As with lighting, much debate has also been centered around indoor yields from hydroponic and soil based cannabis crops. It's been a given in both hydroponic and soil cultivation circles that a well aerated root zone delivers faster growth and higher yields than one that's not as well aerated. Aeration is important because it's how growers deliver oxygen, in the form of air, to the root zone. The problem with making sense of the hydro/soil yield debate is in understanding that the primary difference isn't in the water (as the term hydro implies) but in the aeration, and that both methods can indeed furnish well aerated media. However, because water, air, and media cannot occupy the same space at the same time, as a given volume of soil becomes more and more aerated it will also hold less and less nutrient rich soil and water. Along the path to achieving more soil aeration a point is reached where media nutrient content and water content are sacrificed for more aeration, and the closer a grower gets to providing his roots with all the aeration they can handle, the closer he gets to using a hydroponic media and/or hydroponic (or aeroponic) irrigation methods. This is a physical constraint of soil, the only way around it is to use larger volumes of the aerated soil. As you review Moon Doggie's final analysis you'll see how he was able to isolate the influences of media on crop yield.