Analysis of weed vegetation of no-tillage upland fields based on the multiplied dominance ratio.

The objective of the present study was to clarify the characteristics of weed vegetation in no-tillage upland fields in Japan. Vegetation surveys were conducted in two stages and the obtained data were analyzed based on the multiplied dominance ratio. The first was a two-year survey of a no-tillage field and a tilled field where no-tillage or tillage farming had been carried out for more than 10 years. The no-tillage field surveyed exhibited a different seasonal succession from the tilled field. Summer annuals dominated the tilled field in summer, and winter annuals dominated in spring. Perennials occupied the no-tillage field in spring; summer annuals also dominated in summer. The second survey was of 19 and 22 fields, including some no-tillage fields, in the summer of 2000 and the spring of 2001. The vegetation in both summer and spring was classified into three vegetation types, principally dependent on the no-tillage periods: types I and II consisted mainly of tilled and under 3-year-old no-tillage fields, and type III comprised no-tillage fields three years old or over. Type II vegetation was characterized primarily by the presence of biennials and perennials of Asteraceae, and type III by perennials, such as sweet vernalgrass (Anthoxanthum odoratum ), in addition to the same species as type II. Summer annuals such as southern crabgrass (Digitaria ciliaris ) were abundant in many fields in summer regardless of the vegetation types. [ABSTRACT FROM AUTHOR]