Plant Growth Promotion And Inhibition Of Soilborne Pathegens By Pig Manure-straw Compost Extracts And Their Mechanism Of Action

Compost extracts as natural liquid fertilizers with both bio-control and growth promotion effects have been widely used. Many evidences demonstrated that the compost extracts could suppress certain plant bacterial or fungal diseases, but the suppression effect was unstable. Compost extracts with some organic and inorganic nutrients could also significantly promoted plant growth. Aerated and non-aerated methods are the two dominant approaches in the production of compost extracts, though there is a debate about the necessity of aeration during the production of compost extracts. Therefore, this work compared the different technologies of compost extraction such as direct extraction, aerated fermentation and non-aerated fermentation methods, and then evaluated the plant growth promotion, inhibition of soilborne disease and reduction of tomato root-knot nematodes (Meloidyne incognita) as affected by the application of compost extracts that were produced from pig manure and rice straw. The acting mechanism of the compost extracts was also investigated. The main results are as follows:1. The optimum process parameters were1:8of extraction ratio,36hours of extraction under the aerated condition, while, those under non-aerated condition is1:8of extraction ratio and7days of extraction for the compost extracts.Compared with the direct extraction of pig manure-straw compost extracts, aerated and non-aerated fermentation extracts were rich in nutrient accumulation especially for high molecular weight substances. Non-aerated fermentation extracts of pig manure-straw compost (7days)(NAFEC) had the highest content of total nitrogen (TN) and ammonium nitrogen (NH4+), with an increase of16.4%and67.5%over direct extracts of pig manure-straw compost (DEC) and36%and30%over aerated fermentation extracts of pig manure-straw compost (36hours)(AFEC, with33L·min-1aeration quantity), respectively. When compared with AFEC and NAFEC, the total phosphorus (TP) content of DEC were decreased by12.2%and20.6%, respectively. The total potassium (TK) content of AFEC was lowest of all, and was decreased by4.5%and3.6%comparing with DEC and NAFEC, respectively. Acetic acid and oxalic acid were the two main organic acids with low molecular weights in compost extracts from pig manure-straw composts with different extraction technology. The highest content of oxalic acid and acetic acid was obtained by AFEC.All compost extracts were determined to be dominated by bacteria. When compared with DEC, the bacterial richness index, diversity index and stability index of NAFEC were decreased; however, DEC had the equivalent bacterial evenness index with AFEC and NAFEC.2. The physico-chemical characteristics were evidently affected by different aeration quantity. Aerated fermentation extracts of pig manure-straw compost with11L·min-1aeration quantity (AFEC-1) and AFEC had the high humification, aromatic levels and the low content of carboxyl groups.3. The results of pot experiment showed that all pig manure-straw compost extracts promoted the carbon and nitrogen metabolism in cucumber plants. The maximum shoot dry weights of cucumber plants were obtained with the application of AFEC, which were34.5%,56.3%and63.9%higher than those with the applications of DEC, NAFEC, half-Hoagland and Arnon nutrient solution (CK), respectively. Compared with DEC and NAFEC, AFEC obtained the maximum cucumber leaf carbon and nitrogen metabolism ability.The plant growth promotion of compost extracts was affected by the extraction technology. The aeration quantity affected significantly the growth promotion of aerated compost extracts. When the aeration quantity was11L·min-1, the compost extracts from pig manure-straw compost with aerated extraction technology could have a better growth promotion to cucumber plants.4. There was no evident correlation between the contents of such organic acids as acetic acid and oxalic acid with low molecular weights and cucumber growth promotion by compost extracts from pig manure-straw compost with different extraction technologies. Humic-like substances extracted from AFEC (H-AFEC) obtained the maximum N accumulation content of shoot and root, with an increase of9.1%and34.5%over humic-like substances extracted from DEC (H-DEC),21.8%and20.9%over humic-like substances extracted from NAFEC (H-NAFEC) and19.2%and41.1%over CK. The difference between H-AFEC and other treatments were significant.5. The H-DEC, H-AFEC and H-NAFEC all showed the positive auxin-like activity. The H-DEC was rich in peptidic and carbohydratic groups and showed the most auxin-like activity. The H-NAFEC was rich in phenolic groups and showed the least auxin-like activity. The H-AFEC showed a higher degree of aromatic condensation and humification. Thus, negative auxin-like activity of H-NAFEC could be attributed to the high degree of aromatic condensation and humification, and the low content of phenolic groups. In this experiment, there was no plant growth-promoting microorganism, therefore, the different growth promotion effects on cucumber plants with the application of DEC, AFEC and NAFEC might be caused by the different content of humic substances and distinguishing auxin-like activity.6. Except for Rhizoctonia solania AG4, all compost extracts from pig manure-straw compost were remarkably antagonistic to the soilborne pathogenic fungi. Under different aerated conditions, there was no difference of the antagonistic effect of compost extracts against Fusarium oxysporum f.sp. cucumerinum, Didymella bryoniae and Rhizotctonia solania AG4. Microbial populations, especially for bacteria, were considered the most significant factor contributing to disease suppression of compost extracts. But, bacterial community diversity indexes of pig manure-straw compost extracts did not influence the inhibition effects on soilborne pathogen. It was shown that the inhibition effects of compost extracts on soilborne pathogenic fungi were not consistent, and were affected by the extraction technology and the plant pathogenic fungi variety.All compost extracts could reduce tomato root nematode egg mass and density of soil nematodes more or less. The reduction ratio of root egg mass and density of soil nematodes were33.7%-87.9%and31.3%-51.4%, with the application of DEC, AFEC and NAFEC. In conclusion, the compost extracts from pig manure-straw compost could obtain the better reduction of root-knot nematodes, when extracted with reasonable extraction technology, the best growth promotion and bio-control effects could be obtained from the extracts with NAFEC technology.