BEHAVIOUR OF VEGETABLE SEEDLINGS CULTIVATED ON PEATS WITH DIFFERENT DEGREES OF DECOMPOSITION

In Italy, the production of vegetable seedlings on trays is undertaken using peats with low or medium degrees of decomposition. Several nurseries are located near the sea where the water quality used to grow plants is poor, due to the high salt content. The degree of decomposition/humification of peat has a great influence on the physical and chemical properties of substrates such as total porosity, air and water ratio, bulk density, shrinkage, electrical conductivity, buffering capacity and humic acids. The aim of these studies were to investigate the effects of peats of low and moderate degrees of decomposition on the growth of different vegetable seedlings irrigated with water containing differing salt contents. Trials were carried out using two peats: a less decomposed peat of Northern European origin (H2-H3) in com¬parison with a more decomposed peat originating from the Republic of Ireland (H4-H5). Media were prepared solely from each peat type and in mixtures (25/75, 50/50, 75/25 v/v). Different vegetable species were cultivated in order to determine the influence of substrate on germination rate and length of production cycle. Species and substrates were irrigated with tap water (0.5 dS/m) and tap water amended with NaCl (3 dS/m). Data on the most important morphological and quality parameters were collected together with physical and chemical analysis on substrates before and at the end of the experiments. Results confirmed that the use of saline water reduces plant growth. Substrates containing 50%, 75% or 100% v/v of more decomposed peat (H4-H5) gave superior results in terms of seedling quality and growth, both with high and low salt levels. That behaviour may be related to physical parameters and to the higher buffering capacity of media containing humified (H4-H5) peat.