Allelochemicals in Brassica napus L. residues decomposing in the soil

Abstract

The total content of glucosinolates was lower in winter oilseed rape stubble and roots decomposed for three months in the soil than in those residues after harvest, and contrary in threshing remains it was higher. It was estimated that threshing remains the highest content of volatile organic compounds released after three months of decomposition, while stubble and roots – after seven months. Our results suggest that winter oilseed rape residues decomposing in the soil have allelopathic properties and may have influence on agroecosystem for two years. Studies on the allelopathic properties of oilseed rape are not sufficient to explain the impact of oilseed rape and its morphological parts on soil and agricultural crops that are grown after oilseed rape. To find out influence of allelochemical compounds released by oilseed rape on agrocenosis complex investigations should be carried out. Our studies aim to reveal and scientifically reason the allelopathic effect of winter oilseed rape by identification allelochemicals released by oilseed rape residues during decomposition in the soil. We analysed composition of allelochemical compounds of winter oilseed rape (Brassica napus L.) residues (threshing remains, stubble and roots) after harvesting and ascertained quantitative and qualitative changes of these compounds in residues after different period of decomposition in the soil (3, 7, 14, 19 and 26 months). Phytochemical analysis revealed that total content of phenolic compounds in all investigated oilseed rape residues significantly decreased after three months of decomposition in the soil. Further, during the process of decomposition content of these compounds in residues increased and the highest was after 19 months of decomposition, except winter oilseed rape threshing remains. The highest content of phenolic compounds in winter oilseed rape resides was after earlier – after 14 months of decomposition the soil. After 26 months of decomposition in the roots of winter oilseed the content of phenolic compounds was significantly higher to compare with that after harvest. Qualitative and quantitative analysis of glucosinolates revealed that accumulation of these compounds is significantly higher in stubble and roots of winter oilseed rape than that it threshing remains. The aromatic glucosinolates were dominating.