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On the other hand, as the VPD increases, the plant needs to draw more water from its roots. In the case of cuttings, the plant may dry out and die. For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 and 0.95 kPa.
Moisture stress is a form of abiotic stress that occurs when the moisture of plant tissues is reduced to suboptimal levels. Water stress occurs in response to atmospheric and soil water availability when the transpiration rate exceeds the rate of water uptake by the roots and cells lose turgor pressure .
AgriHouse Smart Leaf Sensor (SG-1000) A leaf sensor is a phytometric device (measurement of plant physiological processes [1]) that measures water loss or the water deficit stress (WDS) in plants [2] by real-time monitoring the moisture level in plant leaves.
In 1907, Edgar Buckingham created the first water retention curve. [2] It was measured and made for six soils varying in texture from sand to clay. The data came from experiments made on soil columns 48 inch tall, where a constant water level maintained about 2 inches above the bottom through periodic addition of water from a side tube.
Physiology of plants and animals characterizes water in organisms in terms of diffusion pressure deficit, and; Meteorology uses vapour pressure or relative humidity to characterize atmospheric water. SPAC integrates these components and is defined as a:
The concept, put forward by Frank Veihmeyer and Arthur Hendrickson, [3] assumed that the water readily available to plants is the difference between the soil water content at field capacity (θ fc) and permanent wilting point (θ pwp): θ a ≡ θ fc − θ pwp
At night, transpiration usually does not occur, because most plants have their stomata closed. When there is a high soil moisture level, water will enter plant roots, because the water potential of the roots is lower than in the soil solution. The water will accumulate in the plant, creating a slight root pressure.
Pores (the spaces that exist between soil particles) provide for the passage and/or retention of gasses and moisture within the soil profile.The soil's ability to retain water is strongly related to particle size; water molecules hold more tightly to the fine particles of a clay soil than to coarser particles of a sandy soil, so clays generally retain more water. [2]