Evolution of organic matter and drainages in wood fibre and coconut fibre substrates

New organic substrates have been introduced in hydroponic culture in order to substitute peat, because is a non-renewable resource, and in less rockwool or perlite due to their problematical recycling. The objective of this work is to evaluate the evolution of two renewable organic substrates, wood fibre (WF) and coconut fibre (CF) throughout one cultivation cycle. Two trials were set up, one with and a second one without crop. Volume, pH and EC of the input solution and the drainage solution were measured in both trials. In the trial without crop the content of NO3−, Cl−, (SO4)2−,Ca2+, Mg2+, Na+, P and K+ was also determined. Physico-chemical characterization of the substrates was determined at the beginning and at the end of the trials. In order to know the loss of organic matter (OM), the dry matter content of the substrates was determined at the beginning and at the end of both trials. It has been observed that in both substrates retention of elements like NO3−, Ca2+, P and Mg2+ occurs. In the study of the physico-chemical properties, it has been observed that the air capacity decreases considerably in both substrates in the trial with crop, especially in the CF, as well as a greater reduction of the C/N rate and percentage of OM. The data of organic matter loosed shows that in the trial with crop both substrates have lost more OM and this loss is slightly superior in CF. Therefore it is important to consider the possible retention of nutrients in the organic substrates to optimise cultivation management, as well as their degradability, which influences on the physico-chemical properties throughout the crop cycle.