Differences in cropping practices, including tillage, inputs and crop rotations are the driving factors affecting weed dynamics (weed abundance, composition and crop-weed competition), which can ultimately affect crop yields. Several experiments were carried out to assess the impact of long-term organic and conventional cropping systems on weed abundance, weed community composition, crop yield and yield loss using a long-term (18 year) alternative cropping systems study (ACS) at Scott, Saskatchewan, Canada. The ACS study consisted of three input systems, namely high (conventional tillage), reduced (no-till conventional) and organic input systems and three crop rotation diversities (low diversity, diversified annual grains and diversified annual-perennials). A statistical analysis of the 18-year rotation revealed that the organic rotations have four and seven times higher weed density and 32% and 35% lower crop yields than the reduced and the high input systems respectively. Weed community composition was consistently different in organic rotations compared to the two conventional rotations throughout the years, but year to year random variations were more profound. All cropping systems showed an increase in weed density, weed biomass and crop yields over time, probably due to an increase in rainfall over time. Increasing the crop rotation diversity with annual and perennial crops did not reduce weeds, but decreased crop yields in all systems. A two-year micro-plot experiment with four additional weed competition treatments on the ACS study revealed that the wheat yields were lower in the organic rotations even in the absence of weeds, implying that lower crop yields were due to soil fertility related factors. A greenhouse pot experiment from soils obtained from both organic and reduced rotations revealed that wheat yields were still lower in organic compared to the reduced input systems, even after excess mineral N and P were added. Furthermore, no differences in crop yield loss due to weed competition among cropping systems were identified. Overall, this study revealed that eliminating tillage and reducing inputs are possible without long-term changes in weed abundance, weed community composition or affecting crop yields. However, eliminating synthetic inputs as was done in the form of organic crop rotations resulted in increased weed abundance, changed community composition and decreased crop yields.

Magistrantūros studijų baigiamajame darbe pateikiami ilgalaikio supaprastinto žemės dirbimo ir tiesioginės sėjos įtaka žieminių kviečių agrocenozei tyrimo rezultatai. Darbo objektas – pagrindinio žemės dirbimo būdai žieminiams kviečiams. Darbo metodai: buvo tirti tokie žemės dirbimo būdai: 1) įprastinis arimas 23–25 cm gyliu; 2) seklusis arimas 12–14 cm gyliu; 3) gilusis purenimas 23–25 cm gyliu; 4) seklusis purenimas 12–15 cm gyliu; 5) tiesioginė sėja į neįdirbtą dirvą. Atlikti šie stebėjimai: Dirvos agrocheminių savybių nustatymas, piktžolėtumo nustatymas, žieminių kviečių daigų tankumas, sliekų kiekis dirvoje, produktyvių stiebų tankumas, derliaus apskaita, bei 1000 grūdų masė. Darbo rezultatai. Nustatyta, kad tiesioginė sėja, bei gilusis purenimas esmingai padidino trumpaamžių piktžolių daigų tankumą žieminių kviečių pasėlyje, o taikant seklaus purenimo būdą esmingai padidėjo daugiamečių piktžolių daigų tankumas lyginant su įprastai suarta dirva. Žieminių kviečių vegetacijos pabaigoje esmingai padidėjo daugiamečių piktžolių masė sekliai artuose, giliai purentuose ir sekliai purentuose laukeliuose, lyginant su įprastiniu arimu. Įprastinį arimą pakeitus giliu purenimu, sekliu purenimu ir tiesiogine sėja į neįdirbtą dirvą, atsinaujinus žieminių kviečių vegetacijai nustatyta esmingai didesnis dirvinio garstuko daigų tankumas. Taikant ilgalaikę tiesioginę sėją žieminių kviečių vegetacijos pabaigoje nustatyta esmingai didesnis paprastosios rietmenės daigų skaičius ir masė... [toliau žr. visą tekstą] / Master's thesis presents the results of the investigation of effects of long-term reduced tillage and direct seeding on winter wheat agrocenoses. Object of work – are the main methods of tillage for winter wheat. Research methods: the following tillage methods were investigated: 1) conventional ploughing at the depth of 23–25 cm, 2) shallow ploughing at the depth of 12–14 cm, 3) deep loosening at the depth of 23–25 cm, 4) shallow loosening at the depth of 12–15 cm; 5) direct seeding into uncultivated soil. The following sampling were performed: soil agrochemical properties, weed abundance, winter wheat seedling density, quantity of earthworms in soil, productive stems density, yield and 1000 grain weight. Results. It was found that direct seeding and deep loosening substantially increased the annual weed seedling density of winter wheat crop, while the shallow method of loosening significantly increased weed seedling density compared to normal ploughing soil. The mass of perennial weeds has increased substantially at the end of the winter wheat growing season in shallow ploughing, deeply loosened and shallow ploughing plots compared to conventional ploughing. When normal ploughing was replaced with deep loosening, shallow loosening and direct seeding in the uncultivated soil after the recurrence of winter wheat vegetation, the density of Sinapis arvensis L. shoots increased significantly. When applying long-term direct seeding at the end of winter wheat growing season, the... [to full text]