Here is a report which I think was only partially published in TMG. Unfortuantely due to lack of interest at all levels the work of the Scientific Committee was abandoned.
"" « SUPER ABSORBENT POLYMERS » – A STUDY
The Scientific Committee
During the early 1960’s the U.S. Dept. of Agriculture (USDA) was engaged on the development of materials to improve water conservation in soils. Prior to this time water absorbing materials were based upon cellulosic products, these having a water holding capacity up to 20 times their weight.
The initial materials, produced by grafting acrylonitrile polymers onto starch based molecules, were found to be capable of holding around 400 times their weight of water. This technology was released by the USDA to several American companies for further development; Japanese companies were, however, excluded. Not withstanding, the latter embarked upon their own developments encompassing a much wider range of polymer forming materials. Over the years the technology has advanced so that there is little, if any, of the initial starch-grafted polymer in use.
Curiously the first commercial products, developed in the 1970’s, were not used to improve water conservation in soils but in hygienic products such as, sanitary napkins and adult incontinence products; the natural extension of this application being their use in babies disposable nappies which appeared on the European market in the early 1980’s.
Super Absorbent Polymers (SAP`s) intended for soil modification tend to be cross-linked acrylic-acrylamide co-polymers containing potassium cations. Those used in disposable hygienic products are based upon cross-linked acrylic homo-polymers containing sodium cations.
The Scientific Committee decided to test one of these SAP`s under Mediterranean conditions at three locations in the Languedoc region of France. The same protocol was used throughout.
The SAP tested is sold under the name of “Water Magic” water retaining crystals via DIY stores and marketed by “Botanica/Nortene” a Division of Solu Garden Leisure Ltd. Botanica is a registered TM. This product is stated to belong to the polyacrylamide gel class of SAP’s. It is a small solid cystal and easy to handle and mix. Prior to use the SAP was mixed, according to the suppliers instructions, into a general purpose potting/seed compost, NFU44-55.
Two litre plastic and terracotta pots were filled with the compost, alone and containing the SAP and planted with four Vicia bean seeds (variety “Feuillance”) which had been soaked in water for 24 hours to encourage quick germination. Each pot was replicated four times. Pots were placed outdoors and watered with tap water.
On average the pots received a minimum of 5-8 hours of direct sunlight with shade temperatures rising to +/-23°C° and falling to +/-3°C. Over the trial period the plant pots were watered as required. Daily records of rain and watering were made.
After six weeks the bean plants were removed from the pots, the roots washed, dried and the sixteen plants, roots and shoots from each treatment weighed.
Results from the three locations are listed below:
Location 1 Carcasonne
plastic pots, without SAP plastic pots, with SAP
ave. plant wt. 64.1 ave. plant wt. 60.8 gm
ave. root wt. 22.3 ave. root wt. 29.8 gm
ave. shoot wt. 40.8 ave. shoot wt. 31.0 gm
terracotta pots, without SAP terracotta pots, with SAP
ave plant wt 31.2 gm. ave. plant wt. 69.6 gm
ave.root wt. 16.3 gm ave. root wt. 38.8 gm
ave. shoot wt. 14.9 gm ave. shoot wt. 30.8 gm
The results show that terracotta plus SAP produced the sturdiest plants and that plastic pots plus SAP generally produced the second best results.
Location 2 Beziers
plastic pots, without SAP plastic pots, with SAP
ave. plant wt. 30.3 gm ave plant wt. 23.6 gm
ave root wt. 15.9 gm ave root wt. 11.8 g
ave shoot wt. 15.0 gm ave shoot wt. 12.9 gm
terracotta pots, without SAP terracotta pots, with SAP
ave plant wt. 26.7 gm ave plant wt. 29.3 gm
ave root wt. 15.0 gm ave root wt. 16.0 gm
ave shoot wt. 12.7 gm ave shoot wt. 14.7 gm
Total volume of water added during the 6 week trial:
Plastic pots and no SAP 2250mls, plastic pots with SAP 2050 ml
Terracotta pots and no SAP 3150 ml, terracotta pots with SAP 3200 ml.
The only firm conclusion is that terracotta pots consume about 50% more water than plastic pots.
Location 3 Uzes
All pots were watered 8 times and the terracotta pots were watered 9times
plastic pots, without SAP plastic pots, with SAP
ave. plant wt 44.7gm ave. plant wt. 51.4 gm
ave. root wt. 31.6gm ave. root wt. 37.3 gm
ave. shoot wt. 13.0gm ave. shoot wt. 14.0gm
terracotta pots, without SAP terracotta pots, with SAP
ave plant wt. 46.2 gm ave plant wt. 56.1 gm
ave. root wt. 36.2 gm ave root wt. 44.8 gm
ave. shoot wt. 10.0 gm ave shoot wt. 11.2 gm
Results were superior with SAP cf no-SAP as far as plant, root and shoot weights are concerned.
Terracotta pots on the hole produced heavier (better?) plants although shoot weight was reduced compared to the plastic pots.
Conclusions. Results from this experiment are inconclusive. The effects of the addition of Super Absorbent Polymers to compost could not be determined accurately.
However at location 1 terracotta pots with SAP, at location 2 terracotta with SAP and at location 3 both plastic and terracotta pots with SAP gave superior results in terms of plant, root and shoot weight compared to similar treatmets without SAP.
Plastic pots require less watering than terracotta pots