The Allelopathic Effect Of Garlic Root Exudate On Different Vegetables And Their Soil Chemical And Biological Properties

Continuous cropping obstacles under intensive cropping system has become a major limiting factor in sustainable production leads to the deterioration of soil ecological environment and exhaustion of agriculture productivity.However,long-term negative plant-soil feedback due to continuous cropping obstacle of vegetables could be resolved completely or partly by maintaining adequate plant diversity in cultivation environment such as multi-cropping.Garlic is considered as a good previous crop in field production,but what is the most suitable for the sake of the next crop? What is the mechanism of its allelopathy?There is no systematic study about it yet.Root exudate is the main way of the previous crop affecting the next crop.In this study,three different methods(bioassay method under aseptic condition,hydroponic co-cultivation method,potting method)were used to explore the allelopathic effect of garlic root exudates on different growth stages of the receptor vegetables(seed germination period,vegetative growth stage,whole growth period)and their growth soil environment.In order to provide theoretical and technical basis for establishing efficient multi-cropping patterns of garlic and receptor vegetables,the allelopathic effect of garlic root exudates on different receptor vegetables were studied from the aspects of their germination,growth,physiological dynamic,yield and fruit quality,soil biological and chemical characteristics.The main findings of current study are as follows:1 To exclude soil and microbial interference,a bioassay experiment under aseptic condition was conducted to verify the allelopathic effect of garlic root exudates on the five receptor vegetables(cucumber,tomato,pepper,chinese cabbage and lettuce).The results showed that garlic root exudates exhibited remarkable allelopathic response towards the five receptor vegetables.The order of the allelopathic intensity of garlic root exudates on five receptor vegetables was pepper > chinese cabbage > lettuce > cucumber > tomato,and the allelopathic effect showed a dose-dependent effect which was positive at lower concentrations and negative at higher concentrations.2 In the hydroponic experiment,cucumber and tomato seedlings were co-cultured with different number of garlic bulbs and the results showed that co-cultured with different numbere of garlic bulbs impelled the phytotoxicity in growth of cucumber and tomato plants,triggering the overproduction of reactive oxygen species,resulted induce oxidative stress andinducing the activation of their defense systems(protective enzymes and antioxidants),while changing the source and sink relationships of cucumber plants.Conversely the soluble sugar content of the cucumber leaves increased to maintain the normal physiological metabolism and the stability of the cell membrane.3 Diverse vegetable rotation systems with garlic revealed the sustainable ecological significance in our study and results indicated that crop rotation with garlic bulbs during three years' field cultivation increased the receptor vegetables' yield,stimulate the growth of the receptor vegetables,and also enhanced the capacity of their defense system.Meanwhile,the relative reduction in crop yield of different vegetables caused by each year continuous cropping phenomenon greatly improved by garlic-base-rotation,and the promotion effect increased along with the increasing number of garlic bulbs,the yield of tomato,pepper,Chinese cabbage and lettuce reached the maximum when cropped rotation with 25 garlic bulbs(cucumber yield was the highest when the number of garlic bulbs were 20).The order of the allelopathic intensity of garlic root exudates on the yield of the five receptor vegetables was tomato > cucumber > pepper > lettuce > chinese cabbage.At the same time,cropped rotation with different number of garlic bulbs for three years could improve part of the nutritional quality of vegetables.4 Cropped rotation with garlic bulbs could maintain the stability of the soil pH,reduced the sharp decrease of cultivable microorganisms number in the soil.And it also improved the soil enzyme of receprtor tomato,pepper,chinese cabbage and lettuce(hydrogen peroxide enzyme,alkaline phosphatase,urease and invertase),promoted the transformation of available nutrients and improved the soil fertility(available nitrogen,phosphorus,potassium,organic carbon),as a result,improved the soil quality and ecological environment of the receptor vegetables.At the same time,the diversity of fungal communities and the number of dominant fungus Ascomycota of cucumber planted soil were significantly increased by cropping with garlic bulbs,however,the effect on the bacterial community was not significant.Based on the above results,it is concluded that garlic can alleviate the continuous cropping obstacle of vegetables in field cultivation condition,the mechanism is to improve the growth and development of receptor vegetables indirectly by reducing the environmental risks resulting from conventional intensive cropping systems.