Date of Award:

1973

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Natural Resources

Department name when degree awarded

Range Science

Advisor/Chair:

Cyrus M. McKell

Abstract

In seasons of above normal precipitation, populations of annual weedy species increase in great abundance in semi-arid desert plant communities. These increases in biomass tie up a considerable portion of the available nitrogen of such ecosystems and may depress subsequent annual grass germination.

A big sagebrush-annual bromegrass plant community was irrigated to simulate a spring growth period of abundant precipitation amenable to annual bromegras s productivity. Productivity and nitrogen content parameters were monitored throughout the spring and summer to evaluate the short and potential long term effects of this seasonal increase in "precipitation".

Irrigation increased annual bromegrass productivity almost 50 percent. This increase was a result of the combined factors of increased soil moisture content and increased nitrogen availability due, apparently, to increased soil microfloral nitrification activity under low water water stress conditions.

The increased annual growth resulted in a greater nitrogen uptake despite an observed decrease in irrigated bromegrass percent nitrogen values. Both the tie up and irrigation effect were maintained throughout the summer and into the subsequent annual germination period. However, total soil nitrogen levels and bromegrass nitrogen mineralization rates suggest that soil nutrient conditions for subsequently germinating bromegrass seedlings do not differ because of previous spring irrigation treatment.

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