Ann: RotoGro Partners with Strategic Organic Produce Group, page-48

The sticking point with hydroponic farms being certified as "Organic" is the source of nutrients, rather than the Growing Environment.
Hydroponic nutrient solutions usually consist of a combination of relatively pure organic and inorganic compounds which are designed to match the plants' nutrient requirements at any point in their growth cycle. The balance between the various chemicals is generally more important than the total available quantities (usually expressed as parts per million when dissolved in water). The solution has to be continually adjusted to achieve optimum results.
Currently, Organic accreditation can only be obtained if the nutrients are extracted from natural sources. This can be done, but the resultant solutions will contain many compounds that are unusable by the plants, which, as the usable nutrients are consumed, can lead to the solution becoming toxic, or requiring more frequent replacement rather than adjustment.
Apparently, hydroponic growers in the US are pushing to have the rules changed so that synthesised nutrients will not be a bar to accreditation. Unsurprisingly, existing organic growers are pushing back. As far as I know, the debate hasn't yet started in Australia.