COMPARISON OF ROCKWOOL AND PEAT SUBSTRATES FOR THE HIDROPONIC PRODUCTION OF GREENHOUSE CUCUMBERS

Soilless hydroponic cultivation of cucumbers (Cucumis sativus L.) has expanded rapidly during the last few decades. One of the key factors in achieving high productivity in industrial greenhouses is the choice of growing medium. Rockwool has become dominant, especially in Europe. However, in addition to energy consumption during production, landfilling of rockwool as a non-biodegradable material is expensive and poses an environmental risk. Therefore, there is increasing use of organic substrates in the soilless cultivation of cucumbers. Coconut coir is most widely preferred for long-cycle production. Nowadays, there is almost no data on the use of peat as a stand-alone substrate in commercial hydroponic cucumber production. Despite recent ecological considerations, peat is attractive to vegetable growers, especially in peat-producing countries as a local, cost-effective, high-quality, reusable resource. Previously, significant problems limiting the use of peat substrates were peat instability, which resulted in reduced air exchange to the roots. Based on new technologies, peat could return to the long-cycle hydroponic cultivation of vegetables. The aim of the study was to determine the suitability of fractioned sphagnum sod peat substrate as an alternative to rockwool for hydroponic production of greenhouse cucumbers in equal microclimate, irrigation and fertilization conditions. The parameters assessed included leaf nutrient status, chlorophyll content in SPAD values, and cucumber yield. Overall, substrates did not statistically influence the concentrations of nutrients in both young and old cucumber leaves. Regardless of the substrate type, leaf nutrient content corresponded to the sufficiency range for cucumbers. The only imbalance was the low K at the end of the growth cycle in both age leaves, regardless of substrates. A strong positive correlation was found between chlorophyll content in SPAD values and N, K, Ca, Mg, S, Mn and Zn concentration in young cucumber leaves. The comparative study showed that cucumber plants had a stable high yield and high fruit quality during the autumn/winter cultivation in both substrates. Within the growth cycle, specially developed peat substrate had fully maintained its stability. Therefore, the sod peat substrate can be successfully used for industrial hydroponic production of high-yielding cucumber varieties without changes in cultivation technology developed for rockwool.