There are a number of nutrient delivery methods currently utilized (both on Earth and in low gravity). Substrate dependent methods include traditional soil cultivation, zeoponics, agar, and nutrient-loaded ion exchange resins. In addition to substrate dependent cultivation, many methods that don't use soil have been developed including the nutrient film technique, ebb and flow, aeroponics, and many others. Because of their high nutrient solution throughput hydroponic systems can produce rapid plant growth. This necessitates large water volumes and substantial recycling of the solution which makes controlling solutions more difficult in microgravity conditions.