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ABCs of Mechanical and Cultural Weed Management
B. Keep weeds on the defensive.
Weed seeds wait each spring for heat and light to induce germination. Don’t
wake them up unless you have a way to take them out.
Several farmers in this book describe their version of a “stale
seedbed.” (See stories about Jim Cavin,
Rich de Wilde, Carmen
Fernholz and Paul Muller.) They do
one or two shallow tillage passes to stimulate germination of surface
weed seeds before crop-planting time. Irrigation or warm, moist
soil conditions spur weed seed germination that triggers a control
pass with tillage or flame. By minimizing subsequent tillage at
planting that would stimulate new weed seeds, the crop comes up
through pre-weeded soil.
Any planter can be less of a weed-helper if it is tooled to leave soil as
loose as possible over the seed row, while still creating good seed-soil contact.
Packer wheels at the surface press light-stimulated weed seeds into moisture.
Ridge-till planters move fresh weed seed from the rows by skimming the top
inch or so of topsoil from the row to the middles, where cultivators can attack
weeds more easily.
Your crops can out-compete weeds through well-planned crop rotations. Manage
the crop sequence to minimize ecological openings for weeds. Mix crop rooting
depth, root type (taprooted or fibrous), and seasonal surface cover. Vary
the timing and depth of tillage. In mature, sophisticated rotations, crops
emerge in ideal conditions while weeds struggle to find an opening to survive.
C. Accept weeds that don’t really matter.
Separate how you feel about weeds in your fields from their potential to diminish
production. Agronomically, weeds are an economic problem only if they decrease
yield—now or in the future—by more than the cost of managing them. If the
aesthetics of a clean field are important, you need to be honest about the
extra cost.
Weed species vary in how much of a threat they pose to crop vigor. Some winter
annuals provide soil protection. Some annual weeds in forage crops provide
nutrition for livestock or abundant residue to build soil. Weeds that don’t
go to seed in a cover-crop stand count as biomass to soil microbes and warrant
only your watchful eye. “
Eradication of all weeds is a virtual ring in the nose of farmers,” claims
organic farmer Terry Jacobson of Wales,
ND. That goal can tempt farmers to over-control with chemicals or
excess tillage, he says.
Jacobson wants to learn more each season about weeds. He wants to know which
ones he can live with, which ones are worth containing and which ones are
telling him where he needs to make improvements in crop or soil management.
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