MULCHING AS A TECHNIQUE TO REDUCE SALT ACCUMULATION IN SOILLESS CULTURE

     The effect of mulching with polyethylene or polypropylene sheets on water and nutrient budgets and on growth and production of roses was evaluated under soilless culture. In a first experiment ‘Anna’ and ‘Sari’ rose plants (on Rosa indica rootstock) were grown for 790 days in raised benches filled with sand: peat (4:1 v/v) with or without black polyethylene sheet mulching. Fertigation was carried out with 25 % leaching fraction. Higher numbers and fresh weight of harvested flowering stems (+ 30%) were recorded in mulched substrate. Reduction in water consumption (-58.8 %), higher calculated water use efficiency and lower electrical conductivity (EC) were recorded with mulching. Mulching also limited the discharge of drainage waters. In a second series of experiments, ‘Anna’ roses (on R. indica) were grown in a closed hydroponics system using long-shaped polypropylene containers (“canalette”) filled with pumice. The nutrient solution was distributed by a sprinkler system laid on the substrate surface near the container wall. This system was used to conduct short-term experiments with or without mulching with polypropylene sheets. Increases in water consumption and in the EC of the recycling nutrient solution (+39.6% and +5%, respectively) were recorded after 72 hours in absence of mulching. In a third experiment some pots with bottom holes were inserted into and filled with the pumice (cultivated) substrate and subjected to mulch and no-mulch. After three months of fertigation the pots were excavated and the substrate divided in upper and lower layers. Each sample was washed ten times with distilled water and the EC of every washing solution was determined. In a second analysis the substrate was dried, ground and extracted with distilled water, determining EC in the clear sample. Salts accumulated in absence of mulching, reaching relatively high concentrations in the upper layer of the pumice. Our results highlight the potential benefits of mulching in open- and closed-soilless culture systems, as they could significantly increase crop productivity, decrease production costs and benefit the environment.

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