Results are presented for the spring survey only. Questionnaire results have not been compiled at the time of paper preparation. Frequency is defined as the number of fields iii which a species occurred and is expressed as a percentage of the total number of fields. It reflects the geographic extent of the weed in the study area. Field uniformity is the number of quadrats in which a species occurred expressed as a percentage of the total number of quadrats and is an indication of the amount of land in the study area that contains a given species.
Density is defined as the average number of plants per square metre.
It is used to rank the contribution of individual species to the weed community and assumes that frequency, field uniformity, and mean field density are of equal importance in estimating the abundance of a species. In general, the results from these twelve fields suggest that weed populations were similar under zero and conventional tillage systems. Regarding individual species, the two tillage systems had similar densities and field uniformities for both the in-field and border surveys. The only exception was wild mustard, which was consistently found at lower levels in the zero tillage fields. There is an indication that zero tillage crop production may support a slightly more diverse weed community, particularly in the field borders.