PREPARATION OF NUTRIENT SOLUTIONS IN SOILLESS STRAWBERRY CROPS: THE ISSUE OF WATER QUALITY

Two nutrient solutions (NS) adapted for everbearing strawberry cultivars were formulated: one for the vegetative period and one for the flowering/fruiting period. Said media offer optimum nutrient conditions favouring full expression of production potential. However, the water used for fabricating the NS may contain excess elements, which can cause imbalances between nutrient elements. Moreover, they may accumulate in the nutrient medium and thus lead to a higher electric conductivity, thereby compromising the recycleability of the NS. It is therefore necessary to define for each element the concentration levels beyond which production is affected (yield and/or quality). A nation-wide survey showed four so-called risky elements, i.e., Cl, SO₄, Ca and Na. Experiments under plastic tunnels and on a peat substrate were carried out using the everbearing cultivar ‘Mara des Bois’ (breeder: Marionnet, France). The study is based on trials using three different treatment methods for each element under consideration; the treatment doses reflect the gradient of the levels observed in the water types. The standard NS contains 8 me of N. The results of two series of trials (2006 and 2007) have made it possible to define concentration limits for Ca, SO₄ and Cl. E.g., the Ca level starts limiting fruit yield and quality when it exceeds respectively 4.5 and 6.0 me. The limit is set at 2.5 me for SO₄ and 1/2.5 me for Cl. The study will continue with the integration of the climate effect; in addition, specific Na-related references are to be acquired.