| Intercropping cassava in young rubber plantation is a common method in rubber tree planting areas.However,there is controversy among the academic community about the rationality of the intercropping pattern,such as the occurrence of the corynespora leaf fall disease of Hevea brasiliensis.Therefore,the effects of cassava allelochemicals(the water extracts from cassava organs,root exudates of cassava,the water extracts from cassava organs decomposed and rhizosphere soil)on the growth of pathogenic bacteria were studied by plates technology.Soil microecology of the rubber tree were researched by pot experiments after irrigating the allelochemicals,and the soil microecology of intercropping rubber tree compared with monoculture were analyzed by field test.It will provide some theoretical supports for the rationality of rubber tree/cassava intercropping and its cultivation techniques.The main results are as follow:The allelopathy of water extracts from cassava organs and their mixtures on the disease is different.Water extracts from root and leaf of cassava was at a low concentration,the allelopathy inhibiting effect is not obvious,As the concentration increased,the allelopathy effect gradually increased and reached a significant difference,but it could almost inhibit the growth of Corynespora cassiicola of Hevea brasiliensis,but there was significantly positive allelopathy effect while the water extracts from stem reaches a certain concentration.This shows that the cassava organs are different,the types and properties of allelochemicals will be different.Allelopathy effect of water extracts from mixture organs of stem and leaf was inhibitingsignificantlywhile the concentration was at 100 mg/mL after 2 days,but it was not obvious during 3-6 days,and when the concentrations increased to 1000 mg/mL,the effect was not obvious until 2-3 days,the positive effect was significant until 4-6 days.The water extracts from mixture organs of root,stem and leaf could inhibit the growth of disease,and the higher the concentration,the longer it takes to show a significantly inhibiting effect.When the ratio of dry cassava to soil sample was 12 g/kg,it’s corrosion had a significantly inhibiting effect on the disease after 2 days;When the ratio of dry cassava to soil sample was 18 g/kg,it’s corrosion had a significantly inhibiting effect on the disease until 2-3 days;When the ratio of dry cassava to soil sample was 24 g/kg,it’s corrosion had a significantly inhibiting effect on the disease during 2-7 days.There was almost a significantly positive effect on the disease while the concentration of root exudates was only at 2.5 mg/mL,and so does the concentration of soil suspension in the root zone of cassava which was only at 10 mg/mL.But the other two concentrations of themwere not obvious.The changes of the microecosystem of rubber soil was observed by pouring the allelochemicals of cassava into the potted rubber.The results showed that:it can significantly increase the total B/F value,pH value,Basic nitrogen content,available potassium content,available phosphorus content,urease and catalase activity of soil via pouring the water extracts from leaf.The water extracts from root can significantly increase total soil B/F value,pH value,alkali-hydrolyzable nitrogen content,available potassium content,and urease activity.but significantly reduced available phosphorus content.Intercropping soil suspension can significantly reduce the total B/F value,soil available phosphorus content,acid phosphatase activity.And it can significantly reduce the total B/F value,soil available phosphorus content,organic matter content,and urease activity of root.A field experiment was conducted to study the differences of micro-ecological system between Intercropping cassava for 1 year in rubber garden and Monotonous rubber garden.the results show:Intercropping can significantly increase the total bacteria/fungi in the rubber garden where include root and non-root soil,but soil organic matter content and urease activity in the non-root zone were significantly reduced;and pH value,alkali-hydrolysable nitrogen,available potassium,available phosphorus,and organic matter content were reduced significantlyin the root zone.We can use High-throughput Sequencing Techniques to analyze the diversity of fungal communities(Chao1、Simpson and Shannon),as we known,the Simpson index of the root zone soil intercropping was significantly increased compared to monocropping soil,the Simpson index of the non-root zone soil was significantly lower than that of monocropping soil.But intercropping has no significant effect on Chao 1 and Shannon index of rubber gargen.By analyzing the diversity of bacterial communities(Chao 1,Simpson and Shannon),we will know that intercropping cassava has no significant effect on Chao 1,Simpson and Shannon index of the Rubber Garden.In the analysis of the relationship between soil fungi gate and environmental factors,It’s found that:Ascomycotina and soil organic matter content showed a significantly negative correlation;basidiomycotina was significantly negative correlation with catalase;there was a significantly negative correlation with urease,alkali-hydrolyzed nitrogen,and available phosphorus.But when analyzing the relationship between soil bacterial gates and environmental factors,we can find that bacterial proteobacteria has a significantly positive correlation with urease and available phosphorus content.Available phosphorus is the main factor of soil nutrientaffecting the soil bacteria gate.In summary,It’s suggested that the cassava organ of stems are removed from the rubber garden in time after harvesting cassava roots in the Rubber Garden intercropping cassava.and organ extracts and root exudates can significantly increase soil total bacteria/fungi,available potassium content and urease activity,so cassava organs such as stems andleaves can be covered on the field after harvesting cassava. |
PDF Full Text Request