Factors involved in emergence of weeds in the field

Weed emergence in the field results from breaking of seed dormancy, seed ge rmination and growth of the seedling to the soil surface. This work reviews the factors that affect these mechanisms. Flushes of weed emergence during certain time periods demonstrate that buried seeds are in a physiological state favorable to germination. However, seeds are not always able to germi nate as they may be dormant or quiescent. Several environmental factors or their combination can initiate germination. The three main factors that hav e been identified as being the most important for seed germination are temp erature, moisture, and light. Since emergence is closely tied to germinatio n, it is often difficult to separate the factors affecting each process. We ed emergence is initiated as soon as the seed germinates. Emergence is also influenced by factors affecting seedling growth until it reaches the soil surface. In temperate regions, in the spring, weed emergence is mainly affe cted by temperature, water and soil physical state. In order to reach the s oil surface, the weed seedling must pass through a soil layer which constit utes a physical barrier. Soil crust can also be an obstacle to weed emergen ce. Seed dormancy and the environmental conditions required for germination and growth vary from species to species and complicate any generalisations that could be made concerning the pattern of emergence of weeds in a given field.