The effect of non-chemical weed control on soil biological properties in the spring oilseed rape crop

Abstract

and in 2015 – in plots where thermal weed control was applied, also in plots where smothering was used (2.8 times). The activity of saccharase significantly 1.8 times increased in 2015 in smothering plots. Soil enzymes activity depended on the soil agrochemical properties. In a soil with a thickened humus layer the highest number and biomass of earthworms was established in 2013 in plots where thermal weed control was applied, in 2014 and 2015 – where smothering was used. In a thickened humus layer, as compared to regular one, the number and biomass of earthworms significantly 1.5 and 1.6 times increased in 2014 in plots where mechanical weed control was applied, in 2015 – in plots where smothering was used, accordingly 2.6 and 3.1 times. The abundance of the earthworms depended on the soil enzymes activity and soil agrochemical properties. The biomass of spring oilseed rape roots significantly increased with increasing crop density. Significantly strongest activity of soil enzymes saccharase and urease and the highest abundance of earthworms was determined in a soil with a thickened humus layer in plots where thermal weed control and smothering was applied. The positive effect of thickened humus layer on soil biological properties, as compared to regular, was higher in the dry years. Soil enzymes activity and abundance of earthworms depended on meteorological conditions and soil agrochemical properties. Soil enzymes activity and abundance of earthworms are the important indicators of soil quality in the organic farming system. The objective of these investigations was to establish the effect of non-chemical weed control on plant root development, soil enzymes activity and abundance of earthworms in the organically grown spring oilseed rape (Brassica napus L.) crop cultivated in a soil with a regular and thickened humus layers. The field experiments were conducted in 2013–2015 at the Experimental Station of Aleksandras Stulginskis University. Soil – Calc(ar)i-Endohypogleyic Luvisol. Treatments of the experiment: weed control systems: 1) thermal (water steam), 2) mechanical (inter-row loosening), 3) smothering (self-regulation). Thermal and mechanical weed control were applied in oilseed rape crop cultivated at a wide row spacing of 48 cm, smothering – at an inter-row spacing of 12 cm. Spring oilseed rape was cultivated in a soil with a regular (23–25 cm) and thickened (45–50 cm) humus layers. It was determined that the highest biomass of spring oilseed rape roots (on average 1.68 t ha-1) was formed in a soil with a regular humus layer where mechanical weed control was applied. The biomass of oilseed rape roots depended on the crop density (r = 0.82–0.96, P < 0.05). In a soil with a regular humus layer different non-chemical weed control systems had a low influence on soil enzymes activity. In a soil with a thickened humus layer the significantly strongest activity of soil enzymes saccharase and urease, to compare with other treatments used, in 2013 and 2014 was obtained in plots where thermal weed control was applied, and in dry 2015 year – where smothering was used. In a thickened humus layer, as compared to regular one, the activity of urease was significantly (1.5–1.6 times) higher in 2013;