Biochar from garden waste as a potential hydroponic growing substrate

Sammanfattning

With an increasing need for food to feed the growing world population, resources like landand water for agriculture are becoming. As a response, hydroponic cultivation has becomemore popular. Hydroponic cultivation consumes less water, requires less land, and consumesfewer nutrients. However, an issue is the growth substrate, which is often wasted after useand ends up in landfills. Therefore, there is a need to find growth substrates that can berecycled and thus have a lower environmental impact. One possible growth substrate isbiochar, formed by pyrolysis of organic waste. Some studies in this area have been made buthave so far been inconclusive; therefore, this thesis aimed to investigate if biochar formedfrom garden waste could be used as a growth substrate in an ebb and flow hydroponiccultivation. Two types of lettuce and two types of basil were germinated and grown indifferent biochar fractions and mixtures: biochar alone (size 0 to 10 mm) and two mixes withperlite, 50/50 with 6 to 8 mm biochar, and with 4 to 6 mm biochar, respectively. Seven keyperformance indicators (KPI) were measured, and the results were compared with those forplants grown in the commonly used growth substrate rockwool. No significant differencebetween the four substrates regarding seed germination was detected. The growthperformance KPIs showed that the plants usually grew better in rockwool than in any of thebiochar mixtures. However, pure and unsieved biochar led to the death of many plants, andthe basil was infested with mold. The study indicated that plants grow better in biochar whenmixed with perlite and grow better in the fraction of 6 to 8 mm fraction compared to the 4 to6 mm, but not as good as in the rockwool substrate. Possible explanations for this differencemay be the biochar fraction size which leads to aeration problems for the roots, thehydroponic cultivation system, the high pH (10) of the biochar, that the biochar adsorbs andreleases different nutrients or a combination.