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A Professional Approach to Lawn Water Requirements

Author

Baileys Fertiliser

Published

31 January 2020

A Professional Approach to Lawn Water Requirements

Water is our most precious resource and the number one priority that you need to get right for a healthy and luscious lawn. Most lawn issues relate to water availability (enough water) or water penetration into the soil. Before looking into other reasons for slow growing, dry or dead patches in your lawn, it is recommended to start with your watering system.
Catch-cups are an easy way to work out how much water your lawn is getting. Catch-cups are small spiked measuring cups that can be placed throughout your lawn area. They allow you to collect and measure how much water a specific part of your lawn is receiving.

Tips for collecting data

  • It is recommended to undertake a catch-cup test on a calm day. Wind will affect and distort your collection data. 
  • When you place your catch cups on your lawn, try to keep the lip of the cups level. Sloping cups can restrict the amount of water entering the cup and distort your data.
  • Placing catch cups in the middle of the spray arc and not too close to the pop up will give you the best representation of the water collected.
  • If you have a buffalo lawn, try to push the cups down as far as they will go. Queensland Blue Couch and Buffalo grasses have stolons. These above ground roots make it a challenge to stabilise the small spike at the bottom of the catch-cups.

Professional calculations

  • The example below steps you through the calculations to determine your station run time (amount of required water) taking into consideration seasonal evaporation.
  • WA Water restrictions allow controlled watering systems to operate twice per week if using scheme water.

Step 1. Collect your water

  • Pick up 10 - 20 catch-cups (dependent on lawn size).
  • The Water Corporation provides a list of catch cup stockists that can be found here: https://www.watercorporation.com.au/save-water/in-the-garden/sprinklers-and-irrigation
  • Next, evenly distribute the catch-cups in the station area that you want to test. 
    • Place the catch-cups in areas that are dry, dead, around boarders and otherwise in an even pattern.
  • Run your system for 5 minutes for spray pop ups, or 20 minutes for rotary nozzles and gear drives.
  • Then measure and collect how much water (mm) is in each catch-cup.
  • Record and plot the data as per the table below.

In the example below, 3-inch spray pop ups were used with Hunter fixed pattern and adjustable nozzles.

  • Total water in 20 catch-cups = 86mm
  • Average water per cup: 86mm/20 (catch-cups) = 4.3mm per 5 mins 
  • Average mm per minute: 4.3/5min = 0.86mm

Investigating water uniformity and efficiency 

  • Look at the lowest quarter of the catch cups to see if there is a uniformity issue with your water coverage.
  • When looking at the table above, you can see that the lowest quarter (lowest 5 cups) = catch cups 4, 5, 11, 14, 15 = 6mm
  • 6mm/5 (catch-cups) = 1.2mm per 5 min (a lot less than the average 4.3mm)
  • The lowest quarter distribution uniformity is worked on average water (mm) in the low quarter divided by overall average (mm) x 100
  • = 1.2ml/4.3ml x 100 = 28%
  • To run efficiently, the lowest quarter results should be above 75%.

Diagnose and correct the problem

  • To correct the issue, we need to understand what is causing the low quarter results e.g.: blocked nozzles, obstructions, a cracked pipe, wrong nozzle selection (not achieving head to head coverage) or a variety of different nozzles used (spray mixed with rotating).
  • In this example, the problem was debris and sand in the sprinkler filter. Inspecting nozzle filters is a great starting point.
  • To inspect a sprinkler nozzle, try using multi-grips to keep the sprinkler stem up while you remove the nozzle. 
  • Remember to always flush the line again after cleaning the nozzle as debris and sand could still be lodged in the pop-up sprinkler stem.

After cleaning the nozzles and running the same test (at 5min) the follow results were achieved.
  • New Total = 120mm
  • Average: 120mm/20 (catch cups) = 6mm per 5 mins 
  • Average mm per minute: 6mm/5min = 1.2mm

Step 2. Calculate your irrigation rate using EPAN

  • On most occasions, irrigation times are an estimate we make to apply a standard drink of 10mm to lawns.
  • EPAN is the terminology used to calculate how much water should be applied to replace moisture loss from evaporation, or evaporation-based irrigation scheduling. This method is used by professional grounds keepers.
  • Monthly evaporation data is available from the Bureau of Meteorology and is provided in the table below.

  • For domestic lawns, EPAN is calculated at 50% of the mean daily evaporation rate.
  • February's average daily evaporation rate is 9.6mm, so EPAN for domestic lawn would be 50% of this: 9.6/2 = 4.8mm
  • To work out how long it would take you to replace this daily, calculate how long it takes to apply 1mm of water.
  • 5 mins (running time)/6mm (average catch) = 0.83min or 50 seconds to apply 1mm of water.
  • 50 sec x 4.8mm (EPAN) = 240 seconds or 4 minutes to apply the 4.8mm of water. 
  • 7 days x 4 min = 28 minutes of watering per week.
  • 28/2 allowed watering days per week = 14 minutes per irrigation cycle.
  • To replace EPAN @ 50% you will require the irrigation system to be running for 14 minutes twice per week. In this example this will deliver 16.8mm (14 x 1.2 average mm per minute) to allow water to soak into the root zone while covering the seasonal evaporation rates.

Other helpful watering tips

  • Apply a high-quality wetting agent to ensure that your water drains evenly into the root zone. Grosorb granular and liquid wetting agents are a professional grade formulation that is guaranteed to perform.    
  • A Buffalo lawn will require a little more water than other lawn types. Signs of stress for a buffalo lawn include seeding and leaf blade discolouration. 
  • High wind areas or lawn areas that are next to heat absorbing surfaces such as corner blocks or excess paving will require extra water.
  • During summer, it is recommended to water early in the morning. Setting your controller to start between 4:00 - 6:00am is a good zone to aim for. It is not recommended to water in the evening - the ground remains wet through the night and will encourage lawn related diseases. Plants use water, plus the energy from sunlight and carbon dioxide to photosynthesis, so water them when they'll be using it, instead of in the evening.

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