Soil temperature is also an important micro meteorological parameter like air temperature. This parameter influences the crop growth starting from seed germination to harvesting. Soil temperature also plays an important role in deciding the microbial activity in the soil. Soil temperature influences the uptake and mineralization of nutrients. The presence of organic matter and the soil texture are influenced by soil temperature.
Measurement of soil temperature Soil temperatures are measured at various depths as recommended by India Meteorological Department. The usual depths include 0, 5,10, 15, 20, 30, 60, 100 and 150 centimetres. The thermometers used to measure temperature beyond 30 cm depth are called as Earth thermometers
Principle: Same as any other mercury-in-glass thermometers. A vessel is an extra part and this is arranged in the corresponding depth whereas its scale is situated above the Earth's surface in order to facilitate the reading. A metal support is used to give strength in mounting.
Operation and measurement1. These thermometers consist of glass vessel (stem) filled with mercury and the glass capillary fused to it for taking measurement.2. It has a bend of 120° in the stem just above the bulb and the rest of the bulb is straight3. When the bulb rests horizontally on the soil at correct depth, the stem is inclined at 120° to facilitate reading of the scale4. An iron stand with an angle of 60° is used to provide support for the thermometers5. The immersion depth is calculated from lower end of the thermometer bulb upto the middle of the bulge situated in upper part of the stem.6. The graduation begins at a distance of 6.5, 17.5 and 35 cm from the bulb in the 5, 15 and 30 cm depth of the soil thermometers.7. The thermometer has a range of -5 °C to 65 °C and can be read with an accuracy of 0.1°C8. It is desirable to keep each thermometer 45 centimetres apart and the scale portion of each thermometer shall be inclined towards the North.9.The measuring field should be free from weeds.10.These are also read at the two usual prescribed timings.
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