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The carbon-to-phosphorus (C:P) ratios of microorganisms were quantified in the rhizosphere and bulk soil collected from six typical fertilization regimes across three long-term experiments in humid (wheat–maize rotation), semiarid (wheat–maize rotation), and arid (maize–wheat–cotton rotation) climate zones. A 32P labeling incubation experiment allowed to test the relationship between microbial biomass P (MBP) turnover time and the C:P stoichiometric imbalance (SoilC:P/MicrobC:P) between soil (dissolved organic carbon:Olsen-P) and microorganisms (MBC:MBP). The MBC and MBN in the rhizosphere were 1.2 and 1.3 times higher than those in bulk soils, respectively, while the MBP was similar. The MBC:MBP ratio in the rhizosphere was 1.1 times higher than that in bulk soil, while the MBC:MBN ratio was similar. This finding suggested that C and P accumulation in the rhizosphere microorganisms was decoupled from that in the bulk soil. Compared to that in bulk soil, the MBP turnover in the rhizosphere was 1.1 times faster and microbially mediated P release was increased by 13% because of the decrease in the SoilC:P/MicrobC:P. Shoot P content was correlated with the rhizosphere SoilC:P/MicrobC:P and P flux mediated by microorganisms. The SoilC:P/MicrobC:P thresholds allowed to predict the start of an intensive competition between plants and microorganisms for P. Concluding, the stronger the SoilC:P/MicrobC:P in the rhizosphere decrease, the faster is the MBP turnover of homeostatic microorganisms, and furthermore, the microbially mediated P release leads to the decoupling of microbial biomass C and P at the root–soil interface. SoilC:P/MicrobC:P may be a predictor of the competition between plants and microorganisms. [ABSTRACT FROM AUTHOR]

No fertilized soils (unfertilized and fallow treatments) and soils subjected to 28-year fertilization regimes, including mineral fertilization (PK and NPK) and manure amendments (NPKM and M), were incubated with or without 13C - glucose. Results showed that compared to mineral fertilization (0.64 − 0.69), the manure amendments significantly increased microbial C use efficiency (CUE) (0.76 − 0.79), mainly due to higher soil pH, lower resource stoichiometric ratios of dissolved organic C (DOC): mineral N, DOC: available P and mineral N: available P, and lower specific activities (per microbial biomass C unit) of β-1,4-glucosidase, N-acetyl-glucosaminidase and acid phosphatase. Glucose addition increased SOC mineralization, inducing positive priming effect (PE) with lower values in the manure amendments (0.11 − 0.12 mg C g−1 SOC) relative to mineral fertilization (0.25 − 0.55 mg C g−1 SOC). The PE was negatively correlated with soil pH and positively associated with resource stoichiometric ratios of DOC: mineral N, DOC: available P and mineral N: available P, mainly due to microbes mineralizing SOM to release nutrients, as indicated by the positive relationships between PE and the specific activities of N-acetyl-glucosaminidase and acid phosphatase. Concluding, relative to mineral fertilization, long-term manure amendment could increase CUE and decrease PE via alleviated soil acidification and resource limitation, thus facilitating soil C sequestration. [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]

The tight coupling between nitrogen (N) and phosphorus (P) suggests that P availability may affect soil microbial N dynamics in terrestrial ecosystems. However, how P addition affects the internal N transformations in P-deficient agricultural soil remains poorly understood. We hypothesized that an increase in gross microbial N rates in P-deficient soil should occur after long-term P inputs in agricultural soils. We thus conducted a 15N pool dilution experiment to quantify the gross microbial N transformation rates after long-term mineral fertilizer applications in an upland fluvo-aquic soil (from Fengqiu with pH 8.55) and upland red soil (from Qiyang with pH 5.49) in China. We found that P addition significantly enhanced the gross N mineralization and immobilization rates when N and K were also applied, probably due to the increased soil total C and N concentrations at both soils. Also, gross nitrification rate was stimulated by P addition, perhaps because of enhanced gross N mineralization rates and associated NH4+ substrate availability. Our results showed that long-term P addition may stimulate soil gross N dynamics and hence increase overall N availability for crops in P-deficient agricultural soils. [ABSTRACT FROM AUTHOR]

The effects of organic and mineral fertilization on four soil organic matter (SOM) fractions (non-protected, physically protected, chemically protected, and biochemically protected) and microbial community composition were investigated by sampling soil of a 35-year-long fertilization experiment. The SOM fractions were investigated by combined physical and chemical approaches, while microbial community composition was determined by phospholipid fatty acid analysis (PLFA). Organic C (SOC) was primarily distributed within the microaggregate-protected particulate organic matter (iPOM) and the hydrolysable and non-hydrolysable silt-sized (H-Silt, NH-Silt) fractions, which accounted for 11.6-16.9, 23.4-28.9, and 25.4-30.6% of the total SOC content, respectively. The contributions of these 'slow' fractions (iPOM, H-Silt, NH-Silt) to the increased SOC were 178-293, 118-209, and 85-109% higher after long-term sole manure or manure in combination with inorganic N fertilization compared with unfertilized soil (control). The combination of manure and mineral fertilizers increased the coarse and fine non-protected C (cPOM and fPOM) contents much more (34.1-60.7%) than did manure alone. PLFAs, bacteria, G (+) bacteria, and actinomycete abundances were the highest in soil with manure, followed by soil treated with manure combined with mineral N. The addition of inorganic and organic fertilization both altered the microbial community composition compared with the control. All SOM fractions contributed to 81.1% of the variance of the PLFAs-related microbial community composition by direct and indirect effects. The change in coarse unprotected particulate organic matter (cPOM) was the major factor affecting soil microbial community composition ( p < 0.001). Our study indicates that physical, chemical, and biochemical protection mechanisms are important in maintaining high SOC level after the addition of manure. A close linkage between soil microbial community composition and cPOM suggests that C availability is an important factor for influencing microbial composition after long-term inorganic and organic fertilization. [ABSTRACT FROM AUTHOR]

Fertilizer application can potentially change soil organic C (SOC) sequestration of croplands. However, how fertilization affects SOC sequestration and soil C fractions has not been sufficiently investigated. Here, we studied this issue in a rice-barley system of eastern China after 23-year repeated organic and chemical fertilizer amendments. The fertilization treatments were as follows: unfertilized control (CK), pig manure (M), chemical fertilizer NPK (NPK), and pig manure combined with NPK (MNPK). Our results showed that M, NPK, and MNPK significantly increased 25, 13, and 30 % of SOC content as compared with CK. Compared with CK, the three fertilizations, especially manure addition, significantly increased the content of SOC fractions such as microbial biomass C, dissolved organic C, labile organic C, and particulate organic C. Compared with the initial SOC stock at 0-20-cm depth (41.2 Mg C ha), M, NPK, and MNPK increased 11, 1, and 16 % of SOC storage, respectively, whereas CK decreased 9 % of SOC pool. The SOC sequestration was positively correlated with the cumulative C input (root residue-C + manure-C) (SOC sequestration = 0.21 × C input − 5.67, R = 0.88, P < 0.001). This linear relationship suggested that (i) the soil had not reached a SOC saturation, (ii) the conversion rate from input-C to SOC was 21 %, and (iii) a C input threshold of 1.17 Mg C ha year was needed for maintaining the initial SOC level. Therefore, manure application is recommended for promoting SOC sequestration in the rice-barley cropping system of eastern China. [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]

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