The influence of spring rape residues decomposed in the soil on weed germination

Abstract

Germination of Sinapis arvensis L. seeds was inhibited by extracts of threshing remains of spring rape after harvest and stimulated by extracts of stubble of spring rape after 14 months decomposition. All concentrations (1:6250,1:1250,1:250,1:50 and 1:10) of rape residues aqueous extracts, compared to distilled water, inhibited germination of Sinapis arvensis L. seeds, except extracts of all residues after 14 months decomposition. All concentrations of this extract, compared to distilled water, stimulated germination of Sinapis arvensis L. seeds from 5.5 to 64.5 %. Germination of Tripleurospermum perforatum L. seeds was stimulated by all concentrations of aqueous extracts of spring rape residues after harvest and the lowest (1:6250) concentration of aqueous extracts of spring rape residues after 7 and 14 months decomposition. However higher concentrations (1:250, 1:50 and 1:10) of aqueous extracts of spring rape residues after 3 months decomposition, significantly inhibited germination of Tripleurospermum perforatum L. seeds from 46.7 to 37.8 %. Most seeds of Sonchus arvensis L. germinated in the aqueous extracts of threshing remains of spring rape. All concentrations of aqueous extracts of rape residues after 3 and 14 months decomposition, compared to distilled water, stimulated germination of Sonchus arvensis L. seeds. Still all concentrations of aqueous extracts of spring rape residues after harvest and after 7 months decompostion compared to distilled water, inhibited germination of these seeds. Allelopathic effect of Brassicaceae plants on weeds germination during early growth is an important factor in agriculture.Modular field experiment was conducted in the Experimental Station of the Aleksandras Stulginskis University and laboratory tests were carried out in the laboratory of Agroecosystems and Soil Science Institute in 2011-2013 in order to evaluate the allelopathic effects of aqueous extracts of spring oilseed rape residues (threshing remains, stubble, roots) after harvesting and decomposed in the soil for a different duration (3, 7 and 14 months) on weeds emergence. Various concentrations: 1:6250,1:1250, 1:250, 1:50 and 1:10 (the ratio of rape residues and water) of aqueous extracts of spring rape residues were evaluated for phytotoxicity. Impacts of extracts on: Sinapis arvensis L., Tripleurospermum perforatum L. and Sonchus arvensis L., grown in Petri dishes on filter paper moistened with prepared aqueous extracts were determined in controlled growth chamber experiments. The total amount of phenolic compounds and optical density were estimated. It was estimated, that the total amount of phenolic compounds in the threshing remains and roots after 3 months decomposition in the soil significantly decreased from 26.9 to 30.2 %. After 7 months - significantly decreased from 13.5 to 22.6 % compared to the total amount of phenolic compounds in these residues after harvest. The total amount of phenolic compounds in the stubble after 7 and 14 months decomposition increased significantly (20.5 %) compared to the total amount of phenolic compounds in these residues after harvest. The highest optical density readings were obtained of aqueous extracts of spring oilseed rape threshing remains, and lowest - of spring oilseed rape roots. The optical density of 1:10 concentration of aqueous extract of all rape residues was by 4.0-12.4 times higher compared to that measured at lower concentrations.