Evaluation of substitutes for rock wool as growing substrate for hydroponic tomato production

Abstract

To reduce the rock wool waste, the present study is focused on the evaluation of sheep wool, Sphagnum and hemp slabs, which may be used as replacement for rock wool as growing substrate for hydroponic tomato production. As such, physical and chemical properties of substrates, the plant growth, yield, fruit characteristics, as well as primary and secondary metabolites of tomatoes were considered.

The marketable fruit yield of plants grown in Sphagnum slabs (12.8 kg plant^-1) was reduced to only a small extent compared to the yield produced by rock wool slabs (13.8 kg plant^-1). Sheep wool (12.3 kg plant^-1) and hemp (10.4 kg plant^-1), however, showed higher deviations. The lowest yield of blossom end rot (BER) fruit was produced by Sphagnum. Compared to this result, the BER-yield was nearly 2-fold higher caused by sheep wool. The soluble solid content in fruit ripened by the hemp material was decreased compared to those caused by the remaining substrates. Furthermore, it was found that the volume of easy available water (EAW) was mainly responsible for changes in plant development. As such, a high correlation was found between EAW and: leaf area (r = 0.851); flowers (r = 0.785); lycopene (r = -0.918); ß-carotene (r = -0.997); penolics (r = -0.918); LAA (r = -0.848).

The findings suggested that Sphagnum slabs can be used as replacement for rock wool slabs, whereas the usage of slabs consisting of hemp and sheep wool is not suitable as growing substrate for hydroponic tomato production.