Study On Inhibition Effect Of Horseweed Composting And Weed Suppression Components On Echinochloa Crus-galli(L)

Barnyard grass [Echinochloa crus-galli(L.)P.Beauv.] is a problematic weed that grows in rice(Oryza sativa L.)fields,chemical herbicides can effectively control the occurrence of barnyard grass,but over-applying herbicide caused environmental pollution and the emergence of resistant weeds.Integrated weed management method can reduce the dependence on herbicides in rice production.This study aimed to develop a weeding fertilizer to control the damage caused by barnyard grass in paddy fields by using horseweed(Conyza canadensis(L.)Cronq.)as compost materials,and the inhibiting effect of the weed suppression components contained in the horseweed composting on the seedling growth of barnyard grass was studied.Moreover,the results of laboratory experiments showed that fulvic acid(FA,a composting product)could inhibit the growth of barnyard grass seedlings at high concentrations.The mechanism underlying the regulation of barnyard grass seedling growth by horseweed weeding fertilizer(HWF)and FA were explored using liquid chromatography-mass spectrometry(LC-MS)and transcriptome sequencing(RNA-seq),and the field experiments were carried out to verify the practical application ability of HWF and FA to control barnyard grass.(1)In this study,the allelopathic plant horseweed was used as composting material to produce organic fertilizer to control barnyard grass.When composting for 21 days,the content of organic matter and total nutrient of HWF were 74.65% and 10.87%,respectively in HWF,which was conformed to the agricultural standard of organic fertilizer(NY 525-2012).The contents of FA and humic acid(HA)were 10.28% and21.37%,respectively in HWF,and the quality of fertilizer was satisfactory.(2)The inhibitory effect of HWF on barnyard grass was determined through the laboratory experiment,and the allelochemicals in HWF were analyzed and verified.Under the condition of flooding,the growth of barnyard grass was significantly inhibited when the composting time of HWF was 21 d and the extract concentration was 5 g/L(150 Kg/mu).Compared with the control group,the shoot length,root length,and fresh weight of barnyard grass seedlings were significantly decreased by 48.19%,83.11%,and 42.34%,respectively,and the subsequent growth was slow.The perishable organics such as amino acids,carbohydrates,and lipids,were degraded in the process of composting.The total weight of the compost was reduced,the humic substances were synthesized,and the compost became mature.The bioassay results showed that the allelochemicals in HWF such as benzoic acid,2-hydroxy-3-nitrobenzaldehyde,salicylic acid,and n-hexanoic acid could significantly inhibit the growth of barnyard grass seedlings,and the growth of barnyard grass could be inhibited by HWF.(3)This study showed that FA could inhibit the growth of barnyard grass seedlings under the condition of flooding,and could be used to control barnyard grass in paddy field.The growth of barnyard grass seedlings was significantly increased in treatment of low concentration FA(0.02 g/L).Compared with the control group,the shoot length,root length,and fresh weight of barnyard grass seedlings were significantly decreased by 35.48%,83.33%,and 40.87 %,respectively,under 0.80 g/L FA treatment.When the concentration of FA exceeded 0.80 g/L in the flooding water,the seedlings became yellow and showed signs of decay.Under the addition of 0.8 g/L FA after 0-6 days of planting,the growth of rice and barnyard grass seedlings was significantly inhibited in flooding conditions;when 0.80 g/L FA was added 8-10 days after planting,the growth of rice and barnyard grass seedlings was significantly promoted.HWF could inhibit the growth of barnyard grass for its high FA content.In transplanting fields,the application of FA could promote the growth of rice seedlings,and control the growth of barnyard grass seedlings so that the plant shoot cannot be higher than the rice canopy.Therefore,FA could be applied to control barnyard grass and reduce the harm of weed to the rice crop in transplanting fields.(4)The metabolomic and transcriptomic analyses showed that FA regulated barnyard grass seedling growth by affecting the synthesis of indole derivatives and flavonoid compounds.Under the HF treatment(0.80 g/L FA),the concentrations of 5-methoxyindole-3-carbaldehyde,methoxyindoleacetic acid,indole,and 3-indoleacetonitrile were upregulated compared with CK(0 g/L FA),while the expression levels of ALDH(aldehyde dehydrogenase)and TDC(L-tryptophan decarboxylase)were downregulated.The upregulation of indole derivative content might increase the auxin content excessively and inhibit the growth of barnyard grass.The indole derivatives mentioned above were slightly down-regulated under LF treatment(0.02g/L FA),and the growth of barnyard grass was promoted.Compared with CK,the concentration of flavonoids,including naringenin,and eriodictyol,kaempferol were downregulated,while the expression levels of CHS(chalcone synthase),CHI(chalcone isomerase)and FLS(flavonol synthase)were upregulated.In contrast,the metabolism and transcription of flavonoids were not significantly changed under LF treatment.The high concentration of FA treatment affected the biosynthesis of flavonoids,and the adaptive mechanism of barnyard grass to reduce reactive oxygen species by regulating the synthesis of flavonoids was destroyed,so its resistance to flooding stress was reduced,and the growth was inhibited.(5)The inhibitory effect of HWF and FA on barnyard grass was verified through the field experiments including two years,three seasons,and two locations.Under the condition of 3?5 cm flooding and water retention for 15 days,the control effect on barnyard grass in transplanting field reached more than 75% by HWF(150 Kg/mu),and 70% by FA(30 Kg/mu).Under flooding conditions,the occurrence of barnyard grass could be effectively controlled by the application of HWF and FA in the transplanting field.The allelochemicals contained in HWF could inhibit the growth of barnyard grass seedlings effectively.FA could affect barnyard grass seedling growth by regulating the synthesis of indole derivatives and flavonoid compounds.