Comparing Zero And Conventional Tillage

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Tillage Loss Leaves Questions

The types and number of weeds in any given field are controlled by a number of factors: soil types, environmental conditions, crop rotations, herbicides used, and tillage - to name a few. However, with the trend towards zero tillage or direct seeding, an important weed control tool has been reduced or eliminated.

Farmers can compensate for the loss of tillage by increasing their reliance on other weed management tools, such as crop rotations and herbicide use. However, this still leaves us with a number of questions. How much of an effect does the loss of tillage really have on weeds? Which weeds should we be paying more attention to? How do we compensate for the loss of tillage?

Survey Looks For Answers

In order to answer some of these questions, a weed survey comparing zero and conventional tillage systems in Manitoba was conducted. Approximately 130 zero and conventional tillage fields were surveyed in 1994, from 27 rural municipalities across Manitoba. For each zero tillage field surveyed, a conventional tillage field was selected nearby that had a similar crop rotation history.

To qualify as a zero tillage field, three years of zero tillage production were required. As well, only fields seeded with knife, spoon or disc type openers were used; those on which cultivator shovels were used at seeding time did not qualify. Fall anhydrous applications were allowed on zero tillage fields, but only if low disturbance knives were used.

Fields qualified under the conventional tillage category if there was a minimum of two tillage operations before seeding (in the spring or previous fall).

The survey sampled both types of fields for weeds in the spring, before spraying, and again in the fall, after harvest. The centre part of each field was sampled, as well as the border, to look for weeds that might have been encroaching from the field's edge.

Results Show Differences In Weed Populations

According to the survey, many perennial weeds had higher densities in zero tillage fields - as well as some annual weeds. However, other annual weeds had higher densities in conventional tillage systems (see Survey Results Charts). Annual weeds included grassy and broadleaf weeds, and volunteer crops.

Annual weeds that had lower densities in zero tillage fields included redroot pigweed, green foxtail and kochia. These weeds have better germination and growth at higher soil temperatures, and the lower densities could reflect lower soil temperatures in the spring in zero tillage systems.

Differences were also observed in weed populations in field borders and the main body of both types of fields. Some weed species had higher densities in the borders, while an equal number had higher densities in the main area of the fields (see Survey Results Charts).

This is an important observation, since it has been suggested that weeds such as dandelion and Canada thistle (with seeds that are spread by wind) might be more abundant in the borders of zero tillage fields - because their seeds are trapped by stubble and litter as they blow in. However, the survey did not indicate this; if these weeds are being spread by wind, they are moving into the main body of the fields as well.

It should be noted that the consistent increase of perennial weeds such as dandelion, perennial sow-thistle, Canada thistle and quackgrass in zero tillage fields has been and still is a concern.

Survey Results Charts

Weeds With Higher Densities In Zero Tillage Fields

Weed With Higher Densities In Conventional Tillage Fields

Weeds With Higher Densities In Borders Of Fields - Both Systems