Can mulching help manage weeds in wheat?
Answer: While mulching has many benefits, the basic idea behind mulching for weed control is to create a physical barrier between the weed and the sunlight and air, thus preventing seeds from sprouting and plants from growing. With enough mulch, weed numbers can be greatly reduced.
Nebraska scientists applied wheat straw in early spring to a field where wheat had been harvested the previous August. At high straw rates, weed levels were reduced by more than two-thirds. Wheat, like rye, is also known to possess allelopathic qualities, which may have contributed to the weed suppression.
Mulches can be organic, such as straw, grass clippings, or dead leaves, or synthetic, like plastic film. Organic mulch is generally cheaper and easier to acquire than plastic mulch — you might even produce it yourself — and its slow decomposition will also add organic matter to your soil. Additionally, it has the ability to cool soil temperature slightly, potentially slowing down weed growth. However, because materials like straw and grass clippings are applied in aggregate, not in a solid sheet, there can still be space for persistent weeds to poke through. When applying organic mulches, verify that the material has not been sprayed with herbicides, which can damage and stunt the growth of your crops.
Plastic mulches are used with heat-loving plants and promote an earlier harvest by raising the soil temperature. Plastic mulches come in a variety of colors that affect the soil temperature differently. Although black plastic mulch doesn’t provide much heat to the soil, it effectively suppresses weeds. Synthetic mulches create a solid barrier that weeds cannot penetrate, and effectively smother all weed growth below them, but they are more costly to purchase and install than organic mulches and are more resource-intensive to produce. Plastic mulch also blocks all water and air movement between the soil and the surface, and thus is best suited to use with a drip irrigation system. Though some plastic mulches are made to be biodegradable, organic certification requires annual disposal of plastic mulch.
Somewhere between organic and plastic mulches lies cardboard mulch—biodegradable, but still providing a physically impenetrable weed barrier. Cardboard mulch breaks down within one to two years. It is subject to premature degradation along its edges. Once the soil or rocks holding it down are no longer holding an attached part of the cardboard, this mulch can be caught by the wind and blown out of place. As with plastic, air has trouble penetrating cardboard mulch, and conditions beneath the mulch can become anaerobic. If the cardboard dries out, it can also become hydrophobic, meaning water won’t be able to penetrate easily, and thus drip irrigation will be necessary.
I recommend that you consult the ATTRA publication Sustainable Weed Management for Small and Medium-Scale Farms. It discusses several strategies, both proactive and reactive, as alternatives to conventional tillage systems. Options include mulching, competition, crop rotations, and low-toxicity control alternatives. You can also read more about the Nebraska study mentioned above.