THE EFFECT OF HEIGHT AND DURATION OF SNOW COVER ON WEEDS IN SPRING BARLEY

The weed monitoring was carried out in the long-term monoculture stand of spring barley in the experimental field station in Nabcice (South Moravia, Czech Republic). The long-term average of annual precipitation is 481 mm and the long-term temperature average is 9.2 degrees C. Monitoring of height and duration of snow cover was carried out in the seven-day intervals. Weed infestation in spring barley stands was evaluated before the application of herbicides. Dates of evaluations were 13. 5. 2005, 22. 5. 2006 and 28. 6. 2007. Number of weeds of each species was counted on the area of 1 m(2). Achieved data of weed infestation were evaluated by the DCA analysis and subsequently by CCA analysis. Based on measurements of snow cover, we can claim that winter between years 2006 and 2007 had very short duration of snow cover. The first snowfall was 2. 11. 2006 and the last snow thawed 22. 3. 2007, continuous snow cover lasted 11 days, the sum of snow layer height was 1529 mm. The winter between years 2005 and 2006 had much longer duration of snow cover. The first snowfall was 21. 11. 2005 and the last snow thawed 23. 3. 2006, continuous snow cover lasted 96 days, the sum of snow layer height was 10595 mm. The winter between years 2004 and 2005 was average in comparison to other two winters. The first snowfall was 20. 1. 2005 and the last snow thawed 17.3.2005, continuous snow cover lasted 39 days, the sum of snow layer height was 3290 mm. RDA analysis showed significant results at alpha = 0.002 for all canonical axes. Based on the results of RDA analysis we can determine the impact and duration of snow cover on the various types of weeds. The obtained results show that long duration and high snow cover can significantly affect the subsequent weed infestation of spring barley. These conditions are advantageous for higher infestation by Amaranthus sp., Echinochloa crus-galli, Lamium purpureum, Stellaria media and Veronica polita. Thawing snow is able to provide enough water during the germination of these species and can stimulate them to higher emergence. But results also showed that some species have lower tolerance to long-lasting and high snow cover. These are Galium aparine, Lamium amplexicaule and Veronica persica. These species have apparently high tolerance to very low temperatures and do not need isolation provided by snow layer. These results show an interesting relationship between the snow conditions and weed infestation in spring. It is important to realize that this is only a three-year observation and further monitoring is necessary to provide more precise conclusions.