The . arcade gaming industry did not adopt the ESRB system, with the American Amusement Machine Association (AAMA) having cited "fundamental differences between the coin-operated and consumer segments of the video game industry" as reasoning. The AAMA, the Amusement & Music Operators Association, and the International Association for the Leisure and Entertainment Industry, adopted their own three-tier "Parental Advisory System" in 1994, which uses three color-coded levels of content intensity (designated by green, yellow, and red stickers affixed to arcade cabinet artwork).  
Earthworms generally exert beneficial effects on plant growth. However, negative effects may be induced under particular situations. The effect on grain yields is also proportional to the earthworm biomass; significant effects start to appear at biomass values> 30 g fresh weight (Brown et al ., 1999), although very high biomasses of single species of earthworms, (. Pontoscolex corethrurus ) may inhibit production under particular situations. Many mechanisms are involved in the growth stimulation. These vary from large-scale effects on soil structure and nutrient availability, to the enhancement of mycorrhizal infection or control of plant-parasitic nematodes. Once the earthworms are established, a dynamic cropping system - involving crop rotations with long cycle crops or perennials with good organic matter additions - contributes to securing long-lasting benefits from earthworm activities.