rameters such as the O 2 and temperature in the rootzone . Using an organic medium that is prone to decomposition will mean that there is no consistency during the growth cycle ( Burnett et al 2016 ). As the organic material is broken down both the physical and chemical characteristics , including the pH will be affected . The rootzone pH as we know has a huge effect on the availability of nutrients to be taken up by plants .
Another important implication relates to the fertilisers being used . In traditional hydroponic production systems , highly soluble inorganic fertilizers are dissolved in water and then applied to crops at regular intervals . This is ideal to maintain the concentration around the roots at maximum for fast uptake . Nutrient solutions are also designed to promote uptake of all nutrients , limiting antagonism between specific nutrients and promote either vegetative or reproductive growth . When tomato plants for instance require a higher potassium concentration to improve the colour and flavour of the fruit , it is easily done by adjusting the nutrient recipe . Under current regulations , the use of these fertilizers are however prohibited and only nonchemically derived nutrients such as fishmanure , seaweed , bone meal etc . can be used . The nutrients in organic fertilizers are not in a form available to be taken up by plant roots , and few microorganisms are present in hydroponic solutions to mineralize the organic compounds into inorganic nutrients . Organic fertilizer therefore needs to be microbially pre-processed before incorporation into hydroponic solutions . The conversion of ammonium to nitrate is especially crucial since ammonium can easily become toxic to crops in a soilless system . The pre-processing is usually conducted in two or more reaction tanks to provide ammonification and nitrification of organic nitrogen compounds . However it was shown recently that adding a fish-based soluble organic fertilizer directly into a hydroponic system yield good results when an inoculum is also added to the system . Bark compost ,
Picture 3 : Cucumber plants in a hydroponic system using untreated organic fertiliser ( front ) and conventional nutrient so ).
field soil , nursery soil , and even sea water can be used as inoculum to promote ammonification and nitrification and thereby increase the N nutrition of crops in a hydroponic system ( Shinohara et al 2011 ).
A lot of progress has thus been made with regards to the fertilization of organic hydroponic crops increasing the productivity and also the adoption of this method . Although the basic principles of organic agriculture did not take into consideration growing crops in soilless systems , this production method can definitely be classified as sustainable .
References Burnett SE , Mattson NS , Williams KA . 2016 . Substrates and fertilizers for organic container production of herbs , vegetables , and herbaceous ornamental plants grown in greenhouses in the United States . Scientia Horticulturae .
Kelly C . and Metelerkamp L . 2015 . Smallholder farmers and organic agriculture in South Africa . A literature review commissioned by the Southern Africa Food Lab and funded by GIZ . SI Projects , Sustainability Institute , Stellenbosch University , Stellenbosch .
Shinohara M , Aoyama C , Fujiwara K . 2011 . Microbial mineralization of organic nitrogen into nitrate to allow the use of organic fertilizer in hydroponics . Soil Sci . Plant Nutr . 57:190 – 203 .