The effects of inorganic fertilizer addition method on the organic-inorganic co-composting process, especially the structure of humic acid and the mechanism of microbial nutrient restriction, are unclear. In this article, the effects of one-time and fractional addition of inorganic fertilizer on the structure of humic acid, extracellular enzyme activity, extracellular enzyme stoichiometry and the culturable growth-promoting bacteria during organic-inorganic co-composting were determined. The results showed that the addition of inorganic fertilizer promoted the humification degree of compost. Compared nitrogen with phosphorus, the fermentation microorganism behaved as N-restricted throughout the process. Compared one-time addition with fractional addition of inorganic treatments, the TOC, WSOC, NO-N and humic acid content in the mature compost of the one-time addition treatment were higher. The contents of nitrogen, oxygen, the carboxyl functional groups, aromatic compounds, and the nitrogen/carbon atomic ratio in the humic acid structure increased as the composting process proceeded, while the contents of hydrogen, aliphatic substances, and the hydrogen/carbon atomic ratio decreased, and the elemental composition and structural changes of humic acids indicated that the humification degree of the one-time addition treatment was higher. The addition of inorganic fertilizer increased the relative abundances of Bacillus megaterium and Bacillus subtilis in the mature compost.

Introduction:Nano fertilizers can provide efficient solutions to the increasing problem of nutrient deficiency caused by low availability. However, the most important prerequisite is to fully understand whether nanomaterials induce phytotoxicity in plants under a variety of different conditions. The mechanisms underlying interactions between molybdenum nanoparticles (Mo NPs) and plants with respect to their uptake and biological effects on crops are still not fully understood. Methods:In this study, the impacts of Mo NPs over a range of concentrations (0, 25, and 100 μg/mL) on tobacco ( L.) seedling growth were comparatively evaluated under foliar applications and root irrigation. Results:The results indicated that more significant active biological effects were observed with root irrigation application of Mo NPs than with foliar spraying. The agronomic attributes, water content and sugar content of Mo NPs-exposed seedlings were positively affected, and morphologically, Mo NPs induced root cell lignification and more vascular bundles and vessels in tobacco tissues, especially when applied by means of root irrigation. Moreover, the photosynthetic rate was improved by 131.4% for root exposure to 100 μg/mL Mo NPs, mainly due to the increased chlorophyll content and stomatal conductance. A significant concentration-dependent increase in malonaldehyde (MDA) and defensive enzyme activity for the Mo NPs-treated tobacco seedlings were detected compared to the controls. Significantly improved absorption of Mo by exposed tobacco seedlings was confirmed with inductively coupled plasma mass spectrometry (ICP-MS) in tobacco tissues, regardless of application method. However, the accumulation of Mo in roots increased by 13.94 times, when roots were exposed to 100 mg/L Mo NPs, higher than that under treatment with foliar spray. Additionally, Mo NPs activated the expression of several genes related to photosynthesis and aquaporin processes. Discussion:The present investigations offer a better understanding of Mo NPs-plant interactions in terrestrial ecosystems and provide a new strategy for the application of Mo NPs as nano fertilizers in crop production.

Some agronomic practices not only promote the development of crop roots and increase overall plant performance but also affect colonisation by rhizosphere microorganisms. However, the composition and temporal dynamics of the tobacco rhizosphere microbiota under different root-promoting practices are poorly understood. Here, we characterised the tobacco rhizosphere microbiota at the knee-high, vigorous growing, and maturity stages under the application of potassium fulvic acid (PFA), γ-Polyglutamic acid (PGA), soymilk root irrigation (SRI), and conventional fertilization (CK) and its correlation with root characteristics and soil nutrients. The results showed that three root-promoting practices notably improved the dry and fresh root weights. Total nitrogen and phosphorus, available phosphorus and potassium, and organic matter contents in the rhizosphere markedly increased at the vigorous growing stage. The rhizosphere microbiota was changed through root-promoting practices. However, with tobacco growth, the change of rhizosphere microbiota showed a pattern of slow first and then fast and the microbiota of different treatments gradually approached. SRI reduced plant-pathogenic fungi but increased chemoheterotrophic and phototrophic bacteria, and arbuscular mycorrhizal fungi. PFA and PGA markedly increased arbuscular mycorrhizal and ectomycorrhizal fungi at the knee-high stage, which benefitted tobacco nutrient absorption. The correlation between rhizosphere microorganisms and environmental factors varied at different growth stages. Notably, the rhizosphere microbiota was more sensitive to environmental factors at the vigorous growing stage, and the interactions were more complex than in other stages. Furthermore, a variance partitioning analysis showed that the influence of root-soil interaction on the rhizosphere microbiota increased with tobacco growth. Overall, all three root-promoting practices could improve root characteristics, rhizosphere nutrient, and rhizosphere microbiota to varying degrees and increase the tobacco biomass, among which PGA had the most obvious effect and most suitable for tobacco cultivation. Our findings revealed the role of root-promoting practices in shaping the rhizosphere microbiota during plant growth and elucidated the assembly patterns and environmental drivers of crop rhizosphere microbiota driven by the application of root-promoting practices in agricultural production.

Biochar application is an effective strategy for improving soil degradation and productivity. However, the effects of the combination of biochar and other fertilizers to improve seedling growth in abiotic stress-affected soils remains unknown. We investigate the effect of biochar derived from reed straw (RBC) and waste seaweed liquid fertilizer (SLF) on tomato (Solanum lycopersicum L.) seedling growth in an acid-affected soil of Jiaodong Peninsula, China. The results revealed RBC, SLF, and the combination of RBC with SLF (RBC+SLF) significantly elevated the dry weight of tomatoes by 23.33 %, 29.93 %, and 63.66 %, respectively. The malondialdehyde content in the tomato seedling roots, stems, and leaves was significantly lower in the RBC+SLF treatment, which might be related to the enhanced contents of proline, soluble sugar, and soluble protein. The synthesis and accumulation of zeatin riboside, indole-3-acetic acid, and gibberellic acid 3 in tomato under RBC+SLF amendment may be attributed to the enhanced plant growth. Moreover, RBC, SLF, and RBC+SLF improved the soil status (including ammonium nitrogen, nitrate nitrogen, laccase, and urease) in the acid-affected soil. Biochar and waste seaweed liquid fertilizer significantly increased the relative abundance of Pseudomonas and Azospira (beneficial bacteria) in tomato rhizosphere. The microbial amino acid metabolism was associated with changes in soil properties and enzyme activities. Consequently, biochar and waste seaweed liquid fertilizer are viable soil conditioners for acid-affected soil.

Long-term continuous cropping of tobacco causes dysbiosis of soil microbial communities, the imbalance of soil nutrients, and the increase of pathogenic bacteria, which will slow the growth and development of tobacco plants, reduce the production quality, and cause significant losses to tobacco production and tobacco farmers. The application of Potassium fulvic acid can not only provide nutrients, but also inhibit the propagation of pathogens in soil along with raising the amount of organic matter in the soil, which is an effective way to improve soil health. In this experiment, Tobacco variety SNT60 was used as the test material, and 6 treatments were set up by pot test, they were: no fertilisation control group (CK), tobacco special fertiliser (NPK), 3.45 g/kg of potassium fulvic acid fertiliser (T1), 4.65 g/kg of potassium fulvic acid fertiliser (T2), 5.85 g/kg of potassium fulvic acid fertiliser (T3), 7.05 g/kg of potassium fulvic acid fertiliser (T4), Ten replications were set up for each treatment and the soil and fertiliser were mixed and potted before transplanting, 70% as basal fertiliser and 30% as supplementary fertiliser. We also analyzed soil properties, soil microorganisms and agronomic traits of tobacco plants in different treatments to provide reference for mitigating tobacco succession barrier. The test results are as follows: 4.65 g/kg of potassium fulvic acid fertiliser (T2) treatment was the best, soil organic matter, quick nitrogen, phosphorus, potassium, pH, soil catalase, soil sucrase, and soil urease content, compared to CK control, increased by 22.04%, 43.12%, 96.21%, 381.79%, 25.43%, 91.69%, 262.07% and 93.16%. In terms of microbial community, application of potassium fulvic acid fertiliser significantly increased the relative abundance of Ascomycetes, Chlorobacterium, Bacillus, Proteobacteria and Tephritobacterium in the soil. Meanwhile, 4.65 g/kg of potassium fulvic acid fertiliser (T2) promoted the growth of tobacco plants, improved leaf photosynthetic capacity, and enhanced plant disease resistance. This experiment provides practical measures to improve the microbial community of tobacco continuous cropping soils and to reduce the incidence of diseases.