Allelopathy and fertilizer efficiency of compost made from Ageratina adenophora on wheat.
Objective: After coming into our country from Myanmar in 1940s, Ageratina adenophora is now widespread in agricultural lands, forests and pastures in Southwest China, which has produced huge economic loss and ecological disaster. The objective of this study is to realize the allelopathic effects of this invasive plant on wheat and the efficiency of organic fertilizer made from A. adenophora, and to provide scientific information for the effective control and resource utilization. Method: A microbial inoculum was made with Pseudomonas putita and Clostridium thermocellum to compost A. adenophora in situ. Then pure culture and pot experiments were carried out to compare the allelopathic effects of extracts from fresh and decomposed A. adenophora on wheat seed germination, young seedling growth and nutrient uptake, and field trial to realize soil microbes, wheat grain yield and quality as affected by organic fertilizer made from A. adenophora. Result: In the culture experiment, the higher concentration of the extracts from fresh A. adenophora (EFA) significantly inhibited the seed germination and decreased the growth rate of the seedlings. In contrast, the seed germination rate, germination index, vigor index, and seedling height increased by 4.73%, 13.06%, 6.58%, and 29.87%, respectively, which were treated by decomposed extracts of A. adenophora (EDA). Meanwhile, EDA treatment increased the chlorophyll concentration, nitrate reductase activity, and root vitality, which was beneficial to photosynthesis, nitrogen assimilation, and nutrient uptake. In the process of wheat germination, EFA significantly slowed the hydrolysis of macromolecular inclusions such as protein, starch and inositol phosphates in wheat seed endosperm. Conversely, EDA increased free amino acids, soluble sugars, and inorganic phosphorus in the seeds, which could be used as the building materials for new plants and supply seedlings with nutrients resulting in fast plant growth. In pot experiment, using EFA to water wheat seedlings, nitrogen absorption by plants decreased by 74.78%, phosphorus decreased by 58.55%, and potassium decreased by 70.77%, and the seedling biomass decreased by 47.77%-58.70%, respectively. However, EDA promoted plant nutrient uptake and the seedling biomass increased by over than 27.53% compared with control. In the field trial, compared with the control (no fertilizer), there was no significant effect of chemical fertilizer application on microbial carbon and nitrogen content, dehydrogenase activity, and Shannon-Wiener diversity index in wheat rhizosphere soil. However, chemical fertilizer in combination with organic fertilizer made from A. adenophora, greatly increased the three microbial parameters above compared with only chemical fertilizer application. Application of this organic fertilizer increased by 8.87% of wheat grain yield and by 10.02% of seed protein in comparison with only chemical fertilizer application. Conclusion: Fresh A. adenophora contained allelopathic toxins, inhibited the hydrolysis of macromolecular inclusions in seed endosperm, and decreased seed germination rate, nutrient absorption by seedlings, including nitrogen, phosphorus and potassium, and inhibited seedling growth. Composted A. adenophora with microbial inoculum contained no toxicant, stimulated seed germination, promoted nutrient uptake, accelerated seedling growth, and enhanced the numbers, activities, and biodiversity of microbes in the rhizosphere of wheat, resulting in wheat yield increment and seed quality improvement. In artificial control and removal of A. adenophora, therefore, to produce organic fertilizer by composting A. adenophora with microbial inoculum in situ could realize harmless treatment and resource utilization.