Improving Drip Irrigation for Grape Vines

Dr. Franklin GaudiIrrigation Training and Research

Center (ITRC) at Cal Poly

1

However….

• Before you can schedule irrigations, we need to make sure the system is performing well.

• Have you conducted a DU evaluation?

What is DU?

• Distribution Uniformity

– The measure of how evenly water is applied to the field

– Always expressed as a decimal value

– DU of 0.90 is achievable with PC emitters

DU

(NEVER PERFECT)GOOD UNIFORMITY

Depth of

Water

(NEVER PERFECT)GOOD UNIFORMITY

Depth of

Water

GOOD UNIFORMITY

Depth of

Water

Depth of

Water

Depth of

Water

POOR UNIFORMITY

Depth of

Water

How is DU calculated?

• DU = Avg. depth of the low quarter

Avg. depth infiltrated over the entire field

1

0

1

2

3

4

5

6

25 50 10075

Contribution to Target = 2.75 avg.

2.25 = Avg. Low 1/4 Inf.

Portion of AreaS

urf

ace L

oss

Infi

ltra

ted

Dep

th o

f W

ate

r

Underirrigation = 0.25 Avg.

Deep Perc. = 0.25 Avg.

Avg. Applied = 3

Target = 3

3 SMD

Is DU Different than Efficiency?

• YES!

– Efficiency describes how much water was beneficially used compared to what was applied

– Always expressed as a percentage

– Efficiency can be high, especially if you under-irrigate.

Efficiency

Efficient

Depth of

Water

Efficient

Depth of

Water

Depth of

Water

Depth of

Water

Not Efficient

Depth of

Water

What are Beneficial Uses?

• Crop ET

• Leaching

• Cover crop

• Climate control

• Weed germination

Irrigation Managers prefer…

• DU over Efficiency

– DU is repeatable

• It can be maintained

– Efficiency can only be determined after the event or the season

• It can be different each event depending on the duration and the initial soil moisture content

Water Destination Diagrams

• These are used to graphically show how well your system is performing and how efficient the event was.

– It also shows were the losses are and what is beneficially used

Water Destination Diagram:Under-Irrigation

Depth of Water (inches)

Field Area (%) 1000

0

D max

D min

Deep Percolation

SMD

Stored for Plant ET

Pre-Infiltration Losses

Deficit

Water Destination Diagram:Over-Irrigation

ITRC/BRAE

1000

Depth of Water (inches)

Field Area (%)

0

D max

D min

Deep Percolation due to DU

SMD

Stored for Plant ET

Pre-Infiltration Losses

Deep Percolation due Poor Timing

Basic Idea for Improvement #1

• Achieve a high DU

– ITRC offers a week long training on Irrigation System Evaluation

• Next Class is June 18-22, 2018 at Cal Poly

• www.itrc.org for more details

Things to Check• There are two basic ideas:

– #1. Ensure the pressures throughout the vineyard are as uniform as possible• This means adjusting pressure regulators so that

each manifold has the same inlet pressure

• Look for large pressure losses at the filters or along the manifolds

• Remove hose screen washers

Pressure Regulators

Things to Check• There are two basic ideas:

– #2. Ensure that the flow from each of the emitters is uniform.

• Flush hose ends and manifolds at least monthly

• Ensure good filtration

• Don’t just add emitters

Testing Emitters

Make sure your water goes to all plants uniformly

Avg. DU = 0.86

Basic Idea for Improvement #2

• Keep Records

Can you look back…

• 5 years and tell me what day you applied water in June?

• And tell me how much water you applied?

Good records help you look back and see what worked and what didn’t work.

Basic Idea for Improvement #3

• Always use flow measurement

– Do you have a flow meter?

– How often do you record the volume of water applied?

• If you can’t measure it, you can’t manage it!

• You need good flow rate measurements, to avoid driving without a speedometer.

Basic Idea for Improvement #4

• Really learn about your crop.

In Paso, is there just one “ET rate” for wine grapes – given one day and one age?

For Wine Grapes, a big factor influencing ET is

* The % canopy cover, or

“% ground shading at noon”

The cover crop ET is higher than the vine ET

Basic Idea for Improvement #5

• Technology can be helpful…

– But if you get too fancy, or if you believe in magic, it’s probably not going to work for you.

Just a thought…

What does a soil moisture sensor such as a “capacitance meter” tell you, in a drip/micro irrigated orchard?

And very specifically, how will you use the NUMBERS?

What a soil moisture sensor tells you with drip irrigated vines.

• When the water reaches a depth (assuming you have a real-time data logger on that sensor)

• The approximate moisture content or stress within about 2” of that sensor.

What a soil moisture sensor does NOT tell you with drip irrigated vines.

• The ET of the vines.• The average soil moisture content• The average soil moisture tension

***Instead, it is a POINT measurement. It is NOT a representative sample.

Never rely exclusively on one technique for irrigation scheduling.

Use a combination of

- ET based scheduling

- Plant indicators

- Soil moisture indicators

What about telemetry?!

You don’t need exquisite hourly or daily values.

Weekly values of ET are fine.

Keep in mind that digging backhoe pits, auger holes, and using soil moisture sensors are all helpful.

Just don’t start believing in magic!!

Keep your hand on your wallet when talking to people selling all sorts of

fabulous sensors.

Basic Idea for Improvement #6

• Use technology to improve your yield.

Google and Satellite Remote Sensing now

provide fantastic information.

Poor stand in a portion(Notice the lower ETc in that area)

Variability

• Do these areas have similar yields (quantity/quality)?

• Not Likely

• Should they?

Basic Idea for Improvement #7

• Look at the big picture.

Single Irrigation Block

• If this system is a single block

• Where are tissues sampled?

• How do you manage deficits?

Could we Split the Irrigation Blocks

• Now we have more options

• Probably need a VFD

• Proper injection equipment

• Provides more uniform pressures– Remember the idea of DU?

Targeted Nutrient Applications

Now we have options:

• Ground based variable rate application

• Inject at main supply and operate blocks differently

• Inject at individual blocks (blocks operated at the same time)

Basic Idea for Improvement #8

• Don’t just add on to an existing block!

– That affects the hydraulics of the system

– It also affects the operation of the pump

– Together this greatly reduces the pressure available in the hoses

• Rather do the opposite if needed, add blocks.

Basic Hydraulics

• More flow in the mainline means more friction

• More friction means lower pressures at the manifolds

• Lower pressures at the manifolds means reduce flow rates

– PC emitters have helped limit this problem.

Pump Curve

• A larger flow requirement in the field means the pump needs to supply more flow

• More flow from the pump means the pump produces less pressure

• So you start with lower pressure and then you have more friction too!

– This means dismal pressures in the field

Sample Pump Curve

0

20

40

60

80

100

120

140

160

180

200

0 500 1000 1500 2000 2500 3000

TDH

(ft

)

Flow Rate (GPM)

Pump Curve

Pump Curve

Microspray and Drip

Pressure

Differences -

44.9%

Plugging, Wear,

Manufacturing

Variation - 51.5%

Unequal

Drainage - 1.1%

Application Rate

- 2.5%

Get a Resource

• ITRC wrote the book on drip/micro irrigation systems.

– It is available at www.itrc.org

Questions?