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GringoCArlos

Feb 8, 2013, 11:39 PM

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Super absorbents and water savings

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For those who use lots of water on your landscaping or lawns, or are tired of watering your plants or property every day or two when it’s dry, here is one way to save a bunch of irrigation water using super absorbents.

I still chuckle remembering when we slyly dumped a teaspoon of this stuff in our professor’s morning coffee back in the 1970s and it was instantly gelled. All he wanted was to wake up and get moving. We stopped him before he took a swig.

Here is a short video that shows exactly what one form of this material does: http://www.youtube.com/watch?v=EuzNm84-rQU

What is a super absorbent? It’s a material that will absorb 300-500 times its own weight in water, and then slowly release it to plant roots.

Some background- one of the first commercial products that were attempted back in the 1970s was called Super Slurper. In the 1970’s they were trying to find a market for these absorbents. Here is a follow-up article on the man who came up with this material:
http://www.ars.usda.gov/is/ar/archive/may96/starch0596.htm

One of the first commercially successful products using this material were baby diapers. Baby would wet, but no longer would the moisture get out. Tampons followed until toxic shock deaths ended its use. So far, they haven’t been as successful in agriculture due to the high cost. The current cost for ag land application in Mexico would be about 20,000 pesos per hectare, while rent runs about 6,000 per year. Still high.

Here in Mexico, soils are generally sandy/rocky with low organic matter. About 10 seconds after your sprinklers dump water on it, the water goes straight down, most goes on past the plant roots and returns to the aquifer over time.

Little by little, these super absorbent materials are now being offered for sale in Mexico at a cost between 100 and 500 pesos per Kg. There are different particle sizes available, depending on the intended use. They are sold here in Mexico under names like Hidrogel or Acua Gel. Google is your friend.

Once they are applied, they will generally last for 5 years before they are broken down in the soil, and it would need to be reapplied. In the rainy parts of the year, the material will fill up to its capacity, and any excess water will just do as it always does, and soak down past it.

Here is some commercial information on the Hydrosorb product sold in the US (this is not a plug, I don’t know the company and it’s just more information that’s out there on the material)
http://www.hydrosorb.com/docs/HydrosorbAG.pdf

What’s the benefit to you in using this type of product here in Mexico? Trees or potted plants would only need to be watered once every three or four weeks. Lawns, maybe once deeply every two or three weeks to maintain nice green grass. Your water use drops 50% +, and your water supplier doesn’t have to come up with as much water. The expansion and contraction of the material also helps with soil aeration if the soil has much clay in it.

The material cannot be applied on the surface, it should be placed 4” to 6” deep where the.roots can get the water it’s holding. Applying too much would result in soggy feeling soil after watering and would be detrimental to the plants.

Thinking about existing lawns and the low cost of labor here, a gardener with a flat spade could open slices in a line which are 6” deep, apply a sprinkle of the material and stomp the slice back in place. In 2 or 3 weeks, the slices would have disappeared. A grid of slices a foot apart should work for existing lawns. Before planting a new lawn, just apply it and then till it into the soil.

-Flower beds would need 50 grams/sq meter;
-potted plants would use 3 grams per liter of soil (= 30 grams in a 3 gallon pot),
-lawns would need 1 kg per 100 sq meters (on a 1 foot grid layout, that would be about 1.5 grams per running foot of the slices into an existing lawn)
-I have seen some reports which say this material shouldn’t be used for vegetable gardens (although the Hydrosorb website looks like they're promoting it for commercial vegetable production).

The payback for using this material here should be only 3 or 4 months. After that, you’re saving money (ESPECIALLY if you are on the DAC electricity rate and running irrigation pumps), time, and lots of water. Many people who move here can’t stand the thought of living without extensive landscaping around their new home. Don’t we owe it to our hosts to save water if it’s possible?

(This post was edited by GringoCArlos on Feb 8, 2013, 11:47 PM)