Irrigation Systems and Irrigation Management in Xeric Gardens - New Mexico State University

1. Irrigation Management
g g
Module 6

2. Irrigation Systems
and
Irrigation Management
I i ti M t
in
Xeric Gardens

3. The Water Cycle
y ET
Evaporation
ration
Runoff
Infiltration
Transpir
Soil Root
Surface Storage in Absorption
T
root zone
Deep Drainage
Desirable Pathway
y
Undesirable losses

4. Goal of Efficient Irrigation
Provide enough supplemental water (above
precipitation) to satisfy the plant’s requirements for
plant s
adequate growth and/or desired quality.
quality.
Prevent water waste via runoff excessive
runoff,
evaporation, or deep drainage below the plant’s root
zone.
zone

5. Xeriscape Garden
Efficient Irrigation Management
g g
Success depends on knowledge of three essential
components:
t
The output and efficiency of the irrigation system
(including individual emitters).
The water-holding characteristics of the soil.
water-
The estimated water required by each plant for
‘acceptable’ growth and quality.

6. The Irrigation System
g y
To schedule irrigations effectively you must know the
output (water flow rate or water application rate) of
the irrigation system.
system.
The flow rate is usually measured in volume per unit time
(i.e. gallons per minute [gpm] in sprinkler systems and gallons per hour
ie [gpm]
[gph] in drip systems).
gph]
The application rate is usually measured in depth p unit
pp y p per
time (i.e. inches per hour [in/hr]).
[in/hr]).
One can be converted to the other if the wetted area is
known (measured).

7. Irrigation System Output
(Flow Rate)

8. The maximum flow rate
Determined by direct measurement from a spigot
using a bucket and stopwatch
Procedure:
Using a watch, time
how long it takes to
fill a container having
a known volume.
Example: Suppose it takes 30 seconds to fill a
p
5-gallon bucket.
Flow rate = 5 gallons/0.5 minute = 10 gpm.
gpm.

9. Determining the flow rate of an existing
irrigation system using a flow meter or
installed water meter
Most water meters show total
gallons.
gallons.
To determine the flow rate of
your irrigation system:
system:
Insure only irrigation system is
running.
running.
Record an initial flow meter
reading.
Run system for a timed period
(i.e. 10, 15, 30 minutes for a
sprinkler system; a few hours for a
drip system)
system)
Record the final meter reading.
reading.
Subtract the initial reading from
the final reading.
Divide the result by the time in
minutes.

10. Example (Flow Meter)
Suppose the meter reading was 24,000 gallons
before turning on the irrigation system and was
24,600 gallons after running the irrigation system
for 30 minutes
minutes.
Total gallons used = 24,600 – 24,000 = 600.
Flow rate in gpm = 600/30 = 20 gpm
This might be a typical flow rate for a small 8-sprinkler
g yp p
irrigation zone (2.5 gpm from each sprinkler).

11. Drip Systems
p y
Because of the very low flow rates of drip systems, you
may h
have t run the system for 2 to 3 hours to get
to th t f t h t t
accurate flow rates with a water meter.
meter.
Flow rates can be expressed in gallons per hour (gph)
(gph)
instead of gallons per minute (gpm).
(gpm).
Example with a flow (or water) meter:
Water meter reading before irrigation start-up = 24,000 gallons
start-
Water meter reading after running the system for
2 hours = 24,300 gallons.
Total gallons used = 24,300 – 24,000 = 300
Flow rate in gph = 300/2 = 150 gph.
gph.
• This might be a typical flow rate of a drip system irrigating a moderate
sized (100 plant) xeriscape garden Smaller plants may be irrigated
garden.
with only 1 emitter while larger plants may be irrigated with 2 or 3
emitters.

12. Drip Emitter Flow R t
D i E itt Fl Rates
Drip emitters are designed to have a specific flow rate and
many are marked (or color-coded) to designate that flow rate in
color-
gallons per hour (i.e. 0.5, 1.0, 2.0, 5.0 gph, etc.).
gph,
To estimate the flow rate for the entire system j
y just add up the
p
flow rates of the individual emitters.
If you’re uncertain (or, if you just want to verify) you can measure
the t t f
th output from each emitter using a stop watch (or watch with a
h itt i t t h
second hand) and a measuring cup.

13. Example
Place a measuring cup below the normally positioned
emitter and mark the time.
After 1 minute, remove the cup and record the volume.
Suppose you measured ¼ cup or 2 ounces.
Flow rate = 2 ounces/minute or 120 ounces/hour.
There are 128 ounces in a gallon, so…
so…
The flow rate is about 1 gallon per hour
(120 oz./128 oz. = 0.94 gph)
gph)

14. Troubleshooting for Leaks
g
In buried irrigation systems, on sandy soils, it may be difficult
to visually detect a leak in the system.
If you know the output of each of your sprinklers, or emitters
(available from the dealer or manufacturer if the model number is
known), you can add these up to get an estimate of what the
total flow rate should be (at a given pressure).
If the calculated flow rate using your meter readings is much
more than the estimated theoretical flow rate there might be
rate,
an underground leak.

15. Precipitation Rate
(Sprinklers)
The average precipitation rate of a sprinkler
system can be…
y
Calculated from the flow rate (Q) and
wetted area (A) or
(A), or…
Directly measured using catch cans.

16. Sprinkler Precipitation Rate
Calculated from flow rate (Q) and wetted area (A).
( )
Equation: PR = 96.3 x Q/A
• Where: PR = water application rate in inches/hour
• Q = flow rate in gallons/minute (gpm)
(gpm)
• A = area in square feet (width x length, feet)
Example:
E l
• Suppose measured flow rate = 20 gpm
• Suppose wetted area = 50’ x 100’ = 5000 sq. ft.
pp q
• Then PR = 96.3 x 20/5000 = 0.39 inches/hour

17. Converting precipitation rate to flow rate
Consider: It takes 0 623 gallons of water to cover
0.623
1 square foot to a depth of 1 inch, so:
so:
To
T convert Precipitation Rate to Flow Rate:
t P i it ti R t t Fl R t
FR = (PR x A x 0.623)/60
• Where;
FR = flow rate in gallons per minute (gpm)
(gpm)
PR = precipitation rate in inches per hour
A = wetted area in square feet
Example from previous slide:
• S
Suppose the wetted area was 50 f
h d 0 feet by 100 f
b feet (A = 5,000 sq. f )
000 ft.)
• The precipitation rate (PR) was 0.39 inches per hour.
Solution:
Solution: FR = (0 39 x 5000 x 0 623)/60 = 20 gpm
(0
(0.39
0.39 0.623)/60

18. Sprinkler System
p y
Direct Measurement of Precipitation Rate
Set out a grid of straight-sided
straight-
catch cans (i.e. tuna cans, soup
cans,
cans coffee cans etc )
cans, etc.)
Run the system for a timed
period and then measure the
water depth in straight-sided
straight-
cans with a ruler.

19. Sprinkler System
p y
Calculating average precipitation rate
To calculate the average precipitation rate:
Find the total of all measurements and divide by the number
of measurements.
Example:
Suppose you set out 10 cans and y ran the sprinkler
pp y you p
system for 30 minutes.
Assume your measurements from the cans were: 0.25, 0.30,
were:
0.30, 0.35, 0.25, 0.20, 0.35, 0.40, 0.20, and 0.30 inches.
The average depth would be:
0.29 inches (the sum of the above measurements [2.9])
divided by 10 ( / )
(2.9/10)
(2.9/10
The irrigation rate would be equal to 0.29 inches
divided by 30 minutes (0 29/30) or 0 0097 inches per
(0.29/30) 0.0097
minute or 0.58 inches per hour (0.0097 x 60).

20. Drip S
Systems
With drip systems
PR = FR/0.623/(D x D x 0.785)
Where:
• PR = precipitation rate in inches
• FR = emitter(s) flow rate in gallons/hour
• D = wetted diameter or plant canopy diameter
Example:
Suppose the emitter flow rate ( ) = 1 gph
pp (FR) gp
Suppose the plant diameter (D) = 3 ft
Then; PR = 1/0.623/(3 x 3 x 0.785) = 0.23 in/hr

21. The Soil
Once you’ve determined the output of your
irrigation system, you need to get an idea of your
soil’s water holding characteristics
characteristics.

22. Soil Water-Holding Characteristics
Water-

23. Soil h ld water lik a sponge!
S il holds t like !
Available Water
Saturated Soil Field Capacity Wilting Point

24. Soil Texture
The amount of water a particular soil will hold
depends on it’s texture (the percentage of sand,
p p g ,
silt, and clay particles).
Sand particles: 0.05 mm to 2.0 mm
Silt particles: 0.002 mm to 0.05 mm
Clay particles: less than 0.002 mm

25. Soil Water Holding Capacity
is Related to Soil Texture
Clayey Soil Texture Sandy Soil Texture
Small particles Larger particles
Low water intake rate High water intake rate
High water holding capacity Low water holding capacity
(heavy soil) (light il)
(li ht soil)

26. Determining Soil Texture
g
Fill a quart canning jar with about 4 inches of tamped soil.
Add water up to about 2 inches below rim of jar.
Seal with lid so it won’t leak.
Shake continuously for about 10 -15 minutes.
Set on flat surface and do not disturb.
After about 48 hours, the soil should settle out in the water
into three distinct layers.
Measure the total soil depth and the depths of each distinct
layer.
Sand will be the bottom layer (it settles out first), silt the middle
layer, and clay the top layer (it settles out last).
last)
Calculate the percentages of sand, silt, and clay
(see next page for example)

27. Example
Suppose you measured 4 5 inches of total soil
4.5
depth, 2.5 inches of sand (bottom layer), 1.5 inch of silt
(middle layer) and 0.5 inch of clay (top layer).
y layer).
The texture would be 56% sand (2.5 ÷ 4.5 x 100), 33% silt
(2.5
(1.5 ÷ 4.5 x 100), and 11% clay (0.5 ÷ 4.5 x 100).
To define the soil type see the soil texture pyramid
– next slide.

28. Soil Texture Pyramid
y
2. Draw another
1. Draw a li
1 D line line from upper right
straight across to lower left from
from % clay scale the % silt scale
(
(example = 11%).
p %) (example = 33%).
33%)
Intersection: sandy loam soil (58% sand)

29. Water Holding Capacity
g p y
Once the soil texture has been determined,
the approximate available water holding
capacity can be estimated.
p y

30. Approximate Available Soil Moisture
pp
in Various Textured Soils
Soil Texture In./In. In./Ft.
(available moisture) (available moisture)
Coarse sand and gravel .04 0.5
Sands .07 0.8
Loamy sands .09 1.1
Sandy loams .13 1.5
Fine sandy loams .16 Our example 1.9
Loams and silt loams .20 2.4
Clay loams & silty clay .18 2.1
loams
Silty clays and clays .16 1.9

31. Feel Test for Soil Type and Moisture
yp
% Water Sandy *Loamy Clayey
Of Field Capacity (coarse) (average) (fine)
(fi )
0-25% Dry,loose, slips Powdery, maybe Dry, cracked, not
between fingers forming a slightly easily reduced to
solid crust powder
25-
25-50% Seems dry, does Brittle but sticks Fairly plastic,
not form a ball together when forms a ball when
when squeezed
h d squeezed d squeezedd
50-
50-75% Forms a loose ball Forms a plastic Forms a ball, can
when squeezed ball, sticky when be stretched
but easily falls squeezed between the
apart thumb and index,
smooth to touch
75-
75-100% Forms coherent Forms a very Same as above
ball, not smooth plastic ball, easily
smoothed
*Loam soil is best.

32. Soil Intake Rate
Due to the larger particle size and hence larger
pore spaces, a sandy soil will absorb water faster
than
th a clayey soil.
l il

33. Soil Intake Rates
Basic Intake Rates
Coarse sand 0.75 – 1.00 in/hr
Fine sands 0.5 – 0.75 in/hr
Fine sandy loams 0.35 0.50
0 35 – 0 50 in/hr
Silt loams 0.25 – 0.40 in/hr
Clay loams 0.10 – 0.30 in/hr

34. Water Percolation
i Diff
in Different S il T
Soil Textures (Drip Irrigation)

35. Summary
Because a clay soil holds more water than a sandy soil,
a greater volume of water must be applied to a cla soil
ol me ater m st clay
to penetrate to an equal depth.
However,
However because of the lower intake rate of a clay soil
soil,
the water application rate (precipitation rate) must be less
than on the sandy soil to prevent runoff or excessive
y p
puddling.
Once an equal water penetration depth is reached on both
soils,
soils, the required irrigation frequency will be less on the
clay soil since it holds more plant available water than the
sandy soil.
y

36. Notes
Most native, xeric plants prefer a sandy soil with good drainage.
Root rot may occur in heavy clay soils that hold too much water.
water.
If irrigated properly using drip irrigation deep drainage and
properly, irrigation,
runoff will not occur in a Xeriscape™.

37. Determining Soil Chemistry & Fertility
g y y
Sample
Sampling Kit can be obtained Examine
from NMSU Cooperative
Extension Services throughout
the state.
Ex. NMSU CES San Juan
County 213-A S. Oliver Ave.
213-
Aztec,
Aztec, NM 87410
Phone: 505-334-
Phone: 505-334-9496

38. In Fi ld Soil Moisture
I Field S il M i t
During the year, periodically examine the top foot of your soil
near the base of your plants using a long screwdriver or
similar rod.
i il d
By experiencing what the soil feels like when it’s wet and when
it s dry you ll
it’s dry, you’ll be able to estimate how much water each plant
is using and you’ll be able to manage your irrigations much
more effectively.

39. Plant Water Requirements
Saving
S i water i the l d
in h landscape i more a f
is function of careful
i f f l
irrigation management than of plant selection.
selection.
Many xeric (drought-tolerant) plants can (and will) use just
(drought-
as much water as non-xeric plants, if this water is available
non-
to them.
them.
The difference is – xeric plants can survive and prosper under
low-
low-water conditions that would be detrimental to (or kill)
species not adapted to arid conditions.

40. Additional C
Additi l Considerations
id ti
With landscape plants, economic yield or plant size is not of
p
primary concern.
y concern.
The primary goal is to provide just enough water, fertilizer, etc.
to result in an acceptable plant specimen for a quality landscape
landscape.

41. Evapotranspiration (ET)
Evaporation – loss of water directly from soil and plant surfaces.
surfaces.
Transpiration – loss of water from plant internal tissues through
the leaf stomates, during photosynthesis.
stomates,

42. ET is related to…
Atmospheric demands (weather)
(weather)
Air temperature
Solar radiation
Relative humidity
Wind
Generally, ET increases with higher temperature,
greater solar radiation higher wind and lower humidity
radiation, wind, humidity.

43. ET is also related to…
Size of the plant.
plant.
Live leaf area (canopy) of the plant.
plant.
Microhabitat (i e microclimate) and other factors
(i.e. factors.

44. Estimating ET
for Irrigation Scheduling
For many years, irrigation managers have used climate-based
climate-
reference (or potential) ETR values, along with correction factors
(crop-coefficients or KC values) to help them efficiently schedule
crop-
irrigations on agricultural crops and turfgrass.
turfgrass.
Due to a lack of research, the technique has received limited
use for scheduling irrigations on landscape plants, particularly
xeriscapes.
xeriscapes.
i

45. How th system works
H the t k
A reference ET (ETR) is calculated from weather data
(ET
collected from an approved, standard weather station.
See: http://weather nmsu edu.
See: http://weather.nmsu.edu.
http://weather.nmsu.edu
ETR is then multiplied by a correction factor (crop coefficient) to
estimate the ET of a crop based on the plants size, canopy
area, maturity, etc.
t it t
Generally, for alfalfa the crop coefficient (KC) is equal to
(K
1 during most of the year.
year.
Cool Season Turf: 0.8, Warm season turf: 0.6
The canopy area for alfalfa and grass is usually considered
py g y
to be 100% of the (irrigated) area.
area.
™
The canopy area for a well-developed, mature Xeriscape
well-
may be 60% or less of the total (irrigated) area
area.

46. Automated Weather Station – Calculation of ETO
Wind Speed Wind Direction
Solar Radiation Air Temperature
Precipitation
Data Logger
D t L Relative H midit
Relati e Humidity
Solar Charger
12V Battery

47. Xeriscape™ Water Requirements
Based on observations of differentially irrigated xeric
plants at the A i lt l S i
l t t th Agricultural Science C t at F
Center t Farmington,
i t
a crop coefficient of between 0.2 and 0.4 should be
sufficient for most xeric plants (compared to 1 0 for alfalfa
1.0
and 0.8 and 0.6 for cool season and warm season turf,
respectively).
Also,
Also, the canopy area for a well-developed, mature
well-
Xeriscape™ is generally considered to be about 60% of
p g y
the landscape (compared to 100% for alfalfa and grass).
grass).

48. Drip Irrigation Scheduling
Considerations
Reference ET and irrigation recommendations are usually
provided in inches but drip emitter flow rates are expressed in
gallons.
gallons.
It takes 0.623 gallons of water to cover 1 square foot to a
depth of 1 inch.
inch.
With xeric landscape plants, the wetted area (or plant canopy
area) is usually circular.
circular.
Formula
Form la for converting ET (or irrigation or precipitation) depth
con erting
in inches to gallons for a landscape plant:
Gallons = ET x 0.623 x A
• Where:
ET = Irrigation or precipitation depth in inches
A = wetted or plant canopy area in square feet
• A f i l diameter squared (d2) x 0.785
Area of a circle = di t d 0 785

49. Summary
Determining the water requirement in gallons
for a xeriscape plant:
Gallons = ETR x KC x 0 623 x CA
0.623
Where:
• ETR = reference ET from weather station data (inches)
• KC = correction factor (or crop coefficient)
• 0.623 = constant to convert inches to gallons
• CA = crop canopy area in square feet

50. Climate-
Climate-Based Irrigation Scheduling
™
Example P bl
E l Problem f a X i
for Xeriscape Plant
Pl t
Given:
The reference ET (ETR) for the week is 2.0 inches.
The plant to be irrigated has a canopy diameter (D) of 4 feet.
feet.
The crop coefficient (KC) or correction factor is 0.3.
There is one 2 gph emitter at the base of the plant.
plant.
Questions:
Questions:
What is the plant’s canopy area (CA)?
• A
Area = D x D x 0 785 = 4 x 4 x 0 785 = 12 56 sq. ft
0.785 0.785 12.56 ft.
How many gallons should be provided per week to satisfy the
recommended irrigation (or plant ET) depth?
• Gallons = ETR x KC x 0.623 x A =
2 x 0.3 x 0.623 x 12.56 = 4.7 gals.
gals.
How long will the system need to be run to provide the
recommended precipitation depth.
depth.
• 4.7 gallons ÷ 2 gph = 2.35 hours or 2 hrs and 20 minutes

51. Average Daily Reference ET in inches per day (ETR)
(ET
and plant ET Estimates in Gallons for Xeric Plants at
Different Canopy Areas (CA) during a Typical Season
in Farmington, NM (KC = 0.30)
Farmington,
Month May June July Aug Sept
Days of 1-15 16-
16-31 1-30 1-31 1-31 1-15 16-
16-30
Month
ETR per day
p y 0.35 0.40 0.42 0.38 0.28 0.25 0.22
Plant D in ft. Gallons of Water per Plant per Week*
(CA, ft2)
1 (0.8) 0.4 0.4 0.4 0.4 0.3 0.3 0.2
2 (3.1) 1.4 1.6 1.7 1.5 1.1 1.0 0.9
3 (7.1)
(7 1) 3.2
32 3.7
37 3.9
39 3.5
35 2.6
26 2.3
23 2.0
20
4 (12.6) 5.7 6.6 6.9 6.2 4.6 4.1 3.6
5 (19.6) 8.9 10.2 10.7 9.7 7.1 6.4 5.6
6 (28 3)
(28.3) 12.9
12 9 14.7
14 7 15.5
15 5 14.0
14 0 10.3
10 3 9.2
92 8.1
81
*Gallons/week/plant = ETR x 0.3 x 0.62 x CA x 7 days

52. More complete detailed list at:
p
http://cahe.nmsu.edu/aes/farm/documents/2007xericrevproceedingsforia.pdf
http://cahe nmsu edu/aes/farm/documents/2007xericrevproceedingsforia pdf
http://cahe.nmsu.edu/aes/farm/documents/2007xericrevproceedingsforia.pdf
://cahe

53. When irrigations are scheduled properly a
properly,
™
Xeriscape garden can save significant amounts of
water compared to turfgrass.
Refer to next slide.
Assumptions
• Cool season turf KC = 0.80; coverage = 100%
• Warm season turf KC = 0 60 coverage = 100%
W t f 0.60;
• Xeriscape KC = 0.30; coverage = 60%

54. Average Monthly Reference ET (ETR) and
g y (
Required Irrigation per 1000 Square Feet:
Turf vs. Xeriscape™ (XSCAPE)
Month ETR CS Turf WS Turf XScape
inches Gallons/1000 sq. ft.
May 11.6
11 6 5781 4336 1301
June 12.6 6280 4710 1413
July 11.8 5881 4411 1323
Aug 8.7
87 4336 3252 976
Sept 7.1 3539 2654 796
Total 51.8 25817 19363 5809

55. Xeriscape Irrigation Summary
™
The irrigation requirement of xeric plants depends upon the
species,
species, the plant size, and the weather (including
precipitation).
precipitation).
While many xeric plants, once established, will grow and
plants,
exhibit acceptable q
p quality without irrigation…
y g
Most will benefit from between 4 and 10 gallons of
supplemental irrigation water per week (8 to 20 gallons
every 2 weeks) during mid-summer.
mid-summer.

56. End of Module 6
IRRIGATION MANAGEMENT