Blast furnace and recycled plastic residues as greenhouse substrates and effect of substrates temperatures on lettuce cultivation

Aim of the research was to compare innovative substrates as blast furnace and recycled plastic residues with traditional substrates as peat, perlite, and expanded clay, and to investigate the effects of substrate temperature on greenhouse lettuce cultivation. Substrates temperatures, solar radiation, air temperature and relative humidity were measured. Heat capacity of the substrates was determined on dry and irrigated samples. Experiments showed that lettuce marketable yield ranged from 24.4 t/ha for recycled plastic, to 37.1 t/ha for peat. Differences were observed in substrate daily temperature fluctuations. The standard deviation of the substrates temperature fluctuations ranged from the lowest value of 5.1 °C for perlite, to the highest value of 11.4 °C for expanded clay. The results obtained showed that lettuce higher productivity was related to lower daily substrates temperature fluctuations, with the other greenhouse environmental conditions being equal.