There has been a major move away from the'kill everything and sterilize approach' for nutrient solutions to a more integrated and environmentally friendly method of allowing microbes to exist naturally in a well run, fully aerated system. Sterilization of the nutrient has proven many times to be difficult and expensive to carry out, often resulting in plant damage, nutrient problems and residues of sterilization chemicals. Using sterilization techniques such as H2O2 and Chlorine in nutrients solutions requires a high dose to kill some of the persistent plant pathogens and this has been shown to damage young and sensitive roots in many crops. 100ppm H2O2 is required to kill spores of some of the common hydroponic pathogens, but even a level of 8ppm was found to damage lettuce seedling roots. The same problem exists with the use of chlorine. Studies have also found that after nutrient sterilization when all microbes and algae have been killed, re-growth of these occurs very rapidly in the nutrient, and this can in fact result in some of the pathogenic microbes re-establishing fastest, causing many new problems in the systems. A better approach, which is used by many commercial growers, is to start with a clean, sterilized water source, add in the nutrients, then inoculate the nutrient solution with a mixture of beneficial microbes.
