Briefly describe the role of Scholander pressure chamber, Leaf porometer and sap flow system in water stress detection and irrigation management (slide 02 – 19-21)

 

A pressure bomb or pressure chamber or Scholander bomb is an instrument with which it is possible to measure the approximate water potential of plant tissues. A leaf attached to a stem is placed inside a sealed chamber and pressurised gas is added to the chamber slowly. As the pressure increases at some point sap will be forced out of the xylem and will be visible at the cut end of the stem. The pressure that is required to do so is equal and opposite to the water potential of the leaf.

The Leaf Porometer is a battery-operated, menu-driven device used to measure stomatal conductance of leaves. Stomatal conductance is a function of the density, size,and degree of opening, of stomata, which are pores in plants that open to the outside air.The Leaf Porometer measures stomatal conductance by putting the conductance of aleaf in series with two known conductance elements, and comparing the humidity measurements between them.

Sap flow sensor consists of a flexible heater, a thermopile to measure radial heat loss, and differential thermocouple pairs to measure the axial temperature differences qu-qd. All of these sensors and heater are mounted on a cork substrate and housed inside white, reflective foam, thermal insulating collar. Once the sensor is installed on the stem surface, both the sensor and the stem sections above and below the sensor are completely covered by a heat insulator to minimize thermal perturbations caused by the ambientenvironment. Power is supplied continuously to the heater from a regulated DC power source. The Dynamax loggers have a power down mode so that power is saved at night and the stem is preserved from overheating. During the power down mode and at the transitions to power on, the sap flow is not computed to maintain the accumulated flow accurately during this unbalanced transition. Figure 1 shows a stem section and the possible components of heat flux, assuming no heat storage.

 

 

17. Specify the definition and the types of drought (drought  – 2-4)

 

A drought is an extended period of months or years when a region notes a deficiency in its water supply whether surface or underground water. Types of drought: Meteorological drought, Agriculture drought, Hydrological drought, Socio-economic drought.

Meteorological drought is defined usually on the basis of the degree of dryness (in comparison to some “normal” or average amount) and the duration of the dry period. Definitions of meteorological drought must be considered as region specific since the atmospheric conditions that result in deficiencies of precipitation are highly variable from region to region.

Agricultural drought links various characteristics of meteorological (or hydrological) drought to agricultural impacts, focusing on precipitation shortages, differences between actual and potential evapotranspiration, soil water deficits, reduced groundwater or reservoir levels, and so forth. Plant water demand depends on prevailing weather conditions, biological characteristics of the specific plant, its stage of growth, and the physical and biological properties of the soil.

Hydrological drought is associated with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (i.e., streamflow, reservoir and lake levels, groundwater). The frequency and severity of hydrological drought is often defined on a watershed or river basin scale.

Socioeconomic definitions of drought associate the supply and demand of some economic good with elements of meteorological, hydrological, and agricultural drought. It differs from the aforementioned types of drought because its occurrence depends on the time and space processes of supply and demand to identify or classify droughts. The supply of many economic goods, such as water, forage, food grains, fish, and hydroelectric power, depends on weather.

 

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