Allelopathic effects of decomposed leaf litter from intercropped trees on rape

Abstract

The allelopathic effect of decomposed litter from trees interplanted with crops is a key problem in the intercrop agroforestry business that could influence the economic benefits and sustainable development of ecoagriculture. In our study, the litter from 12 common intercropped tree species was collected from the Guanzhong Plain (Shaanxi Province, China) and mixed with soil, incubated to allow decomposition for 120 days, and then extracted using water. The water extracts at different concentrations were used for filter paper-dish cultivation of rape (Brassica napus) seeds. Indicators of the germination and growth of seedlings were measured to investigate the allelopathic effects of decomposed litter on rape. The results showed that in rape the most sensitive indicators of harmful allelochemicals derived from decomposed litter were the germination speed index and catalase activity of seedlings. Moreover, extracts of decomposed medium (soil) containing litter from Paulownia fortunei, Acer truncatum, Zanthoxylum bungeanum, Juglans regia, Diospyros kaki, Prunus persica, Prunus armeniaca, and Ziziphus jujube were beneficial to the germination and seedling growth of rape at all concentrations examined, and thus these trees could be safely interplanted with rape. Extracts from Eucommia ulmoides, Populus canadensis, and Malus pumila inhibited the germination and seedling growth of rape, and thus the use of these trees in intercropping should be reduced. Extracts from Pyrus bretschneideri showed growth promotion at lower concentrations (10 and 20 mg mL-1) but were growth inhibitive at a high concentration (40 mg mL-1); thus, it could be intercropped with rape but at a low density.