Irrigation Principles Test 3
Terms in this set (25)
The lack of water in the plant can reduce growth by reducing tugor pressure in plant cells
Water flow from the roots to the leaves of the plant is driven by differences in water potential
The measurement of leaf water potential can indicate when irrigation is needed, but does not directly give the amount of irrigation required
The solute potential in plants is always a positive pressure
A soil layer with a low bulk density will tend to have more plant roots than a compacted soil layer with a very high bulk density
On a daily basis, the amount of water used by a plant for photosynthesis is much greater than the amount of water flowing through the plant by transpiration
If a plant is supplied with adequate water (no water stress), the leaves will be much warmer than the surrounding air during the daytime
In irrigation management, the managed depth of root zone should NOT be the maximum depth of rooting, but should correspond to the depth at which most of the active plant roots are able to meet transpirational demand
A crop water stress index (CWSI) of zero means that the plants are experiencing maximum water stress
Air with a vapor pressure deficit of 0 is saturated (100% relative humidity)
Which component(s) of total plant water potential change(s) when a plant undergoes osmotic adjustment to cope with water stress?
Solute potential and hydrostatic pressure potential
Which of the following is NOT a function of water in plants?
a. Raw material for photosynthesis
b. gives tugor to plant cells
c. medium for organic and inorganic solute transport
d. none of the above
None of the above
A certqin plant has a constant internal leaf CO2 concentration (Cci) of 270ppm. Assuming that atmospheric pressure and VPD are constant, which atmospheric CO2 concentration (Cca) will result in the highest leaf transpiration efficiency for the plant?
a. Ca= 360ppm
d. Ca= 350 ppm
e. none of the above
Which component of total plant water potential is the primary factor affecting growth or cell expansion?
Hydrostatic pressure potential
The water use efficiencies of four irrigated fields are given below. All fields had the same area and produced the same amount of total dry matter (biomass). Which field had the highest total ET?
Field B: WUE = 40lb/in of water
Which instrument is useful in determining the crop water stress index?
On a summer day, the midday lead water potential of a crop is measured using a pressure chamber and is found to be -24 bars. The threshold (lowest) midday leaf water potential that indicates the need for irrigation is -17 bars. Assuming that irrigation water is readily available, what should you do?
Start irrigation as soon as possible.
When using an indicator plant to signal the need for irrigation, what characteristic should the indicator plant have?
its shoot (top) to root ratio must be greater than the main crops
On a certain day, the actual vapor pressure of the air is observed to be 0.62 kPa while the saturation vapor pressure is 4.19 kPa. What is the vapor pressure deficit in the air?
When considering root water extraction from root zone, the entire root zone depth can be divided into quarter sections. In a uniform soil with no restrictive layers, which quarter section will have the greatest root water extraction?
Top quarter of the root zone
The crop water stress index (CWSI) does not tell you how much water needed to be applied. What additional information is required to determine how much water is needed?
correlation between CWSI and soil water deficit
Which plant-based technique uses color change in the foliage to indicate the need for irrigation?
A plant has roots with the following water potential components Yp = 3.1 bars; Ym= -1.9 bars; Ys=-8bars, Yg=-0bars
a Determine the total water potential of the plant roots
b. if the total water potential of the soil surrounding the roots is -1.7 bars, will the roots be able to extract water from the soil? why or why not?
a. 3.1+-1.9+-8+0=-6.8 bars
b. Yes, because the total water potential is still negative. Root potential is lower than the soil potential will move into the root because the water will move from a high point to a low point.
On 26 July 2013, a lettuce plant has a foiliar temperature (Tf) of 27 degrees celsius compared to an air temperature (Ta) of 29 degrees celsius. The baseline (lower limit) for dT can be estimated using the equation:
dTl = 4.18 - (2.96*VPD)
Where VPD is the vapor pressure deficit of air in kilopascals (kPa) and dTl is in degrees celsius. The actual vapor pressure (ea) is 1.33 kPa while the saturation vapor pressure (es) is 4.01 kPa. The upper limit (dTu) corresponding to maximum stress is 7.4 degrees celsius. What is the crop water stress index for the lettuce plant?
dT = 27 - 29 = -2 degrees celsius
D= VPD = 4.01-1.33=2.68 kPa
dTl = 4.18-(2.96*2.68)
dTl-3.7528= 4.18 - 7.9328
(-2-(-3.7528))/(7.4-(-3.7528)) = 1.7528/11.1528 =0.1571 CSWI
The following data are given on 26 July 2013 at Fort Collins, Colorado
air temp: T=29.0
Atmospheric CO2 concentration Cca= 385 ppm
Actual vapor pressure of air, ea = 1.33 kPa
Saturation vapor pressure of air, es = 4.01 kPa
Atmospheric pressure, pa= 84.2 kPa
On that day, a corn leaf has an internal leaf CO2 concentration (Cci) of 196 ppm
a. Calculate the leaf transpiration efficiency (A leaf/ E leaf) of corn leaf. Give your answer in part CO2 per million part H2O ppm
b. Given the same es, and K value from A, what would happen to the corn leaf transpiration efficiency if there was less humidity in the air (ea is lower)?
K=11139.66 kPa ppm
b. The transportation efficiency would decrease
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