Field Fertilization Experiment Research Articles

Phosphorus limitation regulates the responses of microbial carbon metabolism to long-term combined additions of nitrogen and phosphorus in a cropland

Microorganisms play central roles in the decomposition and retention of soil organic carbon (SOC), but how nutrient addition in intensively managed croplands influences microbial C metabolism remains uncertain. Here, we investigated the effects of coupled phosphorus (P) and nitrogen (N) additions on microbial respiration, growth rate, C use efficiency (CUE), and biomass turnover time in a continuously managed Zea mays cropland, by combining an 18-year field fertilization experiment with the 18O–H2O labeling approach. Results showed that adding P at 50 and 100 kg P ha−1, combined with 150 kg N ha−1, increased respiration by 109% and 50.7%, increased growth rate by 207% and 135%, and increased CUE from approximately 0.26 without P addition to around 0.33 and 0.35, respectively. Conversely, adding N at varying rates (0, 100, 150, and 250 kg N ha−1), combined with 50 kg P ha−1, generated variable responses. These findings underscore the significance of P as the primary limiting element for microbial metabolism in this system. Ecoenzyme stoichiometry analysis further revealed that P addition decreased microbial P vs. N limitation, as well as decreased relative C limitation. In total, changes in P vs. N limitation with P and N additions accounted for 39.6% of the variation in microbial respiration, and in conjunction with relative C limitation, co-explained 51.4% of variations in growth rate and 44.0% of variations in CUE. Furthermore, our investigation identified positive associations of CUE with the activities of N and P-acquiring enzymes, but not with SOC. These results demonstrate flexible responses of microbial C metabolism to long-term anthropogenic N and P additions, highlighting their dependence on soil nutrient limitation. Consequently, optimizing the P-to-N fertilization ratio to alleviate relative P and C limitations may maximize microbial C assimilation and SOC retention in agroecosystems.

Vertical migration and leaching behavior of antibiotic resistance genes in soil during rainfall: Impact by long-term fertilization

The vertical migration and leaching behavior of antibiotic resistance genes (ARGs) during rainfall in soils subjected to long-term fertilization remain largely unclear. In this study, ARGs in vertical profiles (0−60 cm) and leachates from three soils (acidic, neutral, and calcareous) in a long-term (13 years) field fertilization experiment were monitored by high-throughput quantitative PCR after each rainfall event throughout an entire year. The results showed that, compared with unfertilized soils, long-term manure fertilization mainly promoted the vertical migration and leaching of aminoglycoside, beta-lactam, and multidrug resistance genes in the soil profiles. As a result, the annual cumulative loads of ARGs in leachates from the three soils with long-term manure fertilization were significantly increased compared to the controls and were in the order of acidic soil > neutral soil > calcareous soil. SourceTracker analyses revealed that manured soil was the predominant source of the ARGs in the soil leachate samples. Pseudomonas, Anaeromyxobacter, IMCC26256, and MND1 were identified as the dominant potential hosts responsible for the vertical migration and leaching of ARGs in the three soils. PiecewiseSEM analysis further showed that long-term manure fertilization affected the vertical migration of ARGs during rainfall mainly by altering soil properties (i.e., pH, soil organic carbon, and sand). Our results suggest that the ARGs in soils with long-term manure fertilization are a significant potential source of ARG pollution in groundwater, and the measures should be taken to mitigate the vertical migration and leaching of ARGs during rainfall.

Nitrogen reduction enhances crop productivity, decreases soil nitrogen loss and optimize its balance in wheat-maize cropping area of the Loess Plateau, China

In winter wheat-summer maize double cropping, fertilization changes the nitrogen (N) balance in the soil N pool, grain N uptake, N loss, and nitrogen use efficiency (NUE), ultimately impacting crop productivity and environmental health. For agricultural systems to maintain yields at lower environmental costs, N budgets must be balanced. Still, there is a deficiency in the reporting of N budgets of farming systems that incorporate all N flows. We evaluated the effects of various N fertilizer application rates on soil N balance and crop productivity in the 2017–2021 winter wheat-summer maize growing seasons. These rates included non-N fertilization (N0), 75 kg·N·ha−1 (N75), 150 kg·N·ha−1 (N150), 225 kg·N·ha−1 (N225), and conventional N fertilizer application rate, 300 kg·N·ha−1 (N300). Our analysis was based on a long-term field fertilization experiment and in-situ observation (established in 2010). The results show that fertilization significantly increased crop yields (wheat: 29.2 %–97.6 %; maize:25.4 %–98.1 %; annal: 27.0 %–96.7 %), among which N225 showed the highest increase value, compared with N0. Moreover, the N225 maximized grain N uptake by 201.0 %, reducing N losses and increasing N sequestration compared to the conventional N application rate of N300. N balance changes from negative to positive as the N application rate increases (wheat: −63.78–85.24 kg·ha−1; maize: −55.77–82.25 kg·ha−1; annal: −119.58–167.46 kg·ha−1·yr−1). Combining years of N inputs and outputs, the N225 is more balanced. Therefore, our study shows that an appropriate reduction of N fertilizer (N225) can help maintain agricultural productivity and promote N sequestration in farmland by reducing environmental N loss. Maintaining the virtuous cycle of N in the farmland ecosystem is beneficial and essential for the efficient utilization, high yield, and sustainable development of farmland resources.

Assessing the Alteration of Soil Quality under Long-Term Fertilization Management in Farmland Soil: Integrating a Minimum Data Set and Developing New Biological Indicators

The key role of soil quality improvement in achieving sustainable agricultural development based on highly intensive use of farmland is increasingly being recognized, as is the ponderance of suitable evaluation of the soil quality. The overarching goal of this study was to determine an accurate assessment framework by the comparison of the scoring function (linear and non-linear) and integration method (area and weighted additive), which integrally evaluates the soil quality of an eleven-year field fertilization experiment (including CK, no fertilizer; CF, conventional fertilization; SF, formulated fertilization; SFO, SF with organic fertilizer). Thirty-three properties, including eighteen physiochemical-related and fifteen biological-related properties, associated with soil functions were measured as potential soil quality indicators, and the soil multifunctionality (SMF) was applied to validate the soil quality indices (SQIs). Principal component analysis and relationship analysis were used with indicators sensitive to management to determine a minimum data set (MDS). The results showed that the electrical conductivity, large macroaggregate-associated total nitrogen, small macroaggregate-associated organic carbon, carbon fixation, and enzyme activities of phenol oxidase and cellulase were chosen as the MDS. All the SQIs were significantly correlated with the SMF (p < 0.05). The fertilization strategies affected most indicators in different ways, and the index developed using the non-linear function and weighted additive integration method (SQI-NL) had the best sensibility and discriminability. The SQI value with the SQI-NL-MDS method was higher following the fertilization treatments than that of no fertilizer (p < 0.05), and the treatment of the organic fertilizer had the highest SQI value (0.66). Soil quality evaluation in long-term fertilized farmland suggested that the soil quality constraints between treatments of synthetic and organic fertilizer are related to the soil functions of nutrient cycling and sustain biological activity due to their higher contribution rates to the SQI in the organic fertilizer treatment, which provides insights into ways to reduce the gap in soil quality. The framework method can provide an accurate quantitative tool for the evaluation of soil quality from the target indicators by bridging management objectives and field-level actions.

Impacts of fertilization methods on Salvia miltiorrhiza quality and characteristics of the epiphytic microbial community.

Plant epiphytic microorganisms have established a unique symbiotic relationship with plants, which has a significant impact on their growth, immune defense, and environmental adaptation. However, the impact of fertilization methods on the epiphytic microbial community and their correlation with the yield and quality of medicinal plant was still unclear. In current study, we conducted a field fertilization experiment and analyzed the composition of epiphytic bacterial and fungal communities employing high throughput sequencing data in different organs (roots, stems, and leaves) of Salvia miltiorrhiza, as well as their correlation with plant growth. The results showed that fertilization significantly affected the active ingredients and hormone content, soil physicochemical properties, and the composition of epiphytic microbial communities. After fertilization, the plant surface was enriched with a core microbial community mainly composed of bacteria from Firmicutes, Proteobacteria, and Actinobacteria, as well as fungi from Zygomycota and Ascomycota. Additionally, plant growth hormones were the principal factors leading to alterations in the epiphytic microbial community of S. miltiorrhiza. Thus, the most effective method of fertilization involved the application of base fertilizer in combination with foliar fertilizer. This study provides a new perspective for studying the correlation between microbial community function and the quality of S. miltiorrhiza, and also provides a theoretical basis for the cultivation and sustainable development of high-quality medicinal plants.

Comparative analysis of archival data on yields of main field crops from fertilizer experiments on different soil types in Bulgaria

The main aim of the study was to systematize and summarize archival data on yields from main field crops from multiple fertilizer experiments of Nikola Poushkarov ISSAPP on various soil types in Bulgaria. A large set of results from the field fertilizer experiments carried out on four different soil types: Calcareous Chernozem (Trastenik village), Haplic Chernozem (Gorni Dabnik village), Haplic Luvisol (Nikolaevo village) and Planosol (Sekirovo village) in the geographical network of Bulgaria of the Nikola Poushkarov ISSAPP has been accumulated. Eight fertilization variants were tested with annual application of potassium (0, 8, 16 and 32 kg/da K2 O) on two backgrounds of nitrogen (N) and phosphorus (P) fertilization. Crop rotation during the individual years was as follows: wheat (Triticum aestivum L.), maize (Zea mays L.), sunflower (Helianthus annuus L.) and sugar beet (Beta vulgaris L.), grown under non-irrigation conditions. Optimum rates of fertilization with the main nutrients, N, P and K have been established for the different soil types. There are complex interactions between the different rates of fertilization with the main macronutrients and this has a significant impact on the quantity and quality of agricultural crop yields. The difference in yields between the two investigated periods (1963-1970 and 1971-1975), at the same levels of fertilization, shows that the level of yields and accordingly, the use of nutrients are also determined to a significant extent by the climatic conditions. With an increase in the fertilizer rate, the yields also increase, and the rates of 16 kg and 32 kg K2 O remain the most effective, regardless of the occurrence of potassium accumulation in these variants. This was also confirmed by the results of the analysis of variance of the yields of cultivated crops. There was a pronounced increase of the effect of potassium fertilization in soils less supplied with this element, i.e. the Haplic Luvisol (Nikolaevo village) and Planosol (Sekirovo village). The effect of the potassium fertilization increases and expands in well supplied with potassium soils, but possessing unfavorable conditions for nutrition with this element, as in the case with the Calcareous Chernozem (Trastenik village). There was also an effect of potassium fertilization, although inconsistent, in soils well supplied with potassium, such as Haplic Chernozem (Gorni Dabnik village).

Soil multifunctionality predicted by bacterial network complexity explains differences in wheat productivity induced by fertilization management

Fertilization will cause changes in crop growth, soil microbial community and multiple ecosystem functions, but it is unclear whether and how the optimal productivity obtained by manure application and optimizing nitrogen is driven by microbial community and ecosystem multifunctionality. We explore this mechanism based on a field fertilization experiment using a split-plot design that began in 2014 with five N rates (N0, N75, N150, N225, N300) as main plots and two manure rates (M0, NPK group; M1, MNPK group) as subplots, respectively. In general, (1) grain yield was parabolically related to the N application rate. The N rates that obtained the highest yield were 150 kg ha−1 and 225 kg ha−1 for the MNPK and NPK groups, respectively. The average yield of the MNPK group was 10.5% higher than that of the NPK group. (2) Long-term fertilization management resulted in regular changes in soil multifunctionality (SMF) and the properties of various microbial communities. The richness, network complexity and soil multifunctionality of bacterial and fungal communities also increased initially and then decreased as the N rate. On average, the response ratio of soil multifunctionality to N75, N150, N225, N300 (control is N0) and M1 (control is M0) were 0.11, 0.41, 0.53, 0.44 and 1.19, respectively. The soil multifunctionality of MNPK was 260%, 722% and 101% higher than that of NPK at the tillering, jointing and harvest stages, respectively. (3) Soil multifunctionality not only always had a significant positive effect on aboveground biomass at all growth stages, but also had significant positive correlations with bacterial richness and network complexity. Based on the existing framework, we further demonstrated that high microbial richness supports multifunctionality by ensuring strong associative complexity among microorganisms. However, only bacterial network complexity always positively drove soil multifunctionality and indirectly influenced wheat growth at all growth stages in SEMs where multiple drivers were considered simultaneously (i.e., pH, SOC and biological factors). Random forest regression analysis showed that rare bacterial taxa had stronger predictive effects on soil multifunctionality than abundant taxa. Our results validate that M1N150 can ensure high yield in the study area while maintaining a high level of ecosystem function in the soil, which also contributes to the reduction of adverse environmental risks caused by fertilizer application. Importantly, the potential of microbial network complexity, especially bacterial network complexity, to influence crop growth by driving farmland ecosystem functions deserves to be explored under different crop types, cropping systems, and irrigation conditions, compared to previous microbial richness that has been simply quantified.

Optimization of fertilization scheme based on sustainable wheat productivity and minor nitrate residue in organic dry farming: An empirical study

The substitution of chemical nitrogen fertilizer with manure holds the potential for a synergistic rise in wheat grain yield and protein concentration, while minimizing residual nitrate in soil. We conducted a 6-year field fertilization experiment including two manure treatments (with or without) and five nitrogen applications rates (0, 60, 120, 180 and 240 kg ha−1). The study investigated the impact of single chemical nitrogen (CN) and manure substitution for nitrogen fertilizer (MN) on the grain yield (GY), grain protein concentration (GPC), plant nitrogen uptake (PNupt) and plant nitrogen requirement (PNR) of wheat, and the dynamic change of soil nitrate-N. The findings revealed that: (1) the MN demonstrated a greater advantage over CN, as evidenced by a 13.4–16.0 % increase in GY, a 2.6–3.8 % increase in GPC, a 7.2–15.7 % increase in PNupt and a 1.5–4.7 % reduction in PNR. (2) Soil nitrate accumulation (SNA) significantly increased when fertilizer rates ≥180 kg ha−1 and the peak annually shifted to deeper layer. The MN increased the SNA0–100 by 20.9–21.8 %, but significantly reduced SNA0–200 by 11.8–13.5 % compared with the CN. Topsoil nitrate content (SNC0–20) can be adopted as a substitute for SNA0–100 to make the fertilization schedule convenient. (3) Regression analysis revealed (taking the MN for example) that the optimum N rates for the maximum GY (5417 kg ha−1) and GPC (15.3 %) were 164 and 211 kg N ha−1, respectively. The nitrate-N safety threshold was 62 kg ha−1 at the fertilizer rate of 89 kg N ha−1. Based on this, nitrogen fertilizer input reduced by 44.8–57.2 % and SNA0–200 by 17.9–33.6 %, with achieving 91.8–95.0 % of maximum GY and 89.7–92.9 % of maximum GPC. Substituting manure for nitrogen fertilizer achieved the potential of maintaining the grain yield and protein concentration while the minimization in soil nitrate residue. This study offers a feasible way for fertilization recommendation and nitrate residue controlling in dry farming.

Green manuring relocates microbiomes in driving the soil functionality of nitrogen cycling to obtain preferable grain yields in thirty years.

Fertilizers are widely used to produce more food, inevitably altering the diversity and composition of soil organisms. The role of soil biodiversity in controlling multiple ecosystem services remains unclear, especially after decades of fertilization. Here, we assess the contribution of the soil functionalities of carbon (C), nitrogen (N), and phosphorus (P) cycling to crop production and explore how soil organisms control these functionalities in a 33-year field fertilization experiment. The long-term application of green manure or cow manure produced wheat yields equivalent to those obtained with chemical N, with the former providing higher soil functions and allowing the functionality of N cycling (especially soil N mineralization and biological N fixation) to control wheat production. The keystone phylotypes within the global network rather than the overall microbial community dominated the soil multifunctionality and functionality of C, N, and P cycling across the soil profile (0-100 cm). We further confirmed that these keystone phylotypes consisted of many metabolic pathways of nutrient cycling and essential microbes involved in organic C mineralization, N2O release, and biological N fixation. The chemical N, green manure, and cow manure resulted in the highest abundances of amoB, nifH, and GH48 genes and Nitrosomonadaceae, Azospirillaceae, and Sphingomonadaceae within the keystone phylotypes, and these microbes were significantly and positively correlated with N2O release, N fixation, and organic C mineralization, respectively. Moreover, our results demonstrated that organic fertilization increased the effects of the network size and keystone phylotypes on the subsoil functions by facilitating the migration of soil microorganisms across the soil profiles and green manure with the highest migration rates. This study highlights the importance of the functionality of N cycling in controlling crop production and keystone phylotypes in regulating soil functions, and provides selectable fertilization strategies for maintaining crop production and soil functions across soil profiles in agricultural ecosystems.

Chemical fertilizer reduction combined with organic fertilizer affects the soil microbial community and diversity and yield of cotton.

The soil microbial community plays an important role in modulating cotton soil fertility. However, the effects of chemical fertilizer combined with organic fertilizer on soil chemical properties, microbial community structure, and crop yield and quality in arid areas are still unclear. This study aimed to explore the effects of different organic fertilizers on soil microbial community structure and diversity and cotton growth and yield. High-throughput sequencing was used to study the soil bacteria and fungi in different growth stages of cotton. The field fertilization experiment had five treatments. The results indicated that the treatments of chemical fertilizer reduction combined with organic fertilizer significantly increased soil available nitrogen and phosphorus in cotton field. There were significant differences in the abundance of the bacterial and fungal communities in the dominant phyla among the treatments. At the phyla level, there were not significantly different in the diversity of bacteria and fungi among treatments. There were significant differences in the composition and diversity of bacterial and fungal communities during the entire cotton growth period (p = 0.001). The rhizosphere bacterial and fungal community structure was significantly affected by soil TK, NH4+, AK, TP, AN, and NO3-. The different fertilization treatments strongly influenced the modular structure of the soil bacterial and fungal community co-occurrence network. A reduction in chemical fertilizer combined with organic fertilizer significantly improved cotton stem diameter and seed yield, and the effect of the biological organic fertilizer on plant growth and yield formation was greater than that of ordinary organic fertilizer. This study provide a scientific and technical basis for the establishment of environmentally friendly green fertilization technology for cotton in arid areas and the promotion of sustainable development of cotton industry.

Nutrient use efficiency has decreased in southwest China since 2009 with increasing risk of nutrient excess

The optimal application of nutrients, such as nitrogen and phosphorus, to the soil is crucial for achieving high crop yields with minimal environmental impact. However, the effect of spatio-temporal changes in soil nutrient supply on crop yield is poorly understood in China. Here, we present a framework that combines environmental data, fertilizer field experiments, and machine learning to estimate the rice yield responses to different nutrient conditions and overall farmland nutrient sustainability in southwest China from 2009 to 2019. The results show that the fertilizer input has contributed to the long-term increase in rice yield over the past ten years. The fertilizer use has increased rice yield by 2.3–2.4 tons per hectare per year. However, the nutrient use efficiency decreased, with the fertilizer contribution ratio declining from 29.3% in 2009 to 27.5% in 2019. Further, 19% of the rice-growing farmlands are at risk of nutrient excess, and 36% are at risk of nutrient degradation. Controlling nitrogen and phosphorus input is key to nutrient regulation, and our approach may guide the sustainable use of nutrient resources on farmlands.

Double-cropping, tillage and nitrogen fertilization effects on soil CO2 and CH4 emissions

Double-cropping is increasingly embraced for its economic advantages in irrigated crops within the Ebro Valley region. However, the implications of this practice for soil carbon dioxide (CO2) and methane (CH4) emissions remain poorly understood. This study aimed to assess the impact of legume-maize double-cropping on soil CO2 and CH4 emissions and to identify optimal tillage systems and nitrogen fertilization rates for enhancing soil carbon budget. Conducted in Agramunt (NE Spain), the research transformed a long-term tillage and nitrogen fertilization field experiment initiated in 1996 under rainfed conditions. It transitioned into a maize monocrop system in 2015 and a diversification experiment in 2018. Maize monocrop was compared to a legume-maize double-cropping with two tillage systems (conventional tillage and no-tillage) and three mineral nitrogen fertilization rates (zero, medium and high). The legumes used were pea for grain (2019), vetch for green manure (2020) and vetch for forage (2021). The use of legumes in the double-cropping system had a significant impact on CO2 fluxes. CO2 emissions in the double-cropping ranged from 250 to 8070 mg CO2-C m−2 day−1, while in the monocropping, the fluxes were in the range of 150–5790 mg CO2-C m−2 day−1. Due to the higher biomass production and extended crop cycle in the double-cropping, along with increased residue decomposition due to the higher amount of residue provided, the cumulative CO2 emissions were higher in the double-cropping. Within the double-cropping, the response of cumulative soil CO2 emissions to tillage depended on the legume used and residue management. For legumes with a low nitrogen content, conventional tillage resulted in lower cumulative CO2 emissions, while for legumes with a high nitrogen content, the lowest emissions were observed in the no-tillage system. The increased incorporation of crop residues in the combined approach of double-cropping and no-tillage led to a greater net ecosystem carbon budget, reaching 1960 kg C ha−1. However, the use of high or medium nitrogen fertilization rates did not have a significant impact on CO2 emissions or the net ecosystem carbon budget. Cumulative soil CH4 emissions were only affected by soil tillage in 2019 and 2021, with greater net CH4 uptake under no-tillage compared with conventional tillage. This work underlines the importance of using legume-maize double-cropping together with no-tillage and N fertilization reduction to control the soil CO2 and CH4 emission yields, while maintaining crop yields under Mediterranean conditions.

Organic amendment substitution improves the sustainability of wheat fields changed from cotton and vegetable fields

Long-term excessive use of chemical fertilizers and continuous cropping in vegetable and cotton production lead to a decline in farmland soil quality and crop productivity, endangering sustainable agricultural development. Organic amendment substitution (OAS) or farmland use change or can potentially enhance soil quality and crop yield. However, it remains unclear whether their combined application can improve the sustainability of wheat fields when changing from cotton and vegetable fields. In this study, continuous cropping cotton and vegetable fields were changed to wheat fields (C-W and V-W), and then field fertilization experiments (non-fertilization, NF; chemical fertilizer alone, CF; chemical fertilizer reduced by 20%, RF; and organic amendment substituted 20% of inorganic nitrogen, OAS) were conducted for three years (2018–2020) to explore their effects on wheat productivity and soil quality. The findings revealed that the combined farmland use change and fertilization improved soil quality in wheat fields compared to pre-change cotton and vegetable fields. OAS improved soil quality index (SQI-TDS by 0.36–0.82 and 0.32–0.82; SQI-IDS by 0.37–0.90 and 0.40–0.88) by improving soil properties and increasing microbial diversity compared to NF, CF and RF in C-W and V-W. Meanwhile, OAS increased nutrient use efficiency, crop productivity index (CPI, by 13.69%−72.46% and 8.52%−41.45%) and the sustainability index (SI, by 14.14%−49.35% and 12.56%−40.00%). Moreover, microbial biomass carbon and nitrogen (MBC and MBN), pH, available nitrogen (AN), soil organic carbon (SOC) and ACE index were key soil factors affecting yield. These indicators can be used to construct important dataset to simplify soil quality evaluation systems. Overall, the present study revealed the mechanism by which OAS improved wheat field sustainability by increasing wheat productivity and soil quality after farmland use changes, contributing to sustainable agricultural development. Moreover, it provides valuable reference methods and evaluation ideas for future research on farmland soil quality and sustainability evaluation.

Leaf nitrogen affects photosynthesis and water use efficiency similarly in nitrogen‐fixing and non‐fixing trees

Abstract Nitrogen (N)‐fixing trees are thought to break a basic rule of leaf economics: higher leaf N concentrations do not translate into higher rates of carbon assimilation. Understanding how leaf N affects photosynthesis and water use efficiency (WUE) in this ecologically important group is critical. We grew six N‐fixing and four non‐fixing tree species for 4–5 years at four fertilization treatments in field experiments in temperate and tropical regions to assess how functional type (N fixer vs. non‐fixer) and N limitation affected leaf N and how leaf N affected light‐saturated photosynthesis (Asat), stomatal conductance (gsw) and WUE (WUEi and δ13C). Asat, WUEi and δ13C, but not gsw, increased with higher leaf N. Surprisingly, N‐fixing and non‐fixing trees displayed similar scaling between leaf N and these physiological variables, and this finding was supported by reanalysis of a global dataset. N fixers generally had higher leaf N than non‐fixers, even when non‐fixers were not N‐limited at the leaf level. Leaf‐level N limitation did not alter the relationship of Asat, gsw, WUEi and δ13C with leaf N, although it did affect the photosynthetic N use efficiency. Higher WUE was associated with higher productivity, whereas higher Asat was not. Synthesis: The ecological success of N‐fixing trees depends on the effect of leaf N on carbon gain and water loss. Using a field fertilization experiment and reanalysis of a global dataset, we show that high leaf‐level photosynthesis and WUE in N fixers stems from their higher average leaf N, rather than a difference between N fixers and non‐fixers in the scaling of photosynthesis and WUE with leaf N. By clarifying the mechanism by which N fixers achieve and benefit from high WUE, our results further the understanding of global N fixer distributions.

Soil organic carbon priming co-regulated by labile carbon input level and long-term fertilization history

Labile carbon (C) input and fertilization have important consequences for soil organic matter (SOM) decomposition via the priming effect (PE), thereby impacting soil fertility and C sequestration. However, it remains largely uncertain on how the labile C input levels interact with long-term fertilization history to control PE intensity. To clarify this question, soil samples were collected from a 38-year fertilization field experiment (including five treatments: chemical nitrogen fertilizer, N; chemical fertilizer, NPK; manure, M1; 200 % manure, M2; NPK plus M2, NPKM2), with strongly altered soil physiochemical properties (i.e., soil aggregation, organic C and nutrient availability). These soil samples were incubated with three input levels of 13C-glucose (without glucose, control; low, 0.4 % SOC; high, 2.0 % SOC) to clarify the underlying mechanisms of PE. Results showed that the PE significantly increased with glucose input levels, with values increasing from negative or weak (−2.21 to 3.55 mg C g−1 SOC) at low input level to strongly positive (5.62 to 8.57 mg C g−1 SOC) at high input level across fertilization treatments. The increased PE intensity occurred along with decreased dissolved total nitrogen (DTN) contents and increased ratios of dissolved organic C to DTN, implying that the decline in N availability largely increased PE via enhanced microbial N mining from SOM. Compared to N and NPK treatments, the PE was significantly lower in the manure-amendment treatments, especially for low input level, due to more stable SOM by aggregate protection and higher N and phosphorus availability. These results suggested that manure application could alleviate SOM priming via increased soil C stability and nutrient availability. Collectively, our findings emphasize the importance of long-term fertilization-driven changes in labile C inputs, SOM stability, and nutrient availability in regulating PE and soil C dynamics. This knowledge advances our understanding of the long-term fertilization management for soil C sequestration.

Long-term fertilization promotes soil organic nitrogen accumulation by increasing the abundance of keystone microbial cluster across aggregates

Nitrogen (N) in soil mainly occurs in organic forms, with soil organic nitrogen (SON) playing an essential role in supplying N to crops. However, it is unclear how the content and distribution of SON vary among different aggregate sizes, and how SON content is related to soil microorganisms. In this study, we investigated the associations between SON content and various microbial community characteristics across different aggregate sizes using data from a long-term field fertilization experiment in paddy soils. We also performed functional prediction to explore potential microbial mechanisms underlying SON accumulation. The results showed that SON content decreased as aggregate size decreased, with macroaggregates having the highest SON content and the silt-clay fraction having the lowest. Furthermore, our linear regression and structural equation modeling analysis revealed that keystone microbial clusters (highly interconnected taxa within Firmicutes, Proteobacteria, Chloroflexi, Actinobacteriota, and Ascomycota) were significantly correlated with SON content. Finally, functional prediction analysis suggested that this relationship may be due, at least in part, to the large number of metabolic pathways involved in biosynthesis of N-containing compounds present in keystone microbial clusters. Overall, our study highlights the importance of keystone microbial clusters in influencing the accumulation of SON and contributes to our understanding of soil N biogeochemical cycling.

Coupling amendment of biochar and organic fertilizers increases maize yield and phosphorus uptake by regulating soil phosphatase activity and phosphorus-acquiring microbiota

Biochar and organic fertilizers are important alternatives to mineral fertilizers. Thus, it is important to understand how the co-application of biochar and organic fertilizers influences crop productivity and soil-plant phosphorus (P) trade-offs. Herein, we conducted a field fertilization experiment for eight years with maize-cabbage rotation. This experiment contained five treatments: no fertilization (CK), mineral fertilizers (CF), CF + biochar (BF), 20% substitution of mineral nitrogen (N) with organic fertilizers (OF), and OF + biochar (BOF). The fertilization regimes of all plots were maintained since 2013. The results showed that soil P pool composition but not P bioavailability differed significantly between the five treatments. Compared with the CF treatment, soil labile-P content in the BF, OF, and BOF treatments significantly increased by 12–23% and soil stable-P content decreased by 13–19%. Besides, the soil moderately labile-P content in the OF and BOF significantly decreased by 40% and 10% and increased by 31% in the BF as compared to the CF. The activities of soil acid (ACP) and alkaline phosphatase (ALP) in the BF, OF, and BOF significantly increased by 8–44% and 16–49% respectively compared to the CK. Furthermore, the abundance of P-acquiring genes (bpp, phoD, phoX, ppx, ppk, and phnK) in the BF, OF, and BOF increased by 22–114% compared to the CK. Plant P uptake and maize yield were significantly correlated with soil ACP and ALP activities as well as the abundance of phnK, ppx, phoD, phoX, and pqqC genes but not to the contents of soil P components. In conclusion, the co-application of biochar and organic fertilizer on maize productivity increases was mainly related to the improvement of soil phosphatase activity and P-acquiring gene abundance.

Sewage sludge application stimulated soil N2O emissions with a low heavy metal pollution risk in Eucalyptus plantations

Sewage sludge (SS) has been extensively used as an alternative fertilizer in forest plantations, which are beneficial in supplying timbers and mitigating climate change. However, whether the extra nitrogen (N) applied by SS would enhance the soil nitrous oxide (N2O) emission, an important greenhouse gas, in forest plantations have not been well understood. The objective of this study is to evaluate the ecological effects of SS application on soils, by investigating the soil N2O emission and the toxicity of the potentially toxic elements (PTEs) in soil. A field fertilization experiment was conducted in Eucalyptus plantations with four fertilization rates (0 kg m−2, 1.5 kg m−2, 3.0 kg m−2, and 4.5 kg m−2). The soil N2O emissions were monitored at a soil depth of 0–10 cm using static chamber method, soil chemical properties, and PTEs were determined at soil depths of 0–10 cm, 10–20 cm, and 20–40 cm. The average soil N2O emission rate was 8.1 μg N2O–N h−1 m−2 in plots without SS application (control). The application of SS significantly increased the soil N2O emissions by 7–10 times as to control. The increased N2O emissions were positively related to the soil total phosphorus and nitrogen and negatively correlated with copper and zinc, which increased with the SS application. However, the potential ecological risk index (Ei) and the comprehensive potential ecological risk index (RI) of PTEs were lower than 40 and 150 respectively, which indicating a low toxicity of PTEs to soil health. After seven months of SS application, the priming effects of SS on soil N2O emissions gradually diminished. These findings suggest that the application of SS may increase N2O emissions at the initial stages of application (<7 months) and may have a low PTEs pollution risk, even at a high SS addition rate (4.5 kg m−2).

Mineral-microbial interactions in nine-year organic fertilization field experiment: a mechanism for carbon storage in saline-alkaline paddy soil

Mineral-microbial interactions in nine-year organic fertilization field experiment: a mechanism for carbon storage in saline-alkaline paddy soil

Different responses of nitrous oxide emissions to liming and manure amendment of an acidic ultisol are controlled by autotrophic and heterotrophic nitrification

Long-term lime and manure amendment can alleviate soil acidification, but their impacts on nitrous oxide (N2O) emissions and their production pathways remain largely unclear. Here, a 15N tracing study was conducted to explore the effect of lime and manure amendment on N2O production pathways and gross nitrogen (N) transformation rates of an acidic Ultisol. Soils were sampled from a 33-year field fertilization experiment, including three treatments of mineral NPK fertilizer (NPK), NPK plus lime (NPKL), and NPK plus manure (NPKM). Compared to NPK, N2O emissions increased by 25.2% for NPKL but decreased by 22.1% for NPKM, indicating that different pH-raising substances may have different effects on N2O emissions. The 15N tracing analysis indicated that heterotrophic nitrification-derived N2O played a dominant role in N2O emissions while NPKL significantly increased autotrophic nitrification-derived N2O production. The increased relative contribution of autotrophic nitrification to N2O emissions by NPKL resulted in an increase of N2O emissions in the acidic Ultisol. In contrast, NPKM decreased heterotrophic nitrification and autotrophic nitrification-derived N2O production, leading to a decrease of N2O emissions. Our results show that lime and manure amendment can have different impacts on N2O emissions due to their differential effects on autotrophic and heterotrophic nitrification, providing important insights for the sustainable management of acidic arable soils.