Many claim there are. I would prefer to smoke organically grown cannabis - organic fertilizers are available for soil and hydro systems. The tolerance levels of many areas have forced growers indoors where hydroponic growing is easier to hide and often more efficient. I have heard some people refer to cannabis grown in soil as tasting more earthy or light. As long as the plant is leeched or flushed out with water only for the last period of the growing stage both types should smoke almost identically. The fertilizers and growth enhancers need to be flushed out so the cannabis burns better. If you look at the ash in your pipe and it is gray and breaks up easily this means it was properly flushed. If the ash is more sticky or clumpy then it could have been flushed better but this isn't a life or death problem. Hydro growers might not cut back on the additives, enhancers and fertilizers as early as they should because they are looking to increase bloom and bulk. It is very possible for a soil grower to do this too, but in hydro growing you are in complete control of which nutrients the plant gets. There is a lot of debate on which is better.