Explanation:

1. Weeds provide a vegetative cover that protects the soil surface against erosive action of rain and wind.
2. Weeds play an important part in nutrient recycling. Roots of weeds tap nutrients from the lower soil depths and return these to the soil surface as litter when the weeds shed their leaves or when the entire plant plants die and decays.
3. Weeds add organic matter to the soil both from the roots and from the above ground parts.
4. Many plants that are designated weeds are used as potherbs e.g. Talinum triangular.
5. Weeds are sources of pesticides e.g. Chrysanthemum cinerariifolium which provides insecticide pyrethrum.