Soil labile organic carbon fractions and soil organic carbon stocks as affected by long-term organic and mineral fertilization regimes in the North ChinaPlain.

Microbiomes are important for crop performance. However, a deeper knowledge of crop-associated microbial communities is needed to harness beneficial host-microbe interactions. Here, by assessing the assembly and functions of maize microbiomes across soil types, climate zones, and genotypes, we found that the stem xylem selectively recruits highly conserved microbes dominated by Gammaproteobacteria. We showed that the proportion of bacterial taxa carrying the nitrogenase gene (nifH) was larger in stem xylem than in other organs such as root and leaf endosphere. Of the 25 core bacterial taxa identified in xylem sap, several isolated strains were confirmed to be active nitrogen-fixers or to assist with biological nitrogen fixation. On this basis, we established synthetic communities (SynComs) consisting of two core diazotrophs and two helpers. GFP-tagged strains and 15N isotopic dilution method demonstrated that these SynComs do thrive and contribute, through biological nitrogen fixation, 11.8% of the total N accumulated in maize stems. These core taxa in xylem sap represent an untapped resource that can be exploited to increase crop productivity.

Different fertilization regimes can substantially influence soil fungal community composition, yet fewer studies try to control for the effects of nitrogen input. Here, we investigated the impact of fertilization with equal nitrogen upon soil properties and soil fungal diversity and community composition in the North China Plain in a long-term field experiment. Long-term (32 years) fertilization regimes were applied with equal amounts of nitrogen: no chemical fertilizer or organic manure; chemical fertilization only; organic manure fertilization only, and; combination of 1/2 chemical fertilizer and 1/2 organic manure. Then we investigated the influence of these four fertilization regimes to soil properties, fungal diversity and community composition. The results showed that applying organic manure significantly influenced soil properties. Illumina MiSeq sequencing and its analysis revealed that organic manure fertilization significantly changed soil fungal alpha diversity, but chemical fertilization did not. Although soil fungal community composition did not differ significantly among all the fertilization regimes at the phylum and class levels, they did show differences in the abundance of dominant fungi. Yet at the genus level, soil fungal community composition, abundance, and beta diversity was affected by all fertilization regimes. Application of organic manure also reduced the abundance of soil-born fungal pathogens such as Fusarium. Our results suggest that long-term application of organic manure could markedly improve soil properties, altering soil fungal community composition and its diversity. Moreover, organic manure fertilization could limit soil-born fungal diseases, to further contribute to soil ecosystem sustainability.

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Humic acids (HAs) incorporated into urea fertilizers are highly effective at increasing yield and decreasing fertilizer-derived nitrogen (N) loss from soil, but reports of the optimal proportion in fertilizers remain widely inconsistent. In this study, we examined the effects of urea enhanced with 0.2–5.0% HAs (UHAs) on the yield, biomass production, N uptake, and N residue in fluvo-aquic soil in winter wheat cultivated over two growing seasons from 2018 to 2020 in the North China Plain. UHAs application significantly enhanced wheat grain yield, aboveground dry biomass, total and fertilizer-derived N uptake by wheat, and residue in soil, while reducing the loss of fertilizer-derived N. Additionally, UHAs treatments increased fertilizer-N residues in soil, especially in the top 30 cm soil layer, which increased with the proportion of added HAs. These positive effects were attributed to a higher spike number under UHAs treatments compared to conventional urea. Clustering analysis of the different treatments showed that 0.2% HAs were more similar to conventional urea, while 0.5% had similar effects to HAs at higher proportions. UHAs application significantly enhanced wheat grain yield, mainly via increasing spike number, and optimized the fertilizer-N fate. Among UHAs treatments, 0.5% HAs showed the highest increase in economic benefit.

Plant endophytes exhibit an excellent ability to promote plant growth and control plant diseases. However, the influence of long‐term fertilisation regimes on the diversity and community of plant endophytes has seldom been reported. In this research, Illumina MiSeq sequencing was used to investigate the effect of 34 years of different fertilisation regimes on the diversity and community of wheat (Triticum aestivum L.) leaf endophytes. Results showed that different fertilisation regimes could significantly influence the diversity and community of wheat leaf endophytes. The diversity of leaf endophytes after organic manure fertilisation was different from the diversity after chemical fertilisation and no fertilisation. The endophyte community was significantly different under different fertilisation regimes. Pseudomonas has higher abundance after chemical and organic manure fertilisation than in the no fertilisation treatment. The abundance of Brevundimonas in the organic manure fertilisation treatment group is higher than in chemical and no fertilisation treatment. Redundancy analysis (RDA) showed that the endophyte communities in the chemical and organic manure fertilisation were positively correlated with wheat height, stem diameter, leaf area and yield. This research lays the foundations for understanding the diversity and community of wheat leaf endophytes under different fertilisation regimes and provides useful information for further scientific research on fertilisation.

Humic acid (HA) can improve the use efficiency of phosphate fertilizer, although its optimal proportion in fertilizers remains unknown. In this study, we conducted soil column experiments over two growing seasons to compare the effects of different HA proportions in phosphate fertilizer on wheat yield and phosphorus uptake, utilization, and soil available phosphorus. At harvest, grain yields were 0.23%-13.21% higher under HA-enhanced phosphate (HAP) compared to treatments with conventional phosphate fertilizer (P). Among different HAPs, wheat treated with HAP with 1.0% HA (HAP10) or 2.0% HA (HAP20) had the highest 2-year grain yield. Furthermore, total phosphorus uptake and its allocation in grains were both higher under HAP treatments compared to P treatment. The apparent use efficiency, agronomic efficiency and partial productivity of phosphorus in HAP10 and HAP20 treatments were also significantly higher than those treated with P in both growing seasons. In addition, HAP10 and HAP20 treatments resulted in the highest content of available phosphorus in the 0-60 cm soil layer compared with other HAPs or P alone. Incorporating HA into phosphate fertilizer at proportions of 0.5%-5.0% can increase wheat yield, phosphorus uptake, phosphate fertilizer use efficiency, and soil available phosphorus content, 1.0% or 2.0% HA in HAP shows the highest effects on these indexes. Given the economic benefits, 1.0% level is an optimal level for enhancing the effects of phosphate fertilizer in winter wheat crops.

BACKGROUND: Humic acid (HA)-enhanced urea (HAU) is the top-selling efficiency-enhanced urea in China. Comprehensive investigation into the structure and efficacy of HA complex formation with urea (HACU)the main reaction product during HAU's productionis required to clarify the reaction mechanism between HA and urea, and to provide guidance for the development of high-efficiency HAU.RESULTS: HACU showed discrepant structural and compositional features from raw HA. Nitrogen (N) content in HACU was 7.3 times greater than that of HA. Several high-resolution analytical methods showed a sharp increase of ammonia in the gaseous product during HACU pyrolysis, suggesting that urea contributed N to HACU. HACU was characterized with significantly fewer carboxyl groups than in raw HA, implying that the carboxyl group was the main group in HA to participate in the reaction between HA and urea. The presence of amide-N in HACU verified the structure of the reaction product. Furthermore, both HACU and HA could enhance the biomass in hydroponically grown maize seedlings, but the highest stimulation for HACU came about when its carbon concentrations were 50-100 mg L −1 , higher than the optimal carbon concentration for HA (25 mg L −1 ), attributed to the lower carboxyl group content for HACU to some extent. CONCLUSION: During HAU's production, reaction with N derived from urea to form amide-N decreased the carboxyl groups in HA, leading to higher concentrations for HACU required to achieve the similar bioefficacy of HA.