. Con una humedad relativa baja, la humedad consta principalmente de agua absorbida. A humedades relativamente más altas, el agua líquida tiende a ser cada vez más importante, dependiendo del tamaño de los poros. En materiales de madera, sin embargo, casi toda el agua es absorbida a humedades por debajo del 98% de humedad relativa.

En aplicaciones biológicas también puede haber una distinción entre agua absorbida físicamente y agua "libre" - el agua absorbe físicamente es aquella que está estrechamente asociada y es relativamente difícil de eliminar de un material biológico. El método utilizado para determinar el contenido de agua puede afectar si el agua presente en esta forma contabiliza. Para una mejor indicación de agua "libre" y "enlazada", debería considerarse la actividad del agua de un material.

Las moléculas de agua también pueden estar presentes en materiales estrechamente asociados con moléculas individuales, como "agua de cristalización", o como las moléculas de agua que son componentes estáticos de la estructura de la proteína.

The Earth and agricultural sciences

In soil science, hydrology and agronomy, water content plays an important role for groundwater recharge), agriculture and soil chemistry. Many recent scientific research efforts have been oriented toward understanding the forecast of water content in space and time. Observations have generally revealed that spatial variation in water content tends to increase as global humidity increases in semiarid regions, to decrease as global humidity increases in humid regions and to peak in regions with intermediate humidity and temperature conditions.[5]​.

There are four standard water contents that are routinely measured and used, described in the table below:.

And finally, the available water content"), θ, which is equivalent to:.

which can range between 0.1 in gravel and 0.3 in peat.

When a soil becomes too dry, plant transpiration drops because water is binding more and more tightly to soil particles by suction. Below the point of "permanent wilting") plants are no longer able to extract water. At this point, they wither and transpiration ceases entirely. Conditions in which the soil is too dry to maintain reliable plant growth is known as agricultural drought, and is a particular focus of irrigation management. Such conditions are common in arid and semi-arid environments.

Some agricultural professionals are beginning to use environmental measurements such as soil moisture to schedule irrigation. This method is known as smart irrigation or land cultivation.

In saturated groundwater aquifers, all available pore spaces are filled with water (volumetric water content = porosity). Above the capillary fringe"), the pore spaces have air in them.

Most soils have a water content less than porosity, which is the definition of unsaturated conditions, and constitute the subject of hydrogeology called the unsaturated zone. The capillary strip) of the water table is the dividing line between saturated and unsaturated conditions. The water content in the capillary fringe decreases with increasing distance above the surface of the water table.

One of the main complications that arises in the study of the unsaturated zone is the fact that the unsaturated hydraulic conductivity is a function of the water content of the material. When the material dries, the wet connecting paths through the medium become smaller, the hydraulic conductivity decreases with lower water content in a non-linear manner.

A water retention curve") is the relationship between the volumetric water content and the water potential of the porous medium. It is characteristic of different types of porous medium. Due to hysteresis, different wetting curves can be distinguished.

Direct methods

Water content can be measured directly using a known volume of material and a drying oven. The volumetric water content, θ, is calculated[3]​ using:.

where.

For materials that change volume with water content, such as coal, the water content, u, is expressed in terms of mass of water per unit mass of wet sample:

However, geotechnics requires that the moisture content be expressed as a percentage of the dry weight of the sample.

i.e.: % moisture content =

where.

For wood, the convention is to report the moisture content in the drying oven (i.e. the sample is usually dried in an oven at 105 degrees Celsius for 24 hours). In wood drying"), this is an important concept.

Laboratory methods

Other methods that determine the water content of a sample include chemical titrations (e.g., Karl Fischer titration), determination of mass loss upon heating (perhaps in the presence of an inert gas), or after freeze-drying. In the food industry, Dean Stark's method is also commonly used.

According to the ASTM (American Society for Testing and Materials) Annual Book of Standards, the total evaporable moisture content in Aggregate (C 566) can be calculated with the formula:.

where is the fraction of the total evaporable moisture content of the sample, is the mass of the original sample, and is the mass of the dried sample.

Geophysical methods

There are several geophysical methods that allow you to calculate the approximate water content of the soil in situ. These methods include: time domain reflectometry (TDR), neutron probe, frequency domain sensor, capacitance probe, electrical resistivity tomography, ground penetrating radar (GPR), and others that are sensitive to the physical properties of water. Geophysical sensors are often used to monitor soil moisture continuously in agricultural and scientific applications.

Satellite remote sensing method

Microwave remote observing satellites are used to estimate soil moisture based on the large contrast between the dielectric properties of wet and dry soil. Data from microwave remote sensing satellites such as: WindSat, AMSR-E, RADARSAT, ERS-1-2, Metop/ASCAT are used to estimate surface soil moisture [1].

Contenido

La humedad puede estar presente como humedad adsorbida en las superficies internas y como agua condensada capilarmente en los poros pequeños. Con una humedad relativa baja, la humedad consta principalmente de agua absorbida. A humedades relativamente más altas, el agua líquida tiende a ser cada vez más importante, dependiendo del tamaño de los poros. En materiales de madera, sin embargo, casi toda el agua es absorbida a humedades por debajo del 98% de humedad relativa.

En aplicaciones biológicas también puede haber una distinción entre agua absorbida físicamente y agua "libre" - el agua absorbe físicamente es aquella que está estrechamente asociada y es relativamente difícil de eliminar de un material biológico. El método utilizado para determinar el contenido de agua puede afectar si el agua presente en esta forma contabiliza. Para una mejor indicación de agua "libre" y "enlazada", debería considerarse la actividad del agua de un material.

Las moléculas de agua también pueden estar presentes en materiales estrechamente asociados con moléculas individuales, como "agua de cristalización", o como las moléculas de agua que son componentes estáticos de la estructura de la proteína.

The Earth and agricultural sciences

In soil science, hydrology and agronomy, water content plays an important role for groundwater recharge), agriculture and soil chemistry. Many recent scientific research efforts have been oriented toward understanding the forecast of water content in space and time. Observations have generally revealed that spatial variation in water content tends to increase as global humidity increases in semiarid regions, to decrease as global humidity increases in humid regions and to peak in regions with intermediate humidity and temperature conditions.[5]​.

There are four standard water contents that are routinely measured and used, described in the table below:.

And finally, the available water content"), θ, which is equivalent to:.

which can range between 0.1 in gravel and 0.3 in peat.

When a soil becomes too dry, plant transpiration drops because water is binding more and more tightly to soil particles by suction. Below the point of "permanent wilting") plants are no longer able to extract water. At this point, they wither and transpiration ceases entirely. Conditions in which the soil is too dry to maintain reliable plant growth is known as agricultural drought, and is a particular focus of irrigation management. Such conditions are common in arid and semi-arid environments.

Some agricultural professionals are beginning to use environmental measurements such as soil moisture to schedule irrigation. This method is known as smart irrigation or land cultivation.

In saturated groundwater aquifers, all available pore spaces are filled with water (volumetric water content = porosity). Above the capillary fringe"), the pore spaces have air in them.

Most soils have a water content less than porosity, which is the definition of unsaturated conditions, and constitute the subject of hydrogeology called the unsaturated zone. The capillary strip) of the water table is the dividing line between saturated and unsaturated conditions. The water content in the capillary fringe decreases with increasing distance above the surface of the water table.

One of the main complications that arises in the study of the unsaturated zone is the fact that the unsaturated hydraulic conductivity is a function of the water content of the material. When the material dries, the wet connecting paths through the medium become smaller, the hydraulic conductivity decreases with lower water content in a non-linear manner.

A water retention curve") is the relationship between the volumetric water content and the water potential of the porous medium. It is characteristic of different types of porous medium. Due to hysteresis, different wetting curves can be distinguished.