Quantifying allelopathic effect of rapeseed on germination and seedling growth of maize under different salinity levels@@@Rapsų alelopatinis poveikis kukurūzų sėklų sudygimui ir daigų augimui skirtingo druskingumo substratuose

Brassica species have been reported as having allelopathic effect, reducing seed germination and emergence of subsequent cereal crops when grown in a rotation. Therefore, laboratory and greenhouse experiments were conducted to determine the allelopathic potential of rapeseed (Brassica napus L.) on germination and seedling growth of maize (Zea mays L.) under different salinity levels. Laboratory experiment consisted of two factors including different plant parts (root, shoot, leaf and whole plant) and their various concentrations (0, 5, 10, 15 and 20 %). In a greenhouse experiment three factors were studied including different salinity levels (0, 4 and 8 %), crop residue concentrations (0, 2 and 4 %) and decomposition time (2 and 4 weeks). The experiment was laid out in a completely randomized design with factorial arrangement where treatments were repeated five times for germination experiment conducted in Petri plates and three times for soil bioassay experiment conducted in pots. The results showed that extracts of different plant parts could not affect the germination, while different concentrations showed significant effect on maize seed germination. The interaction of extracts of different plant parts with different concentrations significantly affected the growth. Root and leaf extracts at 5% concentration produced maximum root length, shoot length and plant dry weight as compared to other plant parts at other concentrations. For the second experiment or greenhouse experiment the results showed that neither plant parts nor decomposition period could influence germination significantly. However, salinity levels showed inhibitory effect on germination with increase in salt concentration. The rapeseed residue concentration of 2% with 4% salt concentration produced maximum plant fresh and dry weight. Rapeseed showed allelopathic potential on germination and seedling growth of maize, but this influence was decreased gradually with the increase of salinity.