United States Department of Agriculture 449-CPS-1

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NRCS reviews and periodically updates conservation practice standards. To obtain the current 

version of this standard, contact your Natural Resources Conservation Service State office or 

visit the Field Office Technical Guide online by going to the NRCS website at 

https://www.nrcs.usda.gov/ and type FOTG in the search field. 

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Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

IRRIGATION WATER MANAGEMENT 

CODE 449 

(ac)

DEFINITION 

The process of determining and controlling the volume, frequency, and application rate of irrigation water. 

PURPOSE 

This practice is used to accomplish one or more of the following purposes: 

• Improve irrigation water use efficiency 

• Minimize irrigation-induced soil erosion 

• Protect surface and ground water quality 

• Manage salts in the crop root zone 

• Manage air, soil, or plant microclimate 

• Improve poor plant productivity and health 

• Reduce energy use 

CONDITIONS WHERE PRACTICE APPLIES 

This practice is applicable to all currently irrigated lands. 

CRITERIA 

General Criteria Applicable to All Purposes 

Develop an irrigation water management (IWM) plan that defines when irrigation is needed (timing) and

the amount and rate of water to apply for each irrigation event. 

Base the timing of irrigation on one or more of the following methods: 

• Evapotranspiration of the crop, using appropriate crop coefficients and reference evapotranspiration

data, 

• Soil moisture monitoring, 

• Computerized irrigation scheduling, utilizing local real-time climate data, soil, and crop growth

characteristics (e.g., remote telemetry data systems coupled with cloud-based irrigation scheduling

using the soil-water balance method), 

• Plant monitoring (e.g., leaf water potential or leaf/canopy temperature measurements). 

Base the volume (depth) of water needed for each irrigation event on the following that are relevant to a

crop or field: 

• Available water-holding capacity of the soil for the crop rooting depth, 

• Management allowed soil water depletion, 
• Current soil moisture status, 

• Current crop/forage growth stage, 

• Distribution uniformity of the irrigation event, 

• Water table contribution, 

• Computerized irrigation scheduling recommendation. 

For variable rate irrigation systems, such as center pivots, in addition, base the amount and application

rate of irrigation water on spatially identified field parameters such as variations in past yield data, soils,

crop growth, topography, or computerized irrigation scheduling recommendations. 

When irrigation water is not available on demand, such as when it is provided by an irrigation district, use

the planned availability as a factor to determine the timing of the irrigation event. Adjust irrigation amounts

appropriately to account for the periodic availability of water. In all situations where water is limited, ensure

that the IWM plan will meet critical crop growth stages. 

In locations where rain is expected during the growing season, and where a soil-water balance is

calculated, include measurements from an onsite rain gauge, interpolated predictions based on local

weather stations, rain gauges, or other accurate method for determining local rainfall for the area under

irrigation. 

For surface irrigation, apply irrigation water at a rate that achieves an acceptable distribution uniformity

and minimizes irrigation-induced erosion. 

Additional Criteria for the Protection of Surface and Ground Water Quality 

Plan the rate and volume of irrigation water to minimize the transport of sediment, nutrients, and

chemicals to surface waters and ground water by— 

• Controlling the rate of water application to limit the transport of nutrients and chemicals through the

soil profile to ground water. 

• Ensuring that the volume and rate of application does not result in damaging irrigation-induced

erosion and/or contaminated runoff and offsite transport. 

Where the topography is steep enough to cause erosive flow velocities, provide permanent soil cover,

increased crop residue, and/or use polyacrylamide according to NRCS Conservation Practice Standard

(CPS) Anionic Polyacrylamide (PAM) Application (Code 450) in lieu of or in combination with structural

measures to control erosion. 

Do not conduct fertigation or chemigation operations if rainfall that may produce runoff or deep percolation

is expected. Limit the application rate and volume of water to the amount necessary to apply the

chemicals or nutrients to the soil depth recommended by the manufacturer. Limit the application of

chemicals or nutrients to the minimum length of time required to deliver and flush the pipelines. Ensure

that the irrigation and water delivery systems are equipped with properly designed and functioning valves

and other components necessary to prevent backflows of nutrients or pesticides into the water sources.

Base the timing and application of nutrients and/or pesticides on the criteria in NRCS CPS Nutrient

Management (Code 590) and Pest Management Conservation System (Code 595), respectively. 

Additional Criteria for Managing Salts in the Crop Root Zone 

Ensure the irrigation application volume is sufficient to provide an appropriate salt balance in the soil

profile. Base the determination of the required water volume on the leaching procedure contained in

NRCS National Engineering Handbook (NEH) (Title 210), Part 623, Chapter 2, “Irrigation Water

Requirements,” and 210-NEH, Part 652, “Irrigation Guide,” Chapters 3 and 13. 

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Additional Criteria for Managing Air, Soil, or Plant Microclimate 

To provide protection from heat or cold, ensure that the irrigation system can apply the required rate of

water as determined by the methodology contained in 210-NEH-623-2. 

Additional Criteria for Reduced Energy Use 

Provide analysis to demonstrate reduction of energy use from practice implementation. 

Calculate the reduction of energy use as the average annual or seasonal energy reduction compared to

previous operating conditions. 

CONSIDERATIONS 

Consider the following when planning irrigation water management: 

• Increased crop residue left on the field will reduce the potential for irrigation-induced erosion,

increase the infiltration of water into the soil, and reduce evaporation from the soil surface. 

• There is a potential for spray drift and odors when applying agricultural and municipal waste waters.

Time irrigation based on prevailing winds to reduce this potential. In areas of high visibility, consider

irrigating at night. 

• The development of detailed topographic soil maps and the identification of environmentally

sensitive areas can help with the development of site-specific irrigation plans that better meet crop

needs while minimizing adverse environmental impacts. 

• Plan the location of end guns so that overspray will not reach public roads or other unintended

locations. 

• Periodic inspection of irrigated areas for the presence of pesticides, animal wastes, or other

contaminants prior to irrigation can allow these problems to be addressed before they cause a

water quality problem. 

• The quality of irrigation water can adversely affect crops and soils. Testing and assessment of

irrigation water can help to address adverse impacts of the water on crop quality, plant

development, and soil properties such as crusting, pH, permeability, salinity, and structure. 

• Avoid operating heavy equipment on wet soils to minimize soil compaction. 

• To reduce the potential for ground water contamination, schedule salt leaching events to coincide

with low levels of residual soil nutrients and pesticides. 

• Manage water so it does not drift or come in direct contact with surrounding electrical lines,

supplies, devices, controls, or components that could cause loss of electrical power or the creation

of an electrical safety hazard to humans or animals. 

• Consider how the interruption of power to irrigation systems from load control, interruptible power

schedules, repair and maintenance downtime, and harvest downtime may change the plans for

irrigation water management. 

• The use of new technologies for data collection such as drones, advanced imaging technology,

remote sensing technology, yield monitoring, and data logging to calculate water use can lead to

more efficient water application. 

• The use of energy saving technologies, such as low energy precision application irrigation and use

of alternative energy sources can result in significant energy saving versus conventional methods. 

• Crop species selection in situations where drought or water deficits are recurrent. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications that describe the requirements for applying the practice according to the

requirements of this standard. As a minimum, include in the plans and specifications— 

• A plan view showing the layout of the irrigation system including irrigated areas, planned crops,

soils, pipelines, and location and installation information for any moisture sensors, rainfall gauges,

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or other sensing equipment. 

• Methods to be used to measure or determine the flow rate and volume of the irrigation applications. 

• Documentation of the scientific method used for scheduling the timing and amount of irrigation

applications. 

• The seasonal or annual planned water application volumes by crop. 

• The management allowable depletion and depth of the managed crop root zone for each crop. 

• An estimate of the irrigation system distribution uniformity, based on testing, evaluation, or

observation. 

• The specific soil moisture monitoring objectives if soil moisture sensors are used. Indicate how data

from the soil moisture sensor locations and depths will be considered to make field-wide irrigation

decisions. 

• Information on how to recognize irrigation-induced erosion and how to mitigate it. 

OPERATION AND MAINTENANCE 

Prepare an operation and maintenance (O&M) plan for the operator. As a minimum, include in the O&M

plan: 

• Record keeping documents to be used by the operator to record irrigation water management

activities. 

• Requirements for recording each irrigation event, including the amount or depth of water applied,

duration of the event, and the date of application. 

• Requirements for recording the methods used for determining the timing and amount of irrigation

events. 

• Requirements for recording other pertinent data used to implement the irrigation water

management plan. 

• Reference other O&M plans for the irrigation equipment and water delivery systems used. 

REFERENCES 

Glenn, E.P., P.L. Nagler, and A.R. Huete. 2010. Vegetation Index Methods for Estimating

Evapotranspiration by Remote Sensing. Surveys in Geophysics 31:531-555. DOI 10.1007/s10712-010-

9102-2 

Schimmelpfenning, D. 2016. Farm Profits and Adoption of Precision Agriculture. Economic Research

Report Number 217. Economic Research Service. Washington, D.C. 

Stubbs, M. and P. McGee. 2016. Irrigation in U.S. Agriculture: On-Farm Technologies and Best

Management Practices. Congressional Research Service. Washington, D.C. 

USDA NRCS. 2007. Technical Note (Title 190), Agronomy Technical Note 1, Precision Agriculture: NRCS

Support for Emerging Technologies. Washington, D.C. https://directives.sc.egov.usda.gov/

USDA NRCS. 1993. National Engineering Handbook (Title 210), Part 623, Chapter 2, Irrigation Water

Requirements. Washington, D.C. https://directives.sc.egov.usda.gov/.

USDA NRCS. 1997. National Engineering Handbook (Title 210), Part 623, Chapter 9, Water

Measurement. Washington, D.C. https://directives.sc.egov.usda.gov/.

USDA NRCS. 1997. National Engineering Handbook (Title 210), Part 652, Irrigation Guide. Washington,

D.C. https://directives.sc.egov.usda.gov/.

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