Efficacy of a hydrophilic polymer declines with time in greenhouse experiments

The effect of a hydrophilic polymer (Broadleaf P4(R); HP) on growth of cucumber seedlings (Cucumis sativus L.) was investigated. Furthermore, the efficiency of HP to absorb water over a period of time was studied. Predetermined amounts of HP (0.0%, 0.1%, 0.2%, 0.3%, and 0.4% dry-weight basis) were mixed with moderately calcareous sandy loam soil in pots. At the end of the first experiment (42 days), the growth of the seedlings was recorded, as well as the maximum soil water-holding capacity (WHC), The same pots were left for a drying period ranging from 2 to 5 months and then used for another four successive experiments. Soil WHC increased significantly with increasing level of HP, but decreased after each experiment. After five experiments, the WHC had decreased 17.3% and 27.8% where HP was added at the rate of 0.1% and 0.4%, respectively. The bulk density of soils decreased significantly with addition of HP and had increased after five growing experiments at each HP rate. Cucumber seedling growth was stimulated by addition of the polymer. The greatest vegetative growth, expressed as leaf area and shoot fresh and dry weights, was observed at 0.3% HP in the first and second experiment, but at 0.4% in the third and fourth.