HOW MUCH WATER

Water is a critical component to managing quality turf.  Especially Bentgrass and we have 50  acres of bentgrass including tees, fairways, and greens.  All turf requires water and different turf species require different amounts.  Zoysia and Bermuda require the least amount, followed by tall fescue, then bluegrass, and finally bentgrass and poa annua having the highest requirement especially mowed at 1/2" and shorter.

We use different tools to determine how much water the turf needs to survive each day.  We break it down into daily needs and try to supplement each day what the turf requires to maintain healthy turf.  One of the first things we look to is Evapotranspiration.

Evapotranspiration-
Evapotranspiration (ET) is the loss of water from a vegetative surface

through the combined processes of plant transpiration and soil evaporation
(ET is equivalent to and frequently referred to as consumptive use). 
Both environmental and biological factors affect ET. Important environmental
factors include solar radiation, temperature, atmospheric dryness (vapor 
pressure deficit), wind and soil moisture.  Biological factors affecting ET
include type of vegetation, foliage geometry and foliage density.  Paul W. Brown Extension Biometeorologisthttp://ag.arizona.edu/azmet.

On average in the summer months we see daily ET numbers between .10" to .25".  

Precipitation Rates-

We must determine the precipitation rates for our sprinkler heads.  Precipitation rate is the amount of water the sprinkler head  puts out in inches per hour.  Knowing this number is critical to managing water.  We look to the manufacturer of the sprinkler head to find the precipitation rates and other data for the sprinklers.

Calculations-

We know how much water we need and we know how much water our sprinkler  heads put out.  For example if we need to apply .10" of water and our sprinkler heads put out .6" of water per hour we will water 10 minutes to replenish the water loss for that day.

Calculating water need after a rain event can be tricky.  If the rain comes hard and fast sometimes it doesn't soak in.  I have seen a .5" rain event and the turf required watering within 24 hours.  I have also seen a .5" rain last three days before turf needs water again.  I scout the  golf course following rain events to evaluate irrigation needs paying special attention to the mounds and low basins as the two will be vastly different in the water needs after a rain event.  Typically we can go a day or two after a rain event before we water resume irrigating after a rain event.

I use a 4" screw driver to determine the water content in the soil.  I push the screwdriver into the soil paying attention to how much force it takes to sink the screwdriver in the soil.  Extremely dry soil is nearly impossible to get any penetration. Saturated soil the screwdriver will go in with ease.  I target somewhere in the middle.  

Central Control System-

We have an elaborate system that controls our sprinkler heads.  The majority of our sprinkler heads are valve in head meaning each sprinkler head has its own self contained shut off valve.  We have satellite controllers on the course  that are wired to the sprinkler heads.  The satellite controllers have computer components in them that are capable of communicating with the central control computer that is located in my office.  This irrigation control package allows us to operate the sprinkler heads from a smart phone, in the field with the satellite boxes, or from the computer.  The central computer that is located in my office is the brain of the system.  We built the central computer this spring loading into the control system database extensive information about the system including sprinkler head type for each station including precipitation rate, flow rate in gallons per minute, radius arc of the sprinkler head, nozzle type and how many heads are wired to that station.  We are continually editing this database and each day we get a little more detailed in our data entry.  We are now to the point that we are determining soil types for each zone and dialing the system to account for clay or sand soils that drain differently requiring different irrigation needs.  This is a work in progress but we are making progress each day.  Our next goal is to upload an aerial image of the golf course and map our irrigation heads on this map so we are more detailed in our management of the sprinkler heads factoring shade and other components that factor into the irrigation requirements.  We hope to have the mapping portion of the database completed this winter.

Water Flow Management-

Another important task for the central control system is to manage how much water flows through the pipes on the course.  Engineers determine the safe flow rates for irrigation pipes.  They use a rule of 5 feet per second for safe water flow through a pipe.  Our central control system takes this into account when it runs the sprinkler heads on the course.  We have a pump station that is capable of pumping 2500 GPM.  Each golf hole is capable of flowing approximately 200 gallons per minute with the pipe size that we have supplying these holes.  Flow management is a critical and proper flow management reduces irrigation leaks with less water hammer and supplies the sprinkler heads with adequate pressure to optimize the performance of the sprinkler as it irrigates the turf.  

Greens Water Management  

We micromanage greens.  We use TDR meters to manage moisture in our putting greens.  I have used these meters for three years.  They are the industry standard for managing moisture in putting greens.  The meter tells us the volumetric water content in the green.  We test the top 4" of the green and the meter tells us the VWC number.  We know that a golf green that has approximately 15%-20% VWC holds approach shots well and has proper water to air balance in the open pore spaces in the sand based root zone of the green.  We also know that our greens will wilt if they drop  below 10% VWC.  We water with our sprinkler heads to target a 20% VWC each morning and then we supplement the dry areas of the greens with a water hose (hand watering) to achieve a consistent 20% VWC across the entire putting green.  I have followed this program for three years with tremendous success.  Following this program we rarely see greens wilt under drought stress and we have dramatically reduced the need to syringe greens in the afternoons improving playing conditions and member satisfaction on the golf course as we are not interfering with play syringing greens in the afternoon.