Date of Award:

1994

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Natural Resources

Department name when degree awarded

Range Science

Advisor/Chair:

Christopher A. Call

Abstract

Complementary greenhouse and field studies investigated the effects of ambient environmental conditions on cattle dungpat moisture, temperature, nutrient concentration, and crust formation dynamics, which in turn influence seed germination and seedling establishment in dungpats. 'Hycrest' crested wheatgrass [Agropyron desertorum (Fisch. ex Link) X A. cristatum (L.) Gaert.] was used as a representative revegetation species.

After collecting feces from Holstein steers that had been fed crested wheatgrass seeds, uniform dungpats were prepared and placed on two soil types (loam and coarse sand) in containers under three watering treatments (field capacity, 1/2 field capacity, and no water) in the greenhouse. Dungpat and underlying soil microenvironmental factors, and germination and seedling development, were monitored for 14 weeks. Moisture and temperature were favorable for germination during the first 4 weeks, but increasing crust thickness prevented most of the developing seedlings from emerging from dungpats. Seedling emergence, development, and survival were greatest at the peripheral region of dungpats on the loam soil at moisture contents of 1/2 field capacity or higher.

Uniform dungpats containing passed seeds and unpassed seeds were placed on a silt loam soil in the field in the spring (late April 1993) under natural and above-normal precipitation regimes and in the fall (late October 1993) under natural precipitation. Unpassed seeds were also broadcast and drill-seeded into soil seedbeds at the same times. Microenvironmental factors and germination and plant establishment were monitored for 49 weeks in the spring experiment and 17 weeks in the fall experiment. For dungpat treatments, seedling emergence and survival were greater for unpassed than passed seeds in both precipitation regimes; however, sufficient numbers of seedlings established from passed seeds, and these plants had greater biomass and similar or greater seed production than plants from unpassed seeds. Slight changes in nutrients in dungpats and underlying soil indicated that partial decomposition and mineralization of dungpats had occurred by the end of the spring experiment.

Both studies indicate that dungpat microenvironmental factors are greatly influenced by ambient moisture, temperature, and insolation, and by the nature of the underlying soil. These studies support the claim that plants established in dungpats could serve as nuclei of seed production for surrounding areas.

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