Growth and yield characteristics and heavy metals content on tomatoes grown in different growing media

This work studied the effects that different growing media (compost and beached Posidonia oceanica) have on the growth, yield, and heavy metals concentrations of tomatoes (Lycopersicon esculentum Mill.) hydroponically grown in a greenhouse. A commercial substrate exclusively composed of pumice was used as a control sample. The choice of beached Posidonia oceanica as a growing media and as a matrix in order to obtain compost is due to the extraordinary accumulation of deposits of the seaweed Posidonia oceanica on the beaches of Sardinia and in general on the beaches of countries of the Mediterranean. Leafy deposits of Posidonia oceanica are treated as refuse and disposed off in waste dumps. In fact, the Italian law prevents the agricultural use of beached P. oceanica plants considering them as heavy metal accumulators and then, a cause of heavy metals contamination in the environment. Nevertheless, it is important to pay great attention to physical and chemical characteristics of the growing media used in order to avoid soil pollution and the danger of introducing harmful substances in the food chain. Growth and yield parameters were calculated during the different stages of plant growth. The total concentrations of some heavy metals [lead (Pb), cadmium (Cd), zinc (Zn), chromium (Cr), copper (Cu)] were determined in growing media, tomato fruits, and in leaves. No statistically significant differences were found between the growth and yields of plants grown in different growing media. The heavy metal concentrations of compost were higher than those of beached Posidonia oceanica or the control sample. However, most metals strongly interacted with the organic matter of compost, limiting the vegetal absorption. Metals concentration in fruits and leaves was essentially the same in all the plants. According to these observations the use of compost and beached Posidonia oceanica as growing media did not cause a metals accumulation in fruits and plants of tomatoes grown in hydroponics.