WICST research themes

Core systems trial:

• Protecting the environment
• Outreach
• Prairie establishment
• Productivity/ profitability
• Soil health and biodiversity
• Soil fertility
• Core trial sites
• Weeds

Cover crops project
Decision aid tools
Grass based dairy
Manure management
Oak savanna restoration
Small grains initiative
Reduced input systems

Weeds

Most farmers and researchers have long believed that letting a large weed seed bank build up in the soil will doom a field to heavy weed pressure and alternatively, that controlling the buildup of weed seeds in the soil is a major part of prevention of weed problems.

WICST has intensively studied weed seed and weed populations in the six cropping systems, and has determined that the relationship between weed seedbanks and weed pressure is not as simple as many believe. We have also experimented with various weed control techniques, comparing various ways of rotary hoeing and the value of post-emergence herbicides in CS3. Here are our major conclusions.

Weed seed numbers in the soil are only weakly correlated with subsequent weed pressure. Plots with outstanding (and non-chemical) weed control have occurred in soils with heavy weed seed banks and plots with heavy weed seed banks have seen seed numbers fall over time even with no herbicide use. Our three cash grain systems have very different levels of weed seeds in the soil, but weed control in soybeans in both CS2 and CS3 is usually good to excellent. The lowest input system (CS3) does often have more weed pressure in the corn than the higher input systems do, and corn yields have sometimes been reduced as a result.

There are many factors affecting the relationship between the number of seeds in the soil and eventual weed pressure in a field.

• The cropping system we choose: A system like continuous corn must rely on fairly aggressive weed control measures, including herbicides, cultivation and tillage. In a more diversified system, one or more of the crops planted may compete well with weeds or effectively interrupt the buildup of some weed species. It is important that the crops be of different growing patterns, offering a change of environment for the weeds, for this to work well. We note that a forage phase works particularly well to reduce weed pressure. Mechanical weed control in the corn years of our forage systems is as effective as chemical weed control in our cash grain systems.
• The way the crops are managed: We plant wide-row soybeans in our lowest input cash grain system so that we can cultivate them. We also delay planting of corn and soybeans to permit better pre-plant mechanical weed control. In our no-till corn-soybean system this is not an option, so we plant narrow row soybeans to better compete with the weeds.
• The producer's expertise with mechanical weed control: Our ability to rotary hoe and row cultivate improved markedly over time.
• The weather: This is the big factor we can't control. Our most variable weed control occurs in our lowest input cash grain system. We have had years of outstanding weed control, and years when weed pressure definitely affected yields because early summer rains interfered with the mechanical weeding operations.

Related publications

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