With margins getting tighter, I’m sure many no-tillers would love to find more economical ways to control weeds than having to clear more room in the budget each year for herbicides.
In that vain, one of more interesting presentations shared at the recent No-Till on the Plains Winter Conference was Randy Anderson’s discussion multi-tiered, “nature-based” approach to controlling weeds and, maybe some day, eliminating the need for herbicides.
The researcher at the USDA’s Agricultural Research Service office in Brookings, S.D., says there are a number of things that diverse rotations, no-till practices, integration of cover crops, crop synergism and soil health can do to reduce the influence of weeds.
Here’s a summary of his main points:
- Warm and Cool. Rotating cool- and warm-season crops helps weed management, Anderson says, because different planting and harvest dates among crops provide opportunities prevent either plant establishment or seed production by weeds.
Long-term rotation studies in the Great Plains in 2007 show the impact of rotating crops is greatest when rotations are arranged in a cycles of four, with two cool-season crops followed by two warm-season crops, he says.
- On the Surface. No-till practices enhance rotation designs and alter weed dynamics by keeping weed seeds near the soil surface and exposing seeds to environmental extremes and predation.
A study that recorded weed seedling emergence in no-till and tilled treatments across four sites on the Great Plains, for 3 years, found that by the third year weed emergence was eight-fold greater with tillage than with no-till.
- Role of Covers. Integrating cover crops with seasonal intervals lessens herbicide needs, Anderson says. In diverse rotations that include crops with different life cycles, such as small grains, a niche exists for fall-planted cover crops that suppress weed growth effectively, but minimize crop damage.
In a sequence of winter wheat-oat-soybeans, he says, covers like winter rye or a mix of oats-dry peas-radishes effectively suppress fall weeds and weed emergence grown in soybeans the next year is reduced and delayed, he says.
A 2009 study in Brookings found that when compared with a conventionally tilled system, weed density is 80% lower due to the 3-year interval of no-till, as well as crop residue from small grains and cover crops. Peak emergence was also delayed 4-5 weeks.
- More Tolerance. Crop tolerance to weeds increases with soil health, Anderson says, citing a 2010 study at the Rodale Institute’s research farm in Pennsylvania where cover crops were grown between each cash crop of a corn-soybean-spring wheat rotation and compared with a control with no covers.
After 25 years, a series of uniform weed infestations were established to estimate crop tolerance to weed interference. When weed biomass was 100 g/m2, yield loss in corn was only 5% in the soil health treatment, but 25% in the control. And corn yield loss was less at all weed-infestation levels than in the control plots.
Researchers found cover crops increased organic matter, microbial biomass and activity and soil aggregation.
If you’re already no-tilling, some of these concepts are not new. But Anderson’s point is that a broader approach to weed management that includes synergism between no-till, cover crops and rotation can move you, perhaps, toward a “herbicide-free no-till” system down the road.
And that would certainly be easier on your pocketbook.