Irrigation Water Management (IWM). Don Pitts, IL NRCS Agricultural Engineer. Conservation Practice Standard 449 Irrigation Water Management (IWM).
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Irrigation Water Management (IWM) Don Pitts, IL NRCS Agricultural Engineer
Conservation Practice Standard 449 Irrigation Water Management (IWM) • Definition: IWM is the process of determining and controlling the volume, frequency, and application rate of irrigation water in a planned and efficient manner.
Purposes for IWM • Manage soil moisture to promote desired crop response • Optimize use of available water supplies • Minimize irrigation induced soil erosion • Decrease non-point source pollution of surface and groundwater resources • Manage air, soil, or plant micro-climate • Proper and safe chemigation or fertigation • Improve air quality by managing soil moisture to reduce particulate matter movement
What’s the Issue? • Water Quantity? • or • Water Quality? Both – Due to relatively high water tables and sandy soils in most irrigated situations in Illinois, water quality is probably primary. So the focus of IWM in Illinois is somewhat different from that of Western Kansas.
Some Criteria… • Irrigation system with sufficient capacity to meet crop water requirements • Uniform distribution of water • Means for the measurement of flow rate (as part of the evaluation procedure) • Knowledge and skill to manage the irrigation system • Minimum standard for Distribution Uniformity (DU) 75% • If fertigation or chemigation is applied, backflow prevention is required
IWM: an Umbrella Term that Includes Several Activities… • Irrigation System Performance Evaluation • catch-can and pressure analysis • Irrigation Management (Scheduling) • when to irrigate and how much to apply • Irrigation System Conversion • Surface to Overhead (CP) • Center-pivot to Micro (Drip) • Irrigation System Physical Modifications • Conversion to lower pressure or drop nozzles
What is Needed for an IWM Program that Includes Irrigation System Evaluations? • Clientele that want the service • Trained and experienced technicians • Some equipment
Irrigation Water Management (449) Program Components • Client identification • Client interview • Data collection • Date processing and analysis • Product delivery • Follow-up • Retest (e.g. 10%)
Irrigation Water Management (449) Statement of Work Steps: • Current management information • Preliminary system information collected from client • Field assessment of irrigation system and data collection • Statistical analysis - Computation of flow weighted DU • Irrigation scheduling procedure - Determining when to irrigate, how much to apply • Recommend actions
Some Client Interview Questions: • Irrigation System Information • Capacity, pressure, based on original design • Current management – • How is scheduling done? How much water is typically applied at each irrigation? • Maximum hours of operation • Are hours of operation limited by electric contracts? • Grower’s current idea of system performance • How much water is applied at a certain speed? • Chemigation needs • Is fertigation practiced? • Other management constraints
Irrigation System Information(Obtained by observation before starting catch-can evaluation) • Irrigation system brand name (manufacturer) and model • Sprinkler or sprayer type – • Does the system have regulators? • Drive type (e.g. electric or hydraulic) • Distance to end-tower (ft) • Number of towers • Distance to last nozzle • Capacity of the end gun • Is backflow prevention device complete?
Field Assessment of the Irrigation System • Weather Information • Wind direction and speed, temperature, and relative humidity (time of day) • System pressure • at first tower (and last tower) • Observe sprinklers for proper installation and operation • Catch-can test • Determine hours of operation for complete cycle • Determine irrigated acres • Observe system flow at pivot or first tower • Determine system application rate (in/hr) • Determine maximum application rate for most limiting soil
Spacing between cans ~ 30 ft New: Two lines of collector cans (lines should be ~ 15 ft in distance) Catch-can Layout
Advantages • - Lower pressure • - Less evaporation • and drift • Disadvantages • - High application rate • Less uniform application point sprays • start-stop effect • canopy interception Drop Sprayers
Catch-can Layout At what speed should the catch-can test be conducted?
IWM Field EvaluationStatistical Components • Average catch-can depths (amounts) • Average of lowest ¼ of catch-can depths • Compute Distribution Uniformity (DU) • DU = Depth (LQ)/ Average Depth must be converted to a flow weighted DU
Equations Used for Converting to a Flow-weighted DU Where: Pi is the depth of water collected in catch-can, Di is the distance of every catch-can from the pivot point (m). DU = 100 – 1.59 (100 – CU)
Example Center-Pivot Catch Can Data CU= 90 DU = 86 Mean = 0.78” Mean and uniformity measures non-weighed
Example Center-Pivot Catch Can Data CU= 80 DU = 68 Mean = 0.78 “ Mean and uniformity measures non-weighed
Some Causes of Non-uniformity • Worn or plugged sprinkler nozzles or spray heads • Sprinkler not rotating • Improper retrofit • Improper system design • Pump performance has changed • Wind • End-gun operation
Determinates of the Field Evaluation System application uniformity (DU) Flow/area weighed DU = Meanlq/Meanall System speed verses application depth Irrigation scheduling parameters Soil type Rooting depth Determine application depth per irrigation Identify causes of non-uniformity From observations and/or pressure and flow measures Use the CPED program
Some Computations from Input Data Note: Problems with terms and definitions in Excel program
Statistic Computations from Catch-Can Data Efficiency: Volume of water beneficially used by the crop divided by the amount of water applied.
Causes of Non-uniformity and Recommendations for Correction • If DU is below the system standard (75%), list causes of non-uniformity (if known) and recommend corrective actions • Follow-up after 90 days to determine if grower has made recommended improvements
Phase II – Irrigation Management • Scheduling irrigation means: • Determining how much water to apply • Determining when to apply it
Steps in Determining Irrigation Amount • Determine effective Rooting Depth of Plant • Determine Available Soil Water Holding Capacity • Determine Allowable Soil Water Depletion Level • Estimate an Irrigation Application Efficiency from DU computation
To Determine the Effective Rooting Depth - Use the 40-30-20-10 Rule 70% of the plant roots are in the first 50% of the plant root depth
Effective Rooting Depth (ERD) 40% ERD 30% 20% Maximum Rooting Depth ERD will vary during Growing season 10%
Available Soil Water Holding Capacity Source: Soil Survey
Determine Allowable Soil Water Depletion Level • For most crops (corn and soybeans) irrigation is initiated at 50% depletion of available soil water. • For very drought-sensitive crops or horticultural crops, a 33% depletion level is sometimes used.
Estimate an Irrigation Application Efficiency • For properly operating sprinkler systems, 75% application efficiency is often used. • If uniformed is low (based on the system analysis), then application efficiency would be less than 75%
Example Problem • Maximum Observed Rooting Depth = 36 inches • Soil type = Sparta • Crop = Soybeans • Irrigation system hydraulic analysis = 75% DU
How Much to Apply at Each Irrigation? - Example Solution • Effective rooting depth = 18 inches • Available soil water content = 0.065 • Soybeans: allowable soil water depletion level = 50% • Estimated application efficiency = 75% 0.065 x 18 x 0.5 Solution: --------------------- = 0.78 inches 0.75
Irrigation Scheduling - When to Irrigate…Methods: • Water Budget • Calendar method • ET estimate method • Soil Moisture Sensors • Tensiometers • Gypsum Block
Tensiometers – one type of soil moisture sensor • Require maintenance • Need for frequent observation on sandy soil
Whatever Scheduling Method is Used – Record Keeping is Required • Precipitation amounts and dates • Irrigation amounts and dates • Soil moisture sensor readings or • ET estimates
Product Delivery • Hand deliver IWM evaluation package, discuss results with decision maker • Compare uniformity to a standard (e.g. 75% DU) • Offer good graphics--can improve clients understanding of what he/she is being told • Offer recommendations for improvements or repairs to the system • Discuss management (e.g. water applied v soil water holding capacity - assume 50 % depletion) • A quality product is important for grower and public support of the program
Follow-up (some ideas) • Phone interview of all clients by a another person - not the evaluator • Some questions to consider: • Was information provided useful? • Were recommendations implemented? • Did evaluation result in changes in operation or management of the irrigation system? • Would you be interested in assistance on management (scheduling)? • When can we meet to develop a management plan? • Re-evaluate 10% percent of systems after implementation of recommendations
Reasons for the IWM Program • Improved yield from better management • Reduced pumping costs from more efficient irrigation • Improved application of nutrients and chemicals from more uniform water application • Water conservation from more efficient application of irrigation water • Improved water quality from proper amounts and more uniform application of irrigation water
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