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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.

Fertilizer management influences the accumulation of soil organic C and N in agricultural soils. The combined use of chemical and organic fertilizers is considered a good method to enhance soil fertility, but it is still unclear about the effects of substituting manure for fertilizer on aggregation and aggregate associated organic C and N. We selected a 4-yr-old soil fertility experiment to examine the aggregation and aggregate associated organic C and N in response to substituting manure for fertilizer. In comparison to control, no fertilizer added (CK); substituting manure for fertilizer significantly increased organic C and N by 11.61 to 47.97% and 21.05 to 32.63% in 0- to 20-cm bulk soil, respectively. It promoted organic C in the silt + clay fraction, microaggregates, small macroaggregates, and large macroaggregates by 3.17 to 17.15%, 12.94 to 34.09%, 10.99 to 50.20%, and 25.32 to 52.09%, respectively. Aggregate associated N also presented significant increases under substituting manure for fertilizer compared to CK. The mass distribution of small and large macroaggregates were 8.16 to 15.54% and 8.89 to 49.51% higher in the manure-substituted plots than CK, respectively. Organic C and labile C were generally greater in macro- than microaggregates in the manure-substituted plots; redundancy analysis confirmed that macroaggregates had positive effects on organic C and N sequestration in bulk soil and aggregates. Based on these results we suggested that substituting manure increases macroaggregate associated organic C and N, and the formation of small and large macroaggregates is accelerated by organic amendment in the test soil compared to CK.

The effects of land use and fertilization regimes on soil denitrification potential (SDP) are often investigated, but less is known about the responses of SDP to different types of land use with different fertilization regimes in soils derived from the same parent material. We conducted a study using soil samples from 2 long-term (over 30 years) fertilization experiments to determine the difference in SDP between paddy soil and upland soil derived from the same quaternary red clay parent material. The results showed that the SDP in paddy soil was 6.82 times higher than the upland soil, which was due to the higher abundances of narG, nirS, and nirK genes and nirS-denitrifying bacteria (Bradyrhizobium, Cupriavidus, and Herbaspirillum) in paddy soil. Inorganic fertilization regimes did not significantly affect the SDP of upland soil over the control group, whereas SDP in the NPK and 2NPK treatments in paddy soil were reduced relative the control group by 26.48% and 75.65%, respectively. Compared with the control, the NPKOM treatment consistently yielded the highest SDP in both soils, with 2.47 times and 2.86 times higher for paddy soil and upland soil, respectively. The SDP of paddy soil was significantly correlated with narG and nirS genes mainly regulated by amorphous aluminum oxide, whereas the treatment effect on SDP for upland soil largely depended on differences in nirS-denitrifying bacteria at the genus level (Herbaspirillum, Sulfuritalea, and Cupriavidus) and species level, which were mainly controlled by soil pH. Partial least squares path models further demonstrated that the direct effects of functional genes on SDP were greatest for paddy soil, whereas nirS-denitrifying bacterial communities played a larger role in upland soil. The results presented herein represent a key step toward understanding the mechanisms that govern SDP under land use and long-term fertilization.

A 2-year field experiment was conducted on the North China Plain to assess the effects of two straw management practices and different nitrogen fertilizer addition levels on soil organic matter (SOM) fractions and microbial properties under a winter wheat-summer maize cropping system. Eight treatments (two straw management practices and four nitrogen fertilizer input levels) were established using a randomized complete block design. The straw management practices were no straw return and straw return. Each straw management practice received nitrogen fertilizer rates at 0 (N0), 270 (N270), 360 (N360), or 450 (N450) kg N ha−1 year−1. The soil properties measured included SOM fractionation, enzyme activities, community level physiology profile (CLPP), and microbial community abundance and composition, which were represented by phospholipid fatty acid (PLFA). Compared to no straw return, the addition of straw significantly increased soil total organic carbon and nitrogen, particulate organic carbon and nitrogen, and occluded particulate organic carbon and hot water extractable organic carbon by 7–29%. Invertase, protease, urease, and dehydrogenase activities increased by 22–40%. The biomasses of Gram-positive bacteria and fungi also increased. The increase in SOM fractions may be attributed to the decomposition of the added straw by more active enzymes, which may result from the shift of microbial community composition. In addition, hot-water extractable organic carbon, NO3-N, urease activity, and fungal biomass in the N270, N360, and N450 treatments significantly increased, independent of the nitrogen application rate, which indicated that N input level had a non-linear effect on soil properties in this area. Short-term straw return combined with a modest nitrogen fertilizer input (270 kg N ha−1 year−1) can increase SOM contents and microbial activity, which may help improve soil fertility in this region.

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.

Irrigation and nitrogen (N) fertilization in excess of crop requirements are responsible for substantial nitrate accumulation in the soil profile and contamination of groundwater by nitrate leaching during intensive agricultural production. In this on-farm field trial, we compared 16 different water and N treatments on nitrate accumulation and its distribution in the soil profile (0-180cm), nitrate leaching potential, and groundwater nitrate concentration within a summer-maize (Zea mays L.) and winter-wheat (Triticum aestivum L.) rotation system in the Huang-Huai-Hai Plain over five cropping cycles (2006-2010). The results indicated that nitrate remaining in the soil profile after crop harvest and nitrate concentration of soil solutions at two depths (80cm and 180cm) declined with increasing irrigation amounts and increased greatly with increasing N application rates, especially for seasonal N application rates higher than 190kgNha-1. During the experimental period, continuous torrential rainfall was the main cause for nitrate leaching beyond the root zone (180cm), which could pose potential risks for contamination of groundwater. Nitrate concentration of groundwater varied from 0.2 to 2.9mgL-1, which was lower than the limit of 10mgL-1 as the maximum safe level for drinking water. In view of the balance between grain production and environmental consequences, seasonal N application rates of 190kgNha-1 and 150kgNha-1 were recommended for winter wheat and summer maize, respectively. Irrigation to the field capacity of 0-40cm and 0-60cm soil depth could be appropriate for maize and wheat, respectively. Therefore, taking grain yields, mineral N accumulation in the soil profile, nitrate leaching potential, and groundwater quality into account, coupled water and N management could provide an opportunity to promote grain production while reducing negative environmental impacts in this region.

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.

This paper was primarily devoted to reveal the stock of soil organic carbon (C) as well as its lability and to compare their differences existing among tillage and residue practices, aiming to identify the effects on the accumulation process of organic C and its association with macroaggregation. Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution, organic C content and its lability. A wet-sieving method was used to fractionate aggregate fractions including > 2000 μm large macroaggregates, 2000–250 μm small macroaggregates, 250–53 μm microaggregates, and

Humic substances are recalcitrant and might act as persistent binding agents to form macroaggregates. The focus of this study is in investigating the contribution of humic carbon (HC) to soil aggregation in response to various tillage and residue managements. Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution and stability and HC fractions including humic acid (HA) and fulvic acid (FA). The contribution of HC to aggregation was divided into three special effects including positive effect (PE), negative effect (NE), and combined effect (CE), and these effects were measured using aggregate fractionation techniques. As well as to promote structural stability, HC bounds predominantly with the silt + clay fraction and secondarily with microaggregates to form larger aggregates. The PE increased with increasing aggregate size, whereas the NE followed the opposite pattern. A positive CE was observed for large and small macroaggregates, whereas the CE for microaggregates and the silt + clay fraction was negative. Compared to continuous tillage, reduced- and no-tillage decreased the PE for large and small macroaggregates by 1.58–30.98% at the 0–20 cm depth, and straw returning also slightly decreased the corresponding PE relative to straw removing. By contrast, a significantly higher NE for small macroaggregates at the 0–10 cm depth while 6.33–81.11% decreases in CE for large and small macroaggregates at the 0–10 cm depth as well as for large macroaggregates at the 10–20 cm depth, were observed under reduced- and no-tillage. The extraction of HC significantly reduced the aggregate stability and reduced- and no-tillage effectively limited its decrease magnitude. Small macroaggregates and microaggregates made larger contributions to soil HC accumulation than did other fractions. An averagely increased contribution from large or small macroaggregates was observed under both reduced-/no-tillage and straw returning at the 0–20 cm depth. A significant and positive relationship was found between the mass proportion of macroaggregates and the HC accumulation in 0–20 cm soil. Large macroaggregates had significantly higher HA/FA ratios than small macroaggregates, and reduced- and no-tillage significantly increased these ratios both in large and in small macroaggregates. The CE for large or small macroaggregates was also significantly negatively correlated with their HA/FA ratios. Overall, the HC accumulation in soil is likely to play a key role in macroaggregation, but conservation tillage might decrease the contribution magnitude of HC to large or small macroaggregation through increasing the corresponding HA/FA ratios.

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.

The objective of this study was to investigate microbial responses when seaweed fertilizer was added to maize straw compost. The metabolic characteristics and bacterial communities were assessed using 16S rRNA sequencing and Biolog analysis. Results showed that the urease, dehydrogenase, and metabolic activities improved on day 21 after the addition of seaweed fertilizer. Firmicutes, Proteobacteria, and Actinobacteria were the dominant phyla in the compost. The relative abundances of Proteobacteria and Actinobacteria were increased by addition of seaweed fertilizer during the early composting stage. Temperature, NH4+-N, NO3--N concentrations, and carbon source metabolism had close relationships with bacterial community variation during composting. A network analysis revealed that NO3--N content had a positive association with Aeromicrobium, and seaweed fertilizer application improved the growth of keystone species related to N cycling. These results suggested that seaweed fertilizer influenced bacterial community succession through its effects on N concentrations during the composting process.

Manure application is widely recognized as a method of improving soil structure and soil fertility due to additional organic matter and nutrient inputs. However, the salinity of animal manure may have a detrimental effect on soil aggregation. The objective of this study was to determine the effects of long-term animal manure application on soil aggregation, binding agents (soil organic carbon, SOC and glomalin-related soil protein, GRSP), and dispersing agents (e.g., Na+) and their relationships based on nine long-term fertilization experiments (12 to 39 yr) across China. The two red soil experiments (Qiyang, QY and Jinxian, JX) and one paddy soil experiment in Jinxian (JX-P) were conducted in southern China (precipitation above 1200 mm yr−1), whereas the other six experiments were established in semi-humid or arid regions in China with precipitation in the range of 500–900 mm yr−1. Each experiment included three treatments as follows: no fertilization (Control), inorganic fertilizer (NP or NPK), and a combination of inorganic fertilizer and animal manure (NPM or NPKM). Long-term animal manure application not only significantly increased the biological binding agents (i.e., SOC and GRSP) in the nine experiments but also considerably increased the dispersing agents (i.e., exchangeable Na+) (P

High-throughput sequencing and network analysis were used to investigate the dynamic changes and the effects on bacterial community structures in green waste compost after biochar addition. Biochar addition led to higher thermophilic temperatures and total nitrogen (TN) concentrations and a longer thermophilic period compared with no biochar addition. Biochar also greatly influenced the composition of the bacterial community. Nitriliruptoraceae and Bacillaceae abundances increased in the poultry manure after biochar treatment, and Alcaligenaceae, Rhodispirillaceae and Xanthomonadaceae were more abundant in the cattle manure. Dissolved organic carbon (DOC) and TN emerged as the key determinants of bacterial community composition. Network analysis revealed that DOC had strong positive associations with some taxa (e.g. Comamonas, Leucobacter and Acidimicrobiales), whereas TN had negative associations with other taxa (e.g. Microbacteriaceae and Aeromicrobium). This study has revealed the key taxa related to the carbon and nitrogen cycle during composting with biochar.

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.

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.

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.

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

Agricultural fertilization plays a crucial role in crop production, and the fungal communities catalyze transformation of soil nutrients in support of crop production. However, it remains controversial about the optimal strategy for fertilizer inputs and the adaptive mechanisms of fungal communities across China. By using seven long-term field fertilization experiments in China, we analyzed crop yields, soil properties and fungal communities in soils that were treated for > 25 years with no fertilizer (control), inorganic fertilizers (NPK) and organic-inorganic fertilizers (NPKM). Long-term NPK resulted in significant acidification up to a decline by 1.20 pH units, while NPKM prevented acidification and increased pH up to 6.39 in three acidic soils with pH 8.11, both NPK and NPKM led to only marginal decline of soil pH, and NPK and NPKM showed comparable crop yields. Some members of Ascomycota in alkaline soils were both enriched by NPKM and NPK. Soil available P and C:N ratio, rather than pH, directly or indirectly affect crop yield in alkaline soils. High crop yield can be achieved by the sole use of inorganic fertilizers in alkaline soils, but acidic soil productivity should be maintained by organic amendment to counteract acidification by inorganic fertilization. Our study advances a mechanistic understanding for optimizing fertilization strategies towards sustainable agriculture under increasingly intensified fertilizer inputs.

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.

Elevated CO2 would increase rice yields and may lead to nitrogen limitation and potentially influence the sustainability of agricultural production. Blindly increasing the amount of chemical fertilizer will damage the environment and is very unwise. Therefore, clarifying the response of soil nitrogen mineralization capacity to elevated CO2 is critical for both sustainable agriculture production and environmental protection. Here, we relied on Free-Air CO2 Enrichment (FACE) platform and used a waterlogged incubation method to investigate the effects of elevated CO2 on soil nitrogen mineralization capacity under different fertilization levels when planted different rice cultivars (strong and weak-CO2 response rice). According to the first-order kinetic equation fitting, compared with Ambient, elevated CO2 increased soil potential mineralized nitrogen (Np) by 16.18%. Path analysis indicated that fertilization status, rice cultivar, soil organic carbon and soil C: N ratio might affect Np. There was a significant positive correlation between soil nitrogen mineralization rate and Np. Under different fertilization conditions and rice cultivars, the improvement degree of soil nitrogen mineralization capacity (Np and soil nitrogen mineralization rate) by elevated CO2 was different. These findings suggest that more parameters and influencing factors should be taken into account when studying soil nitrogen cycle models under the condition of global change.

The North China Plain (NCP) is a strategic grain production base in China with a wild distribution of fertile soils. During the past 20 years, high-input intensive agriculture with excess chemical fertilizer application has sustained high grain yields, but may have resulted in contamination of some elements in farmland. In this study, the accumulation and transfer of arsenic (As) and mercury (Hg) in typical Calcaric Fluvisols with long-term different fertilization practices were investigated. Field experiments with seven treatments were launched in 1989, and soil and plant samples were collected and analyzed periodically. The treatments include OM (organic manure), OM + NPK (50 % organic manure + 50 % chemical fertilizer), NPK, NP, PK, NK, and CK (the control experiment with no fertilizer). With over 20 years (1989–2009) of cultivation, various extents of As and Hg accumulations were really observed in the soil. The higher As and Hg contents were found in P fertilizers than those in N, K, or OM fertilizers. As a result, the long-term P fertilization slightly promoted Hg accumulations with decreased soil Hg concentrations in the order of NPK ≈ NP ≈ PK ≈ OM + NPK > OM > NK ≈ CK, which was similar to the order of crop yields. At the tillage layer (0–20 cm), Hg accumulation in the soil was enhanced by crop production, due to the highly accumulated Hg in plant roots finally remained in the soil. However, no significant differences of soil As concentrations can be found between treatments with and without P fertilizers probably due to water leaching and plant uptake. Soil As and Hg were mainly contributed by fertilizers, irrigation, and atmospheric deposition in recent years, but they did not exhibit in significant accumulations in the soil. The contents of As and Hg were not above the critical safe levels of soils for crop production (As

The quick assessment approaches for accurately measuring water-use efficiency (WUE) in maize under water stress are important to water-saving agriculture. We investigated how and whether carbon isotope composition (δ 13C) and specific leaf area (SLA) could be used to assess WUE for maize as influenced by water stress. A pot experiment was conducted twice during six typical maize (Zea mays) growth stages of seedling, jointing, booting, tasseling, filling and maturity, respectively. The ratio between the activities of ribulose 1,5-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase decreased bundle sheath leakiness (φ) under water deficiency, caused more 13C to be assimilated, and resulted in increased δ 13C in leaves. Water stress increased the fractionation of 13C when assimilates were transported from leaf to stem, indicating that water stress affected leaf expansion and translocation of assimilates from leaf to stem, and resulted in thicker leaves and lower SLA. WUE showed significant positive correlations with leaf δ 13C and SLA, implying that leaf δ 13C and SLA could effectively reflect the drought adaptation and high WUE under different water conditions.

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

A field experiment was conducted to study the effect of biochar amendment (0, 2.5, 5, 10, 20, 30 and 40 t·ha− 1) on rapeseed and sweet potato yields, aggregate particle size distribution, aggregate stability, soil organic carbon, total N content and C:N ratio in soil water stable aggregate under a rapeseed–sweet potato rotation system in upland red soil in Jiangxi Province of southern, China. The results were as follows: compared with control treatment (CK), when the amount of biochar was 40 t·ha− 1, rapeseed and sweet potato yields were increased by 36.02% and 53.77% respectively; the soil water stable aggregate (> 0.25 mm) in the 0–15 cm soil layer had a remarkable increase than other treatments, especially the macroaggregate with particle size larger than > 2 mm. In the rapeseed harvest season, the mean weight diameter of soil water stable aggregate was enhanced by 28.02% compared to CK with the application rate of biochar being 40 t·ha− 1. A significant increment in soil organic carbon, total N and C:N ratio was observed in the > 2 mm, 2–0.5 mm, 0.5–0.25 mm and

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.

Fertilization has a large impact on the soil microbial communities, which play pivotal roles in soil biogeochemical cycling and ecological processes. While the effects of changes in nutrient availability due to fertilization on the soil microbial communities have received considerable attention, specific microbial taxa strongly influenced by long-term organic and inorganic fertilization, their potential effects and associations with soil nutrients remain unclear. Here, we use deep 16S amplicon sequencing to investigate bacterial community characteristics in a fluvo-aquic soil treated for 24 years with inorganic fertilizers and organics (manure and straw)-inorganic fertilizers, and uncover potential links between soil nutrient parameters and specific bacterial taxa. Our results showed that combined organic-inorganic fertilization increased soil organic carbon (SOC) and total nitrogen (TN) contents and altered bacterial community composition, while inorganic fertilization had little impact on soil nutrients and bacterial community composition. SOC and TN emerged as the major determinants of community composition. The abundances of specific taxa, especially Arenimonas, Gemmatimonas, and an unclassified member of Xanthomonadaceae, were substantially increased by organic-inorganic amendments rather than inorganic amendments only. A co-occurrence based network analysis demonstrated that SOC and TN had strong positive associations with some taxa (Gemmatimonas and the members of Acidobacteria subgroup 6, Myxococcales, Betaproteobacteria, and Bacteroidetes), and Gemmatimonas, Flavobacterium, and an unclassified member of Verrucomicrobia were identified as the keystone taxa. These specific taxa identified above are implicated in the decomposition of complex organic matters and soil carbon, nitrogen, and phosphorus transformations. The present work strengthens our current understanding of the soil microbial community structure and functions under long-term fertilization management and provides certain theoretical support for selection of rational fertilization strategies.

Returning crop straw into fields is a typical agricultural practice to resolve an oversupply of straw and improve soil fertility. Soil microorganisms, especially eukaryotic microorganisms, play a critical role in straw decomposition. To date, microbial communities in response to straw amendment at different moisture levels in Chinese fluvo-aquic soil are poorly understood. The aim of this study was to explore the effects of straw amendment and moisture on microbial communities in Chinese fluvo-aquic soil. Two soils (one was applied with organic manure, and the other was not applied with any fertilizer) from a long-term field experiment in the North China Plain were collected. Soils with and without straw amendment at 25 and 55 % of the average water-holding capacities of the two soils were incubated at 25 °C for 80 days. All treatments were sampled 20 and 80 days after the start of incubation. Microbial biomass and community structure were analyzed by phospholipid fatty acids (PLFA) assay, and the eukaryotic diversity and community composition were assessed via barcoded pyrosequencing of the 18S ribosomal RNA (rRNA) gene amplicons. PLFA analysis showed that straw amendment increased the biomass of Gram-positive bacteria, Gram-negative bacteria, actinobacteria, and fungi and shifted microbial community structure. The varied straw availability resulted in a large variation in microbial community structure. In the presence of straw, actinobacterial and fungal biomass both decreased under high moisture content. 18S rRNA gene pyrosequencing indicated that straw amendment decreased eukaryotic diversity and richness and probably restructured the eukaryotic community. Under identical moisture content, long-term organic manure-fertilized soil had higher eukaryotic diversity and richness than the unfertilized soil. In the amended soils under high moisture content, the relative abundance of dominant fungal taxa (Dikarya subkingdom, Ascomycota phylum, and Pezizomycotina subphylum) decreased. Straw amendment increases microbial biomass, shifts microbial community structure, and decreases eukaryotic diversity and richness. High moisture content probably has a negative effect on fungal growth in the amended soils. In conclusion, microbial communities in Chinese fluvo-aquic soil are significantly affected by straw amendment at different moisture levels.

Continuous application of organic and inorganic fertilizers can affect soil and food quality with respect to heavy metal concentrations. The risk of cadmium (Cd) contamination in a long-term (over 20 years) experimental field in North China with an annual crop rotation of winter wheat and summer maize was investigated. The long-term experiment had a complete randomized block design with seven fertilizer treatments and four replications. The seven fertilizer treatments were (1) organic compost (OM), (2) half organic compost plus half chemical fertilizer (OM + NPK), (3) NPK fertilizer (NPK), (4–6) chemical fertilizers without one of the major nutrients (NP, PK, and NK), and (7) an unamended control (CK). Soil samples from 0 to 20 cm were collected in 1989, 1999, and 2009 to characterize Cd and other soil properties. During the past 20 years, various extents of Cd accumulation were observed in the soil, and the accumulation was mainly affected by atmospheric dry and wet deposition and fertilization. In 2009, the average Cd concentration in the soil was 148 ± 15 μg kg−1 and decreased in the order of NPK ≈ OM + NKP ≈ PK > NP ≈ NK > OM ≈ CK. Sequential extraction of Cd showed that the acid-soluble fraction (F1, 32 ± 7 %) and the residual fraction (F4, 31 ± 5 %) were the dominant fractions of Cd in the soil, followed by the reducible fraction (F2, 22 ± 5 %) and oxidizable fraction (F3, 15 ± 6 %). The acid-soluble Cd fraction in the soil and Cd accumulation in the crops increased with soil plant available K. Fraction F3 was increased by soil organic C (SOC) and crop yields, but SOC reduced the uptake of soil Cd by crops. The long-term P fertilization resulted in more Cd buildup in the soil than other treatments, but the uptake of Cd by crops was inhibited by the precipitation of Cd with phosphate in the soil. Although soil Cd was slightly increased over the 20 years of intensive crop production, both soil and grain/kernel Cd concentrations were still below the national standards for environmental and food safety.

Soil phosphorus (P) composition and phosphatase activities in aggregates are essential for agricultural productivity and remain poorly understood. A field experiment was conducted from 2007 to study the effect of tillage systems (conventional tillage, T and no tillage, NT) and crop residue management (0, 50% and 100% crop residue incorporation/coverage) on P composition determined by 31 P nuclear magnetic resonance (NMR) and phosphatase activities in soil aggregates (>2 mm, 0.25–2 mm and 0.053–0.25 mm). The results showed that crop residue input influenced the concentrations of soil phosphate monoesters and diesters, alkaline phosphomonoesterase (AlP), acid phosphomonoesterase (AcP), phosphodiesterase (PD) activities, and soil aggregate stability significantly, and the addition of crop residue was significantly more effective than tillage. The NT had significantly higher soil phosphatase activities than tillage treatment but not more soil P content. The 0.25–2 mm aggregates showed higher total P, organic P, concentrations of monoesters and diesters, and AlP activity. The structure equation model showed that soil aggregate stability could increase concentrations of monoesters and diesters indirectly by its direct effects on soil phosphatases. Our results suggest that NT and crop residue input could increase the P store and sustainable supply in soil aggregates and that the 0.25–2 mm size aggregates may play an important role in soil organic P maintenance and transformation.

An 80-d incubation experiment was conducted to investigate straw decomposition, the priming effect and microbial characteristics in a non-fertilized soil (soil 1) and a long-term organic manure-fertilized soil (soil 2) with and without 13C-labeled maize straw amendment under different moisture levels. The soil 2 showed a markedly higher priming effect, microbial biomass C (Cmic), and β-glucosidase activity, and more abundant populations of bacteria and fungi than the soil 1. Also, soil CO2 emission, Cmic, β-glucosidase activity, and bacterial and fungal population sizes were substantially enhanced by straw amendment. In the presence of straw, the amount of straw mineralization and assimilation by microbes in the soil at 55% of water holding capacity (WHC) were significantly higher by 31% and 17%, respectively, compared to those at 25% of WHC. In contrast, β-glucosidase activity and fungal population size were both enhanced as the moisture content decreased. Cmic decreased as straw availability decreased, which was mainly attributed to the reduction of straw-derived Cmic. Amended soils, except the amended soil 2 at 25% of WHC, had a more abundant fungal population as straw availability decreased, indicating that fungal decomposability of added straw was independent of straw availability. Non-metric multidimensional scaling analysis based on fungal denatured gradient gel electrophoresis band patterns showed that shifts in the fungal community structure occurred as water and straw availability varied. The results indirectly suggest that soil fungi are able to adjust their degradation activity to water and straw availability by regulating their community structure.

Different irrigation and fertilization managements can greatly affect plant potassium (K) uptake in soils. A continuous extraction experiment was used to analyze the influence of poor-quality irrigation water on K release from soils under long-term copping with different fertilizations. The results demonstrated that K release kinetics included a rapid stage and a subsequent slow one. K leached in the solution with Ca:Mg ratio 75:25 and sodium adsorption ratio (SAR) 45 was minimum (146 mg kg−1), while K leached in the solution with Ca:Mg ratio 25:75 and SAR 5 was maximum (212 mg kg−1). Due to the specific ion effect, Mg2+ played a more important role in the release of K than Ca2+. The K release rates and quantities of released K in the soils without K fertilizers were lower than others. Long-term planting without K fertilizers results in the decrease of K fertility. Power equation and parabolic equation fully simulated the process of K release, suggesting a diffusion-controlled process. The K extracted by ...

The objective of this study was to examine the effects of addition of inoculant to high-nitrogen (N) fertilized timothy on fermentation, nutritive value, and feed intake of silage. The silage of timothy cultivated with a N fertilizer rate at two levels (high level (H), standard level (S)) was prepared with (SI, HI) or without (SC, HC) an inoculants. The CP content of H increased by 38 g&middotkg-1 DM compared with that of S, and the WSC and ADF contents decreased compared with those of S. Regarding the fermentation of silage, the pH and NH3-N ratio was significantly lower in the silage with inoculant (SI and HI), showing improvement of the fermentation compared with those of the silage without the addition (SC and HC). The CP content was significantly higher in HC and HI than in SC and SI, and the NDF content was the lowest in HI among the four treatments. The CP digestibility of HC and HI was significantly higher than those of SC and SI. The EE digestibility of SI was significantly higher than that of SC, and that of HI was significantly higher than that of HC. The DCP contents were significantly higher in HC and HI than in SC and SI. The TDN content was the lowest in SC and highest in HI. The DCP intakes of HC and HI were significantly higher than those of SC and SI. When the N fertilizer rate was increased, the DCP content and DCP intake of the silage increased, and the addition of inoculant improved the fermentation and increased the TDN content.

This study investigates the effects of residue incorporation coupled with plant growth and soil moisture level on wheat biomasses, soil nutrients, labile organic carbon (LOC), microbial metabolic profiles, and community composition. Four management practices were used in a 180-day pot experiment: (1) control (CON), (2) maize (Zea mays L.) residue incorporation without plants (MR), (3) wheat (Triticum aestivum L.) plants without maize residue (WP), and (4) maize residue incorporation with wheat plants (MRWPs). Each management practice included soil moisture at both 40 and 80% of field capacity. At wheat harvest, soil nutrient contents in the WP and MRWP treatments were significantly lower than in the CON and MR treatments. In comparison with the CON treatment, MR, WP, and MRWP treatments resulted in 35, 23, and 67% increases in dissolved organic carbon content; 17, 12, and 34% increases in hot-water extractable organic carbon content; and 78, 50, and 150% increases in microbial biomass carbon content. Furthermore, microbial utilizations of carboxylic acids and polymer carbon sources in the MR, WP, and MRWP treatments were 261 and 88%, 239 and 105%, and 300 and 126% higher than in the CON treatment. The MR and CON treatments had similar phospholipid fatty acid (PLFA) content but the WP and MRWP treatments had significantly increased gram-negative content and changes to community composition compared with the CON and MR treatments. The wheat biomass, LOC, and PLFA contents significantly increased with greater soil moisture. Overall, these results suggest an additive effect of residue incorporation and plant growth on LOC contents, primarily due to the changes in microbial utilization of carbon sources and community composition.

Initial soil pH has been reported to have a great impact on the decomposition of added organic materials and hence to determine the direction and magnitude of subsequent soil pH changes. However, most previous investigations have been conducted on different soil types differing in initial pH and other soil properties. Here, we investigated the effects of initial soil pH on the subsequent soil pH and N mineralization changes caused by addition of crop residues to two soils (a Paleudalf and a Plinthudult) with different pHs induced by treatment with direct electric current. This produced pH gradients of 6.50–3.20 and 6.74–3.81, respectively. Three typical field crop residues differing in C/N ratio, i.e. rice straw C/N = 42, canola residue C/N = 36 and Chinese milk vetch C/N = 14 (vetch), were incubated with the soils for 102 days. With both soils, total CO2 fluxes differed between the type of added crop residues, with vetch > canola residue > rice straw, and decreased with decreasing initial soil pH. The incorporation of crop residues into the two soils at all pHs increased soil pH except for the Paleudalf at pH 3.81 and 4.25 amended with rice straw and canola residue, where pH slightly decreased. As expected, vetch incorporation caused a greater pH increase than the two non-legume residues (rice straw and canola residue), but this effect was transient in soils of higher initial pH. The pH declined rapidly with time in soils of initial pH ≥ 4.40 treated with vetch, while addition of rice straw and canola residue maintained stable pHs. Irrespective of crop residue addition, soil pH continuously increased or remained steady over the 102-day incubation period in the highly acidic soils (pH ≤ 4.25). While NH 4 + accumulated in highly acidic soils, NO 3 − accumulated in higher pH soils. Contrasting effects on nitrification and subsequent pH changes occurred between soil pH ≤ 4.25 and pH ≥ 4.40. However, no clear relationship between net N mineralization and soil pH was found. This study demonstrated that low soil pH greatly inhibited nitrification, while net N mineralization was generally less affected. This, in turn, affected the direction and extent of soil pH changes after addition of crop residues.

Soil samples collected from a long-term (19-year) experimental field with seven treatments were analyzed for fatty acids methyl esters (FAMEs) to determine fertilization regime effects on microbial community structure in sandy loam soils. The amounts of FAMEs in bacteria, actinomycetes, and fungi were highest with the two organic manure (OM)-fertilized treatments (OM and 1/2 OMN – half OM plus half mineral fertilizer), lowest with the NK treatment, and fell in the middle levels with three mineral P-fertilized treatments (NPK, NP and PK) and the control with no fertilizer (CK), with the exception of fungi which showed no significant difference among the five treatments without OM fertilization. Principal component analysis of FAME patterns indicated that NPK was not significantly different from CK, but the two manure-containing treatments and the P-deficiency treatment (NK) were significantly different from CK and NPK. Redundancy analysis plot showed that FAME amounts significantly correlated to soil organic C and total N contents, while soil available P and total P contents, which were greatly decreased by the NK treatment, also had positive and substantial effects on soil microbial FAMEs. The results demonstrated the importance of P fertilization as well as organic manure in maintaining soil microbial biomass and impacting community structure.

Nitrate-nitrogen (NO − 3 -N) dynamics and nitrogen (N) budgets in rice ( Oryza sativa L.)-wheat ( Triticum aestivum L.) rotations in the Taihu Lake region of China were studied to compare the effects of N fertilizer management over a two-year period. The experiment included four N rates for rice and wheat, respectively: N1 (125 and 94 kg N ha −1 ), N2 (225 and 169 kg N ha −1 ), N3 (325 and 244 kg N ha −1 ), and N0 (0 kg N ha −1 ). The results showed that an overlying water layer during the rice growing seasons contributed to moderate concentrations of NO − 3 -N in sampled waters and the concentrations of NO − 3 -N only showed a rising trend during the field drying stage. The NO − 3 -N concentrations in leachates during the wheat seasons were much higher than those during the rice seasons, particularly in the wheat seedling stage. In the wheat seedling stage, the NO − 3 -N concentrations of leachates were significantly higher in N treatments than in N0 treatment and increased with increasing N rates. As the NO − 3 -N content (below 2 mg N L −1 ) at a depth of 80 cm during the rice-wheat rotations did not respond to the applied N rates, the high levels of NO − 3 -N in the groundwater of paddy fields might not be directly related to NO − 3 -N leaching. Crop growth trends were closely related to variations of NO − 3 -N in leachates. A reduction in N application rate, especially in the earlier stages of crop growth, and synchronization of the peak of N uptake by the crop with N fertilizer application are key measures to reduce N loss. Above-ground biomass for rice and wheat increased significantly with increasing N rate, but there was no significant difference between N2 and N3. Increasing N rates to the levels greater than N2 not only decreased N use efficiency, but also significantly increased N loss. After two cycles of rice-wheat rotations, the apparent N losses of N1, N2 and N3 amounted to 234, 366 and 579 kg N ha −1 , respectively. With an increase of N rate from N0 to N3, the percentage of N uptake in total N inputs decreased from 63.9% to 46.9%. The apparent N losses during the rice seasons were higher than those during the wheat seasons and were related to precipitation; therefore, the application of fertilizer should take into account climate conditions and avoid application before heavy rainfall.

The impact of fertilization on maize (Zea mays L.) yield and soil properties was investigated in a long-term (> 18 y) experimental field in N China. A completely randomized block design with seven fertilizer treatments and four replications was used. The seven fertilizer treatments were (1) compost (COMP), (2) half compost plus half chemical fertilizer (COMP1/2), (3) balanced NPK fertilizer (NPK), (4–6) unbalanced chemical fertilizers without one of the major elements (NP, PK, and NK), and (7) an unamended control (CK). In addition to maize yield, soil chemical and biological properties were investigated. Compared to the balanced NPK treatment, maize yield from the COMP treatment was 7.9% higher, from the COMP1/2 was similar, but from the NP, PK, NK, and CK treatment were 12.4%, 59.9%, 78.6%, and 75.7% lower. Across the growing season, microbial biomass C and N contents, basal soil respiration, and fluorescein diacetate hydrolysis, dehydrogenase, urease, and invertase activities in the COMP and COMP1/2 treatments were 7%–203% higher than the NPK treatment. Values from all other treatments were up to 60% lower than the NPK treatment. Maize yield is closely related to the soil organic C (OC) and biological properties, and the OC is closely related to various biological properties, indicating that OC is a suitable indicator for soil quality. Our results suggest the most limiting nutrient for improving the yield or soil quality was P, followed by N and K, and balanced fertilization is important in maintaining high crop yield and soil quality. Additionally, increases in OC, N, and biological activities in COMP and COMP1/2 treatments imply that organic compost is superior to the chemical fertilizers tested.

Inorganic phosphate solubilizing bacteria (iPSB) are essential to facilitate phosphorus (P) mobilization in alkaline soil, however, the phylogenetic structure of iPSB communities remains poorly characterized. Thus, we use a reference iPSB database to analyze the distribution of iPSB communities based on 16S rRNA gene illumina sequencing. Additionally, a noval pqqC primer was developed to quantify iPSB abundance. In our study, an alkaline soil with 27-year fertilization treatment was selected. The percentage of iPSB was 1.10~2.87% per sample, and the dominant iPSB genera were closely related to Arthrobacter, Bacillus, Brevibacterium and Streptomyces. Long-term P fertilization had no significant effect on the abundance of iPSB communities. Rather than P and potassium (K) additions, long-term nitrogen (N) fertilization decreased the iPSB abundance, which was validated by reduced relative abundance of pqqC gene (pqqC/16S). The decreased iPSB abundance was strongly related to pH decline and total N increase, revealing that the long-term N additions may cause pH decline and subsequent P releases relatively decreasing the demands of the iPSB community. The methodology and understanding obtained here provides insights into the ecology of inorganic P solubilizers and how to manipulate for better P use efficiency.