Terms in this set (23)
The water balance method of ET can be used even if you don't know the amounts of infiltration, deep percolation, and final soil water conten
Increasing the air temperature decreases the capacity of the air to hold water vapor
plant root depth and proliferation does not have any effect on the ET rate of the plant
The drop in water level in an atmometer after a period of time can be used as an estimate of reference crop ET for that period
PLant residues on the soil surface can reduce evaporation of water from soil
The method and timing (day-time versus night-time) of irrigation has no effect on ET
If the water stress coefficient (Ks) is equal to zero (Ks=0.0) then the plants have stopped transpiring.
Alfalfa-based crop coefficients can be multiplied with grass-reference ET (Short reference ET) values to calculate crop ET
If the root zone soil water content is always less then field capacity, then there will alwats be deep percolation or damage from the root zone
For computing ET, the ASCE standardized Penman-Monteith equation requires mean daily wind speed at 2 meters height
Assuming all factors are the same, which average daily wind speed will result in the lowest ET?
Which type of data is not needed in the Penman-Monteith equation?
Assuming all other factors are the same and there is no soil water stress, which crop leaf area index (LAI) value will result in the highest ET rate?
In ET-based irrigation scheduling, the irrigator keeps track of the soil water deficit (D) that increases daily because of water lost through ET. A certain depth of managment allowed depletion (dMAD) is used to determine when to irrigate. Irrigation water should be applied when
D is greater than or equal to dMAD
In a certain field, the remaining readily available water in the root zone is 3.5 cm of water. Ther average ETc rate is 0.8 cm/day. How many days can you wait before you need to irrigate, assuming that there will be no rainfall in the near future?
It is an indicator of the amount of water present in the air.
Actual vapor pressure
In an experiment for developing crop coefficients for buffalo grass, the measued crop ET was 0.13 inch/day, the calculated alfalfa reference ETr was 0.19 inch/day , and the calculated grass reference ETo was 0.16inch/day. What was the alfalfa-based crop coefficent of buffalo grass?
What information do you need to use the Blaney-Criddle method of estimating ET?
Mean monthly air temperature and monthly percentage of total daytime hours of year
Several plots of roses at the same grother stage (same Kc) are experiencing water stress. The levels of water stress in the plots were quantified using soil water stress coefficent (Ks). Which plot of roses would have the lowest crop ET rate?
Plot 3: Ks=0.34
Using the standardized Penman-Monteith ET equation, it is found that the alfalfa reference ETr is 8.73 mm/day. For that day, a fully irrigated corn crop has a grass-based crop coefficient (Kco) of 094 and an alfalfa-based crop coefficient (Kcr) of 0.79. What is the corn crop ET for that day?
Which method of estimating crop ET requires frequent measurements of change in vertical wind speed and vapor pressure?
Which management strategy can conserve water by decreasing ET?
Keeping mulch or plant residue on the soil surface
A field of garlic has a root zone depth of 40 cm. Over the course of 7 days, you made initial and final observation of soil moisture content by volume (theta v) and infiltration (I) given in the table below. For the following questions, show your solutions step-by-step.
July 6 (initial) 0.34 (theta v), 0.0 (I, cm)
July 13 (final) 0.35 (theta v), 3.8 (I, cm)
a. What were the initial (Si) and final (Sf) depths of stored water (cm) in the root zone?
b.Assume that deep percolation, lateral flow, and capillary rise were all zero during the 7-day period. Estimate the total crop ET (cm) that occurred from July 6- 13 using the water balance method.
c. The depth of water field capacity (dFC) is 15.6 cm and the depth of management allowed depletion (dMAD) is 2.4 cm. Estimate daily ETc for the 7-day period from your answer in question b and determine how many days are left after July 13 until the garlic field needs irrigation.
a. Si = 0.34*40cm = 13.3cm
Sf= 0.35*40cm = 14cm
c. # days = 0.8cm/3.4 cm/7-days = 1.6 days
dMAD- D 2.4-1.6=0.8cm
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