INFLUENCE OF WEATHER CONDITIONS AND SOIL TILLAGE TREATMENTS ON WEED INFESTATION IN WINTER WHEAT-SOYBEAN CROP ROTATION

One of the most important roles of soil tillage, especially conventional one, based on mouldboard ploughing, is the control of biotic factors, among them weed control. Research of influence of different soil tillage treatments on weed population in winter wheat crop has been undertaken at chernozem soil type in Eastern Croatia, during four years (2002-2005), with very different weather patterns. Eight soil tillage treatments, different in intensity of depth and frequency of soil tillage operations, were applied for winter wheat crop, in crop rotation after soybean. For each crop, four treatments had continuous soil tillage system (CT: mouldboard ploughing tillage, DH: disk harrowing tillage, CT: chiselling tillage and NT: no-till) and another four treatments had discontinuous soil tillage system (conventional tillage for one crop, and disk harrowing or no-tillage for another crop, where applied conventional systems for winter wheat were CWDS and CwNs, diskharrowing in CSDW and No-till in CsNw). Applied herbicides showed very high effectiveness for all soil tillage treatments. In droughty season 2003/04, in comparison with seasons 2001/02 and 2004/05, number of weed species (2.03, 3.19 and 2.78 weed species m(-2), respectively) and number of weeds (118, 128 and 141 weeds per m 2, respectively) were significantly lower. In comparison with CT, only CwNs showed higher number of weeds (134 vs. 211 weeds m(-2)). CWDS, CSDW, CH and NT all had lower number of weeds than CwNs (71, 77, 84, 97 and 211 weeds m(-2), respectively). Regarding w. wheat grain yield, there were no statistical differences between CT (5.62 t ha(-1)) and CH, CSDW, CsNw, DH and CWDS (+140, +60, 0, -30 and -120 kg ha-1, respectively), thus presenting proper soil tillage systems instead of mouldboard ploughing.