Aiming at the problems of plant growth inhibition, frequent Fusarium wilt and microbial community imbalance caused by continuous cropping obstacle of watermelon, the effects of Helianthus tuberosus straw biochar on growth promotion, disease inhibition and microbiological mechanism were explored.

Two kinds of H. tuberosus straw biochar were used as test materials, and four treatments were set up, including 1% (w/w) biochar-continuous cropping soil mixed treatment (denoted as J04 and J13, respectively), carbendazim control (Y) and blank control (CK). The effects of biochar on the growth of watermelon seedlings and the occurrence of Fusarium wilt were investigated by pot experiment. The effects of H. tuberosus straw biochar on soil bacterial community structure and diversity were analyzed by Miseq high-throughput sequencing technology.

Compared with CK, the two biochar treatments significantly promoted the accumulation of watermelon seedling biomass and reduced the Fusarium wilt disease index. At 35 d after transplanting, compared with CK, the whole plant dry weight of J04 and J13 treatments significantly increased by 10.8% and 27.6%, the incidence significantly decreased by 28.8% and 48.5%, and the disease index significantly decreased by 21.1 and 30.8. The incidence of carbendazim treatment (Y) was significantly lower than that of CK by 59.1%, the disease index was significantly decreased by 38.1, and the dry weight of the whole plant was significantly increased by 4.3% (P＜0.05). Compared with CK, the α diversity of soil bacterial community in J04 and J13 treatments decreased significantly, and the Shannon index and Invsimpson index were significantly lower than CK. H. tuberosus biochar treatment significantly changed the soil bacterial community structure (R² =0.690, P=0.009). At the phylum level, J13 treatment significantly increased the relative abundance of Actinobacteriota and Firmicutes, and inhibited Acidobacteriota and Myxococcota. At the genus level, J13 treatment significantly enriched potential beneficial bacteria such as Gemmatimonas and Devosia. The FAPROTAX function prediction further indicated that J13 treatment significantly increased the abundance of microbial groups related to functions such as chemical heterotrophy and urea decomposition, which may promote the rhizosphere nutrient cycle.

The addition of H. tuberosus straw biochar (J13) can effectively alleviate the continuous cropping obstacle of watermelon, and its growth-promoting and disease-inhibiting effects are closely related to the improvement of rhizosphere bacterial community structure and the enrichment of potential beneficial bacteria with specific functions.

This paper aimed to clarify the effect of farmland flooding on the soil environment of continuous pepper cropping, and to provide the technical basis for reducing the soil sickness caused by continuous pepper cropping.

In this experiment, the flooded and non-flooded soil of continuous cropped pepper in Hexian County of Anhui Province were analyzed, with non-flooded soil as control. The determination of chemical property and microbial community structure in soil with flowing analyser, qPCRand Illumina MiSeq sequencing explored the effect of flooding on the soil. Besides, the pepper was used as plant material to explore the effects of flooded and non-flooded soil on seed germination and seedling growth by the Petri dish method.

Soil flooding significantly decreased the soil EC value, organic matter, nitrate N, ammonium N, available K, and Olsen P. Quantitative PCR analysis showed that soil flooding significantly increased the bacterial community abundance (P<0.05), however decreased that of the fungal communities. Illumina MiSeq sequencing showed that the soil flooding significantly increased the relative abundances of Actinobacteria and Myxococcota, which decreased the Firmicutes and Mortierellomycota at phylum level. The soil flooding decreased the relative abundance of potential pathogenic fungi, such as Fusarium spp., positive correlation with nitrate N. The soil flooding increased potential Azotobacter, including Azoarcus, Gemmatimonas, Sideroxydans, Candidatus_Solibacter, Bryobacter, Sideroxydans spp. and plant-beneficial potential such as Aspergillus and Acremonium spp., which were negatively correlated with nitrate N. The soil microbial community structure and composition was significantly affected by soil nitrate N. In petri dish, the seed germination rate, seeding fresh weight and root length of peppers planted in flooded soil were significantly higher than those in non-flooded soil.

Soil flooding significantly reduced the EC value and abundance of potentially pathogenic microbial community and increased the abundance of potentially beneficial bacterial, but significantly reduced the content of available nutrients. At the same time, Soil flooding was conducive to the seed germination and seedling growth and alleviated the pepper continuous cropping obstacles.

This study aimed to investigate the impact of cover crops (wheat and common vetch) on the growth of Chinese cabbage seedlings and the structure of the soil microbial community. The findings could provide the theoretical and technical support for using wheat and common vetch cover crops to alleviate continuous cropping obstacles in Chinese cabbage production.

In this experiment, there were four treatments: wheat cover crop treatment (W), common vetch cover crop treatment (P), mixture of wheat and common vetch treatment (WP), and no cover crop treatment (CK). The effects of different cover crop treatments on the growth of Chinese cabbage seedlings were studied. Moreover, the effects of wheat and common vetch cover crops on the microbial community of Chinese cabbage rhizosphere were also investigated through qPCR and Illumina MiSeq techniques. In addition, Spearman correlation analysis was conducted to identify the key soil microbial taxa related to Chinese cabbage growth. Then, the changes in soil chemical properties on soil microbial community structure were explored by environmental factor correlation analysis.

Compared with CK, the cover crop treatments had positive effects on Chinese cabbage growth and decreased soil electrical conductivity (EC) value. The mixed cover crop treatment significantly decreased soil available potassium content, whereas wheat cover crop treatment increased soil pH. The qPCR results showed that the abundance of soil bacterial community was not significantly affected by the cover crop treatment, but increased the abundance of soil fungal community. Both common vetch cover crop treatment and mixed wheat and common vetch cover crop treatment significantly reduced the abundances of Bacillus spp. and Pseudomonas spp. communities. The Illumina MiSeq analysis showed that the relative abundance of genus TM7a was significantly increased by cover treatments, while the relative abundances of Leptolyngbya_EcFYyyy-00, Lophotrichus, Acaulium, and Sodiomyces were decreased. The mixed cover crop treatment significantly increased the relative abundance of Sphingomonas and Massilia and significantly decreased the relative abundance of Fusarium. Spearman correlation analysis showed that Sphingomonas, TM7a, Massilia, and Gemmatimonas were positively correlated with growth. Leptolyngbya_EcFYyyy-00, Acaulium, Lophotrichus, Sodiomyces, and Fusarium were significantly negatively correlated with the growth of Chinese cabbage. Moreover, these cover crop treatments influenced bacterial and fungal diversity indices. The Shannon index and inverse Simpson index for soil bacterial community and Shannon index of soil fungal community significantly decreased in cover common vetch treatment. In contrast, the inverse Simpson index of soil fungal community was increased. The mixed cover crop treatment increased the fungal Shannon index, while the inverse Simpson index of soil fungal community decreased. Principal Coordinates Analysis (PCoA) showed significant differences in soil microbial community structure, with soil EC value as a major environmental factor affecting the structure.

The cover crop treatments exhibited growth-promoting effects on Chinese cabbage seedlings, and the best effect was found in the mixed cover crop treatment. The relative abundances of some Sphingomonas, TM7a, Massilia, other potential growth-promoting bacteria were increased in the cover crop treatments. The relative abundances of some potential plant pathogens Leptolyngbya_EcFYyyy-00 and Fusarium were decreased and the relative abundance of potential biocontrol agent Chaetomium was increased in the mixed cover crop treatment.

To clarify the effects of catch crop decomposition liquid on the growth and blight of continuous pepper seedlings, and to provide the theoretical basis and technical support for wheat and broad bean catch crop to alleviate the continuous cropping obstacles of peppers.

Pepper and pepper continuous cropping soil were used as the research object. Firstly, seven catch crop treatments were set up, including wheat (A), broad bean (B), large-leafed skunk cabbage (C), wheat and broad bean mixture (AB), wheat and large-leafed skunk cabbage mixture (AC), broad bean and large-leafed skunk cabbage mixture (BC), and wheat, broad bean and large-leafed skunk cabbage mixture (ABC), and the non-catch crops were used as the control (CK). Study the effects of different treatments on the pepper growth and blight. Secondly, in order to ascertain the role of its catch crop decomposition liquid in promoting growth and disease control, four treatments with different concentrations of wheat and broad bean mixture straw decomposition liquid (0.01, 0.03, 0.05, and 0.07 g·mL^-1) were set up to investigate different treatments the effects on the growth and blight of pepper seedlings, using distilled water as the control (CK).

When transplanting for 20 and 30 d, the fresh weight of the whole plant, dry weight of the whole plant and plant height of pepper after mixed catch crop treatment of wheat and broad bean were significantly higher than those no-catch crops treatments, and the incidence and disease index were significantly lower than those no-catch crops treatments. The disease index of the wheat and broad bean mixed catch crop treatment was significantly lower than that of all other treatments. The whole plant fresh weight of pepper was significantly increased at 20 d and 30 d of treatment with wheat and broad bean mixed straw decomposed liquids. At 30 d, the dry weight of the whole pepper plant was significantly increased except for 0.01 g·mL^-1 treatment. Compared with distilled water treatment, 0.03 g·mL^-1 treatment significantly increased the root length, average diameter of roots, root surface area, root volume, root tip number and leaf peroxidase (POD) and polyphenol oxidase (PPO) activities of pepper (P<0.05). The mycelial diameter, zoospore germination rate and sporulation yield of Phytophthora capsici treated with different concentrations of wheat and broad bean mixture straw decomposed liquids were significantly lower than those of distilled water treatment (P<0.05). The mycelial diameter and zoospore germination rate of 0.03 g·mL^-1 treatment were significantly lower than those of other treatments, and the inhibition effect of 0.03 g·mL^-1 treatment on phytophthora blight and blight was the best.

The mixed catch crop of wheat and broad bean had a growth-promoting and disease-inhibiting effect on continuous cropping pepper seedlings, and its straw decomposed liquids played an important role in which the decomposed liquids concentration of 0.03 g·mL^-1 when the best effect, and its role was closely related to the direct inhibition of the phytophthora blight and improved the activity of the plant defense enzymes.