Effect of olive mill waste water on young hydroponically grown tomato plants

Margine (olive mill waste water) is considered as phytotoxic and thus an environmentally hazardous material. Therefore, alternative areas of application have been discussed; one of these might be its use as an additive in growing media for horticultural purposes. However, phytotoxic responses might occur at higher concentrations. The objective of the present study was to determine threshold levels for margine either in raw or fermented (biomargine) state. The hypotheses were that (i) high concentrations of raw margine are detrimental to plant growth, (ii) tyrosol, a compound of margine, equivalents mimic the degree of growth depressions caused by raw margine and that (iii) growth reductions caused by raw margine may be removed through fermentation of margine prior to addition. In general, low concentrations of raw margine as well as of tyrosol equivalents did not result in reduced shoot and root length of three week old tomato seedlings. However, higher concentrations of both compounds showed significant differences in almost all of the evaluated parameters. In order to compare the effect of raw and biomargine, hydroponically grown tomato plants were exposed either to nutrient solution with or without 5% of biomargine and raw margine. To quantify the effect of phenolic compounds in raw margine, 5% of tyrosol equivalents were added to the control treatments for all three variants. Addition of biomargine resulted in significantly increased growth, shoot length and fresh weights of roots, shoot and leaves compared to all other treatments. However, no effect could be stated regarding dry weights. Further, addition of biomargine compensated for the effect caused by additional supplement of tyrosol. Addition of raw margine resulted in decreased growth performance.