Study On Allelopathy Of Garlic Stalk Decomposition And Identification Of Allelochemicals

Garlic (Allium sativum L.) stalk is a byproduct of garlic production that is normallythought of as waste but is now considered to be a useful biological resource. It is necessary toutilise this resource efficiently and reasonably to reduce environmental pollution and achievesustainable agricultural development. This paper manily studied allelopathy of garlic stalkdecomposition under various decomposied conditions, and researched the allelopathic effectof garlic stalk decomposition on different tested plants. Allelochemicals of garlic stalkdecomposition were identified and verified in this study. The results of allelopathy of garlicstalk decomposition and identification of allelochemicals are as follows:1. Garlic stalk decomposition could significantly affect the physical and chemicalproperties of the soil. The values of soil pH and electrical conductivity were significantlyincreased by garlic stalk decomposition. In addition, total nitrogen and organic carbonconcentration were significantly increased by decomposing stalks at40°C, with a5:100ratioand for10or60days. The highest activities of sucrase, urease and alkaline phosphatase insoil were detected when stalk decomposition was performed at the lowest temperature (10°C),the highest concentration (5:100), and the shortest duration (10or20d). The favorable effectof garlic stalk decomposition allelopathy was performed at shortest duration (10d), the lowesttemperature (10°C), the highest concentration (5:100).2. The allelopathic effect of decomposed garlic stalk over different durations ofdecomposing (10,20,30,40,50and60d) was investigated in this study using wheat(Tricicum aestivum L.) and lettuce (Lactuca sativa var. crispa L.) as test plants. Garlic stalk inearly stages of decomposition (10and20d) inhibited the growth of wheat and lettuce plants,but promoted plant growth in later stages (30and40d). Longer durations of garlic stalkdecomposition (30,40,50and60d) significantly increased the shoot and root fresh weight ofwheat and lettuce, whereas shorter decomposing durations (10and20d) significantlydecreased the shoot and root fresh weight. Garlic stalk decomposed for30days significantlyincreased the content of chlorophyll and protein, and significantly promoted the activities ofSOD and POD. Garlic stalk at different decomposition durations increased the activities ofurease, sucrase and alkaline phosphatase in the soil in which wheat or lettuce was planted. The greatest favorable allelopathy on the growth and development of wheat and lettuce andthe soil properties with planting them was performed at30d of garlic stalk decomposition.3. The allelopathic effect of decomposed garlic stalk at different temperatures wasinvestigated in this study using wheat and lettuce as the allelopathic test plants. Highertemperature (40℃) of decomposed garlic stalk significantly increased roots and shoots lengthof wheat and lettuce, however, lower temperature (10℃) significantly decreased their growth.Garlic stalk decomposed at40℃significantly inhibited the content of MDA of wheat andlettuce leaves, but promoted the activity of SOD. Nevertheless, garlic stalk decomposed at10℃significantly promoted the activity of PAL of wheat and lettuce leaves. Garlic stalkdecomposed at10℃significantly increased the soil EC value and activity of soil sucrasewith wheat and lettuce planted. The greatest favorable allelopathy on the growth anddevelopment of wheat and lettuce was performed at highest temperature (40℃). But thegreatest inhibitive allelopathy was performed at lowest temperature (10℃).4. The allelopathy of decomposed garlic stalk at different ratios (0:100,1:100,3:100and5:100) was investigated in this study using wheat and lettuce as the allelopathic test plants.Lower concentration of decomposed garlic stalk promoted wheat and lettuce plant growth, buthigher concentration inhibited growth. The highest ratio of stalk to soil (5:100) significantlyincreased the root length and fresh weight of lettuce but decreased the shoot length and freshweight. Lower ratio of stalk to soil significantly increased the content of protein andchlorophyll and the activity of plant enzymes of wheat and lettuce leaves. Increasing theconcentration of decomposed garlic stalk increased the activity of soil sucrase, urease andalkaline phosphatase with wheat and lettuce planted. The greatest favorable allelopathy on thegrowth and development of wheat and lettuce was performed at3:100(ratio of stalk to soil).But the greatest inhibitive allelopathy was performed at5:100(ratio of stalk to soil).5. The promoted or inhibited allelopathy of garlic stalk decomposition on various testedplants. Garlic stalk decomposition significantly increased the length of root and shoot, thefresh weight of shoot, and the activity of SOD of Chinese cabbage. Garlic stalkdecomposition significantly promoted the content of chlorophyll and the activity of SOD oftomato. However, garlic stalk decomposition significantly inhibited the length and freshweight of root and shoot and the activities of POD and PAL of tomato. Garlic stalkdecomposition significantly increased the length of root and shoot and the activity of SOD ofcucumber and cowpea. Garlic stalk decomposition significantly decreased the length of rootand the activities of SOD and POD of maize. The garlic stalk decomposition had favorableallelopathy on Chinese cabbage, cucumber and cowpea, but had inhibitive allelopathy ontomato and maize. 6. Garlic stalk resolved or created new allelochemicals during it decomposing whichwere identified by the method of GC-MS. Caffeine, N-à-(tert-Butoxycarbonyl)-L-Valine anddiflunisal were detected from petroleum ether, ethyl acetate and chloroform extractions ofgarlic stalk decomposition, respectively. The petroleum ether and ethyl acetate extractions hadthe favorable allelopathy on lettuce bioassay, but the chloroform extractions had the inhibitiveallelopathy. The results of bioassays of exogenous chemical reference substance showed thathigher concentration of caffeine, N-à-(tert-Butoxycarbonyl)-L-Valine and diflunisal had theinhibitive allelopathy on lettuce bioassay. The results were the similar as the results ofdifferent organic reagent extractions and the general rule of allelopathy. And the threesubstances were verified the effective allelochemicals of garlic stalk decomposition.