INFLUENCE OF HYDROPHILIC GEL POLYMERS ON WATER RELATIONS AND GROWTH AND YIELD OF BARLEY AND CANOLA

Hydrophilic super-absorbent polymers retain large amounts of plant-ava ilable moisture and have been promoted for use as soil amendments in d rought-prone regions. This controlled-environment study evaluated the capacity of two commercial polymer gels, Grogel and Transorb, to mitig ate the effects of recurring moderate water-deficit stress (dry-down t o 50% field capacity before rewatering) on growth and yield of barley and canola. Rates of 0.03, 0.12, 0.47 and 1.87 g polymer kg(-1) sandy loam soil (1, 4, 16 and 64 times the recommended commercial applicatio n rate) were tested. Plants were grown at a soil moisture content of a pproximately 50% of field capacity. Neither polymer was effective at t he commercially recommended rate. Barley and canola grain yields were unaffected at any Grogel rate, and Transorb had no effect on barley gr ain yield. Grogel at the highest rate enhanced early shoot mass, matur e biomass production and grain yield of barley and increased leaf RWC. Canola had greater early and late vegetative biomass, but pod yield w as not increased by Grogel at any rate. Transorb was most effective at four times the recommended rate, significantly increasing tiller and fertile spike number and mature biomass production at that rate. Leaf RWC were unaffected by Transorb treatment. Grogel stimulated root grow th of barley but had no effect on roots of canola. Both polymers tende d to increase consumptive water use. Spatial restriction was found to drastically reduce the water retention of both polymers and limit the absorbency of both polymers in this study. The high rates of polymer r equired to elicit a crop yield response under relatively mild water-de ficit conditions limit the value of these polymers for agricultural fi eld use of the crop species tested.