Pulse 

and Drip Irrigation 
Management of Vegetables 

Timothy Coolong
Timothy Coolong
Department of Horticulture
University of Kentucky
Non sustainable irrigation practices
 Water and plants
Water and plants
• For
For every gram of organic matter (growth) 
every gram of organic matter (growth)
made by a plant on average 500 g of water is 
absorbed
• Water is required for:
– Cell expansion/growth (turgor
C ll i / th (t pressure))
– Solute transport
– Cooling the plant
l h l
 Irrigating vegetable crops
Irrigating  vegetable crops
• Most
Most horticulture crops are 
horticulture crops are
sold fresh
– Contain 80‐90% water by 
Contain 80 90% water by
weight
– Sold on appearance, must 
Sold on appearance must
have high quality
 Water related disorders

• Blossom end rot
• Blossom drop
 Irrigation Systems
Irrigation Systems
• Overhead systems
Overhead systems
– Center pivot
– Traveling gun
– Fixed/Solid set
– Drip Irrigation
 Irrigation Efficiency
Irrigation Efficiency
• Iwue‐
Iwue Irrigation water use efficiency
Irrigation water use efficiency‐
Water used for plant growth / Amount of 
i i i
irrigation water applied
li d
• Surface ‐30‐50% 
• Overhead‐70‐90% 
• Drip
Drip‐ 90
90‐95%
95% 
 Drip Irrigation
• For many vegetable growers drip irrigation is 
the most practical solution
the most practical solution
 Drip Irrigation Systems
Drip Irrigation Systems
• Drip irrigation
Drip irrigation
– Surface drip
– Surface under plastic
– Sub‐surface drip
Why Drip Irrigation? Advantages…
Why Drip Irrigation? Advantages…

• Reduced
Reduced water
water
• Usually fewer weeds between rows
• Space between rows remains hard & 
dry for equipment, harvesting
• Low pressure low flow
 Why Drip?
• Overhead irrigation can 
increase disease 
potential
– Flooding can spread soil‐
borne diseases
– Overhead can spread 
foliar diseases
foliar diseases
Why Drip Irrigation? Disadvantages…
Why Drip Irrigation? Disadvantages…

• Expensive and labor intensive‐large fields
Expensive and labor intensive‐large fields
• Clean water needed to prevent clogging
• Rodent & insect damage
Rodent & insect damage
Small system costs (Annual Costs)
Small system costs (Annual Costs)
Annual per acre expenses:
Annual per acre expenses:
8‐10 mil drip tape + embossed black plastic 
mulch (1 25 mil 4 ft wide roll): approx 4 5
mulch (1.25 mil, 4 ft wide roll): approx. 4.5 
cents/ft x 7260 linear feet = $450

plus depreciation or rental costs on mulch 
layer, waterwheel setter, etc.  
Backflow valve‐a must for city water‐well water
Screen Filter‐good for 
municipal or clean well water
municipal or clean well water
Disk Filter‐good for 
municipal or clean well 
water  creek although will 
clean dirtier water than a
clean dirtier water than a 
screen filter‐not good for 
sand
 Irrigation management
Irrigation management
• Irrigation is essential in most vegetable crops
Irrigation is essential in most vegetable crops
• How to manage it
– When to irrigate
When to irrigate
– How long to irrigate
• Crop demand (evapotranspiration) based 
p ( p p )
irrigation (checkbook method)
– Weather and crop coefficients
• Soil moisture based irrigation
– Maintain soil moisture between certain thresholds
 How much to irrigate?
g
Crop Inches/acre Critical times
Lettuce 8‐10 Establishment
Carrots 10‐15 Emergence
Beans 10 15
10‐15 Bloom and pod set
and pod set
Beets 10‐15 Establishment
Melons 15‐20 Vining to first net
Broccoli 20‐25 Heading
Tomato 20‐25 Bloom ‐ harvest
Cabbage 20‐30 Throughout growth
Onion 25‐30 Bulbing
Potato 20‐40
20 40 Vining‐tuber
Vining tuber initiation
initiation
Corn 20‐35 Tassel formation and ear development
 Evapotranspiration

Crop evapotranspiration ‐ Guidelines for computing crop water requirements ‐ FAO Irrigation and drainage paper 56

 Evapotranspiration in Lexington
in Lexington
Annual distribution of Eto
12

10 ETo

8
Eto (mm/day)

0
1/0 1/30 2/29 3/30 4/29 5/29 6/28 7/28 8/27 9/26 10/26 11/25 12/25
Day of year 2010
y y
 Temporal distribution of weekly moving average of Eto during 
Temporal distrib tion of eekl mo ing a erage of Eto d ring
crop growth
10

ET
ETo
9
day)

8
Eto (mm/d

5
6/28 7/12 7/26 8/9 8/23 9/6
Day of year 2010
Irrigating Based on Estimated Crop Use
Irrigating Based on Estimated Crop Use

• Crop water requirements.
– 1 acre inch is 27,000 gallons of water
– Usually 33‐50% of land is drip irrigated
U ll 33 50% f l d i d i i i t d
• Crops that require 1 inch of water/wk need 13,500 gallons per acre
• Peak Et
Peak Etc (water use) usually 0.2 
(water use) usually 0 2 – 0.3 in./day.
0 3 in /day
– 5,430 – 8,146 gal/acre/day.
– Usually 33‐50% of an acre is drip irrigated.
y p g
 Determining Irrigation Time and Amounts

• If crop Et
p c c ((water use)) is 0.20 acre inches/day then 
/ y
crop used (0.2 x 27,154 gal/acre in. x .50 [area covered by 
plastic]) or 2,715 gal of water.

• If field has 6 ft rows and uses 0.42 gpm/100’ drip 
tape Operating properly this is 30 gal/ac/min Rate
tape. Operating properly this is 30 gal/ac/min. Rate 
per hr. is 1,800 gal.

• 1.5 hrs application time (2715 gal/acre / 1800 gal.) 
 Consideration: Pipe Size 
Requirements
• General size requirements
General size requirements
Gallons per minute Pipe Size
5 ½
10 ¾
15 1
25 1 ¼
35 1 ½
55 2 
85 2 1/2 
125 3
 Soil moisture based irrigation
Soil moisture based irrigation
• Monitor
Monitor soil moisture and supply water as 
soil moisture and supply water as
needed
– How do you measure soil moisture
How do you measure soil moisture
• Tensiometer, watermark sensor, touch?
– How much water do you add?
How much water do you add?
• Irrigation shallow or deep?
• Soil type, structure and rooting depth
yp , g p
 Water Management and Schedule

• Available water key to crop growth.
y pg
– Relationship between plant‐soil‐water
– Soil that contains plants roots is water reservoir
• Field Capacity ‐ water stored in soil 12‐24 hrs after 
saturation.
• Permanent Wilting Point
Permanent Wilting Point – water no longer available 
water no longer available
to plant.
• Available Water Holding Capacity
Available Water Holding Capacity ‐difference
difference 
between Field Capacity and Wilting Point.
 Irrigating to saturate soil
Irrigating to saturate soil
• An ideal loam soil will be:
An ideal loam soil will be:
– 45% “soil” ie. minerals
– 25% micropores
25% micropores (small air spaces between soil 
(small air spaces between soil
particles‐hold water)
– 25% macropores
25% macropores (root and worm holes, etc‐hold 
(root and worm holes etc‐hold
air and water)
– 5% organic material
5% organic material
 Soil Available Water
Soil Available Water
V
Very tightly bound
ti htl b d

Hygroscopic (unavailable) 
water Capillary (available) water

Drainage
 Sand

Silt

Clay

Sand 0.5‐2.0mm Silt 0.002 to 0.05 Clay <0.002  mm

 Moisture release curve for silt loam 100

Soil moistture tension (cb)
80

60

40

20

0
1200 0.20 0.25 0.30
Volumetric water content
on (cb)

1000
Soil moissture Tensio

800
Permanent Wilting Point (Death)
600
Saturation (Flooding)
Saturation (Flooding)
400

200

0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
Volumetric Water Content
 500
450
400
e Tension (cb)

350
Clay loam
300
Silt loam
250
Soil Moisture

200
150
100
Sandy loam
50
0
0.05 0.10 0.15 0.20 0.25 0.30
Volumetric water content %
 How long do I irrigate?
How long do I irrigate?
• Irrigate deep
Irrigate deep‐then
then have a reserve.
have a reserve
– Not necessarily
• Depends on subsoil 
Depends on subsoil
• Irrigate based on maximum rooting depth of 
vegetables
– Peppers: Approximately 12”
– Tomato: Approximately 18”

R ti d it b d th
Rooting density by depth
70
Weight

60
Tomato
Perccentage of Roots by W

50
Pepper
40
30
20
10
0
0"‐3" 3"‐6" 6"‐9" 9"‐12" 12"‐15"
 Irrigating too deep?
Irrigating too deep?
• With
With heavy clay subsoils
heavy clay subsoils irrigate more 
irrigate more
frequently and shorter duration
• How else can you influence irrigation depths 
How else can you influence irrigation depths
and water use
– Flow rate on drip tape
Fl t di t
 “Pulsing”
Pulsing  irrigation
irrigation
• Wanted
Wanted to look at more frequent but shorter 
to look at more frequent but shorter
irrigation regimes to save water
– Previous research funded by New Crops 
Previous research funded by New Crops
Opportunities Grant
– NRCS funded Conservation Innovation Grant for 
NRCS funded Conservation Innovation Grant for
2010/2011
• Tomatoes and peppers, blackberries and blueberries
p pp ,
 35 6" depth 8

ntent 
12" depth
rainfall
oil water con
30 6

(cm3 cm‐3)
Pulsed
25 4
Volumetric so

20 2

15 0
V

7/1 7/21 8/10 8/30 9/19

35 Date 8
ntent 
oil water con

30 6
(cm3 cm‐3)

25 4 Manual
Volumetric so

20 2

15 0
V

7/1 7/21 8/10 8/30 9/19

Date
 Poblano pepper research
Treatment Total Total Run Time days, Average  Water  Water use 
Number  hours, minutes Run Time  Used efficiency
of Events (min.)
30/25 cb 83 5 days 4 hrs 25 min 90 225,720 0.09 lbs/gallon
40/35 72 5 days 18 hrs 35 min 115 251,460 0.08 lbs/gallon
50/45
/ 63 6 days 8 hrs 38 mins
6 days 8 hrs 38 mins 145 276,900 0.08 lbs/gallon
0.08 lbs/gallon
50/10 
(manual) 49 4 days 13 hrs 48 mins 135 199,200 0.09 lbs gallon

This suggests keeping soil slightly wetter through 
shorter more frequent irrigations rather than 
letting it dry out completely allows it to re‐wet 
quicker and use less water
 Using flow rate or emitter spacing 
to better manage irrigation
• Some
Some growers prefer to use a short 4
growers prefer to use a short 4” spacing 
spacing
to wet top of bed quicker
• Or‐keep the same emitter spacing but use 
Or keep the same emitter spacing but use
different flow rates
– Flow rate will alter wetting pattern
Fl t ill lt tti tt
Wetting patterns: High emitter 
d h
discharge rate (>0.5 gpm
( 100’)
’)
Wetting patterns: Low discharge rate 
(
(<0.50 gpm 100’)
’)
 Future directions
• Develop more water budgets for drip and 
plastic
l i
• Automation…….to stop irrigation
Questions