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Accurate determination of evapotranspiration (ET) has tremendous potential in guiding irrigation and improving the efficiency of water resources utilization in the North China Plain. Eddy covariance (EC) method is currently a popular method for determining field-scale ET. However, due to varying foot print and unclosed energy balance, the applicability of EC in different regions needs to be tested and corrected. In present work, we compared the ET of the winter wheat – summer maize rotation cropland measured by the EC method with the ET measured by large-scale lysimeters on different time scales. The degree of energy balance closure of EC measurements in this region is 78%. After adjusted by using Bowen ratio forced closure method, the ET monitored by EC is comparable with those monitored by large-scale lysimeters. The results also indicated that the consistency of the observed ET by the EC and lysimeters got better with an increasing time scale, especially for the multi-year average ET values with a relative deviation of less than 1%. The short-time events such as irrigation and precipitation and the mismatch of the varying footprint area of the EC and the small fixed source area of the lysimeter should be responsible for the discrepancy of ET in two methods on daily scale. However, the factors of crop biomass, total available water, and local climate condition exert more effects on the observed ET on large time scale. Overall, the EC technique is responsible for ET measurement of winter wheat – summer maize rotation cropland of the North China Plain.

Wheat (Triticum aestivum L.) cultivars vary in their resistance to Fusarium head blight (FHB), while it is poorly understood how different cultivars influence FHB-causing Fusarium graminearum abundance in rhizosphere soil. A field experiment was conducted to investigate the influence of three wheat cultivars on FHB index, rhizosphere soil F. graminearum abundance, chemical properties, and microbial community composition and metabolic profiles. The cultivars were Sumai3 (SM), Yangmai13 (YM), and Annong8455 (AN), representing high, intermediate, and low resistance to FHB, respectively. Both wheat FHB index and rhizosphere F. graminearum abundance were ranked as SM

To investigate the effects of long-term fertilization on microbial decomposition of residues and priming effect (PE), 13C-labeled maize (Zea mays L.) residues were supplied to arable soils with a 20-year application of compost (COM), mineral NPK fertilizer (NPK), or without any treatments, the no-fertilizer control (NF). The soils that had been stored for 6 years were used in the present incubation experiment. The release of CO2–C and the microbial incorporation of residue-derived C determined by phospholipid fatty acids (PLFAs) analysis were monitored over a 90-day incubation period. Residue additions significantly increased cumulative CO2–C emission and induced positive PE. Cumulative residue-derived CO2-C emission and PE mainly occurred within the first 15 days. The COM soil had significantly higher cumulative residue-derived CO2–C emission but lower PE than the NF and NPK soils. Residue additions significantly increased microbial abundance and changed the composition of main microbial groups. The COM soil showed a significantly lower relative fungal abundance (mol%) but a higher relative actinomycetes abundance than the NF and NPK soils. The incorporation of residue-derived C within fungi was the highest among all the main microbial groups and decreased from 15 to 45 days, while the incorporation of residue-derived C within actinomycetes increased with time in three soils. The incorporation of residue-derived C within fungi was the highest in the COM soil over the course of incubation. The long-term compost input promoted fungal use of residue C and stimulated residue decomposition.

Field decomposition of wheat and maize straws was monitored for 20 months using litterbag method in Calcaric Fluvisol soils with three different textures (sand, sandy loam, and silty clay). Residual straw samples were collected at 0 or after 4, 6, 10, and 20 months of decomposition. The chemical structure of straw was analyzed by solid-state 13C nuclear magnetic resonance (13C-NMR) spectroscopy, and the composition of main microbial groups was evaluated by phospholipid fatty acid analysis. Regardless of the straw type and soil texture, the straw biomass and C loss increased steadily in the first 10 months and then leveled off in the following 10 months; both the chemical structure of straw and the composition of main microbial groups differed during incubation. During the first 4 months of wheat straw degradation, the decrease in di-O-alkyl and O-alkyl C and the increase in alkyl and N-alkyl/methoxyl C contents were related to the enrichment of fungi (18:1ω9c) and Gram-negative bacteria (18:1ω7c and 16:1ω7c), while the degradation of maize straw was associated with the decrease in the fungal (18:1ω9c) abundance and the increase in the abundance of Gram-negative (18:1ω7c and 16:1ω7c) and Gram-positive (a15:0) bacteria. During the 6–10-month period, the decrease in di-O-alkyl and O-alkyl C and the increase in alkyl, aryl, and carboxyl/amide C contents were related to the enrichment of arbuscular mycorrhizal fungi (AMF) (16:1ω5c) and Gram-negative (cy19:0ω8c) bacteria and the decrease in fungal (18:2ω6,9c) abundance, with AMF playing an important role in the degradation of both straw types. The altered chemical structure of wheat and maize straws had opposite links with fungal abundance during the first 4 months, while alterations occurring during the 6–10-month period mainly depended on the variation in the AMF abundance.

The ability of soil microorganisms to uphold a variety of ecosystem services is of increasing interest, but our understanding of the linkage between cropland ecosystem services and the soil microbiome under long-term different fertilizer regimes is still limited. Here, we measured 15 response variables commonly used as indicators of cropland ecosystem services, and employed a shotgun metagenomic sequencing technology to determine microbiome taxonomic composition and functional composition in a sandy loam soil amended with organic and inorganic fertilizers for 28 years. Long-term application of fertilizers had overall positive effects on the variables that indicate soil C and nutrient status, organic material decomposition, nutrient transformation, and plant productivity, but the strength of these effects differed between organic and inorganic fertilization. In long term, organic fertilizers significantly increased the abundance of Sphingomonas and Acidobacteria as well as genes involved in C and N metabolism and degradation of aromatic organic compounds. The observed differences in the indicators of overall biological activity, litter decomposition, nutrient transformation, cropland fertility and productivity were associated with changes in taxonomic composition and functional composition of the soil microbiome. Network analysis revealed that soil organic C, total N, L-leucine aminopeptidase, phosphatase, microbial biomass C and N, and the multifunctionality index showed strong positive associations with Acidobacterium, Lysobacter and Nitrososphaera. These microbes are implicated in the decomposition of organic material, soil C and N transformation, and plant growth promotion. The present study deepens our understanding of the relationship between the soil microbiome and agro-ecosystem functioning, and provides support for the use of organic fertilization strategy to enhance multiple ecosystem services in croplands.

Dielectric techniques are fundamental methods for measuring soil water content, and they commonly rely on the conventional laboratory calibration of the dielectric permittivity models between a dielectric constant and water content. As a non‐negligible factor, porosity has been constructed differently in some models as a calibration constant, but the systematic porosity variations during the laboratory model calibration and field applications are not yet well addressed. Based on time‐domain reflectometer laboratory calibration experiments, this study investigated this issue using three preestablished dielectric permittivity models: the Purdue calibration equation (American Society for Testing and Materials model [ASTM]), the complex refractive index model (CRIM), and a piecewise CRIM model (CRIMP). Results demonstrate that a generalized porosity constant used in the calibration would bring in additional structural bias compared with the calibration using variable porosities, and its magnitude varies with the model structure. The deviation of the generalized porosity constant can further amplify the structural bias of ASTM and CRIM for soils with low clay content, but it is insensitive for the soils with high clay content due to the overwhelming role of model structure error. Only the model CRIMP with a “perfect” model structure can effectively cope with the systematic porosity variation and keep a stable built‐in capability for estimating calibration constants from readily available soil data. These findings highlight ignoring porosity variation should not be taken for granted for calibrating and applying the preestablished models.

Elevated CO2 and nitrogen addition can increase rice yield and stimulate rice to absorb more nutrients from the soil. The aim of this study was to investigate how soil organic carbon and aggregates change under such high-output conditions. Rice cultivars IIY 084 and WYJ 21 (strong and weak response to elevated CO2, respectively) were planted in free-air CO2 enrichment (FACE) platforms. Treatments included: 1) elevated CO2 without nitrogen addition (EC); 2) nitrogen addition and ambient CO2 (EN); 3) combined elevated CO2 and nitrogen addition (ECEN); and 4): ambient CO2 without N addition (CK). Soil organic carbon (SOC), readily-oxidizable organic carbon (ROC) and soil aggregate components were measured. Treatment EC increased SOC and ROC, while EN decreased SOC and ROC compared to CK in soil under either rice cultivar. EC and EN decreased the percentage of large macroaggregates (LM) and the mean weight diameter (MWD) of aggregates compared to CK in ‘WYJ 21’ soil, while they increased LM and MWD in ‘IIY 084’ soil. ECEN increased LM and MWD compared to CK in soil under either rice cultivar. High productivity of ‘IIY 084’ through long-term cultivation under current N fertilization in future climatic conditions of elevated CO2 could be achieved due to increased soil aggregate stability and SOC.

Structural changes in fulvic acid (FA) in response to fertilization strategies, especially P-deficiency fertilization, have critical implications for soil carbon dynamics. This study examined how long-term fertilization influenced chemical compositions of soil FA and its humification degree. Advanced solid-state 13C nuclear magnetic resonance techniques were used to evaluate structural changes of FAs from two soils (a Fluvisol and an Anthrosol) under four fertilizer treatments: organic fertilizer combined with or without NPK fertilizer (OF and NPKOF), deficient in phosphorus only (NK) and Control. The greater aromaticity, hydrophobicity and alkyl/O-alkyl (A/O-A) ratios of FAs were observed in the Anthrosol than in the Fluvisol. The Anthrosol FAs contained more alkyl and aromatic C but fewer O-alkyls (mostly being protonated) than did the Fluvisol FAs. Both FAs comprised some nonprotonated aromatics, which decreased with applications of organic and NK fertilizers. This trend was less obvious for the Anthrosol than for the Fluvisol. Organic fertilizer treatments (OF and NPKOF) in the Fluvisol increased the A/O-A ratio and aromaticity compared with P-deficient soils (NK and Control), indicating organic fertilization promoted the humification degree of its FA. The NK treatment in the Fluvisol increased H/C ratio of FA. Compared with the Fluvisol FAs, the Anthrosol FAs displayed similar chemical natures, implying their formation followed similar processes with a similar humification degree. The findings suggest that long-term fertilization differently influenced the FAs from the Fluvisol and Anthrosol. Clearly, the Anthrosol FAs shared more common features among the treatments compared with the Fluvisol FAs, whereas P-deficiency rendered the Fluvisol FAs simpler.

Soil microorganisms are considered the most effective decomposers of applied crop residues, but it is poorly understood which communities are primarily responsible for decomposition under different conditions. A pot experiment was conducted in a greenhouse to follow the cycling of C and N derived from maize (Zea mays L.) residues labeled with both 13C and 15N to a subsequent winter wheat (Triticum aestivum L.) crop and to soil pools under planting with winter wheat (+P) or an unplanted control (–P), both in soil maintained at field moisture capacities of 40% and 80%. Soil microbes involved in residue decomposition were investigated by 13C phospholipid fatty acid (13C-PLFA) analysis technique. At wheat maturity, a total of 68% of residue N was recovered in the +P treatments, in which 26% was recovered from wheat plants and another 42% from soil total N (TN), independent of the water regimes, while only 50% was recovered from TN in the –P treatments. More residue C was recovered as soil organic carbon in +P than –P treatments (33% vs. 27%), and the trend became more significant with soil moisture. In addition, the +P soil had 35–48% larger microbial biomass carbon (MBC) than the –P soil, and more residue C was recovered as MBC in +P than –P treatments (7% vs. 4%), suggesting the induced microbial utilization of the applied residues. The distribution of the residue-derived PLFA-C showed that only 16:1ω7c and 18:1ω7c had larger relative abundances in the +P than the –P soils, suggesting that they were mainly stimulated by the presence of wheat and that they may be the most important fatty acids to define the different recoveries of residue N and C between the planted and unplanted conditions. Our results demonstrate that the enhanced recovery of residue-C and -N by the presence of wheat plants was mainly from the induced microbial utilization of applied residues by altering the activities of specific microorganisms.

Conservation tillage has been gaining increasing recognition for its role in improving soil quality and maintaining agricultural sustainability. This is the first in a series of papers describing the impacts of reduced/no-tillage with and without residue based on the field experiment in the North China Plain. The experiment was established in 2006 on a sandy loam soil and involved a winter wheat-summer maize rotation system per year. The objective of this study was to investigate the impacts of different conservation tillage systems on crop yield and soil fertility that was quantified by a minimum data set and integrated index. Soil samples were collected since 2011, and the stocks of soil organic matter (SOM), total nitrogen (TN), alkali-hydrolyzale nitrogen (AN), total phosphorus (TP), available phosphorus (AP), total potassium (TK) and available potassium (AK) were measured for each year as well as soil aggregates were fractionated for 2016. Compared to continuous tillage, the reduced/no-tillage, regardless of residue, significantly increased the macroaggregate mass and soil nutrient stocks at the 0–10 cm depth, while further improvements in these soil attributes apart from TK were observed at the 0–10 and 10–20 cm depths for residue returning relative to residue removing. The accumulations of soil nutrients were closely related to soil macroaggregation. The path analysis revealed that TN was the most important soil attribute to directly determine wheat and maize yields while other soil attributes apart for TK primarily made indirect contributions to the yields. The first two factors extracted using 8 soil attributes through factor analysis were selected as the integrated indicators for the minimum data set, and their integrated score was calculated to quantify soil fertility. It was found that reduced/no-tillage did not improved soil fertility at the 0–20 cm depth. Consequently, an average 6.9% decrease in wheat yield across all years was observed under no-tillage while reduced tillage only increased the yield in the first two years in a periodic reduced tillage event. No significant difference was observed for the mean maize yield among the three tillage regimes averaged across all years and residue managements. Wheat and maize yields were significantly correlated with the integrated score for soil fertility, and thus significant increases in grain yields of wheat and maize were observed for residue returning. It can be concluded that grain yields of wheat and maize within a given residue management practice were not significantly higher for reduced/no-tillage than continuous tillage, regardless of the effects of tillage on aggregates and soil nutrients.

The formation of aggregates plays a key role in shaping soil microenvironment, which in turn influences microbial community structure and organic carbon (C) dynamics in soil. The objective of this study was to identify the linkages between soil macroaggregation and microbial community as well as organic C accumulation using field samples following 9 years of conservation tillage. A wet-sieving method was used to fractionate soil aggregates and soil microbial abundance and community composition were determined using phospholipid fatty acid (PLFA) analysis. Compared to continuous tillage, reduced/no-tillage and straw returning significantly promoted soil macroaggregation and consequently increased organic C, C/N ratio and soil moisture but decreased the porosity and computed effective oxygen diffusion coefficients. The changes in these soil characteristics were closely related to the abundance and composition of microbial community. The abundance of microbial PLFAs in reduced/no-tillage soils was 30.0% higher in Gram-positive bacteria, 11.6% higher in Gram-negative bacteria, 71.7% higher in fungi and 45.4% lower in actinobacteria, whereas straw returning significantly increased all microbial PLFA abundances relative to straw removing. The ratios of bacteria/fungi (B/F) and monounsaturated/branched (M/B) PLFAs were significantly correlated with the volumetric soil water content, porosity, or computed effective oxygen diffusion coefficients. Soil macroaggregation and microbial community composition collectively explained 82.4% variation in organic C accumulation and their interaction made the largest contribution. Overall, soil macroaggregation under conservation tillage might cause a shift in microbial community to more fungi and anaerobes through primarily influencing soil moisture and aeration, which could effectively promote organic C accumulation in soil.

Spatial variability and influential factors are important to evaluate soil organic C (SOC) and the C pool in large areas. In the present study, sampling was conducted from May to November 2011 in Henan Province, a typical agricultural region of Central China, to study the effects of soil properties and anthropogenic factors on SOC variability in cropland. Physicochemical properties of soil samples collected at 280 sites from the surface layer (at a depth of 0–20 cm) were analyzed, and related data about the sampling sites were also collected from the Second State Soil Survey of China, conducted in 1981. Firstly, we found increasing trends in SOC density (SOCD) and SOC pool (SOCP) were obvious from 1981 to 2011, and we concluded that cropland presents great C sequestration potential for the future. Carbon pool ability varied with soil properties: the order of fixed Camount in different soil types was found to be Inceptisols > Luvisols > semihydromorphic soil > Anthrosols, and the average SOCP increased significantly from 1981 to 2011. Secondly, soil bulk density, pH, and returning straw were the key influential factors for SOCD in the past 30 yr. Thirdly, although random factors (returning straw) only explain 29.1% of SOCD variability, more attention should be paid to the factors, because application of returning straw was the most dominant anthropogenic factor, which can be used to improve cropland productivity and C sink capacity within a short period if they are properly managed in the future.

Soil organic carbon (SOC) is the key to soil fertility and quality. However, SOC has severely declined in the past several decades due in part to inappropriate nitrogen (N) and phosphorus (P) input levels. Thus far, the influences of N and P input levels on the accrual of different SOC fractions and relevant microbial traits at aggregate scales remain uncertain. Here, a 3-year field experiment was used to reveal the effects of N and P input levels on SOC fractions in a Mollisol. Treatments included straw return (SR) and combinations of high nitrogen (N) and high phosphorus (P) inputs (N + P + SR), high N and low P inputs (N + P1/2 + SR), and low N and high P inputs (N1/2 + P + SR). Macroaggregates (>0.25 mm), microaggregates (0.25–0.053 mm), and clay and silt (

Fertilization-induced changes in soil properties from the paddy soil and upland soil may directly regulate bacterial community composition, which usually coincide with shifts in molecular composition of soil organic carbon (SOC) in the upland soil. However, systematical comparisons lack on how regulators vary with cropping systems under the same weather conditions and soil parent materials. Here, we simultaneously investigated the changes of soil physicochemical parameters and shifts in the bacterial community and SOC molecular composition in two adjacent rice and maize fields that have received five fertilization regimes for more than 30 years. The separation of the bacterial community composition among the treatments from the paddy soil was mainly determined by soil nitrate-N, and that from the upland soil was mainly determined by soil available P (AP) and pH. The SOC molecular composition from the paddy soil was separated by the treatments with N application or not, with those treatments with N application being enriched with CCH3 and aromatic C C, and those without N application being enriched with aromatic C H. These changed C functional groups showed close association with amorphous Fe2O3. For the upland soil, the SOC molecular composition was separated by the treatments with P application or not, with those treatments with P application being enriched with OCH, and those without P application being enriched with CH/CH2. These changed C functional groups had close association with AP and total P. Our results indicated inconsistent separation patterns and regulators of the bacterial community and SOC molecular composition among the treatments of the paddy soil and upland soil, and suggested that the relatively dominant role of the fertilization-induced changes in soil properties or other soil microbes that controlled the SOC molecular composition over the bacteria measured in the present study.

The Calci-Aquic Vertisols comprise one of the largest areas with low crop yields in China normally characterized with black color, high smectite contents but low organic matter contents. This study aims to establish a physical method for extracting black matter from the Calci-Aquic Vertisols, and explore the formation mechanism of black nano-organo-mineral complexes of the soils. The alternation of freezing-thawing and adding dispersant followed by oscillation and multi-level ultrasound(HOMU) method were proposed and tested to disperse soil and extract black matters from the topsoil layers (0−40 cm) and black soil layers (40−70 cm) of three Calci-Aquic Vertisols. Six different components including POM, white, light white, light black, black and nano-black were extracted successively and analyzed for blackness, organic matter content, particle gradation, mineral composition and elemental oxides. The nano-organo-mineral complexes are found be responsible for the Calci-Aquic Vertisols appearing black. Smectite (SM) absorbing organic matters mainly through cation bridges of Fe3+ and Al3+, hydrogen bond, van der Waals force formed the black nano-organo-mineral complexes which consists the main parts of the black matters in the Calci-Aquic Vertisols. Agricultural activities increased the organic matter contents in the topsoil layers, but the difference of formation environment resulted in the poorer crystallinity and higher content smectites and thus higher nano-organo-mineral complex contents and blackness in the black soil layers in the Calci-Aquic Vertisols. The result in this research is of great value for understanding the organic matter turnover and improving the productivity of the Calci-Aquic Vertisols.

Despite our current understanding of soil C and N interactions, less is known about the response and feedback of C mineralization to soil P availability driven by microorganisms. To better understand these interactions, soils with long-term P-sufficient NPK fertilization (available P: 13.4 mg kg −1 ) and P-deficient NK fertilization (available P: 0.96 mg kg −1 ) were incubated with and without glucose. CO 2 emissions were monitored to characterize C mineralization during the incubation. The soil bacterial community structure, quantity and metabolic activity were evaluated using high-throughput sequencing, qPCR and microcalorimetric dynamics. Compared with P-sufficient soils, P-deficient soils had significantly lower basal respiration, but a significantly higher net mineralization of added glucose, probably due to higher energy cost of soil microorganisms. Glucose addition promoted microbial biomass and activity, particularly in P-deficient soils, and this improvement was maintained for at least 70 days. Shifts in bacterial community composition were induced by a predominance of several specific taxonomic groups, all of which were capable of solubilizing P in soils. P-deficiency decreases the retention of exogenous labile C into soil. Adding labile C to P-deficient soils may shift P from relatively unavailable soil-bound pools into microbial biomass pools through pool cycling. Our results indicated negative effects of P-deficiency on soil C retention, as well as positive effects of labile C on soil P availability in arable soils.

This paper was primarily devoted to reveal the composition of soil organic carbon (C) at a molecular level and to compare the differences existing among tillage practices after 8 years of contrasting managements, aiming to identify the effects of conservation tillage on the accumulation process of soil organic C and its association with macroaggregation. A sandy loam soil following 8-year conservation tillage was collected to identify the dynamics of organic components and their associations with macroaggregation. The content of particulate organic matter within macroaggregates was determined using aggregate fractionation techniques. Conservation tillage improved the accumulation efficiency of different C functional groups in large and small macroaggregates, and resulted in a higher soil organic C level. The content of C functional groups was significantly and positively correlated with the C amount of subfractions in macroaggregates. The accumulation of organic components, particularly the methoxyl/N-alkyl C in the 0–5 cm layer and the O-alkyl C in the 5–10 cm layer, in turn, accelerated soil macroaggregation. Overall, organic component accumulation and soil macroaggregation were interacted on each other. Our results suggested that the enrichment of methoxyl/N-alkyl C and O-alkyl C in the test soil following conservation tillage could effectively promote organic C accumulation and macroaggregation.

Investigating the effects of residue chemical composition on soil labile organic carbon (LOC) will improve our understanding of soil carbon sequestration. The effects of maize residue chemical composition and soil water content on soil LOC fractions and microbial properties were investigated in a laboratory incubation experiment. Maize shoot and root residues were incorporated into soil at 40% and 70% field capacity. The soils were incubated at 20 °C for 150 d and destructive sampling was conducted after 15, 75, and 150 d. Respiration, dissolved organic carbon (DOC), hot-water extractable organic carbon (HEOC), and microbial biomass carbon (MBC) were recorded, along with cellulase and β-glucosidase activities and community-level physiological profiles. The results showed that the cumulative respiration was lower in root-amended soils than in shoot-amended soils, indicating that root amendment may be beneficial to C retention in soil. No significant differences in the contents of DOC, HEOC and MBC, enzyme activities, and microbial functional diversity were observed between shoot- and root-amended soils. The high soil water content treatment significantly increased the cumulative respiration, DOC and HEOC contents, and enzyme activities compared to the low soil water content treatment. However, the soil water content treatments had little influence on the MBC content and microbial functional diversity. There were significantly positive correlations between LOC fractions and soil microbial properties. These results indicated that the chemical composition of maize residues had little influence on the DOC, HEOC, and MBC contents, enzyme activities, and microbial functional diversity, while soil water content could significantly influence DOC and HEOC contents and enzyme activities.

Multi-scale soil architectures in shallow subsurface are widespread in natural and anthropogenic depositional environments, and acquisition of the surface stratal structure and hydrological properties are essential in quantifying water cycling. Geophysical methods like ground-penetrating radar (GPR) can provide quantitative information like soil architecture and spatiotemporal soil water content distribution for the shallow layer. Concerning the informative multi-dimensional water flow in the surface layer with an undulating bottom at the plot scale, this study assesses the feasibility of efficiently estimating soil hydraulic properties using a few time-lapse multi-channel GPR observations, namely soil water storage and layer thickness of the surface layer, at reclamation land near an old river channel. We show that effective hydraulic properties of the surface layer can be obtained with a small number of time-lapse GPR measurements during a rainfall event. Additionally, we analyze the effect of some key factors controlling the informative lateral water redistribution on the results of the proposed approach using synthetic simulations.

Pot experiments are a low-cost and easy-to-use technique for studies of soil evaporation and plant transpiration in controlled environments. However, little attention has been paid to the applicability of evapotranspiration (ET) measured in pot experiments to the field. The objective of this study was to determine whether a pot experiment can be used for measuring field ET. Evapotranspiration experiments with winter wheat and summer maize were conducted in pots and lysimeters under various water-deficit conditions. The measured ET values in the pot experiments under different water conditions were considerably different from those of the lysimeters. Causes of such differences in ET were analyzed, and a series of corrections were proposed to eliminate the effects of different crop densities, representative areas per plant, and soil moisture conditions on pot experiment results. After these corrections, the discrepancy in the total ET of wheat-maize seasons between pots and lysimeters was greatly reduced from a maximum of 117% to only approximately 10%. The relative mean square errors (RMSEs) for daily ET values also decreased from a maximum value of 4.56 mm to less than 1.5 mm for the wheat season and from a maximum value of 6.02 mm to approximately 2 mm for the maize season. Possible measures were proposed to further improve the accuracy of the corrected ET obtained from pot experiments. In sum, pot experiments can serve as a feasible tool for estimating ET in the field just with a few routine measurements at regions where large-scale weighing lysimeters, an eddy covariance device, and even meteorological data are not available. The proposed corrections can also be used for upscaling small-scale ET measurements to a large scale.

The importance of soil saprotrophic fungi in agroecosystems is receiving increasing attention. However, the linkages between saprotrophic fungal communities and soil fertility and stoichiometry in agroecosystems are poorly understood. Here, four long-term field fertilization experiments with three treatments (i.e., no fertilizer (control), chemical nitrogen (N), phosphorus (P), and potassium (K) fertilizer (NPK), chemical combined with organic fertilizer (NPKM)) were performed to evaluate the associations of saprotrophic fungal communities with the soil fertility index (SFI) and stoichiometric carbon (C):N:P ratios. Long-term NPKM application increased the SFI by 57.66%–129.50% at the four sites, and the SFI was strongly correlated with the saprotrophic fungal community composition, which indicated that exogenous organic matter improved soil fertility to a large extent and stimulated the growth of saprotrophic fungi in arable soils. The soil C:P and N:P ratios were notably decreased in the fertilization treatment, indicated that P was sufficient. Further, the composition of saprotrophic fungi was significantly related to the C:N and N:P ratios, suggested that N status is an important factor for soil saprotrophic fungal communities. Our study provides empirical evidence that the saprotrophic fungal communities in arable soils are strongly associated with soil fertility and stoichiometry and offers guidance for improving soil fertility by regulating the saprophytic fungal community.

The supposition that cropping system might affect fertilization-induced changes in chemical composition of soil organic carbon (SOC) and microbial community composition has mostly derived from field experiments in different sites, which may have been disturbed by different climate conditions and parent materials. Here, two adjacent long-term field experiments were used, which contained similar four fertilization regimes of NPK, 2NPK, NPKOM, and an unamended control (Control), while contrasting annual cropping system of rice–rice and maize–maize, to investigate how fertilization-induced changes in SOC chemistry differ in paddy soil from upland soil, and whether they correlate with different bacterial taxa. The bacterial community composition of the paddy soil was mainly determined by NO3–-N and total N, and that of the upland was mostly explained by SOC. The NPK, 2NPK, and NPKOM treatments from the paddy soil increased CCH3, decreased OCH, and reduced CH/CH2, while those from the upland soil decreased CH/CH2, increased OCH, and raised CH/CH2, respectively, indicating opposite shifts of OCH and alkyl C (i.e., CCH3 and CH/CH2) in each paired fertilizer treatment of the two soils. In the paddy soil, the CCH3 from the NPK treatment showed no association with any bacterial taxa, the OCH from the 2NPK showed a negative association with NO3–-related species, and the CH/CH2 from the NPKOM showed a negative association with Proteobacteria and Bacteroidetes. In the upland soil, the CH/CH2 from the NPK negatively associated with Thermogemmatisporales and Acidobacteriaceae subgroup 1, the OCH from the 2NPK positively associated with Thermogemmatisporales, and the CH/CH2 from the NPKOM positively associated with copiotrophic bacterial taxa. Our results provided direct evidence that cropping system mediated the shift direction of specific functional group under specific fertilization regimes, and implied that completely opposite shifts of OCH and alkyl C in each paired fertilizer treatment of the paddy soil and upland soil can likely be attributed to different fertilization-induced shifts in the microbial community composition resulting from soil N change in the paddy soil and soil C change in the upland soil.

Soil microbes play a key role in terrestrial ecosystems. In the saline-sodic environment, the microbial communities and their community assembly processes, especially throughout soil profiles, however, are not well understood. Here, we characterized the soil microbial communities across three sodicity/salinity gradients to 1.0 m depth in the western Songnen Plain, Northeast China. Soil sodicity (exchangeable sodium percentage) and salinity (electrical conductivity) exerted a strong influence on bacterial community compositions compared with other soil properties. These filtering effects of sodicity/salinity were strong on the microbial communities in the layer of 0–60 cm across the three sites, with more contributions of deterministic processes over stochastic processes. As sodicity/salinity decreased, some potential biomarkers for a high community tolerance to salt or soda, such as KSA1, Halomonas, Euzebya and Bacillus, were depleted; meanwhile, some taxa associated with decomposition of organic matter and nutrient transformations, such as Arthrobacter, Mesorhizobium, Pseudomonas and Nitrospira, were enriched. Within each soil profile, the turnover in community composition was lower than between sites, and the stochastic processes (homogenizing dispersal) dominated the microbial assembly. Yet, the surface and deepest depth (80–100 cm) of saline-sodic soils still harbored some distinct microbial communities. The near-surface (20–40 cm) may serve as a gating role for limiting surface microbial penetrance into the deeper depth. Taken together, our results show that sodicity/salinity can strongly structure soil microbial communities, and emphasize the importance of soil depth as an environmental gradient on the assembly processes in saline-sodic soils.

The changes of chemical structure and decomposer community during straw degradation have been inconsistent in previous reports, showing either convergence or divergence of chemical structures or microbial communities among different straw types. Hence the strength of their relationship remains unclear. Here, we directly measured the chemical structures and bacterial and fungal communities of wheat (Triticum aestivum L.) and maize (Zea mays L.) residues after four-year decomposition in three Calcaric Fluvisols that varied in soil textures. Separation of the chemical structures among the six soil-straw combinations (two straw types × three soil textures) were generally coupled with trends in the communities of bacterial and fungal decomposers, but the nature of their coupling differed. In the sand soil, soil texture was the central feature that shaped bacterial and fungal communities for both straw types, driving in turn the convergence of chemical structures of both decomposing straws. In contrast, in the sandy loam and silty clay soils, straw type was the primary regulator of the colonizing bacterial and fungal communities, which resulted in the divergence of chemical structures according to straw type.

The microbiomes inhabiting plant roots and their adjacent soil environment play significant roles in plant growth, health, and ecological services. Recent studies have provided detailed insights into many phytomicrobiomes, but our understanding of the root-associated microbiomes of perennial ryegrass is still very limited. Here we carried out a stratified rhizobox experiment involving a fluvo-aquic soil and red soil under elevated (750 ppm) and ambient (350–400 ppm) CO2, and used deep amplicon sequencing to investigate the ryegrass root-associated bacterial microbiomes across compartments (the bulk soil, 2-mm outer rhizosphere, rhizosphere, rhizoplane, and endosphere). We observed increased relative abundances of Proteobacteria (mainly Rhizobiaceae and Enterobacteriaceae) in the rhizosphere, rhizoplane, and endosphere compared with the bulk soil and outer rhizosphere. The dominant bacterial genera (mainly Methylobacterium, Rhizobium, Pseudomonas, Stenotrophomonas, and Enterobacter) which facilitate plant growth and soil nutrient cycling were enriched in the rhizosphere, rhizoplane, and endosphere compared with outer rhizosphere. PICRUSt predicted moderate functional differentiation of bacterial microbiomes across compartments. The bacterial α-diversity showed a decreased trend along a spatial gradient from the bulk soil to the endosphere. The β-diversity and network analyses indicated significant differences in the root-associated bacterial microbiomes between the fluvo-aquic soil and red soil. In conclusion, our study suggests that the filtration and acquisition of the ryegrass root-associated bacterial microbiomes are largely controlled by indigenous soil microbial communities, rather than the changes in root rhizodeposition caused by elevated CO2.

Variations in temperature and moisture play an important role in soil organic matter (SOM) decomposition. However, relationships between changes in microbial community composition induced by increasing temperature and SOM decomposition are still unclear. The present study was conducted to investigate the effects of temperature and moisture levels on soil respiration and microbial communities involved in straw decomposition and elucidate the impact of microbial communities on straw mass loss. A 120-d litterbag experiment was conducted using wheat and maize straw at three levels of soil moisture (40%, 70%, and 90% of water-holding capacity) and temperature (15, 25, and 35 °C). The microbial communities were then assessed by phospholipid fatty acid (PLFA) analysis. With the exception of fungal PLFAs in maize straw at day 120, the PLFAs indicative of Gram-negative bacteria and fungi decreased with increasing temperatures. Temperature and straw C/N ratio significantly affected the microbial PLFA composition at the early stage, while soil microbial biomass carbon (C) had a stronger effect than straw C/N ratio at the later stage. Soil moisture levels exhibited no significant effect on microbial PLFA composition. Total PLFAs significantly influenced straw mass loss at the early stage of decomposition, but not at the later stage. In addition, the ratio of Gram-negative and Gram-positive bacterial PLFAs was negatively correlated with the straw mass loss. These results indicated that shifts in microbial PLFA composition induced by temperature, straw quality, and microbial C sources could lead to changes in straw decomposition.

The influence of compost and mineral fertilization on soil organic carbon (SOC) and physical properties varied greatly in previous studies because of differences in site conditions such as climate and soil. This study was conducted as a long-term (1989–2012) field experiment to evaluate the effects of mineral fertilization and compost application on SOC content and some physical properties of an intensively cultivated sandy loam soil in the North China Plain. The experiment consisted of seven treatments: organic compost (OM); half organic compost plus half mineral fertilizer NPK (1/2OM1/2NPK); mineral fertilizer NPK (NPK); mineral fertilizer NP (NP); mineral fertilizer PK (PK); mineral fertilizer NK (NK); and unfertilized control (CK), each with four replicates. Relative to CK, the SOC content was higher in all of the compost and mineral fertilizer treatments, but increments in SOC under the compost application treatments were higher than mineral fertilization application. Compost application (OM, 1/2OM1/2NPK) decreased soil bulk density and increased total porosity significantly in comparison with that in the CK plots. Soil bulk density and total porosity for the mineral fertilization treatments, except NP, did not significantly differ from CK. The lowest penetration resistance at 0–20 cm soil depth was observed in the NK plots, and the highest penetration resistance was found in the CK plots. Compost application increased the total amount of water-stable macro-aggregates (>0.25 mm); however, MWD was not significantly affected by compost application. The MWD in the NK treatment was lower than in CK by 0.2 mm, while its variation among NPK, OM, 1/2OM1/2NPK, NP, PK, and CK was not significant. The compost- and mineral fertilizer-treated soil had 34.6–91.7% higher volume of macropores than the CK soil. The OM and 1/2OM1/2NPK-treated soil had a significantly higher proportion of small pores (

Continuous applications of organic and inorganic fertilizers can affect soil and food quality with respect to selenium (Se) concentrations. A long-term (over 20 years) experimental field study, started in 1989, was conducted to investigate the changes in soil Se fractions and its uptake by crops, as affected by different fertilizer practices, in the North China Plain with an annual crop rotation of winter wheat and summer maize. The long-term experiment was arranged in a complete randomized block design consisting of 4 replications with 7 fertilizer treatments: 1) organic compost (OC), 2) half organic compost plus half N-P-K chemical fertilizers (OC + NPK), 3) N-P-K fertilizers (NPK), 4) N-P fertilizers (NP), 5) P-K fertilizers (PK), 6) N-K fertilizers (NK), and 7) an un-amended control. Soil samples from the surface (20 cm) were collected in 1989, 1994, 1999, 2004 and 2009 to characterize Se and other soil properties. In 2009, the average soil Se concentrations in the treatments (149 ± 8 pg kg−1) were higher than those in the soil samples collected in 1989 at the beginning of the experiment (112 ± 4 pg kg−1), and decreased in the order of OC > OC + NPK > NPK ≈ NP > PK ≈ NK > control. Sequential extraction showed the oxidizable fraction (50.06% ± 3.94%) was the dominant form of Se in the soil, followed by the residual fraction (24.12% ± 2.89%), exchangeable fraction (15.09% ± 4.34%) and Fe-Mn oxides fraction (10.73% ± 4.04%). With an increase of soil K, the exchangeable Se concentrations in the soil increased. The Se concentrations in the soil tillage layer (0–20 cm) were mainly related to soil organic carbon (SOC), although different contributions came from atmospheric deposition, irrigation and fertilizers. With the accumulation of SOC, the uptakes of soil Se by two crops were inhibited. For the OC and OC + NPK treatments, Se concentrations in wheat grains were lower than the critical standard of Se in stable food (100 µg kg−1). Additionally, Se concentrations in grains were also decreased by the deficiencies of major soil nutrients, especially P.

Low-cost, simple, rapid and accurate approaches for measuring soil hydraulic properties are of great importance in the application of hydrologic models of the vadose zone. A recently proposed method of constant-saturation absorption (MCSA) for determining Brooks-Corey (BC) model parameters is promising. However, this method has not been tested using experimental data. In this paper, measured soil-water diffusivity or soil-water retention curves (SWRCs) of 20 soil samples were used to test the reliability of MCSA. The results indicate that MCSA consistently estimated soil-water diffusivities by the Bruce and Klute method, but it substantially overestimated air-entry suctions (h(d)) and thereby soil suction. A new method (MCPA) is proposed herein to overcome the problems associated with MCSA. Using the improved method, estimated SWRCs are consistent with observation. With the estimated soil hydraulic parameters, HYDRUS-1D generated very accurate simulations of the cumulative absorption curves. Compared with direct or other indirect methods, MCPA is a more accurate, low-cost, and simple method, and it is especially useful for rapid determination of SWRC for soil-water movement simulations. However, if unsaturated soil-water diffusivity is of greater concern, our results also indicate that MCSA more accurately predicts this quantity and thus should be preferred. (C) 2015 Elsevier B.V. All rights reserved

Solonetz soils are typically characterized with excessive saline-alkali content, and physiochemical methods are often employed for solonetz reclamation. However, increasing lines of evidences have suggested that microbiomes play a pivotal role in sustaining soil fertility than previously appreciated, and it remains poorly understood about the taxonomic identity of microbiomes in solonetz soils and the underlying mechanisms that govern the community assembly of solonetz restoration. In this study, we show that significant increase of rare phylotypes occurred after solonetz restoration by natural grassland and reclaimed farmland, and prokaryotic community assembly was dominated by deterministic rather than stochastic processes. The exchangeable sodium decreased significantly from 27.04% in solonetz, to 4.35% in grassland and 0.52% in farmland. Soil organic carbon (SOC) increased significantly with 4.17- and 2.18- fold in grassland and farmland soils relative to solonetz, respectively. Real-time quantitative PCR indicated drastic increases in the abundance of functional genes responsible for nitrogen fixation and nitrification. High-throughput sequencing of 16S rRNA genes further revealed that 180 and 215 phylotypes could be considered as key taxa showing significant increase after solonetz restoration by grassland and farmland. Intriguingly, more than 96% of these key phylotypes were originally rare phylotypes with

Improvement of Shajiang black soil in the Huanghuai plain is crucial for sustainable agricultural production; however, the effects of intensified fertilizer input on microbial communities in this soil type remain uncertain. Here, we conducted a long-term field trial using a wheat-soybean-maize cropping system, which had five treatments: organic material (soybean cake) (OM), mineral fertilizers (NPK), standard nitrogen (N) (half from OM and half from NPK) (MNPK), high N (1.6-fold higher than other treatments, with half from OM and half from NPK) (HMNPK), and unfertilized control. The organic carbon (C) composition of the soil was analyzed by 13C nuclear magnetic resonance spectroscopy, and bacterial community structure was determined based on 16S rRNA gene sequencing analysis. Addition of NPK resulted in soil acidification, which was effectively alleviated by organic amendment. NPK significantly (P

Soil bacteria and fungi are essential constituents of arable ecosystems. Long-term phosphorus (P) deficiency has been proven to significantly affect microbial community diversity and composition. However, how P deficiency impacts the interplay between bacteria and fungi remains unclear. The objective was to explore the bacterial-fungal co-occurrence patterns in soil as influenced by long-term P deficiency, using network analysis. Bacterial and fungal community datasets were obtained from soils which have consistently and continuously been fertilized with P (+P) or without P (−P) for >20 years in three long-term field experiments in China. Our results showed that the −P network was less complex and less efficient as indicated by fewer edges, lower average degree and higher average path length. Chronic P deficiency simultaneously decreased positive and negative bacterial-fungal edges, implying that both synergistic and antagonistic interactions were enhanced by P application. The keystone species differed between +P and −P network, and those from the +P network showed significant correlations with less soil properties, indicating the −P network was more sensitive to environmental disturbances. Four major modules were observed in both +P and −P networks, and they related with different soil properties, suggesting distinct habitat heterogeneity or niche partitioning. All the modules had similar ecological roles, while the module composition was altered by long-term P deficiency, indicating a possible ecological redundancy. Most of the fungi from the −P treatment were distributed in a special module negatively correlated with available P, indicating that fungi may prefer niches with low P concentration. Taken together, our results illustrated the crucial roles of P availability in microbial community assembly and investigated the responses of co-occurrence patterns to long-term P deficiency by regulating the topological properties, keystone species and module composition of the bacterial-fungal network.

Background and aims This paper was primarily devoted to understand the interactions of soil aggregates, organic carbon (C) and carbon cycle enzymes in aggregates under different fertilization managements, aiming to identify the effects of organic and inorganic fertilizer amendments on soil organic C accumulation and the activities of carbon cycle enzymes within aggregates in Vertisol. Methods A Vertisol soil following 4-year compost and inorganic fertilizer amendments, i.e. no fertilizer (CK), mineral fertilizer (FR) and 60% compost N plus 40% fertilizer N (FRM), was collected to identify the dynamics of organic C, enzymes activities and their associations with macroaggregation using aggregate fractionation techniques. Results The organic C content in all FR and FRM treatments was 8.24–41.15% higher than that in CK. An increased amounts of carbon cycle enzymes in aggregates or 0–20 cm bulk soil were also observed in FRM plots. Compared to FR, FRM significantly strengthened the structural stability of macroaggregates and the intimate connection between enzyme activities and macroaggregates. Conclusions As a recommended measure, supplementation with organic manure such as compost strengthened the process of mutual promotion between carbon cycle enzymes and macroaggregates, and the synergistic effect would be highly beneficial to soil organic C sequestration.

Soil organic matter (SOM) and interparticle forces, including the electrostatic repulsive force (ERF), surface-hydration repulsive force (SHRF) and van der Waals attractive force (vDWAF), play crucial roles in aggregate stability. However, few studies investigated their coupled effects on aggregate stability in variably charged soils, in which soil particle interactions are more complex than in permanently charged soils due to the coexistence of positive and negative charges and the variable surface charge characteristics. Therefore, this study aims to: 1) investigate the combined effects of soil solution pH and the overlapping of electric double layers (EDLs) between positively charged Fe/Al (hydro)oxides and negatively charged SOM on the ERF and aggregate stability before (control) and after SOM removal and after straw incubation for 240 days; and 2) evaluate the importance of soil interparticle forces and SOM for aggregate stability in a permanently charged temperate soil (Vertisol) and a variably charged subtropical soil (Ultisol). Soil aggregate stability was determined by measuring the release of small particles (w(

Sustainable agricultural production is of vital importance to food supply security. This study aimed to investigate crop yield response to spatial variability of soil quality at a county scale in the North China Plain (NCP) and subsequently derive key soil quality indicators. Soil samples were geo-referenced and taken in 2008 from both surface (0–20 cm) and subsurface (20–40 cm) layers in 132 fields throughout the Fengqiu County, located in the centre of the NCP, for subsequent soil properties' analyses. Annual crop yields were obtained from the same fields where soil samples were collected. Soil quality was evaluated based on a fuzzy set with 13 soil properties, and its spatial distributions were investigated by integrating geostatistical analysis and geographic information system (GIS) techniques. Soil quality indices were classified into five grades, and their spatial distributions were mapped within the county. The surface soil qualities were about one to two grades higher than the subsurface soil. The quality indices for surface and subsurface soils were positively associated with the annual crop yields, suggesting the importance of both. Soil organic matter, total nitrogen, available P, and available K contributed 50% of the combined weight to the soil quality index and were identified as key indicators of soil quality status in the area in terms of sustainability.

The Green–Ampt model (GAM) is a widely used water infiltration model. However, it lacks a reliable theoretical basis to independently and simultaneously determine the GAM parameters of effective hydraulic conductivity (Kₑ) and the average matric pressure head at the wetting front (Hf) from those commonly measured soil hydraulic properties. In this paper, we derived an approximate analytical solution similar to GAM for one-dimensional vertical infiltration into soils with initially uniform soil moisture distribution, with Kₑ and Hf being simultaneously related to the Brooks–Corey (BC) model parameters. The new relationships are not restricted to the piston-type moisture profile or delta-type water diffusivity like in the traditional GAM (TGAM). Infiltration experiments on three soils of various textures were conducted to validate the new approximate analytical solution and the corresponding GAM parameters. It was demonstrated that the predicted cumulative infiltrations and soil moisture profiles by the GAM with Kₑ and Hf calculated by the new expressions (new GAM, NGAM) generally agreed well with the numerical solutions, especially for initially dry soils. In contrast, cumulative infiltrations were considerably over-predicted by the TGAM using Kₑ = Kₛ and Hf calculated by Neuman’s equation. Our theoretical analysis further indicated that even without air entrapped during infiltration, the effective hydraulic conductivity can still be less than the saturated hydraulic conductivity Kₛ. The relative effective hydraulic conductivity ζ (Kₑ/Kₛ) and the relative average matric pressure head at the wetting front η (-Hf/hd where hd is absolute value of the air-entry suction) show a dependency only on soil pore structure index (n) and effective initial soil-water saturation (Sᵢ). The values of ζ increased but η decreased with Sᵢ and n. The theoretical ranges of ζ and η were from 0.5 and 2 for dry heavy-texture soils to 1 and 0 for saturated soils, respectively, which are consistent with the experimental values reported in literatures.

It is of ecological significance to investigate microbial communities in response to straw amendment and moisture in arable soils. However, in Chinese fluvo-aquic soils, these responses are still poorly understood. We designed an incubation experiment involving two soils with and without the addition of maize stubble at two moisture levels, and bacterial community structure at days 20, 80, and 200 after the start of incubation was assessed via bar-coded pyrosequencing of the 16S rDNA amplicons. In the presence of stubble with identical moisture level, we observed higher bacterial diversity and richness in long-term organic manure-fertilized soil compared with the unfertilized soil at days 20 and 80, which we attributed to the different quality and quantity of organic matter between the two soils. However, there was no significant difference in bacterial diversity and richness between the two soils at day 200, indicating that long-term straw amendment probably lessens the difference in bacterial community structure between the two soils. In the amended soils bacterial diversity, richness, and community composition at 25% of the water-holding capacity distinctly differed from those at 55% of the water-holding capacity, indicating that moisture strongly affects bacterial distribution in the amended soils. As stubble-C availability declined over time, the dominance of copiotrophic population weakened, and oligotrophic population was moderately abundant. Finally, our study suggests that dissolved organic carbon, which drives redistribution in copiotrophic and oligotrophic categories in response to the varying water and stubble-C availability, is a determinant of bacterial community composition in the amended soils. (C) 2014 Elsevier B.V. All rights reserved.

Organic manure (OM) fertilization has a profound impact on agroecosystems. However, little is known about temporal responses and roles of the specific soil microbial guilds involved in the increases of soil fertility and crop yield triggered by OM fertilization. To unravel these interactions, a series of fresh and archived soil samples from a fertilization experiment started in 1989 in North China Plain (NCP) was systematically investigated. Molecular assays of contemporary fresh samples unravel that Bacillus asahii responded most distinctly to OM fertilization, while no shifts in microbial community structure were observed between chemical fertilizations and the control without fertilization; a series of archived soil samples from 1989 to 2009 reveal that the indigenous B. asahii took 2e4 years to become specifically dominant and its ratio fluctuated between 40% and 72% during 20 years. Culture-dependent assessments of isolated B. asahii strain further indicate that its rise subsequently played a key role in the increases of both crop yield and soil fertility, especially via accelerating carbon and phosphorus cycling. This insight deepens our understanding of how OM impacts agroecosystems through soil microbial processes, and highlights the possibility of using archived microbial information as a reference to develop an efficient and sustainable agricultural strategy.

Gaseous nitrogen (N) losses are mainly responsible for low N use efficiency of applied fertilizers and their derivative environmental hazards, while N application rates and soil water regime are important factors regulating these N processes. In this study, gaseous N losses via ammonia volatilization (AV) and denitrification, determined by sponge trapping-KCl extraction and acetylene inhibition-soil core incubation, respectively, were investigated under different coupled water-N management practices with a winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system in the Huang-Huai-Hai Plain. Ammonia volatilization after urea application, particularly after topdressing during maize growing seasons, was the dominant gaseous N loss, amounting up to 53.2 kg N ha−1 (38.6 % of the applied N). Ammonia volatilization generally decreased by increasing irrigation rate applied immediately after fertilization. Denitrification N losses were lower than ammonia-N losses, accounting for 1.3 to 18.7 kg N ha−1 year−1, with more than 90 % occurring during the maize growing seasons. Total gaseous N losses showed a significant (P

Understanding the balance between soil organic carbon (SOC) accumulation and depletion under different fertilization regimes is important for improving soil quality and crop productivity and for mitigating climate change. A long-term field experiment established in 1989 was used to monitor the influence of organic and inorganic fertilizers on the SOC stock in a soil depth of 0–60 cm under an intensive wheat–maize cropping system in the North China Plain. The study involved seven treatments with four replicates: CM, compost; HCM, half compost nitrogen (N) plus half fertilizer N; NPK, fertilizer N, phosphorus (P), and potassium (K); NP, fertilizer N and P; NK, fertilizer N and K; PK, fertilizer P and K; and CK, control without fertilization. Soil samples were collected and analyzed for SOC content in the 0–20 cm layer each year and in the 20–40 cm and 40–60 cm layers every five years. The SOC stock in the 0–60 cm depth displayed a net decrease over 20 years under treatments without fertilizer P or N, and in contrast, increased by proportions ranging from 3.7% to 31.1% under the addition of compost and fertilizer N and P. The stabilization rate of exogenous organic carbon (C) into SOC was only 1.5% in NPK-treated soil but amounted to 8.7% to 14.1% in compost-amended soils (CM and HCM). The total quantities of sequestered SOC were linearly related ( P − 1 yr − 1 was found to be required to maintain the SOC stock level (zero change due to cropping). However, the organic C sequestration rate in the 0–60 cm depth decreased from 0.41 to 0.29 Mg C ha − 1 yr − 1 for HCM and from 0.90 to 0.29 Mg C ha − 1 yr − 1 for CM from the period of 1989–1994 to the period of 2004–2009, indicating that the SOC stock was getting to saturation after the long-term application of compost. The estimated SOC saturation level in the 0–60 cm depth for CM was 61.31 Mg C ha − 1 , which was 1.52 and 1.14 times the levels for NPK and HCM, respectively. These results show that SOC sequestration in the North China Plain may mainly depend on the application of organic fertilizer. Furthermore, the SOC sequestration potential in the 0–20 cm layer accounted for 40.3% to 44.6% of the total amount in the 0–60 cm depth for NPK, HCM, and CM, indicating that the SOC sequestration potential would be underestimated using topsoil only and that improving the depth distribution may be a practical way to achieve C sequestration.

Soil aggregation is one of the key properties affecting the productivity of soils and the environmental side effects of agricultural soils. In this study, we aimed to identify whether biochar could be used to improve aggregate stability. A 2-year field experiment was conducted to investigate the effect of biochar application (0, 2.5, 5, 10, 20, 30 and 40 t ha−1) on aggregate characteristics of upland red soil under a rapeseed–sweet potato rotation in subtropical China. Percentage of aggregate destruction (PAD0.25), mean weight diameter (MWD), geometric mean diameter (GMD) and fractal characteristics of soil aggregates were measured using both wet and dry sieving methods. Results showed that applying biochar significantly decreased the percentage of aggregate destruction and soil fractal dimension and increased the MWD and GMD. The optimal amelioration was observed when biochar was applied at a rate of 40 t ha−1. The decline of the fractal dimension of dry aggregates was 2–9 times as much as that of water-stable aggregates in the 0–15 soil layer and 1–4 times in the 15–30 cm soil layer. These results suggested that biochar could improve the resistance of aggregates to stresses and provide scientific strategies for the agricultural production.

The backward Lagrangian stochastic (BLS) model and open-path tunable diode laser (OPTDL) analyzer were used to monitor ammonia (NH3) emissions from urea applied to winter wheat in the North China Plain. The high-temporal resolution measurements of ammonia concentrations provided an opportunity for estimating the diel patterns of ammonia emissions, as well as valuable information about the factors that influence NH3 emissions. The results showed both large diel variability and daily variability in NH3 volatilization, with NH3 emissions highest during the daytime. The diel pattern of ammonia volatilization depended mainly on the diel variation of wind speed and soil temperature, while the overall pattern of NH3 loss was strongly affected by soil moisture content, soil NH4 +-N concentration, wind speed and soil temperature. At the end of the measurement period, the cumulative NH3 loss was 12.21–16.43 kg N ha−1, calculated based on different time scale average Q BLS. Due to sensitivity of the OPTDL analyzer, the estimated total ammonia loss was still doubtful in this study.