The influence of vermicompost on plant growth characteristics of cucumber (Cucumis sativus L.) seedlings under saline conditions

Graded seeds of cucumber (Cucumis sativus L.), cv. Ekron F-t, were individually seeded in foam trays filled with different substrates: peat compost, vermin compost and a mixture (50% to 50%) of peat compost and vermin compost. Plants were equally irrigated, but no additional nutrient elements were supplied till the second true leaves appeared. Later, a sufficient number of 40 days old seedlings were transplanted in larger plastic pots filled with vermiculite, divided in three equal groups. In the two successive weeks all plants were periodically irrigated with equal amounts of the same nutrient solution (N 150, P 40 and K 200 mg L-1), but differing from each other by the quantity of NaCl (0, 20 and 50 mM) added to the nutrient solution. The relative growth rate (RGR) and its components, net assimilation rate (NAR) and leaf area ratio (LAR) were computed. The relative stem elongation rate (RSER), the relative leaf expansion rate (RLER), root to whole plant dry weight ratio (RWR), root to shoot dry weight ratio (RSR) and the respective fractions of roots, stems and leaf dry mass against total plant weight (RMF, SMF, LMF) were also calculated. A significantly higher relative growth rate (RGR) was found for young seedlings grown in vermin compost compared to commercial peat compost, during the nursery stage. The same trend of RGR was kept during the stand establishment period, but while the morphological differences still existed, the differences regarding to physiological performance of transplanted seedlings were even more significant. The physiological efficiency of transplanted seedlings was drastically reduced due to the increase of nutrient solution salinity, but still relatively higher values were recorded in case of vermin and mixture composts. Higher dry matter per plant and higher relative leaf expansion rate were found for vermin compost prior to transplanting and end of stand establishment period, but no effect was found regarding to dry mass partitioning of young cucumber seedlings.