One of the reasons why the area sown with oilseed rape in organic farms is not expanding is problems with weed, disease, and pest control as well as low seed yield. There is a lack of investigations on oilseed rape cultivated in an organic system, especially employing innovative weed control methods. To fill this gap in knowledge, field experiments were conducted at the Experimental Station of Aleksandras Stulginskis University in 2012-2013 with the aim of identifying and assessing the impact of different non-chemical weed control methods (thermal -TWC, mechanical -MWC and smothering -SMT) on weed competitiveness in winter oilseed rape (Brassica napus L.) crops during the autumn vegetation period in an organic farming system with and without the use of plant bio-activators in a soil with a regular (23-25 cm) (1 st experiment) and with a thickened (48-50 cm) (2 nd experiment) humus layer. It was found, that compared with thermal and mechanical weed control, in the treatment using smothering weed control and spraying with plant bio-activators or not spraying, the density of winter rape crop in the soil with a regular humus layer was significantly (P ≤ 0.05) lower (1.2 to 5.3 times); in the soil with a thickened humus layer, the density of winter rape crop was 1.5 to 5.9 times lower. In winter oilseed rape during autumn vegetation period, 20-22 weed species were found, including 18-19 annuals. Stellaria media (L.) Vill., Veronica arvensis L., Sinapis arvensis L. and Capsella bursa-pastoris (L.) Medik. were the predominant weeds.In the soil with a regular and a thickened humus layer, thermal and mechanical weed control significantly (P ≤ 0.05) decreased the number of weed seedlings (1.1 to 1.9 times) when plant bio-activators were used compared with the smothering treatment. Weed control in the smothering treatment in the soil with a regular and thickened humus layers was not effective. Mechanical weed control was more efficient than thermal. Application of plant bio-activators increased the efficiency of the thermal weed control.

Oilseed rape cultivation under organic farming conditions presents a high risk of increased incidence of weeds, pests and diseases, resulting in low rapeseed yielding capacity. The current study aimed to estimate the effects of nonchemical weed management methods: thermal, mechanical and self-regulation (natural weed / crop competition), on the incidence of fungal diseases in winter oilseed rape (Brassica napus L.) stands and on rapeseed yield in the organic production system. A field experiment was conducted in 2014-2017 at Aleksandras Stulginskis University's Experimental Station. The soil of the experimental site is Endocalcaric Endogleyic Luvisol (LV-can.gln). Under less favourable conditions for the occurrence of phoma stem canker, both thermal and mechanical weed control methods were shown to inhibit the spread of the disease in the oilseed rape crop compared with the selfregulation weed control treatment. However, under the conditions conducive to the spread of phoma stem canker, only mechanical weed control method in combination with the bio-preparations proved to be effective. In 2015 and 2016, the lowest incidence of the verticillium wilt was recorded in the oilseed rape plots where weeds had been managed by steaming. In 2017 significantly, from 2.3 to 3.3 times lower number of verticillium wilt-affected stems was determined in the mechanical weed control plots as compared with that in the plots where other weed control methods had been applied. Application of bio-preparations decreased the number of verticillium wilt-affected stems by on average 11.1-15.6%. The lowest incidence of dark leaf and pod spot was established in the plots where weeds had been controlled by water steam and no bio-preparations had been used. The bio-preparations were found to increase the severity of dark leaf and pod spot on oilseed rape siliques by on average 13.1-79.4%. Significantly the highest rapeseed yield in 2015 and significantly higher compared with self-regulation in 2017 was recorded in the mechanical weed control treatment, while in 2016 the highest rapeseed yield was established in the self-regulation treatment applied with the bio-preparations. In 2017, the verticillium wilt severity in the winter oilseed rape crop was found to negatively, strongly and statistically significantly correlate with rapeseed yield (r 2 = 0.69, P < 0.05).

The current study was aimed to establish the effects of non-chemical weed control methods on the activity of soil enzymes and abundance of earthworms in an organically grown spring oilseed rape crop in the soil with a regular (23-25 cm) and thickened (45-50 cm) humus layers. A field experiment was conducted during the 2013-2015 period at Aleksandras Stulginskis University on a Calc(ar)i-Endohypogleyic Luvisol (LVg-n-w-cc). The following three non-chemical weed control methods were explored: 1) thermal (using water steam), 2) mechanical (interrow loosening) and 3) smothering (self-regulation). In the thermal and mechanical weed control treatments, spring oilseed rape was grown with an inter-row spacing of 48 cm and in weed smothering treatments with an inter-row spacing of 12.0 cm. The highest root dry biomass of spring oilseed rape (on average 1.68 t ha -1 ) had been produced in the soil with a regular humus layer in the mechanical weed control treatment. Spring oilseed rape root dry biomass depended on the crop density (r = 0.82-0.96, P < 0.05). In the soil with a regular humus layer, the different non-chemical weed control methods tested exerted little impact on soil enzyme activity. In the soil with a thickened humus layer, a significantly stronger activity of saccharase and urease enzymes, compared with the other weed control methods applied, was recorded for the plots under the thermal weed control treatments using water steam, while in a dry year of 2015 -in the plots under smothering treatments. Compared with a regular humus layer, the activity of urease enzyme in the thickened humus layer was significantly (1.5-1.6 times) higher in the plots where in 2013 and 2015 thermal weed control had been applied, while in 2015 -in the smothering treatment (2.8 times). The activity of saccharase significantly (1.8 times) increased in 2015 in the plots under smothering treatment. Significantly the highest number of earthworms and their biomass were determined in the plots with a thickened humus layer in which in 2013 thermal weed control had been applied and in 2014 and 2015 in the plots under smothering treatment. Compared with a regular humus layer, in the thickened humus layer the number and biomass of earthworms significantly (1.5 and 1.6 times) increased in the plots in which in 2014 mechanical weed control had been applied, and in 2015 in the plots under smothering treatment (2.6 and 3.1 times, respectively). Soil enzyme activity and abundance of earthworms depended on the meteorological conditions and soil agrochemical properties. The number of earthworms in the soil correlated with the soil enzyme activity. Positive strong and very strong statistically significant correlations were established between saccharase activity and number of earthworms (r = 0.89, P < 0.05), urease activity and number of earthworms (r = 0.99, P < 0.01) as well as between urease activity and earthworm biomass (r = 0.94, P < 0.01).