Quantitative and qualitative evaluation of weed seed bank in organic farming

The influence of organic farming on weed seed bank under two different crop rotations: with and without manure, was investigated in an organic farm of Kazliskiai over the period of 1997-2002. Proven by qualitative index, organic farming increases the diversity pf weed species. Seeds of 10 weed species were found in one experimental field at the beginning of a transition period and, after 6-year organic farming, the diversity of weeds increased almost up to 16 species. In all years of the investigation, seeds of Chenopodium album, Fallopia convolvulus and Stellaria media were found in 0-25 cm soil layer. In the sixth year of organic farming there were found 26.3, 70.0 and 91.2% less seeds of the mentioned species, respectively, compared with the transition period. At the beginning of organic farming, the amount of weed seeds in the soil was 28.0% bigger in fields of crop rotation with manure, compared to crop rotation without manure but, in the sixth year of organic farming, the difference disappeared. All weeds were distributed into 3 biological and 4 ecophysiological groups and 3 types of dispersal. Most of seeds found in 0-25 cm soil layers were therophytes. Most of them germinate in summer, spread by water (barochory), because Chenopodium album dominates. Both in fields of the 1st and 2nd crop rotation and in all experimental years, the quantitative and qualitative distribution of weeds into biological, ecophysiological groups and types of dispersal was even, with the exception of ecophysiological groups in crop rotation with manureVytauto Didžiojo universitetasŽemės ūkio akademij