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<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008Table 1 The influence of crop sequence in crop rotation on weed dynamics at the early stages ofcrops, 2004-2006, plants m -2Number offields Years Crops1. 2004.2005.2006.Average2. 2004.2005.2006.Average3. 2004.2005.2006.Average4. 2004.2005.2006.Average5. 2004.2005.2006.Average6. 2004.2005.2006.Averagetriticale/ ryeoil radish/ryepotatoesrye/w.mustardpotatoesoatspotatoesoatsvetch-oats mix.oatsvetch-oats mix.r. clover, timothyvetch-oats mix.r. clover, timothytriticale/ ryer. clover, timothytriticale/ ryeoil radish/ryeNumber ofannual weeds4.811.2/105021.03.409.04.1028.032.820.34.618.41.48.17.41.29.05.909.213.6/12.07.3Number ofperennialweeds3.849.6/009.54.401.62.001.410.23.96.05.45.25.510.416.81.29.517.48.15.8/6.610.6Total numberof weeds8.660.8/105030.57.8010.66.1029.443.024.210.623.86.613.617.818.010.215.417.417.319.4/18.618.0LSD 0.05 27.5 13.3 37.8Data of second weed accounting (Table 2) show that the total number of weeds in the croprotation before crop’s harvesting in 2004, 2005 and 2006 was 55.8, 99.6 and 43.8 plants m -2 ,respectively, in this composition the annual weeds were – 21.2, 57.6, 27.8 and perennial weeds -34.6, 42.0, 16.0 plants m -2 . Results showed that weed density was higher in the second year of croprotation, less – in the third year. They can also be influenced by meteorological conditions. Theyear 2006 was extremely hot and dry. A high number of annual weeds was observed in 2005 in thestand of triticale where the dominant weed specie was lambsquarter (83 % of the total number ofannual weeds), and in the stand of catch crops – rye and oil radish (80 %). In 2006 in the stand ofcatch crops after triticale lambsquarters there was 48 % of the total number of annual weeds, but itwas not dangerous for the next crops, because the crops grown for green manure are incorporatedin the soil before the seeds of weeds ripen. In 2005 the high number of quackgrass was observed inthe stand of triticale – 88 % of the total number of perennial weeds, but in the stand of next catchcrops (2006) the number of this weed was decreased to 67 %, if compared to quackgrass’ numberm -2 in the previous triticale. The highest amount of common yellow rocket was found in 2004 inthe red clover and timothy stand (38 plants m -2 ), that was 53 % of the total number of perennialweeds. In the next year in catch crops the number of this weed was reduced remarkably in rye, butin the second catch crop - oil radish quackgrass was not established. Thereby we can be agree withother researchers, that crop rotation reduces weed density and maintains species diversity, thuspreventing the domination by a few problem weeds (Doucet et all., 1999). The problem weeds inthe investigated crop rotation organic farming system are quackgrass and common yellow rocket.28
<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008The significantly smaller amounts of weeds among crop rotation links was observed in link rye/ oilradish/ rye – potatoes – oats. Much less successful suppression of weeds was obtained in the croprotation link red clover and timothy – triticale/ rye – oil radish/ rye (Table 2).Table 2 The influence of crop sequence in crop rotation on weed dynamics before harvesting ofcrops, 2004-2006, plants m -2Numberof fieldsYears Crops Number ofannual weedsNumber ofperennial weedsTotal numberof weeds1. 2004.2005.2006.triticale/ ryeoil radish/ryepotatoes33.513.8/ 115.016.045.516.8/ 0.57.079.030.6/ 115.023.0Average2. 2004.2005.2006.Average3. 2004.2005.2006.Average4. 2004.2005.2006.Average5. 2004.2005.2006.Average6. 2004.2005.2006.Averagerye/w.mustardpotatoesoatspotatoesoatsvetch-oats mix.oatsvetch-oats mix.r. clover, timothyvetch-oats mix.r. clover, timothytriticale/ rye38.033.58.02.014.520.231.529.527.110.075.212.032.419.514.525.519.820.417.01.01.06.320.84.513.012.831.09.615.018.522.444.019.028.558.450.59.03.020.850.036.042.539.941.084.827.050.941.958.544.548.3r. clover, timothytriticale/ ryeoil radish/rye11.0152.086.5/76.581.571.0184.065.5/16.598.782.0336.0152.0/93.0180.2LSD 0,05 57.8 60.6 103.3Organic farming does not only increase the number of weed species, it also leads to aconsiderable rise in weed phytomass (Albrecht, 2005). Therefore the weed’s phytomass wasinvestigated. The phytomass of weeds is given as fresh weight that was investigated before thecrop’s harvesting. The results are represented in the Table 3.29
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AGRONOMIJAS VÄSTIS - Latvijas LauksaimniecÄ«bas universitÄte