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Combined organic and inorganic fertilization can improve soil fertility in coal mine reclamation areas. However, the contribution of the bacterial community (especially its occurrence patterns) to soil physicochemical properties and enzyme activity needs further evaluation. The objective of this research was to clarify the bacterial community diversity, composition, and intraspecific interactions in response to combined organic and inorganic fertilizer application in coal mine reclamation areas in the Loess Hilly Region, China. Maize rhizosphere soil samples were collected under four fertilization regimes (CK, no fertilization control; NPK, compound inorganic fertilizer; M, organic fertilizer; and NPKM, combined organic and inorganic fertilization) in a 10-year field experiment in Gujiao city, Shanxi Province. Bacterial communities were characterized using high-throughput sequencing of the 16S rRNA gene V3–V4 region. A cross-treatment Spearman correlation network was constructed to explore the bacterial co-occurrence patterns. Compared with CK, NPK, M, and NPKM decreased the pH by 0.59%, 2.27%, and 0.12%; increased the soil organic carbon by 11.25%, 11.69%, and 27.05%; and significantly decreased the bacterial Shannon diversity by 3.68%, 0.14%, and 3.54%, respectively. Compared with CK, NPKM significantly increased sucrase, urease, and alkaline phosphatase activities (p < 0.05). Critically, oligotrophic Acidobacteria were significantly more abundant in CK than in the other treatments. Gemmatimonadetes were more abundant in NPK and M, and Actinobacteria, Bacteroidota, and Patescibacteria were more abundant in NPKM. In addition, network analysis revealed that the keystone taxa in the different fertilization treatments belonged to different network modules and were significantly correlated with soil nutrient content and enzyme activity. Simultaneously, the Actinobacteria enriched in NPKM formed specific clusters through strong symbiosis, and there were significant positive correlations among sucrase, urease, and alkaline phosphatase. In summary, long-term combined organic and inorganic fertilization improved maize rhizosphere soil fertility by regulating enzyme activity, bacterial community composition, and bacterial species interactions in coal mine reclamation areas in the Loess Hilly Region. [ABSTRACT FROM AUTHOR]

In order to quantify the effect of biochar application on soil pH and provide theoretical basis for biochar application in soil improvement and fertility cultivation, based on the electronic databases CNKI, Wanfang and Web of Science, 413 biochar on soil pH case studies based on the keywords "Biochar", "Biochar", "soil pH" and "soil pH" were collected from 59 published literatures. Meta-analysis was implied to quantify the effect degree of soil conditions, biochar characteristics and biochar application amount on soil pH. The results showed that, compared with no biochar application, biochar application could significantly increase soil pH by 8.70%. In the strongly acidic soil (4.5 shell residue biochar (7.02%) > wood biochar (6.61%) . The biochar prepared at ≤400 °C had the best promotion effect of 15.26% under different pyrolysis temperatures, while, the increasing effect decreased with the increase of pyrolysis temperature, such as the pyrolysis temperature was between 400-700 °C. The increasing effect was higher in 3 months, then the increase gradually slowed down.These results indicated that in strongly acidic soil (4.5

Application of manure can increase soybean yield and soil fertility. There are significant differences in soybean yield and soil fertility in China due to the influence of region, application rate of manure, type of manure etc. However, the reasons for these differences are still not clear. In order to find out the effect of manure fertilizer application on soybean yield and soil fertility in different regions and management measures in China, and the main factors of yield increase effect, this study collected data on a national scale for integrated analysis. According to the searching criteria, 37 literatures including 119 groups of data on the effect of manure application on soybean yield and 11 literatures including 148 groups of data on the effects of manure application on soil nutrients were obtained. The enhanced boosted regression tree (BRT) model was used to quantify the importance of climate factors, soil properties and manure application measures on soybean yield increase. The average soybean yield increased by 12.9% after application of manure in different regions, with the highest yield in south China (18.7%) and followed by North China (14.8%), Northwest China (13.6%) and Northeast China (12.0%). When the application rate of manure was more than 5 000 kg⋅hm-2, the increase of soybean yield was 18.5%. Soybean yield increased by 24.9% after the application of cow manure, followed by the application of pig manure (17.6%), commercial manure (15.3%), chicken manure (12.7%) and manure (8.8%). The average soybean yield was 2 224 kg⋅hm-2 with no fertilizer, whereas it increased by 20.4% to the amount 2 518 kg⋅hm-2 with applying manure alone. The average soybean yield was 2 259 kg⋅hm-2 under the application of chemical fertilizer, whereas it increased by 9.1% to the amount 2 558 kg⋅hm-2 under the combined application of manure and chemical fertilizer. Manure application significantly increased soil available P (43.5%), total P (13.3%) and organic matter (11.0%), but had no significant effect on soil available K (9.4%), alkali hydrolyzable nitrogen (3.4%), pH (2.1%) and total K (1.2%). Based on the BRT results, the BRT model explained 52.83% of soybean yield differences in China. Among them, the application rate of manure had the greatest impact on soybean yield, accounting for 47.0% of the variation, followed by soil properties (41.0%) and climate factors (12.0%). In general, the application of manure (including the single application of manure and combined application of manure and chemical fertilizer) could significantly increase soybean yield, with the largest increase in South China and with the highest increasing production benefit under the application of cow manure. Soybean yield was mostly affected by the application rate of manure. Additionally, the available P, total P and organic matter contents in soybean soil significantly increased under the application of manure. [ABSTRACT FROM AUTHOR]

The storage of soil organic carbon (SOC) in cropland soils is an essential strategy that serves the dual purpose of enhancing soil fertility and mitigating climate change. However, how the stability of stored carbon is altered under long-term fertilization has not been well understood, especially in the double rice cropping system in Chinese paddy soils. In this study, we explored the SOC storage and consequent stability of SOC under long-term fertilization. The soil samples were fractionated chemically to isolate various fractions and constituent pools of SOC (i.e., very labile C/VLC, labile C/LC, less labile C/LLC, and non-labile C/NLC). The following treatments were tested: control (CK), recommended rate of inorganic fertilizer (NPK), double the amount of recommended rate of inorganic fertilizer (2NPK), and NPK combined with manure (NPKM). The results showed that, relative to the initial level, the application of NPKM significantly improved the SOC storage as compared to the control. The long-term NPKM increased the total SOC in the paddy soil and this increased SOC was mainly stored in LLC, as revealed by the highest increase (142%) over the control. Furthermore, the highest proportion of labile pool was associated with unfertilized CK, while the reverse was true for the recalcitrant pool, which was highest under NPKM. This supports the role of combining manure with NPK to improve the stability of SOC, further verified by the high recalcitrance index under NPKM (56.75% for 0–20 cm and 57.69% for 20–40 cm) as compared to the control. [ABSTRACT FROM AUTHOR]

Lime (calcium oxide), animal manure and crop straw soil treatments have been shown to ameliorate soil acidity, yet their effectiveness at concurrently enhancing soil fertility status and improving crop yields is less well understood. In this study, an acidic nutrient deficient red soil (Ferralic Cambisol) received these treatments at various dosage rates (% of DW soil) in pot experiments with maize plants. Lime was applied at four dosage rates (0.05%, 0.10%, 0.15% and 0.20%), pig manure at three rates (0.50%, 1.00% and 1.50%), maize straw or milk vetch at two rates (0.50% and 1.00%) and combinations of lime (0.10% or 0.15%) with maize straw (0.50%) and/or pig manure (0.50%). Soils treated with and without chemical fertilizers were also included as controls. Measurements of soil pH, exchangeable acidity, plant available nutrients and maize shoot biomass were recorded. Maize shoot biomass increased by 4.7–7.6 times under pig manure treatments, 1.1–1.6 times under milk vetch, 0.4–1.5 times under lime and 1.1–6.2 times under combination treatments, compared with the control. Soil pH increased by 0.5–0.9 units under lime, by 0.2–0.4 units under pig manure and by 0.7 pH units under the combination treatment relative to the control. Variance partitioning analysis showed that on an individual basis, soil acidity amelioration (pH, exchangeable H+ and Al3+) or nutrient input (C, N, P, K, Ca, Mg, Zn) explained only 4.3% and 5.6% of improved maize growth, respectively. Whereas, their interaction explained 85.9% of the variation. We also report that the over‐application of pig manure could lead to P saturation and negative impacts on aquatic systems in the wider environment. Therefore, we recommend a combination of lime, pig manure and straw provides an optimal solution for addressing soil acidity and limiting P saturation in acid soils. [ABSTRACT FROM AUTHOR]

The effect and relative contributions of C and P inputs on soil microbial biomass P (MBP) accumulation were studied in three long-term soil fertility experiments with various soil and climate characteristics at Qiyang, Yangling, and Wulumuqi. The maximum of soil MBP in all three sites was 47.8 mg P kg-1. The MBP accumulated per unit in soil (mg P kg-1 soil) was correlated with a 4.91 mg kg-1 increase in Olsen P. For each unit increase in P surplus (kg P ha-1), manure C (kg C ha-1), and stubble C (kg C ha-1), MBP accumulation increased by 330, 3.7, and 13 units (μg P kg-1 soil), respectively. The soil MBP was positively correlated with crop yield and P uptake, making the soil MBP a useful soil P fertility index. The critical levels of the soil MBP pool were 140 kg ha-1, 57–62 kg ha-1, and 33–35 kg ha-1 in acidic red soil, loessial soil, and grey desert soil, respectively. This is the first report to establish a quantitative index of soil fertility based on the soil MBP pool. Our findings demonstrate that C input is a good driver of soil MBP accumulation. Integration of the soil MBP as an index of soil P fertility into agricultural P management is useful to help manage mineral P fertilizers as part of sustainable agricultural practices. [ABSTRACT FROM AUTHOR]

Purpose: Soil organic carbon (SOC) is an important parameter determining soil fertility and sustaining soil health. How C, N, and P contents and their stoichiometric ratios (C/N/P) regulate the nutrient availability, and SOC stabilization mechanisms have not been comprehensively explored, especially in response to long-term fertilization. The present study aimed to determine how the long-term mineral and manure fertilization influenced soil C/N/P ratios and various protection mechanisms underlying the stabilization of OC along with profile in a cropland soil. Materials and methods: The soil was sampled from five depths, viz., 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm, from plots comprising wheat-maize-soybean rotation system subjected to the long-term (35 years) manure and mineral fertilizer applications. Results and discussion: Results revealed that the soil C, N, P stoichiometry and their contents in topsoil depths (0–20 and 20–40 cm) and subsoil depths (40–60, 60–80, and 80–100 cm) varied significantly (p < 0.01) among the soil layers. Compared with CK, the C, N, and P contents were significantly higher (p < 0.05) in NPKM in the topsoil layers, while M alone increased these contents throughout the subsoil. Overall, the C, N, and P contents and their stoichiometry decreased with the increase in depth. Regression analysis showed that C/N, C/P, and N/P ratios associated significantly with the OC fractions in the topsoil layers only. These negative correlations indicated that these ratios significantly influence the C stabilization in the surface layers. However, the results warrant further investigations to study the relationship between soil and microbial stoichiometry and SOC at various depths. Conclusions: Long-term manure applications improved the C sequestration not only in the topsoil but also in the deep layers; hence, these facts can be considered relevant for fertilizer recommendations in cropping systems across China. [ABSTRACT FROM AUTHOR]

Highlights • Manure and synthetic fertilizer accounted for 39% and 21% of crop yields. • Synthetic fertilizer affected yields by weakly increasing soil nutrients and decreasing SOC and pH. • Manure affected yields by strongly increasing soil nutrients, SOC and pH. Abstract Fertilization is an important management strategy for crop yields by mediating soil fertility. However, rare studies quantitatively assessed the interactions among fertilization, crop yields, and soil fertility. Here, data from a 25-year fertilization experiment in the humid subtropical region of Southern China were used to evaluate and quantify the effect of fertilization on crop yields via soil fertility. Seven treatments were chosen: CK (non-fertilizer); N (synthetic nitrogen); NP (synthetic N and phosphorus); NPK (synthetic N, P and potassium); NPKM 1 (synthetic NPK with manure); 1.5NPKM 1 (1.5 times of NPKM 1); and M 2 (manure alone). Overall, the crop yields of wheat and maize under manure (1.36–1.58 and 3.85-5.82 Mg ha−1) were higher than those under CK (0.34 and 0.25 Mg ha−1) and synthetic fertilized treatments (0.27–0.97 and 0.48–2.65 Mg ha−1), as the averaged of 1991–2015. Higher SOC stocks were found under the NPKM 1 , 1.5NPKM 1 , and M 2 treatments with a pronounced increase in SOC over the first 10 years and stable over the last 15 years. By the boosted regression trees, manure, synthetic fertilizer and soil properties (SOC storage, soil pH, and soil nutrients) accounted for 39%, 21%, and 40% of the variation of the relative yield, respectively. Path analysis identified a network of inter-relations of manure, synthetic fertilizer, and soil properties in the relative yields. Compared to synthetic fertilized treatments, manure application strongly and positively affected the relative yield by increasing SOC storage, soil nutrients, and soil pH (path coefficients: 0.90, 0.88, and 0.76). These factors explained 72% of the crop yields' variance. These results suggest that manure application is a viable strategy for regulating crop yields due to its improvement in soil fertility. [ABSTRACT FROM AUTHOR]

The soil microbial biomass, atmospheric carbon dioxide and abundance of decomposer are influenced by rate and addition pattern of glucose carbon. The present study was conducted to evaluate the effect of single and repeated additions of glucose-C on soil microbial biomass carbon (SMBC) and CO2 response in black soil of China. The incubator study comprising of 116-days was conducted in different fertility levels of black soil of Jilin province of China, to determine the effects of glucose addition patterns viz single addition (2% glucose-C once application) and repeated addition (2% glucose-C in five splits) on soil microbial biomass carbon and CO2 accumulation. Fortygram air dried soil was filled into 250 ml Schott bottle and bottles were arranged in CRD-factorial design with 5 repeats. Factor (A), included glucose addition patterns (single & repeated additions). Factor (B), consisted of soil fertility levels: low, medium and high on the basis of soil organic carbon. Thereafter glucose-C (2%) solution was added drop wise to soil. The addition patterns showed positive response on SMBC, CO2 evolved and CO2 accumulation. Over all mean (low, medium and high fertility soils) of repeated addition depicted 32% and 0.92% higher values of SMBC than control and single additions, respectively. The CO2 emission of repeated addition was 21.3% higher in low fertility soil. The mean CO2 accumulation showed higher values in low fertility soil by single addition than repeated and control in all soils. Single glucose-C addition in combination with different soil fertility levels augmented the microbial biomass and triggered carbon mineralization for shorter period (up to 3 weeks). The repeated addition of glucose in combination with different soil fertility levels also enhanced soil microbial biomass carbon and CO2 in longer incubation period. It is concluded from this study that microbial starvation for organic carbon was very high hence; repeated addition may be suggested to meet C demand of microbes. [ABSTRACT FROM AUTHOR]

The phosphorus activation coefficient (PAC, the ratio of available P to total P) is an important indicator of soil P availability and the transformation of P fractions. Understanding the details of the PAC is useful to estimate soil available P status and to provide P management guidance. In this research, soils from five long-term (23 years) fertilization treatments in three croplands were selected to examine the relationships between the PAC and P fractions and to analyse the influencing factors. PAC was affected by both soil types and fertilization treatments. Compared to the unfertilized control (CK) treatment, long-term P application significantly increased the PAC, all of the inorganic P (Pi) fractions and most of the organic P (Po) fractions in all the three soils, particularly in chemical fertilizer combined with manure treatment (NPKM). The PAC was significantly correlated to all of the Pi fractions proportions (P<0.05) except for Dil. HCl-Pi and Conc. HCl-Pi. Compared with CK, the chemical P and chemical P combined with manure treatments increased the ratio of total Pi fractions to total Po fractions (Pit/Pot); furthermore, NPKM significantly increased the organic C (Co) content and decreased the Co/Pot ratio. Stepwise multiple regressions showed that PAC = 0.93 Co+0.69 Pit/Pot-0.07 Co/Pot-0.27CaCO3-3.79 (R2 = 0.924, P<0.001). In addition, the variance partitioning analysis showed that more variance of PAC is explained by soil factors (29.53%) than by P input (0.19%) and climate (0.25%) factors. Our findings demonstrate that P application increased the PAC by changing the Co content and the proportion of P fractions. Moreover, soil factors were the most important drivers of P transformations, and NPKM was optimal for improving soil fertility in Chinese croplands. [ABSTRACT FROM AUTHOR]

Long-term manure application is recognized as an efficient management practice to enhance soil organic carbon (SOC) accumulation and nitrogen (N) mineralization capacity. A field study was established in 1979 to understand the impact of long-term manure and/or chemical fertilizer application on soil fertility in a continuous maize cropping system. Soil samples were collected from field plots in 2012 from 9 fertilization treatments (M0CK, M0N, M0NPK, M30CK, M30N, M30NPK, M60CK, M60N, and M60NPK) where M0, M30, and M60 refer to manure applied at rates of 0, 30, and 60 t ha−1 yr−1, respectively; CK indicates no fertilizer; N and NPK refer to chemical fertilizer in the forms of either N or N plus phosphorus (P) and potassium (K). Soils were separated into three particle-size fractions (2000–250, 250–53, and <53 μm) by dry- and wet-sieving. A laboratory incubation study of these separated particle-size fractions was used to evaluate the effect of long-term manure, in combination with/without chemical fertilization application, on the accumulation and mineralization of SOC and total N in each fraction. Results showed that long-term manure application significantly increased SOC and total N content and enhanced C and N mineralization in the three particle-size fractions. The content of SOC and total N followed the order 2000–250 μm > 250–53μm > 53 μm fraction, whereas the amount of C and N mineralization followed the reverse order. In the <53 μm fraction, the M60NPK treatment significantly increased the amount of C and N mineralized (7.0 and 10.1 times, respectively) compared to the M0CK treatment. Long-term manure application, especially when combined with chemical fertilizers, resulted in increased soil microbial biomass C and N, and a decreased microbial metabolic quotient. Consequently, long-term manure fertilization was beneficial to both soil C and N turnover and microbial activity, and had significant effect on the microbial metabolic quotient. [ABSTRACT FROM AUTHOR]

Changes in total organic C ( C), water-soluble organic C ( C), microbial biomass C ( C), C mineralization, particulate organic C ( C), labile organic C ( C), C management index (CMI), and C storage in surface Hapli-Ustic Cambisol (0-20 cm) under straw incorporation after both 2- and 10-year durations were investigated in a maize ( Zea mays L.) field experiment in northeast China, in order to examine the effectiveness of these active C fractions and CMI as early indicators for total C change. The treatments included straw removal (0%S), 50% of straw incorporation (50%S), and 100% of straw incorporation (100%S). Under the straw incorporation, C concentration and C storage did not significantly change under 2-year duration, while were significantly increased under 10-year duration. However, C, total C mineralization ( C), C, and C, and CMI were significantly increased under the straw incorporation even after only 2-year duration, and the responses were more significant after 10-year duration. There were positive correlations between all these C indicators with each other. Our findings demonstrate that the measured active C fractions (except for C) and CMI can provide an early indication of change in total soil organic C induced by straw incorporation. [ABSTRACT FROM AUTHOR]

The effect of long-term fertilization and cropping on soil potassium (K)-supplying capacity has not been extensively studied. Five treatments [control, nitrogen (N), N-potassium (P), NPK, and NPK + manure (NPKM)] were used to evaluate the quantity and intensity relationship (Q/I) of K in black soil (Luvic Phaeozems soil) after a 15-year (1990-2005) long-term fertilization with a continuous corn cropping located in Changchun, Jilin Province, northeast China. Results showed that the long-term K fertilization of NPK or NPKM markedly increased the values of equilibrium active ratio (AR0K) and nonspecifically available K (-ΔK0) but decreased the potential buffering capacity (PBCK) value. Values of the AR0K and -ΔK0 in the NPK and NPKM treatment were about four and two times greater than those in the control, N, and NP treatments, respectively. Compared with the non-K fertilization, PBCK values were decreased by 40-49% under the K fertilization. The black soil suffered from K deficiency even with NPK fertilization as evidenced from the greater free energies of K+ exchanging for calcium (Ca2+) and magnesium (Mg2+) (-ΔG) (14.7-18.8 kJ mol-1) than the threshold value of 14.6 kJ mol-1, from the lower soil K+ saturation (1.34%-1.44%) than the critical value of 2.00%, and from the response of corn yield to K fertilization. Our results demonstrated that the increment of the current K application rate through fertilizer and/or manure is needed to improve corn yield in the long run in northeastern China. [ABSTRACT FROM AUTHOR]

Abstract: A 12-year field experiment was used to examine effects of return rates of crop straw residue on organic C sequestration by chemical fertilization in surface (0–20cm) soil. The tested soil was a Hapli-Ustic Cambosol (FAO taxonomy) and the used crop was maize (Zea mays L.). The four main treatments were consisted of a gradient of return rate of straw residue, namely 0%, 25%, 50% and 100% of shattered straw residue (referred to as 0%S, 25%S, 50%S and 100%S, respectively). The three sub-treatments contained unfertilized control (CK), unbalanced N fertilization (N) and balanced NPK fertilization (NPK). Along the gradient of straw return rate, topsoil C storage significantly increased. The balanced NPK fertilization was more effective in sequestrating topsoil C than the unbalanced N fertilization. Responses of topsoil C storage to the straw return and fertilization significantly increased with the experimental duration. With increasing straw return rates, C-sequestration effects of the N, and NPK treatments in topsoil changed from not significant to significant or from significant to more significant in statistics. Our findings demonstrate that C-sequestration effects of chemical fertilization in topsoil strongly depend on return regime of straw residue. [Copyright &y& Elsevier]

Potassium (K) fixation by seven soils, including black soil, fluvo-aquic soil, grey desert soil, loess soil, paddy soil, red soil and purple soil, was determined by laboratory simulation under a fifteen-year-period of long-term fertilization. Factors affecting soil K fixation were then discussed by factor analysis and stepwise regression. Magnitude of soil K fixation rate was as follows: the black soil > the purple soil > the loess soil > the fluvo-aquic soil > the paddy soil > the grey desert soil > the red soil. Our results showed that soil K fixation capacity was significantly affected by the clay mineral types in the soils. Potassium fixation capacity of soils, whose 2:1 layer silicates were dominant minerals, was affected by two components extracted by the method of principal component analysis: the first including soil available K, slow available K and K+ saturation, and the second including cation exchange capacity (CEC), soil organic matter (SOM) and <0.002 mm clay contents. Potassium fixation rate was mainly affected by K+ saturation and CEC with lower added K concentration (from 0.4 to 1.6 g/L), and by K+ saturation and <0.002 mm clay content with higher added K concentration (from 2.4 to 4.0 g/L). [ABSTRACT FROM AUTHOR]

A correction to this paper has been published: https://doi.org/10.1007/s00374-021-01563-3 [ABSTRACT FROM AUTHOR]

Potassium thiosulfate (KTS, K 2 S 2 O 3 ) has been shown to function as a nitrification inhibitor, thus has the potential to reduce nitrous oxide (N 2 O) emissions and play an important role in effective N management. The objective of this research was to determine the potential effects of KTS on N 2 O emissions and N transformation processes in comparison with commercial N transformation inhibitors (stabilizers). A laboratory incubation experiment was conducted using urea and ammonium nitrate (UAN) applied at 150 mg N kg − 1 in a Hanford sandy loam soil (coarse-loamy, mixed, superactive, nonacid, thermic Typic Xerorthents). Treatments included three rates of KTS (26, 51, and 102 mg S 2 O 3 2 − -S kg − 1 ), a urease and nitrification inhibitor (Agrotain® Plus), a nitrification inhibitor (N-Serve® 24), and an untreated control. Nitrous oxide emission, soil pH, and mineral N species were monitored for 35 days. Total N 2 O emissions were reduced significantly by all KTS treatments as a function of KTS rate. At 102 mg S 2 O 3 2 − -S kg − 1 , KTS reduced N 2 O emissions by 48% (0.18% of total inorganic N), which was statistically similar to the N-Serve® 24 treatment (60% reduction) although lower than Agrotain® Plus (78% reduction). The KTS resulted in significantly less unaccounted (total N) loss compared to the commercial inhibitors. If the N 2 O emissions reductions observed in this laboratory study are validated in the field, using KTS for this purpose can also provide a fertility benefit and may reduce total chemical inputs into agronomic systems. Future research needs to determine the effectiveness of thiosulfate for improving overall nutrient management while reducing N 2 O emissions under field conditions. [ABSTRACT FROM AUTHOR]

Soil microbes and nematodes are important components of soil biota that strongly affect agricultural productivity and sustainability. Currently, our knowledge on the response of soil biota to agricultural management is restricted. This study aimed to identify the relationship between microbial and nematode communities and explore the resource path that flows within the soil micro-food web under different fertilization practices in a winter-wheat/summer-maize rotation system. The experiment was a randomized complete block design with three replicates for each treatment that included unfertilized control; inorganic N, P and K fertilizer (NPK); NPK plus manure; and NPK plus maize straw. Soil samples were taken at a 0–20 cm depth when wheat and maize were harvested. The results showed that organic manure or maize straw combined with NPK fertilizers had positive effects on the soil microbial and nematode communities. For example, the incorporation of straw increased the fungal biomass. Long-term inorganic fertilization might restrain nematode biomass accumulation especially in fungivorous nematodes. The analysis of the metabolic footprints of nematodes suggested that the incorporation of straw could enhance the carbon resource flow into the soil food web by enhancing nematode biomass. Structural equation modeling analysis suggested that the bottom–up control from the microbial community to the nematode community was more obvious in the wheat season in comparison with the maize season. In addition, a relatively stronger predation relationship was found between omnivores–predators and bacterivores rather than fungivores. Our study suggests that organic management combined with NPK fertilization could effectively enhance the association between microbial and nematode communities, while a crop rotation system with maize may have a negative influence on the structure of the soil micro-food web. [ABSTRACT FROM AUTHOR]

• Straw-induced priming effect (PE) in two arable soils subjected to different fertilization regimes were investigated. • PE in soils under different fertilization regimes was negitively linked to the MAOC/SOC ratio. • The fungal abundances and ratio of fungal/bacterial growth correlated positively with SOM-derived CO 2. • The PE intensities were significantly lower in GZL soil compared to UQ soil. • Manure application greatly decreased PE via increased mineral protection and N availability. Rational chemical fertilizer application, especially combined with manure or straw amendment, serves as a key strategy for facilitating soil organic carbon (SOC) sequestration and soil fertility improvement. However, the effects of fertilization managements on the SOC priming induced by straw return remains unclear. Here, a microcosm was conducted to clarify the mechanisms of 13C-labeled maize straw addition effects on priming effect (PE) in two 29-year fertilized soils (Urumqi, UQ; Gongzhuling, GZL) subjected to four fertilization regimes (no fertilizer, CK; chemical fertilizers, NPK; combined application of NPK with straw, NPKS; combined application of NPK with manure, NPKM). Results showed that straw addition strongly increased native SOC decomposition by 15–44%, inducing positive PEs across sites and fertilization treatments. Compared to CK treatment, the NPK and NPKS treatments significantly increased PE by 26% and 98%, respectively, in the UQ soil, but had little effect on the PE in the GZL soil. The NPKM treatment strongly decreased PE by 51–55%, mainly due to the increased proportion of mineral-associated organic carbon (MAOC) and N availability, and decreased fungal abundances, as compared to the CK treatment in UQ and GZL soils. The PE intensities were significantly lower in GZL soil (5.1–11.7 mg CO 2 -C/g SOC) relative to UQ soil (13.7–54.8 mg CO 2 -C/g SOC), primarily due to the higher MAOC/SOC ratio and N availability in the former across fertilization regimes. Overall, manure application has the potential to mitigate soil C loss via priming, mainly resulting from enhanced SOC stabilization via mineral protection and increased N availability, thus facilitating SOC sequestration in agroecosystems. [ABSTRACT FROM AUTHOR]

Abstract Soil organic carbon (SOC) sequestration at subsurface layers (i.e. >20 cm) remains unclear under long-term fertilization practices. Based on long-term datasets of fertilization experiments in four typical Chinese croplands, representing soils with high fertility at Gongzhuling (GZL, black soil) and Chongqing (CQ, purple soil), and low fertility at Zhengzhou (ZZ, aquatic Chao soil) and Qiyang (QY, red soil), we calculated SOC storage, its change relative to initial condition (ΔSOC) in 0–20, 20–40 and 40–60 cm. We also obtained annual organic C inputs (OCI; stubble, roots and manure amendment) and derived soil C sequestration efficiency (CSE : the ratio of ΔSOC over OCI) in 0–20 cm and 0–60 cm. The fertilization treatments include cropping with no fertilization (CK), chemical nitrogen, phosphorus and potassium fertilizers (NPK) and combined chemical fertilizers and manure (NPKM). Results showed SOC stock significantly increased with fertilizations (i.e. initial, CK < NPK < NPKM). Relative to initial condition, surface (0–20 cm) and subsurface (20–60 cm) SOC stocks significantly decreased under CK at all sites except GZL, a site with elevated SOC stocks under all fertilizations and depths. Subsurface SOC stocks significantly increased at high fertility soils (i.e., GZL and CQ) but remained no change or significantly decreased at low fertility soils (i.e., ZZ and QY) under NPK and NPKM. Accordingly, CSE derived in 0–60 cm was consistently higher than that in 0–20 cm in high fertility soils but lower in low fertility soils. These results demonstrated that subsurface soils (20–60 cm) remained as C sinks in indigenously high fertility sites but experienced substantial C depletions in low fertility sites. This study informed the need to account for subsurface soil carbon changes for accurate estimates of soil C sequestration capacity under long-term fertilization. Highlights • Relative to initial condition, CK reduced SOC stocks in 0–60 cm in low fertility soils. • Relative to initial condition, NPK and NPKM enhanced SOC stocks in 0–60 cm in high fertility soils. • CSE is consistently greater at 0–60 cm than 0–20 cm in high fertility soils. • CSE is consistently lower at 0–60 cm than 0–20 cm in low fertility soils. [ABSTRACT FROM AUTHOR]

Understanding drivers of straw decomposition is essential for adopting appropriate management practice to improve soil fertility and promote carbon (C) sequestration in agricultural systems. However, predicting straw decomposition and characteristics is difficult because of the interactions between many factors related to straw properties, soil properties, and climate, especially under future climate change conditions. This study investigated the driving factors of straw decomposition of six types of crop straw including wheat, maize, rice, soybean, rape, and other straw by synthesizing 1642 paired data from 98 published papers at spatial and temporal scales across China. All the data derived from the field experiments using little bags over twelve years. Overall, despite large differences in climatic and soil properties, the remaining straw carbon (C, %) could be accurately represented by a three-exponent equation with thermal time (accumulative temperature). The lignin/nitrogen and lignin/phosphorus ratios of straw can be used to define the size of labile, intermediate, and recalcitrant C pool. The remaining C for an individual type of straw in the mild-temperature zone was higher than that in the warm-temperature and subtropical zone within one calendar year. The remaining straw C after one thermal year was 40.28%, 37.97%, 37.77%, 34.71%, 30.87%, and 27.99% for rice, soybean, rape, wheat, maize, and other straw, respectively. Soil available nitrogen and phosphorus influenced the remaining straw C at different decomposition stages. For one calendar year, the total amount of remaining straw C was estimated to be 29.41 Tg and future temperature increase of 2 °C could reduce the remaining straw C by 1.78 Tg. These findings confirmed the long-term straw decomposition could be mainly driven by temperature and straw quality, and quantitatively predicted by thermal time with the three-exponent equation for a wide array of straw types at spatial and temporal scales in agro-ecosystems of China. [ABSTRACT FROM AUTHOR]

Understanding the impact of long-term fertilization in different soil types and its effect on soil bacteria and crop production is critical for designing sustainable agricultural practices across diverse landscapes. Here, we investigated the impact of 25–37 years of continuous fertilizer treatments in three parent materials (Phaeozem, Cambisol, and Acrisol) on crop yield, soil properties, and soil bacteria (i.e., the total 16 S rRNA gene abundance, community structure, and its relationship with soil nutrient) across diverse Chinese agriculture areas. Four consistent treatments were included: unfertilized control (CK), inorganic nitrogen fertilizer (N), manure (M), and manure plus nitrogen (MN). The crop yields were significantly increased under MN treatments at the rates of 147 kg/ rotation (3 years) in Phaeozem and 90.6 kg/ rotation (1 year) in Acrisol, while the crop yields remained constant or decreased for CK and N treatments. The relative abundance of Acidobacteria_Gp6 and Planctomycete were significantly higher in manure treatments than in chemical fertilizer treatment. Through the structural equation model (SEM) analysis, species in module 1 were directly correlated with crop yield, and both module 2 and module 3 species were indirectly correlated with crop yield via SOM and NO 3 - contents. Proteobacteria, Acidobacteria, and Firmicutes were dominant bacterial groups in the three modules, respectively. This study reveals the complex role of keystone ecological clusters of soil bacteria on crop yields and identifies the common bacterial taxa that respond to long-term fertilization and thereby, as potential targets for improving soil fertility across soil types. • MN treatment had the best effect of increasing crop yield, and it was beneficial to maintain the abundance of soil bacteria. • Manure application significantly increased Terrisporobacter and Clostridium butyricum abundances at all sites. • The species in module 1, 2, and 3 directly or indirectly influence the grain yield via soil SOM and NO 3 - contents. • Proteobacteria, Acidobacteria, and Firmicutes were dominant bacterial groups in the three modules, respectively. [ABSTRACT FROM AUTHOR]

Labile carbon (C) inputs strongly alter soil organic matter (SOM) turnover by priming, thus affecting soil C dynamics and soil fertility in the long term. The frequency of labile C inputs is expected to affect the intensity of priming effect. We evaluated the effects of single versus repeated additions of 13C-labeled glucose (with added 13C corresponding to 2% of soil organic C content) to five soils with increasing fertility level on the intensity of priming effect and soil C balance. Repeated glucose addition induced 61–108% greater C mineralization due to positive priming than the single addition in all soils. The intensity of priming effect declined with soil fertility level and mineral nitrogen (N) content, but increased with higher activities of N-acquisition enzymes (N-acetyl-glucosaminidase and leucine amino peptidase). Consequently, the decrease in N availability strongly increased the intensity of priming effect presumably by enhancing microbial N mining from SOM. Considering the C balance between SOM losses due to priming and glucose-C retention, glucose addition was responsible for net C losses in the low and moderate fertility soils (−14.0 to −0.30 mg C g−1 SOC after 14 weeks) but led to C gains in the high fertility soils (+0.44 to +4.36 mg C g−1 SOC). Greater retention of glucose-C was attributed to higher N availability and more intensive microbial growth, thus supporting microbial necromass formation and soil C sequestration. Compared to single addition, repeated glucose addition caused larger net C losses or lower C gains due to stronger SOM priming. In conclusion, the frequency of substrate addition and soil fertility are important regulators of SOM priming and the C balance. This knowledge should be informative to interpret soil C dynamics in response to labile C inputs in agroecosystems. • Positive SOM priming was much stronger after repeated versus single glucose addition. • The decrease in nitrogen availability increased the priming effect. • SOM priming declined with soil fertility level. • Increased soil fertility weakened SOM priming and increased glucose-C retention. • Increased soil fertility changed glucose-induced net soil C balance from negative to positive. [ABSTRACT FROM AUTHOR]