Some mid-western irrigators have been touting the benefits of starch-based polymers that are added to the soil to help conserve water. The particular application I was reading was about potato crops growing in sandy, hilltop areas which used to be less productive and require about 15% more water than other areas of the fields. The polymers are not only water retention materials, but are biodegradable and break down in about a years time.
According to one grower the users "..want to change the irrigation schedule to reduce the environment for disease. Now they can irrigate on the dry side and still keep the plant healthy." In fact, one product's initial testing indicated that 25% deficit irrigation with the polymer will provide the same yield as full irrigation without it. This could save quite a bit of water - what with the ability to deficit irrigate every acre by no less than 25%.
I wonder if the polymers are capturing erstwhile recharge waters and resulting in a higher percentage of the pumped and naturally provided water available to the crop rather than returning it to the groundwater system? Reports of it "increasing yields" and "helping to keep plants healthy" seems to imply the plants are getting more water than before. If this is true, I wonder how many users are subsequently using their extra water on newly irrigated acres? I wonder if they can alternatively plant higher planting rates for increased production on the same acres? Or how many are switching to a more water intensive crop to grow? For those who don't do any of the above, I wonder if they can or will be able to market their saved water to some other grower on other acres, or, for some other consumptive use altogether? Of course, if any of these things happen to any degree there is no real water conservation (water use reduction) occurring at all. In fact, more water gets used. It's clearly a more efficient use of water, but not any real reduction in consumptive water use.
But on the positive side, I gotta believe some fertilizer and ag chemical is being prevented from leaching into the groundwater by reducing or eliminating the deep percolation. And you'd have to also believe there would be an energy savings too - so long as the saved water isn't being pumped and used elsewhere. And it'd have to be good for the economy regardless of whether these users grow the same production with less water and inputs, or, increase production with the same water and inputs. All in all, though, it's hard to imagine increased yields and production and healthier crops without more water being available to the plants - one way or another. Any detailed water use studies out there on these polymers?