Objectives Marigold straws have been proved possessing inhibition effect on some harmful microorganisms. At the same time, apple industry is suffering from seriously continuous cropping obstacle restricts. The effect of biological disinfestations of marigold straws was studied, to study the recycle of organic wastes and the reform of aged apple orchards.
Methods A pot experiment was carried out in 2017, the seedlings of Malus hupehensis Rehd. were used as test materials and a continuous cropped soil (26 years' apple orchard) as tested soil. Marigold (Tagetes erecta) straw powder of 0, 12, 30 and 60 g/kg were mixed with soil, watered and mulched with plastic film for 15 days before planting the seedlings. After three months' growth, the seedling samples were collected, and total of three samplings were made every one month interval. Soil samples were collected at the same time. The growth indices, photosynthetic parameters, root respiration rate and protective enzyme activity of Malus hupehensis Rehd. seedlings, and soil microorganisms were measured.
Results Compared with 0 g/kg treatment, the biological disinfestation to soil mixed with marigold powder could significantly increase root respiration rate significantly, raise protective enzyme activity; and then improve the leaf photosynthetic parameters, promote the seedling growth indices; optimize the soil microbial environment. Comprehensively evaluated, the 30 g/kg treatment was the best. Compared with 0 g/kg treatment, the root respiration rate was increased by 56.6%, the activities of SOD, POD and CAT were increased by 48.7%, 113.5% and 115.2% respectively and the plant heights, ground trunk diameters, the fresh weights of plant above ground and leaf chlorophyll contents were increased by 183.3%, 55.5%, 221.5% and 17.3%, respectively. The net photosynthesis rate (Pn) and the water use efficiency (WUE) of leaves increased by 83.6% and 57.1%, respectively. And all the above indices were significantly different from those of 0 g/kg, 12 g/kg and 60 g/kg treatments. The soil bacteria population was increased and the fungi population was decreased after biological disinfestation. The ratio of bacteria to fungi in soil treated with 12, 30 and 60 g/kg were 99.3, 265.7 and 197.3, respectively, which were 1.4, 3.7 and 2.7 times of the 0 g/kg treatment, with significant differences among the treatments. The number of gene copies of Fusarium oxysporum in soil decreased by 18.6%, 57.1% and 40.4% compared with the 0 g/kg treatment, respectively, which were significant differences among treatments. terminal restrietion fragment length polymorphism (T-RFLP) results showed that the soil fungal community structure of 0 g/kg was similar with that of 12 g/kg, and the fungal community structure of 30 g/kg was relatively similar with that of 60 g/kg, both of them were completely separated from that of CK. The powder dosage was not the more the better, 60 g/kg treatment was better than 0 g/kg, but not as good as the 30 g/kg treatment. The merely film mulching treatment (0 g/kg) improved various indices a little bit, but the effect was not significant.
Conclusions Biological disinfestation to soil with marigold powder in a proper rate could reduce the number of gene copies of Fusarium oxysporum in soil, change the fungal community structure within continous cropped soils significantly; enhance root respiration rate and protective enzyme activity of apple seedlings; significantly promote the growth of Malus hupehensis Rehd. seedlings, improve the photosynthetic parameters, and effectively alleviate apple continous cropping barrier. Therefore, marigold straw powder is an effective soil remediation material for continuous cropping, and its suitable addition amount in production needs further study.
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