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Soil moistur

Aug 19, 2014





  • SOIL MOISTURE Prepared by Mohammed Kareem
  • WHAT IS SOIL ? Soil is a natural body that consists of layers (soil horizons), composed primarily of minerals , which differ from their parent materials in their texture, structure, consistency, color, chemical, biological and other physical characteristics. Soil is the end product of the influence of the climate (temperature, precipitation), relief (slope), organisms (flora and fauna), parent materials (original minerals), temperature, and time.
  • A represents soil; B represents laterite, a regolith; C represents saprolite, a less- weathered regolith; the bottommost layer represents bedrock
  • SOIL MOISTURE Soil moisture is the water that is held in the spaces between soil particles. Surface soil moisture is the water that is in the upper 10cm of soil, whereas root zone soil moisture is the water that is available to plants, which is generally considered to be in the upper 200 cm of soil. Soil Moisture Estimation Direct method: Measurement of moisture content in the soil (wetness) Indirect methods: Measurement of water potential or stress or tension under which water is held by the soil.
  • ADIRECT METHODS Gravimetric Methods: Soil sample from the desired depths are collected with a soil auger in air tight aluminum containers.The soil samplesareweighedandtheyaredriedinanovenat105degreeCfor about 24 hours until all the moisture is driven off. After removing from oven,theyarecooledslowlytoroomtemperatureandweighedagain.the differenceinweightisamountofmoistureinthesoil.Themoisturecontent inthesoiliscalculatedbythefollowingformula: MoisturecontentWetweightDryweight onweightbasis =-----------------------------X100 Dry weight
  • Gravimetric Techniques Oven drying a soil sample at 1050C for about 12 hours.
  • Volumetric Method: Soil sample is taken with a core sampler or with a tube auger whose volume is known. The amount of water present in soil sample is estimated by drying it in the oven and calculating by following formula: Moisture content = Moisture content (%) by weight x Bulk Density (%) by volume Volumetric Soil Moisture (gm/cm3)
  • INDIRECT METHODS No water content in the soil is directly measured but the water potential or stress or tension under which the water is held by the soil is measured. 1) Tensiometer 2) Gypsum block 3) Neutron probe
  • The Tensiometer for columns, remote locations, limited access - 1/4 in (6mm) Dia. Sensor Laboratory research in soil columns, in tight corners, or near the soil surfaces cannot be done with a large inflexible standard tensiometer . The Model 2100F Soil moisture Probe is a specialized unit designed for investigation of soil suction in such small regimes. Ideal for laboratory work such as measuring soil suction values at various levels in soil columns. In getting measurements near surface conditions with minimal disturbance or in places where the readout must be remotely located. Advantages : easy to design, cost little, at any conditions in real time, placed in soil easily, Disadvantages : Only measures soil water suction, but only indirect measurement of soil moisture content; during installation, it may break.
  • Remote Sensing Methods Visible & near IR Reflected Solar Thermal IR Surface Temperature Passive Microwave Microwave Emission/Brightness Temperature Active Microwave Backscattering coefficient/dielectric properties
  • Visible Technique: Reflected solar energy is measured. (0.4 1.7 mm) Relationship between Reflectance and SM Depends on reflectance of dry soil, roughness, colour, illumination, organic matter, soil texture.
  • Thermal infrared remote sensing for soil moisture estimation Thermal inertia method Variations in soil moisture have a strong influence on the thermal properties of the soil, which is an intrinsic factor of soil surface temperature change. The amplitude of the diurnal range of soil surface temerature has been found to be highly correlated with the surface soil moisture content Areas having higher soil moisture content are cooler during the day and warmer at night Diurnal range of Surface Temperature ( T maxT min ) (T max-T min) depends on internal and external factors Internal factors : Thermal conductivity(K) and heat capacity (C ) where P = (KC)1/2 is known as Thermal Inertia. K and C increases with Soil Moisture. External Factors : solar radiation, air temperature, RH, cloudiness, and wind.
  • Microwave remote sensing for soil moisture estimation Microwave remote sensing provides a unique capability for soil moisture estimation by measuring the electromagnetic radiation in the microwave region between 0.5 and 100 cm. The fundamental basis of microwave remote sensing for soil moisture is the large contrast between the dielectric properties of water (~80) and soil particles (