“In order to reduce run-off and encourage healthy plant growth, a soils management report shall be completed by the project applicant,” AB1881 requires.
I am totally in favor with the concept that each site has a Horticultural Soils Report that tests for the soils classification, pH, salinity, total soluble salts, sodium, organic matter, and provides a complete set of pre-planting and post-planting maintenance recommendations. The Soils Report should be used in selecting plant material for the site. When high boron or salts are present the plant palette needs to be modified to fit the site conditions. Per the AB 1881 guidelines the soils infiltration information is intended to be the deciding factor when selecting irrigation heads. The guideline wants the precipitation rate of the irrigation head to be less then the infiltration rate of the soil.
Contrary to the above requirements irrigation systems have been designed with application rates that were higher than the infiltration rate prior to AB 1881. Since the 1970’s, irrigation equipment manufacturers have been working with great success to manufacture irrigation heads with “Matched Precipitation Rates”. Even with all that has been accomplished in the irrigation industry with precipitation rates there are studies that show the variances in the precipitation rate are overcome in the soil by the capillary movement of water, in the soil.
I, on the other hand, believe that the old school way of irrigating is actually beneficial and necessary. So when plants are first installed they are watered in with a hose, why use an irrigation system designed to apply water at a precipitation rate below the infiltration rate? For many years the rule of thumb has always been to turn on the irrigation system and record the time it takes for run-off to occur. The controller run time is then reduced by 25%, this prevents the run-off that is such a high priority in AB 1881. This is very beneficial when planting plants with sandy root balls in clay soils, or plants with clay root balls in sandy soils. The benefit of exceeding the infiltration rate flushes the soils and makes it easier to deep water.
The best way to move salts through the soil, move water into the rootball, establish and maintain plants is to manage the applied water to the soil and exceed the infiltration rate without run-off!
What do you think?
It’s “always” a great idea to get a soil report “before” doing any type of design or water audit. As a matter of fact, I insist on a report with all of my clients before I even start a design. Not having a soil report is like driving blind folded (I know… bad analogy). You can’t see where you’re going with a design unless you know the soil type you’re dealing with… The only thing I “don’t” like is big brother forcing yet “ANOTHER” must do law. I’m getting a little fed up with our government getting too pushy in our lives. Enough with the laws… don’t smoke, don’t eat french fries… etc., etc., etc. I think we as a group of professionals can handle the water management issues without government intervention…
Dave Bakke
Irrigation Consultant
As a Landscape Architect my experience has been the soils present at the time the landscape and irrigation design are being created usually do not reflect the soil conditions after the site has been constructed, compacted, backfilled, etc when the irrigation and plants are being installed. Does the AB1881 requirement for a soils test take this into consideration?
I received your Blog posting on AB-1881 “Soil Management Report” and have a few comments. First off, I thought your article was informative and very well written.
Thanks to both of you for the help in getting plugged in to these great informative articles that Valley Crest is producing.
I too feel that a Horticultural Soils Report is important for each site and should be used in plant Selection, soil modification needs, irrigation scheduling, etc.
However I do not feel that the soil infiltration rate should be the one and only driving influence on the irrigation equipment selection. I feel that things like foot traffic, water quality, water pressure, warranty, vandalism threat, etc. should first drive the product selection decision. Then serious consideration to that irrigation products precipitation rate should be factored in. Soil infiltration rate can also be addressed during irrigation scheduling by using controller Cycle and Soak features.
It is not practical to always use a product with a PR rate that is less than the soil infiltration rate. If soil infiltration rate solely dictated irrigation product selection then Drip Irrigation products with their extremely low PR would be the only choice ever for Loam, Clay or compacted soils. That just doesn’t make sense.
To summarize:
I believe that it is important to first select the irrigation product type that best suits the environment that it will live in. Of course some practical sense also needs to be used here; for example you wouldn’t use a high PR rotor on a severe slope.
Then select a PR version of that product type that will best allow for Zero Runoff. Also consider using SAM versions or pressure regulated stems, etc.
Then leverage the features that come with each Commercial controller to create the best schedule to prevent runoff.
Keep the great information flowing.