IRRIGATION WATER IRRIGATION WATER MANAGEMENTMANAGEMENT

Rick Schlegel Rick Schlegel Irrigation Engineer Irrigation Engineer

USDA - NRCSUSDA - NRCS

How is irrigation water managed?How is irrigation water managed?

By efficiently applying the correct amount By efficiently applying the correct amount of water into the soil to meet the needs of of water into the soil to meet the needs of the crop being grown.the crop being grown.

How do we know how much water How do we know how much water should be applied?should be applied?

By knowing how much water is needed in By knowing how much water is needed in the soil for the crop within the root zone of the soil for the crop within the root zone of that crop.that crop.

How do we know how much water How do we know how much water is needed in the root zone?is needed in the root zone?

The method we are going to discuss in this The method we are going to discuss in this presentation is a water accounting method presentation is a water accounting method known as “Checkbook Scheduling”.known as “Checkbook Scheduling”.

CHECKBOOK IRRIGATION CHECKBOOK IRRIGATION SCHEDULINGSCHEDULING

is the concept of managing your irrigation is the concept of managing your irrigation water in the same manner as you would water in the same manner as you would manage your checkbookmanage your checkbook

There are deposits – rainfall and irrigationThere are deposits – rainfall and irrigation There are withdrawals – crop usage and There are withdrawals – crop usage and

evaporation (Evapotranspiration) & deep evaporation (Evapotranspiration) & deep percolationpercolation

There is a balance – the water balance There is a balance – the water balance remaining in the soil available to the crop remaining in the soil available to the crop

CHECKBOOK IRRIGATION CHECKBOOK IRRIGATION SCHEDULINGSCHEDULING

There are overdrafts – if your crop water There are overdrafts – if your crop water usage exceeds the water balance that you usage exceeds the water balance that you are managingare managing

TYPICAL CROP ROOT ZONE

THE ROOT ZONE IS OUR

BANK ACCOUNT

THE ROOT ZONE IS OUR

BANK ACCOUNT

RAINFALL

IRRIGATION

DEPOSITSDEPOSITS

EVAPORATION

TRANSPIRATION

ETEVAPOTRANSPIRATION

ETEVAPOTRANSPIRATION

WITHDRAWALSWITHDRAWALS

DEEP PERCOLATION

““BANK ACCOUNT SIZE”BANK ACCOUNT SIZE”IS DETERMINED BYIS DETERMINED BY

AVAILABLE WATER CAPACITY AVAILABLE WATER CAPACITY (AWC)(AWC)

THE ROOT ZONE CAN ONLY HOLD SO MUCH THE ROOT ZONE CAN ONLY HOLD SO MUCH WATER ( FIELD CAPACITY ). THE REST IS WATER ( FIELD CAPACITY ). THE REST IS LOST TO DEEP PERCOLATION.LOST TO DEEP PERCOLATION.

““AWC” IS THE AMOUNT OF WATER HELD IN AWC” IS THE AMOUNT OF WATER HELD IN THE ROOT ZONE OF THE CROP THAT IS THE ROOT ZONE OF THE CROP THAT IS AVAILABLE TO THE CROP.AVAILABLE TO THE CROP.

AWC

AVAILABLE WATER

CAPACITY

AVAILABLE WATER

CAPACITY

SANDY CLAY LOAM, LOAM, & SILT LOAM1.8 IN/FOOT

SANDY CLAY LOAM, LOAM, & SILT LOAM1.8 IN/FOOT

SANDY LOAM & FINE

SANDY LOAM1.5 IN/FOOT

SANDY LOAM & FINE

SANDY LOAM1.5 IN/FOOT

FINE SAND AND LOAMY FINE SAND

0.9 IN/FOOT

FINE SAND AND LOAMY FINE SAND

0.9 IN/FOOT

CLAY, CLAY LOAM &

SILTY CLAY LOAM

2.0 IN/FOOT

CLAY, CLAY LOAM &

SILTY CLAY LOAM

2.0 IN/FOOT

ACCOUNT BALANCE:(AVAILABLE WATER)

LIMITED BY SOIL TYPE AND ROOT

DEPTH

ACCOUNT BALANCE:(AVAILABLE WATER)

LIMITED BY SOIL TYPE AND ROOT

DEPTH

ALWAYS START WITH A FULL

BANK ACCOUNT (PRE-WATERING IS ESSENTIAL)

ALWAYS START WITH A FULL

BANK ACCOUNT (PRE-WATERING IS ESSENTIAL)

START FULL

EXAMPLE:EXAMPLE:

GROWING COTTON ON CLAY LOAM GROWING COTTON ON CLAY LOAM SOILSOIL

MANAGE 4.0 FOOT ROOT DEPTHMANAGE 4.0 FOOT ROOT DEPTH CLAY LOAM HOLDS 2.0 IN/FOOTCLAY LOAM HOLDS 2.0 IN/FOOT AWC = 4.0 X 2.0 = 8.0 INCHESAWC = 4.0 X 2.0 = 8.0 INCHES

How should we manage this 8.0” How should we manage this 8.0” account ?account ?

Most crops are able to obtain water freely Most crops are able to obtain water freely from the soil until about one half of the from the soil until about one half of the available water is left in the soil (in our available water is left in the soil (in our example: 4.0 inches). At that point the soil example: 4.0 inches). At that point the soil starts to become stingy and the crop has starts to become stingy and the crop has to do more and more work to retrieve the to do more and more work to retrieve the available water. As the available water available water. As the available water goes to zero the crop will start wilting and goes to zero the crop will start wilting and the crop production can be permanently the crop production can be permanently damaged. damaged.

For most crops the account should be For most crops the account should be managed to replace moisture that has managed to replace moisture that has been used by the crop when the account been used by the crop when the account balance reaches one half of the AWC.balance reaches one half of the AWC.

This concept of managing the account is This concept of managing the account is known as “Management Allowable known as “Management Allowable Depletion” or “MAD Water Balance”.Depletion” or “MAD Water Balance”.

In our example the MAD Water Balance is In our example the MAD Water Balance is 4.0 inches (one half of the AWC).4.0 inches (one half of the AWC).

The account will be managed by The account will be managed by scheduling irrigations and recording scheduling irrigations and recording rainfall to keep the MAD Water Balance rainfall to keep the MAD Water Balance above zero. above zero.

AWC

MAD WATER

BALANCE

MAD WATER

BALANCE

MADSTINGY

““MAD” EXAMPLESMAD” EXAMPLES

CROP WITH FOUR FOOT ROOT ZONE:CROP WITH FOUR FOOT ROOT ZONE: CLAY, CLAY LOAM, OR SILTY CLAY CLAY, CLAY LOAM, OR SILTY CLAY

LOAM AWC = 8.0” MAD WB= 4.0”LOAM AWC = 8.0” MAD WB= 4.0” SANDY CLAY LOAM, LOAM, OR SILT SANDY CLAY LOAM, LOAM, OR SILT

LOAM AWC = 7.2” MAD WB= 3.6”LOAM AWC = 7.2” MAD WB= 3.6” SANDY LOAM OR FINE SANDY LOAM SANDY LOAM OR FINE SANDY LOAM

AWC = 6.0” MAD WB= AWC = 6.0” MAD WB= 3.0”3.0”

FINE SAND OR LOAMY FINE SAND FINE SAND OR LOAMY FINE SAND AWC = 3.6” MAD WB= 1.8” AWC = 3.6” MAD WB= 1.8”

AVAILABLE WATER CAPACITY AVAILABLE WATER CAPACITY CAN ALSO BE LIMITED BY:CAN ALSO BE LIMITED BY:

PLOW PAN

AWC

What will I need to do to be able to What will I need to do to be able to manage my water using this manage my water using this

checkbook method?checkbook method?

Work with your local NRCS office to Work with your local NRCS office to develop an Irrigation Water Management develop an Irrigation Water Management plan for each crop and field.plan for each crop and field.

Basic items needed to develop the plan Basic items needed to develop the plan are: Crops to be grown, types of soils, type are: Crops to be grown, types of soils, type of irrigation system, and amount of water of irrigation system, and amount of water available to the fieldavailable to the field

What will NRCS provide?What will NRCS provide? They will develop an Irrigation Water They will develop an Irrigation Water

Management plan for each field that will tell you: Management plan for each field that will tell you: 1. What your MAD Water Balance will be1. What your MAD Water Balance will be 2. How long you will need to operate your 2. How long you will need to operate your

system in order to apply the correct amount of system in order to apply the correct amount of water to the field to refill the root zonewater to the field to refill the root zone

3. How you will need to operate your system to 3. How you will need to operate your system to save water, make maximum use of rainfall, save water, make maximum use of rainfall, prevent erosion or runoff, use of limited water at prevent erosion or runoff, use of limited water at critical crop growth stages, and estimate annual critical crop growth stages, and estimate annual irrigation water requirements. irrigation water requirements.

What will I need to do after the IWM What will I need to do after the IWM plan is provided to me ?plan is provided to me ?

Manage my system in accordance with the Manage my system in accordance with the IWM planIWM plan

Do “Checkbook Scheduling” of my Do “Checkbook Scheduling” of my irrigations by tracking evapotranspiration, irrigations by tracking evapotranspiration, rainfall, and irrigation applicationsrainfall, and irrigation applications

Manage my water balance in the soil to Manage my water balance in the soil to save water or make the best use of water save water or make the best use of water and still meet my crop needs and still meet my crop needs

I know how to determine the I know how to determine the amount of rainfall and the amount amount of rainfall and the amount

of my irrigation application, but how of my irrigation application, but how do I know how much water my crop do I know how much water my crop

uses daily ?uses daily ?

Crop water usage is basically estimated from Crop water usage is basically estimated from Evapotranspiration (ET) dataEvapotranspiration (ET) data

You can get daily ET data from two sources: an You can get daily ET data from two sources: an Atmometer (ETgage) in your field or from the Atmometer (ETgage) in your field or from the Oklahoma Mesonet weather station in your Oklahoma Mesonet weather station in your county county

What is an Atmometer or ETgage?What is an Atmometer or ETgage?

It is a gauge that measures ETa or ETg, that is It is a gauge that measures ETa or ETg, that is relatively inexpensive, can be located in your relatively inexpensive, can be located in your field, and can be read as easily as a rain guage. field, and can be read as easily as a rain guage. It does not have to be read everyday.It does not have to be read everyday.

Since it can be located directly in your field, I Since it can be located directly in your field, I feel it gives a more accurate representation of feel it gives a more accurate representation of your crop water usage than a remote weather your crop water usage than a remote weather station.station.

NRCS can work with you to set up the gauge in NRCS can work with you to set up the gauge in your field and teach you how to use it.your field and teach you how to use it.

EVAPOTRANSPIRATION FROM EVAPOTRANSPIRATION FROM ATMOMETER READINGSATMOMETER READINGS

Evapotranspiration (ET) data using an Evapotranspiration (ET) data using an Atmometer is generally reported either as:Atmometer is generally reported either as:

ETa (ET of fully mature alfalfa) or ETg (ET of ETa (ET of fully mature alfalfa) or ETg (ET of fully mature grass) based on the cloth used with fully mature grass) based on the cloth used with the Atmometer. The Pocket Scheduler you will the Atmometer. The Pocket Scheduler you will use for your records utilizes the ETa readings.use for your records utilizes the ETa readings.

These values are adjusted by crop coefficients These values are adjusted by crop coefficients based on your type crop and stage of growthbased on your type crop and stage of growth

You will be working with ETa values and You will be working with ETa values and multiplying them by your crop coefficients to find multiplying them by your crop coefficients to find your daily ET values for your crop. NRCS will your daily ET values for your crop. NRCS will provide you with the crop coefficients you need. provide you with the crop coefficients you need.

EXAMPLE:EXAMPLE:

Your crop: Cotton at Boll FormationYour crop: Cotton at Boll Formation 7/7/04 ETa = 0.25 inches7/7/04 ETa = 0.25 inches

Crop Coefficient (Kc) = .80 (from NRCS)Crop Coefficient (Kc) = .80 (from NRCS)

ET for your crop = .80 X .25 = .20 inchesET for your crop = .80 X .25 = .20 inches

Your crop used .20 inches of water out of your Your crop used .20 inches of water out of your water balance on July 7thwater balance on July 7th

EVAPOTRANSPIRATION USING EVAPOTRANSPIRATION USING THE OKLAHOMA MESONETTHE OKLAHOMA MESONET

Now what forms do I use to record Now what forms do I use to record all this information ?all this information ?

(or where is my checkbook?)(or where is my checkbook?) NRCS has devised two methods to allow you to NRCS has devised two methods to allow you to

keep your records:keep your records: 1. Irrigation Pocket Scheduler – a booklet that 1. Irrigation Pocket Scheduler – a booklet that

you can carry in your pocket and keep all your you can carry in your pocket and keep all your records, your calculations, and your water records, your calculations, and your water balance on.balance on.

2. Automated Scheduler – using an Excel 2. Automated Scheduler – using an Excel spreadsheet. This spreadsheet will do your spreadsheet. This spreadsheet will do your calculations and tell you when it is time to calculations and tell you when it is time to irrigate.irrigate.

NRCS can assist you with either methodNRCS can assist you with either method

USING MESONET “ET” DATAUSING MESONET “ET” DATA

USING EXCEL SPREADSHEETUSING EXCEL SPREADSHEET

What if my water balance says I am okay using the What if my water balance says I am okay using the scheduler, but my crop appears to be suffering ?scheduler, but my crop appears to be suffering ?

START IRRIGATION IMMEDIATELY!!START IRRIGATION IMMEDIATELY!! Contact NRCS immediately to check your soil Contact NRCS immediately to check your soil

moisture in the field. moisture in the field. Even though the Evapotranspiration method of Even though the Evapotranspiration method of

scheduling has proven to be quite successful, it is scheduling has proven to be quite successful, it is not fool proof. NRCS will ask you to check your not fool proof. NRCS will ask you to check your soil moisture at least once a month by digging a soil moisture at least once a month by digging a hole into your soil profile to compare soil moisture hole into your soil profile to compare soil moisture levels against your water balance.levels against your water balance.

You will do this using the “Feel and Appearance” You will do this using the “Feel and Appearance” method following NRCS Program Aid # 1619. We method following NRCS Program Aid # 1619. We have developed a form for you to use for thishave developed a form for you to use for this

SUMMARYSUMMARY 1. Get an Irrigation Water Management Plan 1. Get an Irrigation Water Management Plan

from your local NRCS office for your crop and from your local NRCS office for your crop and soil.soil.

2. Get daily “ET” data from the Atmometer 2. Get daily “ET” data from the Atmometer (ETgage) or the Oklahoma Mesonet.(ETgage) or the Oklahoma Mesonet.

3. Use the pocket or automated “checkbook 3. Use the pocket or automated “checkbook scheduler” to manage your irrigations by scheduler” to manage your irrigations by recording daily ET, daily rainfall, irrigation recording daily ET, daily rainfall, irrigation applications, and water balance.applications, and water balance.

4. Request assistance from NRCS if you run into 4. Request assistance from NRCS if you run into any problems.any problems.

EQIP Incentive Payment ($10/acre)EQIP Incentive Payment ($10/acre)

Eight basic requirements:Eight basic requirements: 1. Irrigation system meets standards1. Irrigation system meets standards 2. IWM plan is followed2. IWM plan is followed 3. Report flow twice during season3. Report flow twice during season 4. Install two rain guages and record rain4. Install two rain guages and record rain 5. Determine daily ET to use in scheduler5. Determine daily ET to use in scheduler 6. Spot check soil moisture monthly6. Spot check soil moisture monthly 7. Record irrigation amounts and durations7. Record irrigation amounts and durations 8. Keep scheduler & records & submit to NRCS8. Keep scheduler & records & submit to NRCS