Irrigation Water Management Brady S. McElroy, P.E. USDA-NRCS, Lamar, CO Custer County IWM Workshop March 3, 2016

Discussion Topics  What is Irrigation Water Management?  Why Consider IWM?  Science of IWM  Soils  Crops  Water

Discussion Topics  Documentation for NRCS Programs  Other IWM Resources  CoAgMet  eRAMS/WISE

What is Irrigation Water Management?  The process of determining and controlling the volume, frequency, and application rate of irrigation water in a planned efficient manner  Colorado NRCS Conservation Practice Standard definition  IWM is both an art and science

What is Irrigation Water Management?  Goal is to make informed decisions about irrigation events, while recognizing that all irrigation systems operate under constraints, some possibly beyond an irrigator’s control  Delivery volume  Delivery flow rate  Delivery schedule

Why Implement Irrigation Water Management?  From NRCS CPS  Manage soil moisture to promote desired crop response  Optimize use of available water supplies  Minimize irrigation induced erosion  Decrease non-point source pollution of surface and groundwater resources  Manage salts in the root zone

Why Implement Irrigation Water Management?  From NRCS CPS  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  Reduce energy use

Why Implement Irrigation Water Management?  Other Potential Motivations  Utilize limited water in the most profitable way  Reduce labor  Reduce pumping costs  Maximize crop production  Manage fertility  Manage salinity

General Concepts  Crops transpire water  Crop water use is typically referred to as ET  Evaporation from soil and plant surfaces  Transpiration through stomata  Amount is dependent on crop, growth stage, and climate (temperature, wind, etc.)

General Concepts  Soil acts as a reservoir for water  Available storage depends on soil type  Not all stored water is accessible to plants  Effectively balancing the supply of soil moisture to help meet crop demands is a large part of IWM

Soils  Water fills pore spaces in soil during irrigation or precipitation events  Continuum  Saturation  Field Capacity  Wilting Point  Available water holding capacity varies by soil

Soils

Soils  Available Water Holding Capacity

Soils 3 feet

Soils Management depth may not be to full root zone depth

Soils Libeg Extremely Cobbly Sandy Loam 3 feet x 0.6 inches/foot = 1.8 inches Gelkie Sandy Loam 3 feet x 1.2 inches/foot = 3.6 inches Novary Loam 3 feet x 2.3 inches/foot = 6.9 inches

Soils/Crops  Plants can’t physically access all the water stored in soil  Management Allowed Depletion  Considers stress to crop  Varies by crop  May vary by growth stage  50-60% potential value for pasture grass MAD

Soils/Crops Assuming 3 foot root zone and 60% MAD Soil3 Ft. Root Zone Storage (inches) 3 Ft. Plant Available (inches) Libeg Gelkie Novary6.94.1

Crop Water Use/Irrigation Frequency  Pasture grasses may require around 24 net inches of water per year.  Part of requirements is supplied by precipitation  Average daily consumptive use of around 0.2 inches/day during hotter months Soil3 Ft. Plant Available (inches) Irrigation Frequency (assuming 0.2 in/day) (days) Libeg1.15 Gelkie2.211 Novary4.120

Water  Ideal irrigation goal is to fully replenish soil moisture deficit  Gross application amount is a function of irrigation system efficiency  Surface irrigation system efficiency ≈ 50%  Sprinkler efficiency varies by type  65% - 85% efficiency

Water

Water

Water

Water

Irrigator’s Equation

Given:d = 3 inches A = 20 acres Q = 2 cfs Find:Time required to apply d

Irrigator’s Equation

 General guideline  Doesn’t account for advance time  Doesn’t account for uniformity

Recordkeeping Requirements  Conservation Practice Standard and Specification requires some record keeping  Soil moisture condition determined by feel method  Start and stop dates of irrigation events  Volume or flow rate of water applied  Duration of irrigation  Crop growth stage  Precipitation

Recordkeeping

Recordkeeping Philip J. Fry2016 West FieldAlfalfa (3 rd year) Farnsworth Ditch – % estimated moisture.25 rain on 3-20

Sources of Information  NRCS  CSU Extension  Irrigation Handbooks  Consultants

Sources of Information  CoAgMet  Colorado Agricultural Meteorological Network  Estimates evapotranspiration from climate data  Reference ET  Multiple crops

CoAgMet

CoAgMet

CoAgMet  Typical station includes sensors for:  Temperature  Relative Humidity  Wind  Speed  Direction  Solar Radiation  Precipitation  Soil Temperature

CoAgMet

eRAMS/WISE  Environmental Risk Assessment and Management System  CSU online GIS modeling platform  Water Irrigation Scheduler for Efficiency  Free tool for scheduling irrigations  Utilizes NRCS soil data  CoAgMet data for ET  Initial setup through browser, Android and iOS mobile apps available

eRAMS/WISE

eRAMS/WISE

eRAMS/WISE

eRAMS/WISE

eRAMS/WISE

eRAMS/WISE