In arid environments, water availability in soil is often the limiting factor for successful germination and subsequent establishment because seedlings are often more vulnerable to desiccation. To reduce water evaporation from soil and to stabilize soil surface, amendments such as straw mulch and acrylic polymer are used to prepare seedbeds to assist vegetation recovery. This experiment aimed to investigate the combined effects of sterilized straw and Envirotac II, an acrylic polymer, on the germination rate and seedling biomass of 11 species of grasses, forbs and shrubs native to Southeast Arizona. Sixty 5-L pots were planted with 100 seed of these species (88% grasses, 10% forbs, and 2% shrubs). There were three levels of amendment treatment for soil surface - 1 ton/ac of straw and polymer, ½ ton/ac of straw and polymer, polymer alone - besides the control. The pots were watered at three levels for 25 days at 137mm, 101mm, and 55mm of total amount, which were calculated to imitate the amount of rainfall in a high, average and low year in Southeast Arizona.

Results/Conclusions

The germination rate, average and total biomass results for all levels of amendment treatments were not statistically different (P<0.05) for the 7 species that had greater than 2 germinations.  Leptochloa dubia  and Bouteloua gracilis had significantly higher germination rate for high and average watering regiment (81% and 75%, 33% and 28%, respectively, P<0.05). These two species also had significantly higher total biomass for high and average watering (0.17g and 0.13g, 0.15g and 0.14g, respectively, P<0.05). Sporobolus cryptandrus was favored by the low watering treatment (0.014g of biomass vs. 0.001g and 0.002g for high and average watering). It appeared that water availability in soil might not have been a limiting factor, so the straw and Envirotac II did not make a difference in germination success, as there were few species showing statistically different results from the three levels of watering. Leptochloa dubia showed the greatest biomass generation under high level of irrigation and 1 ton/ac straw with Envirotac II. Perhaps there is a threshold for the minimum amount of soil moisture level for germination and biomass generation between average and low irrigation level.