Influence of hydrophilic gel polymers on water relations and growth and yield of barley and canola

Abstract

Hydrophilic super-absorbent polymers retain large amounts of plant-available moisture and have been promoted for use as soil amendments in drought-prone regions. This controlled-environment study evaluated the capacity of two commercial polymer gels, Grogel and Transorb, to mitigate the effects of recurring moderate water-deficit stress (dry-down to 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 application rate) were tested. Plants were grown at a soil moisture content of approximately 50% of field capacity. Neither polymer was effective at the commercially recommended rate. Barley and canola grain yields were unaffected at any Grogel rate, and Transorb had no effect on barley grain yield. Grogel at the highest rate enhanced early shoot mass, mature biomass production and grain yield of barley and increased leaf RWC. Canola had greater early and late vegetative biomass, but pod yield was 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 growth of barley but had no effect on roots of canola. Both polymers tended 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 required to elicit a crop yield response under relatively mild water-deficit conditions limit the value of these polymers for agricultural field use of the crop species tested. Key words: Barley, canola, drought, hydrophilic polymer, soil conditioner, water stress