Soil In Northeast China Research Articles

Effect of repeated freezing–thawing on soil dissolved organic matter: a case study of brown farmland soil in Northeast China

Effect of repeated freezing–thawing on soil dissolved organic matter: a case study of brown farmland soil in Northeast China

The Effect of Uncertainty of Risks on Farmers’ Contractual Choice Behavior for Agricultural Productive Services: An Empirical Analysis from the Black Soil in Northeast China

Regulating farmers’ choice of agricultural production service (APS) contracts can help maintain the stability of transactions, enhance agricultural production efficiency, protect farmers’ rights and welfare, stimulate the healthy and sustainable development of service organizations, and promote the economic benefits of agriculture. Under the uncertainty of risk (RU), farmers’ willingness to sign a regulated service contract after purchasing APS is a key factor in reaching an efficient and high-quality partnership. Based on the survey data of the black soil area in northeastern China, this study uses the Heckman two-stage model and analyzes it under the logical framework of APS purchases and contractual choice behavior (CCB) under the role of RU. The main findings are as follows. First, the RU has a significant “inducing” effect on farmers’ CCB, and the higher the RU, the more farmers tend to make formal written contracts; among them, each unit increase in business risk increases farmers’ choice of written contracts by 0.797 units, which is an important factor affecting CCB. Second, farmers’ personal trust level played a positive moderating role in influencing CCB. Compared to the low trust level group, farmers in the high trust level group had a diminished degree of influence on CCB, but the intensity was relatively weak. Third, farmers’ personal, family, and social characteristics all influence their behavioral decision-making processes. In order to reduce the risk level of cooperation between farmers and service providers, which can promote the standardization of cooperation contracts, this study suggests that the government should use the publication of manuals and other forms to carry out legal literacy, promote labor market information transparency, reduce service risks, and enhance the effectiveness of the linkage between farmers and service providers.

Distribution and co-occurrence patterns of antibiotic resistance genes in black soils in Northeast China.

Black soils (Mollisols) are among the most important soil resources for crop production and food security. In China, they are mainly distributed in the northeastern region. To investigate soil antibiotic resistance distribution patterns and monitor soil quality, we randomly chose nine corn fields in Northeast China and analyzed the antibiotic resistance gene (ARG) distribution and co-occurrence patterns on the basis of high-throughput approaches and network analyses. High genetic diversity (136 unique genes) and low ARG abundances (10-5-10-2 copies/16S rRNA gene copy) were detected, with relatively few interactions among ARGs. Type I integron genes were prevalent in the soil and were positively correlated with ARGs, which may increase the risk of ARG transmission. Most ARGs were strongly associated with microorganisms. Moreover, several ARGs were significantly correlated with antibiotics, nutrients, and metal elements. The generation and dissemination of ARGs, which were most likely mediated by mobile genetic elements (MGEs) and bacteria, were affected by environmental conditions. These results provide insights into the widespread co-occurrence patterns in soil resistomes.

Long-term fertilization altered microbial community structure in an aeolian sandy soil in northeast China.

Soil microorganisms play crucial roles in nutrient cycling and determining soil quality and fertility; thus, they are important for agricultural production. However, the impacts of long-term fertilization on soil microbial community remain ambiguous due to inconsistent results from different studies. The objective of this study was to characterize changes in bacterial and fungal diversity and community structures after 12 years of different fertilization in aeolian sandy soil by analyzing 16S rRNA and ITS rRNA gene sequences and the soil properties to discover the driving factors. Eight different fertilizer treatments have been set up since 2009: no fertilizer (CK), chemical N fertilizer (N), chemical N and P fertilizer (NP), chemical N, P and K fertilizer (NPK), pig manure only (M), pig manure plus chemical N fertilizer (MN), pig manure plus chemical N and P fertilizer (MNP), pig manure plus chemical N, P, and K fertilizer (MNPK). The results indicated that the long-term application of chemical fertilizer reduced soil pH, whereas the addition of pig manure alleviated a decrease in soil pH value. Chemical fertilizer plus pig manure significantly improved soil available nutrients and soil organic carbon. Long-term MNPK fertilization resulted in changes in bacterial diversity due to effects on specific bacterial species; by contrast, all fertilization treatments resulted in changes in fungal diversity due to changes in soil properties. Principal component analysis indicated that fertilization had a significant effect on soil microbial community structure, and the effect of chemical fertilizer combined with pig manure was greater than that of chemical fertilizer alone. Soil available phosphorus, total phosphorus, and pH were the most important factors that influenced bacterial taxa, whereas soil pH, total phosphorus, organic carbon, ammonium nitrogen and nitrate nitrogen were the most important factors influencing fungal taxa after 12 years of fertilization in aeolian sandy soil.

Assessing the Impacts of Fertilization Regimes on Soil Aggregate Dynamics in Northeast China

Determining the effects of fertilization regimes on soil aggregates, carbon (C) and nitrogen (N) distribution, and pH is essential for improving soil structure and soil organic carbon (SOC) accumulation to help in proper soil fertility management. Based on a 41-year field fertilization experiment conducted on dark brown soil in northeast China, we examined the soil aggregate size distribution and associated C, N, and pH to provide a scientific basis for elucidation of the mechanisms underlying the effects of fertilization treatments on soil structure and fertility. Six different fertilization treatments included no fertilizer (CK), low-dose chemical fertilizer (NP), moderate-dose chemical fertilizer (2NP), high-dose chemical fertilizer (4NP), normal-dose organic fertilizer (M), and normal-dose organic fertilizer plus moderate-dose chemical fertilizer (M+2NP). Our findings showed that compared to CK, M and M+2NP significantly increased the proportion of macroaggregates by 40% and 28%, respectively, whereas 4NP significantly decreased it by 19%. The mean weight diameter (MWD) and geometric mean diameter (GMD) under M and M+2NP were significantly higher than that under CK, at 12–21% and 24–36%, respectively. The fractal dimension (D) value of M+2NP was significantly lower than those of 2NP and 4NP by 4% and 5%, respectively. Soil pH under the M treatment was highest, followed by M+2NP. Soil pH under 2NP and 4NP more significantly decreased, by 0.1 and 0.2 units, than under M treatment. Soil pH values were correlated with the proportion of soil macroaggregates, MWD, and GWD, respectively (p < 0.05). Relative to CK, M and M+2NP increased the contents and stocks of SOC (by 40–49% and 89–93%, respectively) and total N (59–68% and 119–123%, respectively). Furthermore, the contents and stocks of aggregate-associated SOC and total N decreased following the order: NP > 2NP > 4NP. Overall, the long-term application of organic fertilization regimes (M and M+2NP) effectively improved soil aggregation as well as SOC accumulation and decreased soil acidification in dark brown soil in northeast China.

Effect of tillage management on the wind erosion of arable soil in the Chinese Mollisol region

Wind erosion is a serious problem in agricultural regions and threatens the regional food production in Northeast China. However, limited information is available on the characteristics of wind erosion in arable soil in Northeast China. As a result, field-based research during periods of vulnerability to wind erosion is essential. This study quantified the characteristics of soil wind erosion under no-tillage (NT) and conventional tillage (CT) treatments in China’s northern “corn-belt.” The results determined the wind erosion transport mode of Mollisols to be generally characterized by creep and supplemented by saltation and suspension in Northeast China. The erodible particles of the creep accounted for 80.37% and 85.42% of the total wind erosion under the NT and CT treatments, respectively. During experiments with erodible particles in the saltation mode from the soil surface to 2 m, the majority of the particles were collected by the sampler at 0.5 m height, with the NT and CT treatments collecting 5.82 kg·m−2 and 6.93 kg·m−2 of erodible particles per unit area, respectively. Wind erosion on agricultural land was observed to be influenced by tillage practices, rainfall, wind speed, and soil moisture content. Average and maximum wind speeds exhibited significant positive correlations with wind erosion during April and May. Moreover, the erodible particles of each wind erosion transport mode (creep, saltation, and suspension) under CT were higher (1.73, 1.41, and 1.35 times) than those under the NT treatment. With less damage and greater protection of the surface soil, the NT treatment was able to decrease the occurrence of wind erosion and influence its outcome on farmland. Therefore, NT treatment should be encouraged as a key initiative for the reduction of wind erosion of arable soil in the Chinese Mollisol region.

Inhibition of root growth by alkaline salts due to disturbed ion transport and accumulation in Leymus chinensis

Soil alkalization severely affects plant growth and agricultural production. Compared with neutral salts, alkaline salts cause a combined stress of ion toxicity and high pH in plants. The alkali-resistant halophyte Leymus chinensis is a dominant grass growing on soda (NaHCO3 and Na2CO3, pH > 9) saline-alkali soil in northeast China. However, the molecular mechanism of alkaline salt tolerance in L. chinensis roots remains unclear. In this study, the seedling phenotype, ion accumulation, root ion dynamics, and gene expression profiles in L. chinensis under neutral salt (100 mM NaCl), alkaline salt (100 mM NaHCO3 and 50 mM Na2CO3), and high pH (pH = 10) stresses were investigated and compared. Phenotypic analysis showed that alkaline salt more severely inhibited the growth of seedling roots compared to neutral salt and high pH. Ion content detection revealed that alkaline salt-treated seedlings had higher Na+ accumulation and lower nutrient content compared to neutral salt and high pH-treated seedlings. Furthermore, the non-invasive micro-test showed that alkaline salt-induced high pH conditions perturb ion flux in seedling roots, which may be associated with impaired nutrient ion uptake and aggravated Na+ accumulation. Moreover, using full-length transcriptome combined with comparative RNA-seq, the identified alkaline salt-specific response genes were most significantly enriched to the transporter activity term, which contained a large number of genes encoding transporters of nutrient ions. Our results provide new insights into the unique response mechanism of L. chinensis roots to alkaline salt.

Validation and inhibition study for toxic expression of quinolone antibiotic resistance genes in agricultural soils of eastern China

With the extensive use of antibiotics, the problem of antibiotic resistance genes (ARGs) has gradually emerged. As agricultural soil is an important enrichment media of antibiotics and ARGs, it is particularly important to study the toxicity of ARGs, the effects of various nutrients and pollutants, and how to control them through source modification and process regulation. In this study, a combination of source modification and process regulation was used to weaken the toxic expression of Quinolones’ (QNs’) ARGs in soils from different agricultural areas. And the influence of soil nutrients and pollutants on this process will be explored. Protein-protein docking and molecular docking were used to construct a target protein complex for the toxic expression of QNs’ ARGs and characterize the toxicity of QNs’ ARGs. The two-dimensional and three-dimensional quantitative structure-activity relationships model construction and sensitivity analysis were used to molecular modification and related validation. Molecular dynamics simulations assisted by sampling survey method based on agricultural soils in Northeast China and the lower-middle reaches of the Yangtze River were carried out to generate four scenarios. The main results are: (a) A functionally improved and environmentally friendly quinolone derivative (ORB–19) was designed. It can effectively inhibit the expression of QNs’ ARGs and weaken the antibiotic selection pressure risk. The application of ORB–19 in agricultural areas could significantly inhibit the toxic expression of QNs’ ARGs (112.75%~169.59%); (b) QNs’ ARGs have a stronger toxic expression in agricultural areas of Northeast China, which have higher nutrient elements; (c) The contribution of different types of agricultural pollution to suppressing the toxic expression of QNs' ARGs in agricultural soils varies; (d) The options of applied field measures given for the inhibition of QNs’ ARG toxic expression varied between plots with different agricultural pollution types. This study provides theoretical support for inhibiting the toxic expression of QNs’ ARGs in the soil environment, reducing the spread of ARGs in microbial populations, replacing green QNs derivatives, and sustainable development of agricultural soils.

Responses of soil respiration and C sequestration efficiency to biochar amendment in maize field of Northeast China

The application of biochar in agricultural ecosystems is a viable strategy for mitigating climate change and ensuring food security. Northeast China is China’s main maize-growing region, as well as the country's greatest commodity grain base. However, due to a lack of long-term field investigations, information on the effects of biochar on soil CO2 emissions and C sequestration in brown soil in Northeast China is restricted. A 3-year field experiment was conducted in Northeast China with biochar applied at 0 (CK), 15.75 (BC1), 31.5 (BC2), and 47.25 (BC3) t ha−1 rates to explore the continuous impacts on soil CO2 emissions, soil enzyme activities, humic substance (HS) composition, and C sequestration efficiency (CSE). The soil CO2-C emissions in biochar treatments were significantly higher (18.04–73.15 %) than in the control during the maize-growing season. Biochar amendment induced a significant increase in soil urease, sucrase, catalase, and β-glucosidase activities and a significant decrease in bulk density (BD). Furthermore, significant positive correlations were observed between soil CO2 emissions and the four enzymes mentioned above. The C content of humin (HU) increased dramatically as the rate of biochar use increased, whereas the C content of humic acid (HA) and fulvic acid (FA) remained unchanged. The soil C storage levels in the 0–60 cm soil depth in BC1, BC2, and BC3 were 13.30 %, 24.41 %, and 39.06 % higher than CK. The CSE ranged from 80.4 % to 87.6 %, depending on biochar addition rates. To conclude, the present study suggested that maize stover biochar incorporation had a great potential for improving soil C sequestration to agricultural soils of Northeast China, even though biochar addition enhanced soil respiration and enzyme activities.

Effects of mechanochemically activated phosphate rock on maize growth and phosphorus use

It is well known that mechanochemically activated phosphate rock (MAPR) could improve extractable phosphorus (P) (extracted in 2% citric acid) greatly in an ecological way. To evaluate the agronomic effectiveness of MAPR, we conducted a field experiment using spring maize in Luvisol (pH 6.47) soil in Northeast China for three consecutive years. Treatments consist of variation of P levels for substitution of triple superphosphate (TSP) (100% TSP, 10% MAPR, 20% MAPR, 50% MAPR, 100% MAPR). Compared with 100% TSP, all the combined applications of MAPR and TSP were as effective on straw yield. Treatments of 10% MAPR and 20% MAPR had similar effect on grain yield and P uptake, while 50% MAPR and 100% MAPR were significantly lower. For P partial nutrient productivity and apparent P recovery with the treatment of 20% MAPR had equal effectivity, likewise. For soil P<sub>Olsen</sub>, treatment of 10% MAPR was equally operative, while 20% MAPR had the similar performance only in the last year (i.e. 2016). It is concluded that 10–20% of TSP can be effectively replaced by MAPR without affecting spring maize yield in soil with neutral pH.

Soil bacterial community as impacted by addition of rice straw and biochar

The application of straw and biochar can effectively improve soil quality, but whether such application impacts paddy soil bacterial community development remains to be clarified. Herein, the impacts of three different field amendment strategies were assessed including control (CK) treatment, rice straw (RS) application (9000 kg ha−1), and biochar (BC) application (3150 kg ha−1). Soil samples were collected at five different stages of rice growth, and the bacterial communities therein were characterized via high-throughput 16S rDNA sequencing. The results of these analyses revealed that soil bacterial communities were dominated by three microbial groups (Chloroflexi, Proteobacteria and Acidobacteria). Compared with the CK samples, Chloroflexi, Actinobacteria, Nitrospirae and Gemmatimonadetes levels were dominated phyla in the RS treatment, and Acidobacteria, Actinobacteria, Nitrospirae and Patescibacteria were dominated phyla in the BC treatment. Compared with the RS samples, Chloroflexi, Acidobacteria, Actinobacteria, and Verrucomicrobia levels were increased, however, Proteobacteria, Gemmatimonadetes, Nitrospirae, and Firmicute levels were decreased in the BC samples. Rhizosphere soil bacterial diversity rose significantly following RS and BC amendment, and principal component analyses confirmed that there were significant differences in soil bacterial community composition among treatment groups when comparing all stages of rice growth other than the ripening stage. Relative to the CK treatment, Gemmatimonadaceae, Sphingomonadaceae, Thiovulaceae, Burkholderiaceae, and Clostridiaceae-1 families were dominant following the RS application, while Thiovulaceae and uncultured-bacterium-o-C0119 were dominant following the BC application. These findings suggest that RS and BC application can improve microbial diversity and richness in paddy rice soil in Northeast China.

Characteristics of maize residue decomposition and succession in the bacterial community during decomposition in Northeast China

Microbes are decomposers of crop residues, and climatic factors and residue composition are known to influence microbial growth and community composition, which in turn regulate residue decomposition. However, the succession of the bacterial community during residue decomposition in Northeast China is not well understood. To clarify the property of bacterial community succession and the corresponding factors regulating this succession, bags containing maize residue were buried in soil in Northeast China in October, and then at different intervals over the next 2 years, samples were analyzed for residue mass and bacterial community composition. After residue burial in the soil, the cumulative residue mass loss rates were 18, 69, and 77% after 5, 12, and 24 months, respectively. The release of residue nitrogen, phosphorus, and carbon followed a similar pattern as mass loss, but 79% of residue potassium was released after only 1 month. The abundance, richness, and community diversity of bacteria in the residue increased rapidly and peaked after 9 or 20 months. Residue decomposition was mainly influenced by temperature and chemical composition in the early stage, and was influenced by chemical composition in the later stage. Phyla Actinobacteria, Bacteroidetes, and Firmicutes dominated the bacterial community composition in residue in the early stage, and the abundances of phyla Chloroflexi, Acidobacteria, and Saccharibacteria gradually increased in the later stage of decomposition. In conclusion, maize residue decomposition in soil was greatly influenced by temperature and residue composition in Northeast China, and the bacterial community shifted from dominance of copiotrophic populations in the early stage to an increase in oligotrophic populations in the later stage.

Factors Affecting the Promotion of Conservation Tillage in Black Soil—The Case of Northeast China

Taking the conservation tillage influences of black soil in Northeast China as the research object, the paper is written according to the advice of relevant experts and technicians in Northeast China, the study also calculates the weight of each influencing factor through the Delphi and Analytic Hierarchy Process (AHP) method. Then, the significance of the factors affecting the benefit of conservation tillage is analyzed. The results show that, based on the comprehensive analysis, it is concluded that the economic factor is the primary factor affecting the benefit of black soil conservation tillage in Northeast China. Among the twelve influencing factors, eight of them have a significant impact on the development of conservation tillage benefits on black soil in Northeast China. Such as the degree of government subsidy; the adaptability of agricultural machinery; the input of new technology; relevant policies, laws and regulations; the quality of conservation tillage; the income of agricultural machinery farmers; practical application capacity; government publicity. Therefore, in the process of implementing the black soil conservation tillage, we should focus on these influencing factors, which will effectively promote the sustainable development of agriculture in Northeast China.

A Quantitative Analysis of Factors Influencing Organic Matter Concentration in the Topsoil of Black Soil in Northeast China Based on Spatial Heterogeneous Patterns

Black soil is fertile, abundant with organic matter (OM) and is exceptional for farming. The black soil zone in northeast China is the third-largest black soil zone globally and produces a quarter of China’s commodity grain. However, the soil organic matter (SOM) in this zone is declining, and the quality of cultivated land is falling off rapidly due to overexploitation and unsustainable management practices. To help develop an integrated protection strategy for black soil, this study aimed to identify the primary factors contributing to SOM degradation. The geographic detector, which can detect both linear and nonlinear relationships and the interactions based on spatial heterogeneous patterns, was used to quantitatively analyze the natural and anthropogenic factors affecting SOM concentration in northeast China. In descending order, the nine factors affecting SOM are temperature, gross domestic product (GDP), elevation, population, soil type, precipitation, soil erosion, land use, and geomorphology. The influence of all factors is significant, and the interaction of any two factors enhances their impact. The SOM concentration decreases with increased temperature, population, soil erosion, elevation and terrain undulation. SOM rises with increased precipitation, initially decreases with increasing GDP but then increases, and varies by soil type and land use. Conclusions about detailed impacts are presented in this paper. For example, wind erosion has a more significant effect than water erosion, and irrigated land has a lower SOM content than dry land. Based on the study results, protection measures, including conservation tillage, farmland shelterbelts, cross-slope ridges, terraces, and rainfed farming are recommended. The conversion of high-quality farmland to non-farm uses should be prohibited.

A new method for weakening slaking of collecting eroded aggregates by water erosion

In most of previous studies about aggregate breakdown caused by water erosion, a critical process that water inevitably fragments the eroded aggregates by water erosion again is generally ignored. This will reduce the accuracy of research results. Hence, alcohol has been added to the collecting device of eroded aggregates to weaken the slaking of eroded aggregates by the researchers, but the optimal alcohol-to-water ratio for protecting the size fraction distribution of eroded aggregates remains unclear. Aggregate with a size fraction of 2–5 mm obtained by dry sieving of black soil in Northeast China was selected as the research object to analyse the effects of five alcohol-to-water ratios on aggregate characteristics and their variation with soaking time. The results showed that the size distribution in terms of mass percentage under different soaking times was similar. For the same soaking time, the mass percentage of 2–5-mm aggregates gradually decreased with decreasing alcohol ratio, but the aggregates with the second-highest mass percentage were gradually distributed among smaller size fractions. Compared with the alcohol soaking aggregates, the mean weight diameter (MWD) of the aggregates soaked in the other ratio of alcohol-to-water decreased gradually with the increase of soaking time, and the disintegration of the aggregates was the most evident at the initial stage of soaking. A percentage of aggregate destruction (PAD) of 20% served as the dividing line to evaluate the stability of soil aggregates. In this case, eroded aggregate collection should be completed within 12 min at an alcohol-to-water ratio of 1:1. Alternatively, eroded aggregate collection should be completed within 6 min at an alcohol-to-water ratio of 2:3. The above results can provide a reference for improving the accuracy of data collection regarding eroded aggregates. Especially in the study of water erosion which needs to collect eroded aggregates, alcohol can be added to the collecting device before the experiment. The amount of alcohol should be added according to the amount of water that may be generated, so as to protect eroded aggregates and weaken the slaking of eroded aggregates.

Effects of Climate Warming on the Key Process and Index of Black Soil Carbon and Nitrogen Cycle During Freezing Period

As an critical part of the global biogeochemical cycle, the winter soil carbon and nitrogen cycles are extremely sensitive to climate warming. Furthermore, the black soil in northeast China is fertile and rich in organic matter and is a vital production base of commodity grains in China. For as long as half a year, the black soil is in a freezing-thawing state. Climate warming will change the snow cover thickness and soil freezing degree on the surface of the black soil in the winter and affect the freezing-thawing cycle frequency and timing of the soil, thus exerting a profound influence on the fixation, transformation, and release of soil carbon and nitrogen during the freezing period and throughout the year. To better understand the effects of climate warming on the black soil carbon and nitrogen dynamics during the freezing period, an experiment was conducted with two warming levels (W1 and W2) using an infrared radiometer to simulate soil warming. The warming increased the surface soil temperature (0 cm soil temperature) by 1.54℃ (W1) and 4.10℃ (W2), respectively, and significantly increased the soil moisture content compared with the control (C) during the freezing period, most likely because of the melting snow. The snow cover thickness, soil freezing depth, soil organic carbon (SOC), and labile organic carbon (LC) content were reduced by both warming treatments. However, the effect of the temperature increase during the freezing period on the key processes and indicators of the nitrogen cycle in black soil was relatively more complicated. With the increase in temperature, the content of nitrate nitrogen (NO3--N) decreased significantly, and the content of total nitrogen (TN) and net nitrogen nitrification rate increased significantly, while the ammonium nitrogen (NH4+-N), total inorganic nitrogen (TIN) content, and the net nitrogen mineralization rate exhibited a significant increase first and then decreased. In summary, climate warming will bring a warmer and more humid environment to the black soil during the freezing period, and the resulting changes in the soil carbon and nitrogen content and transformation processes will have a profound impact on the structure, productivity of the plants and microbial communities, and carbon and nitrogen cycles in the subsequent growing season. The results provide a scientific basis for studying the carbon and nitrogen cycle mechanisms of the northeast black soil during the freezing period.

Effect of urease/nitrification inhibitor on urea nitrogen conversion in black soil and cinnamon soil.

We studied the effects of urease/nitrification inhibitor combinations on urea hydrolysis and nitrification, aiming to screen out the effective inhibitor combinations for black soil and cinnamon soil in Northeast China. Urease inhibitor, N-butyl thiophosphate-triamine (NBPT), and its combination with nitrification inhibitor dicyandiamide (DCD), 3, 4-dimethylpyrazole phosphate (DMPP), 2-chloro-6 (trichloromethyl)-pyridine (CP), 2-amino-4-chloro-6-methylpyrimidine (AM) and 3-methylpyrazole (MP) were added to urea separately. Samples were collected 15 times in each of all the treatments during 125 days. We examined the changes of urea nitrogen, ammo-nium, nitrate, and nitrification inhibition rate in the two soils. Our results showed the hydrolysis of urea in black soil and cinnamon soil was about 7 d, and the addition of NBPT with or without diffe-rent nitrification inhibitors slowed down the hydrolysis to 21 d at least. Compared with the treatment with common urea, inhibitor addition significantly increased soil NH4+-N, decreased soil NO3--N, and maintained the high NH4+-N content in soil for a longer time. In black soil, application with nitrification inhibitor inhibited soil nitrification significantly and lasted for more than 125 d. DMPP and CP combined with NBPT increased the NH4+-N content in black soil by 1.6-1.8 times, while the nitrification inhibition rate was 47.9% and 24.1% at 125 d, respectively. In the cinnamon soil, the application of nitrification inhibitor could prolong the duration of ammonium oxidation from 80 d to 110 d. DCD and DMPP combined with NBPT increased the NH4+-N content in cinnamon soil by 2.1-3.4 times, while the nitrification inhibition rates at 125 d were 25.3% and 23.2%, respectively. Therefore, NBPT+DMPP combination with urea was recommended for utilization in black soil, followed by NBPT+CP. In cinnamon soil, NBPT+DCD combination with urea was recommended, followed by NBPT+DMPP.

Long-term fertilization enhanced carbon mineralization and maize biomass through physical protection of organic carbon in fractions under continuous maize cropping

Long-term fertilization has been recognized as a key factor controlling soil organic carbon (SOC) and crop yields at various scales. Therefore, the impact of long-term nutrient management on SOC contents, fractional distribution, C-mineralization, and crop productivity under maize mono-cropping was investigated in the present work. For this, a typical black soil in northeast China was collected and analysed to measure the organic carbon (OC) content in the bulk soil, the distribution and OC contents of the different SOC fractions including, coarse particulate organic carbon (cPOC) and free particulate organic carbon (fPOC), intra-aggregate particulate organic carbon (iPOC), free silt plus clay (s + c_f) and micro-aggregate derived silt plus clay (s + c_m), and the SOC mineralization dynamics under different fertilizer treatments. Treatments included: 1) unfertilized control (CK), 2) balanced mineral fertilization (NPK), 3) NPK combined with manure (MNPK), 4) NPK combined with high dose (1.5 times) of manure (1.5MNPK), and 5) NPK combined with crop straw (NPKS). Manure treatments (1.5MNPK and MNPK) led to the largest increase in the SOC content of bulk soil (97% for 1.5MNPK and 41% for MNPK respect to CK). In addition, the long-term fertilization improved the proportions of the cPOC, fPOC and iPOC, especially in the case of manure treatments. In this same way, in comparison to CK, manure treatments (1.5MNPK and MNPK) significantly increased the SOC contents in cPOC (by 96 and 57%, respectively), fPOC (by 146 and 91%, respectively), iPOC (by 160 and 113%, respectively), s + c_f (by 51 and 39%, respectively) and s + c_m (by 56 and 50%, respectively) fractions. Similarly, higher values of SOC mineralization were associated with the 1.5MNPK and MNPK treatments as compared to CK, NPKS, and NPK alone. Finally, the application of 1.5MNPK and MNPK resulted in the highest increase in maize grain yield and in straw biomass yield. Therefore, the results obtained clearly indicate that long-term fertilization using manure combined with mineral fertilizer is the best choice to improve the SOC sequestration and mineralization, as well as the crop yields. All these facts can be considered relevant from points of view related to environmental management, soil fertility, and cleaner crop production.

Straw alters the soil organic carbon composition and microbial community under different tillage practices in a meadow soil in Northeast China

Straw retention and tillage practices are the main ways to affect the contents and stocks of soil organic carbon (SOC) components as well as soil microbial traits in order to affect soil fertility and crop yield. Microorganisms are the links between SOC and tillage methods, but the mechanisms of these linkages remain unclear. We evaluated the changes in SOC components, soil microbial traits and crop yields under no-tillage (NT), shallow tillage (ST), deep tillage (DT), no-tillage with straw retention (NTS), shallow tillage with straw retention (STS) and deep tillage with straw retention (DTS) treatments in a 3-year field trial in a meadow soil in Northeast China. Straw retention increased the contents of both labile organic carbon (LOC, by 16.0 %) and recalcitrant organic carbon (ROC, by 19.5 %), while tillage practices increased the highly labile organic carbon (LOC-H) content from 0.4 to 0.6 g kg−1 and decreased the low-labile organic carbon (LOC-L) content from 1.6 to 0.8 g kg-1. The ANOVA and nonmetric multidimensional scaling (NMDS) results suggested that straw retention was the main factor regulating bacterial alpha diversity and reshaping the bacterial community composition. Straw retention also promoted the functions of Acidobacteria and Bacteroidetes in the network, thus influencing SOC component turnover. Structural equation modelling (SEM) revealed that the bacterial Shannon index, richness and community composition were correlated with crop yields due to their regulation of different SOC components, especially LOC-H and ROC. Overall, straw retention with no and shallow tillage increased the soil ROC and LOC contents by increasing the bacterial Shannon index and reducing the richness; thus, these practices improved crop yield, which is an important indicator of soil fertility. This study advances our understanding of the mechanisms underlying the relationships between soil microbial traits and SOC components under different straw management and tillage practices and provides information to support SOC transformation, C stock enlargement and soil fertility maintenance strategies.

Effects of Fertilization Methods on Chemical Properties, Enzyme Activity, and Fungal Community Structure of Black Soil in Northeast China

Understanding the influence of fertilizer on soil quality is vital to agricultural management, yet there are few studies, particularly in black soil. In this study, soils under various treatments, namely no fertilizer, bio-organic + humic acid, bio-organic + chemical, and chemical fertilizer, were sampled to identify their major physiochemical properties, and to investigate the fungal community structure using environmental sequencing techniques. Physiochemical properties and fungal community structure were examined at four important stages of the maize life cycle: seedling, jointing, heading period, and maturity. We found that chemical fertilizer in the mature stage increased the soil available phosphorous (AP) content. Organic matter content was greatly affected by bio-organic + chemical fertilizer during the mature stage. Bio-organic + humic acid significantly increased soil phosphatase activity in maturing maize, whilst chemical fertilizers reduced invertase activity. Taken together, our results clearly illustrated that bio-organic + humic and chemical fertilization indirectly alter fungal community structure via changing soil properties (especially AP). Chemical fertilizer markedly heightened the AP content, thereby decreasing specific fungal taxa, particularly Guehomyces. OM was of positive connection with bio-organic + humic acid and Mortierella abundance, respectively, through RDA analysis, which are in agreement with our result that bio-organic + humic acid fertilization to some extent increased Mortierella abundance. Additionally, bio-organic + humic acid decreased the abundance of Fusarium and Humicola, suggesting that bio-organic + humic acid possibly could help control crop disease. These results help to inform our fundamental understanding of the interactions between fertilizers, soil properties, and fungal communities.