Grass saturated after even a little watering


#1

I’ve got bluegrass laid over Altvan-Satanta loam, which USGS describes as having an AW of 0.16.

I have two overlapping zones both set like this:

  • Root Depth = 4in
  • AW = 0.14 (sod loam on top of the native soil probably has a bit lower capacity
  • Mild slope
  • Soil type = Clay Loam
  • Kc = 0.50 (spring), 0.55 (summer)

I cross-check Rachio’s estimates of ET against my local water authority, which has daily models of ET based on a test site a mile from my house. My Kc settings give good ET correlation between Rachio and my local water authority.

Rachio estimates it deposits about 0.33in per watering, less than 50% of estimated capacity. It does long cycle soaks. I’ve checked with catchcans, and if anything it applies less than 0.33in. The cycle ends long before dawn (drip & garden run after lawn).

Despite all of this, in the morning after watering, I can see signs of runoff and the lawn squelches a bit underfoot as I walk around.

Anyone have any thoughts on what could be going on?

  • AW could be too high. But it seems like only sand and high quality loams have AW of 0.12 or less. Regardless, I could revise this down.

  • Catchcans could be lying to me, I could need to retest

  • There could be something strange with the two zones. I’ve generally treated them separately, but that could be the wrong thing to do? This would probably be tackled by increasing the precipitation rate- but could screw up the areas that don’t overlap.

  • My soil does seem to absorb water quite slowly. It could be that the native soil below the grass is extremely slow to soak up water- but could it be so slow that hours later, it still hasn’t soaked up? This would be fixed by revising my root depth shallower.

The main other observation I would make is that while my settings are fairly aggressively tilted towards saving water (I push AD, ET, etc) the lawn still tends to look pretty plush & grow vigorously. Rachio seems to water before the lawn seems dry, and before the blades are folding. Which makes me second & third-guess my catchcans, and wonder about my ET.

Tricks to help rule out variables would be helpful. Unfortunately, some kind of probe to profile soil moisture content over the day, and before & after watering, is probably exotic & expensive :slight_smile:


#2

Almost sounds like a compaction issue with the native soil. I’m at a loss since you seem to have done your research. Must be very mild climate to have a 50-55% Kc. Definitely recheck precipitation rates throughout the watered area — ideally capturing overlap. Reducing root depth may be the best lever if precipitation rate checks out. Could also try a longer custom soak time.


#3

There’s almost certainly some compaction in the native soil. The sod loam is fine, but the native soil takes a pickaxe to break up. I’ve been making some compost for topdressing and going around with a little manual aerator. May never really fix the problem, but I’m not about to rip it up…

If I reduce root depth, am I trying to set the depth to the depth to the compacted soil?

For longer cycle soaks- it would need to be so many hours, 12-24h, we are really just talking about another run.

Kc certainly doesn’t agree with Rachio, but the ET Rachio comes up with on a default ~0.8 Kc is like 0.30-0.35 a day. Doesn’t agree with local models, nearly two inches a week. Acually, Kc=0.55 doesn’t agree with the local model either, they say they are using Kc=0.7ish, but it makes the ET line up. Somehow, the two are calculating ET very differently. Maybe something to do with altitude, I’m in Northern Colorado. High UV, hot and dry. Although Rachio was founded in Denver…


#4

If you really want to know true RZD, this is what I’ve used and most people around the office. The average for what I’ve seen at my house and around other areas of CO is ~6 inches. This is for the true yard geek.

Instead of soaking for 30 minutes maybe try 45 minutes?

If you want raw ET, just pick a test zone and set the crop coefficient to 100%. The soil moisture graph will show you raw ET, without the crop coefficient offset. We use the closest national weather station data to derive raw ET. Our ET calculator uses the Penman monteith formula (http://www.fao.org/docrep/X0490E/x0490e06.htm) and has been verified using data from stations like this http://agweather.mesonet.org/cgi-bin/public/evap.sitehist.cgi?BIXB+Bixby

Here is what I run in Golden, CO. During cooler periods I might drop crop coefficient down to 70%, and during warmer months move it to 80%. If I feel like it is watering too aggressively I’ll just add a skip every now and then. My recommendation is to make a few simple adjustments then see what the outcome is until its dialed in. Also, some customers like using flexible monthly since it’s much more predictable and frequencies are adjusted each month automatically.

This is my graph, forecasted rain looking pretty good for my watering!

Hope this helps.

:cheers:


#5

@pshyvers have you aerated your lawn in the last year? If not, I’d highly recommend doing so.

I’d also double check your soil type – if you haven’t already, the mason jar test is an easy DIY way to do so over a weekend. Here’s a good example of the test from @Modawg2k