Mulching can reduce weed problems by preventing weed seed germination and by suppressing the growth of emerging seedlings. Mulching provides other benefit as well such moisture retention, prevention of nutrients leaching out of the soil, they improve soil structure and consistency, control pests and improve crop quality. Mulching includes living plants as ground cover, loose particles of organic or inorganic material, as well as other artificial or natural materials that can be laid on the soil surface.
Mulching will stop most weeds that grow from seeds providing a 5-10cm thick layer of mulch is applied. Weeds that grow from bulbs or creeping perennial are more effectively controlled using some form of continuous underlay such as woven fabric weed ‘mats’.
Synthetic mulches such as black plastic mulch or woven fabric weed ‘mats’ suppress weed seedling growth and development through blocking out light and the seedlings ability to reach the surface. While clear plastic mulch works by creating a hydrothermal process of heating moist soil which kills weeds and pests as used in soil solarisation. This method is only suitable where the soil receives enough sunlight to heat the ground through the clear plastic cover (see soil solarisation)
Green Manure or Living Mulch
(After detrashing, sugar cane leaves form a mulch to help control weeds and conserve moisture.)
Green Manure or Living Mulch can be produced from cover crops and both are usually integrated into the soil while still green or just before seeds set. The difference is that usually living mulch will be grown as an intercrop growing with cash-crops while green manure tends to be harvested into the soil prior to planting. Both practices act to improve the soil by recycling nutrients and adding organic matter to soil and both methods work to suppress weeds. Organic matter helps to hold water and nutrients in the soil and prevent wind erosion. Cover crops as green manure or living mulch greatly reduce these problems. Cover crops such as certain grasses and legumes also supper parasitic nematodes. Nematodes frequently damage crop roots resulting in decreased uptake of water and nutrients.
Living mulch can be highly effective in steep agricultural areas which experience heavy rains resulting in soil erosion. For instance banana farms in the Windward Islands are grown under such condition making it difficult to maintain organic soil matter resulting in soil washing off the slopes. A highly effective method for protecting soil against erosion and overcoming weed problems which were resistant to herbicides was to intercrop fast, low-growing shade tolerant cover crops such as melons, tropical alfalfa, mung beans, cowpea, sweet potato and Carioca beans.
Another method is growing a green manure crop is crimp rolling it with a Crimp Roller. The cover-green-manure crop should be grown to at least 600 mm tall. The crop is rolled down and stems are crimped breaking capillary action to the head. This creates a mulch layer anchored to the ground suppressing weeds. Crops can be sown directly into the crimped crop. This is similar to the slasher/mulcher method which slashes green manure crops turning them into mulch.
