Establishment of native Atriplex species evaluated under a line-source sprinkler irrigation system during the summer and winter

Atriplex canescens (Pursh) Nutt., Atriplex polycarpa (Torr.) Wats., and Atriplex lentiformis (Torr). Wats. have been considered candidate perennial shrubs for revegetation of abandoned farmlands in southern Arizona. Objectives of the 1992–1994 field studies were to investigate the establishment characteristics of populations of these species and to estimate water requirements for establishing transplants and/or seedlings under a line-source sprinkler irrigation system. During the summer on a sandy loam soil, seedling establishment occurred at total water amounts greater than 200 mm but was absent at amounts less than 150 mm The poor stand establishment was attributed to high soil temperatures at 1 to 3-cm depth which were not optimum for seed germination. Transplant survival percentages were greater than 89% except for accessions of A. canescens var. linearis (S. Wats.) Munz, which were affected by rabbit herbivory. Transplants were successfully established by planting into a wet soil profile followed by cumulative precipitation amounts of 60 to 70-mm. Establishing Atriplex taxa during the summer using transplants was more promising than direct-seeding. On a silt loam soil during the 1993 winter, stand establishment was not increased under cumulative precipitation and irrigation amounts greater than 100 mm compared to 66 mm of precipitation. On a clay loam soil during the 1994 winter, supplemental irrigations increased the probability of seedling emergence and stand establishment was higher under total water amounts greater than 100 mm. Differences between years in response to the line-source irrigation gradient were attributed to the number of consecutive days when soil moisture at 1 to 3-m depth was high for optimal seedling emergence. During the winter, plant heights were not affected by total water amounts between 182 to 248-mm (1993) and between 119 to 150-mm (1994), whereas heights were reduced at total water amounts less than 100 nun in 1993, and less than 90 mm for all species in 1994 except A. polycarpa. In southern Arizona where precipitation is erratic in amount and timing, supplemental irrigations may increase the probability of successful seedling establishment of Atriplex shrubs.