The objective of this study was to assess the benefit of applying biochar instead of its feedstock in enhancing soil quality. To accomplish this, we investigated the short-term effects of two organic materials and their derived biochars on maize growth, soil properties, and microbial community in fluvo-aquic and red soil with a pot experiment. Five treatments were applied to each soil, namely, the addition of straw, manure, straw-derived biochar, manure-derived biochar, and the control with no addition of any organic materials and biochar. Our results revealed that straw decreased the shoot biomass of maize in both soils, while straw-derived biochar, manure and manure-derived biochar increased it by 51.50, 35.47 and 74.95% in fluvo-aquic soil and by 36.38, 117.57 and 67.05% in red soil compared with the control, respectively. Regarding soil properties, although all treatments increased soil total organic carbon, straw and manure exhibited more pronounced effects on improving permanganate-oxidizable carbon, basal respiration, and enzyme activity compared with their derived biochars. Manure and its biochar had more significant effects on improving soil available phosphorus, whereas straw and its biochar exhibited more ameliorating effects on available potassium. Straw and manure consistently decreased bacterial alpha diversity (Chao1 and Shannon index) and altered bacterial community composition in the two soils by increasing the relative abundances of Proteobacteria, Firmicutes, and Bacteroidota and decreasing those of Actinobacteriota, Chloroflexi, and Acidobacteriota. More specifically, straw had a greater effect on Proteobacteria, whereas manure affected Firmicutes more. While straw-derived biochar had no effect on bacterial diversity and bacterial community composition in both soils, manure-derived biochar increased bacterial diversity in the fluvo-aquic soil and altered bacterial community composition in the red soil by increasing the relative abundances of Proteobacteria and Bacteroidota and decreasing that of Firmicutes. In summary, owing to the input of active organic carbon, straw and manure exhibited more pronounced short-term effects on soil enzyme activity and bacterial community compared with their derived biochar. Furthermore, straw-derived biochar was found to be a better option than straw in promoting maize growth and nutrient resorption, while the choice of manure and its biochar should be determined by the soil type.

Excessive nitrogen (N) fertilization harms the diversity, structure, and function of the soil microbiome. Yet, whether such adverse effects can be repaired through reducing the subsequent N fertilization rate remains not completely clear so far. Here, using a long-term N-overfertilized wheat-maize cropping field, we assessed the effect of reducing various proportions of the subsequent N fertilization rate over six years on crop productivity, soil physicochemical and biochemical properties, and microbiome. Five treatments were employed in our field experiment: the farmers’ conventional N fertilization rate (zero reduction, as a control) and the reduction in the farmers’ N rate by 20%, 40%, 60%, and 100%. The results showed that moderate N reduction (20–40%) enhanced crop productivity and soil fertility but did not affect soil enzyme activity. Soil bacterial and fungal community diversity were insensitive to N fertilization reduction, whereas their community structures changed significantly, with more prominent alteration in the fungal community. Functional prediction indicated that average relative abundance of arbuscular mycorrhizal fungi increased with N fertilization reduction but that of ectomycorrhizal fungi decreased. Moderate N reduction (20–40%) enhanced species interactions and, thus, provided a more complex cross-kingdom microbial co-occurrence network. Both bacterial and fungal community assembly were governed by stochastic processes, and this was not altered by N fertilization reduction. Overall, the response of the soil microbiome to N fertilization reduction was greatly dependent on the reduced N proportion. The findings obtained here shed light on the importance of optimal N fertilization rate in the intensively cultivated, high-input grain production system.

Partial substitution of mineral N fertilizer with manure (organic substitution) is considered as an effective way to reduce N input in intensive agroecosystems. Here, based on a 3-year field experiment, we assessed the influence of different organic substitution ratios (15%, 30%, 45%, and 60%, composted chicken manure applied) on vegetable productivity and soil physicochemical and biochemical properties as well as microbiome (metagenomic sequencing) in an intensive greenhouse production system (cucumber-tomato rotation). Organic substitution ratio in 30% got a balance between stable vegetable productivity and maximum N reduction. However, higher substitution ratios decreased annual vegetable yield by 23.29–32.81%. Organic substitution (15–45%) improved soil fertility (12.18–19.94% increase in soil total organic carbon content) and such improvement was not obtained by higher substitution ratio. Soil mean enzyme activity was stable to organic substitution despite the activities of some selected enzymes changed (catalase, urease, sucrase, and alkaline phosphatase). Organic substitution changed the species and functional structures rather than diversity of soil microbiome, and enriched the genes related to soil denitrification (including nirK, nirS, and nosZ). Besides, the 30% of organic substitution obviously enhanced soil microbial network complexity and this enhancement was mainly associated with altered soil pH. At the level tested herein, organic substitution ratio in 30% was suitable for greenhouse vegetable production locally. Long-term influence of different organic substitution ratios on vegetable productivity and soil properties in intensive greenhouse system needs to be monitored.

The application of phosphate fertilizers significantly influences soil microbial communities and nutrient cycling. Soil enzymes, which are sensitive to nutrient levels, play a critical role in microbial metabolism. However, the impact of phosphate fertilizers on nutrient limitations within the microbial metabolism of agricultural soils remains poorly understood. In this study, soil samples were collected from a depth of 0–20 cm from a wheat crop subjected to a three-year field experiment with six different phosphorus (P) application rates. Soil β-glucosidase (BG) and leucine aminopeptidase (LAP) activities were highest under the P3 (60 kg P₂O₅ ha⁻¹) treatment over the three-year study period. The responses of soil N-acetyl-β-glucosaminidase (NAG) and alkaline phosphatase (AKP) to increasing P additions varied across different years. The EES C:N, C:P, and vector length were significantly greater than 1. Soil nutrient characteristics accounted for 70.71% of the variation in soil enzyme stoichiometry. The vector length and angle of soil enzymes explained by soil nutrient characteristics were 0.65 and 0.73, respectively. Among these factors, ROC exhibited the largest direct and total effect on the soil enzyme vector length and angle. These research findings offer valuable insights for the management of agricultural fertilizers. Consequently, it is recommended to enhance soil carbon levels to alleviate carbon limitations and improve P utilization efficiency.

The application of nitrification inhibitors (NIs) is an effective way to reduce soil nitrogen (N) losses and increase crop N uptake. Yet, the efficacy of NIs commonly varies with dosages, crop systems and soil environmental conditions. Hence, clarifying the suitable type and dosage of NIs is extremely important for structuring the best N management regime at a regional scale. Here, based on microcosm experiments, we evaluated the influence of three widely used NIs [Dicyandiamide, DCD; 3,4-Dimethylpyrazole phosphate, DMPP; 2-chloro-6-(trichloromethyl) pyridine, Nitrapyrin] on the nitrification activity of an intensively cultivated greenhouse soil. The results showed that both DCD and DMPP imposed a transient inhibition on nitrification (less than five days) regardless of the dosages applied, and, on the contrary, Nitrapyrin presented a persistent suppression, with a longer duration of the inhibition action by a higher dosage. Accordingly, the incorporation of Nitrapyrin at 2% of the applied N rate (w/w) is a recommendable dosage for local intensive greenhouse production. Further, we assessed the influence of various dosages of Nitrapyrin incorporation (0%, 0.25%, 0.5%, 2% and 5%) on the abundance and community of three groups of soil ammonia oxidizers [i.e., ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and completely ammonia-oxidizing bacteria (Comammox Nitrospira)] by qPCR and high-throughput amplicon sequencing. Nitrapyrin incorporation strongly lowered both the AOB and Comammox Nitrospira abundances and their community richness even at the lowest dosage. Nitrapyrin incorporation also significantly altered the community structure of all of the tested ammonia oxidizers, and the average relative abundance of some major community members (i.e., the Nitrososphaerales Clade Nitrososphaera, Nitrososphaerales Clade A, Nitrosospira briensis Clade, Nitrosospira multiformis Clade, Comammox Nitrospira Clade A.2 and Comammox Nitrospira Clade A-associated) obviously responded to Nitrapyrin incorporation. Overall, our findings indicated that AOB and Comammox Nitrospira were more sensitive to Nitrapyrin incorporation as compared with AOA. The results obtained here highlight the importance of optimizing the type and dosage of NIs for N fertilization management in intensive greenhouse vegetable production. Nitrapyrin incorporation inhibits soil nitrification probably by suppressing the Nitrosospira multiformis Clade in the AOB community at the level tested herein.

Optimizing biochar use requires understanding its effects on soil microbes and crop yield, yet the role of soil texture remains unclear. In a two-year field experiment with a winter wheat–summer maize rotation on sandy and fluvo-aquic soils, biochar was applied at rates of 0, 10, and 20 t ha⁻¹. In sandy soil, biochar increased maize yield by 9.8% in the first year and by 13.1% in the second year, and wheat yield by 8.0% in the second year. In fluvo-aquic soil, only the 10 t ha⁻¹ rate increased maize yield by 9.7% in the second year. Biochar altered soil properties and enzyme activities in both soils, but microbial community responses varied with soil type, and soil type exerted a stronger influence than biochar application rate. In fluvo-aquic soil, the highest biochar application rate (20 t ha⁻¹) enhanced bacterial richness and diversity with a changed community structure, increasing Acidobacteria and Chloroflexi while decreasing Proteobacteria, whereas no such effects were observed in sandy soil. These community shifts were correlated with available potassium, urease, and sucrase, factors themselves affected by biochar. Fungal diversity and community structure were unaffected in either soil. Biochar increased yields through direct physicochemical improvements in sandy soil, whereas in fluvo-aquic soil it acted via combined physicochemical and microbial effects. Overall, the effects after two years of biochar on soil microorganisms and crop yield strongly depend on soil texture, mediated by complex interactions among soil properties. Given that the study involved a single biochar type and two soil types, further research across broader conditions is needed to verify the generality of these conclusions.