Black Soil Of Northeast China Research Articles

Diversity of common bean rhizobia in blackland of northeastern China and their symbiotic compatibility with two host varieties.

The common bean (Phaseolus vulgaris L.) is an important crop in the world that forms root nodules with diverse rhizobia. Aiming to learn the rhizobial communities associated with the common bean in the black soil of Northeast China, 79 rhizobia were isolated from root nodules of two host varieties (Cuican and Jiadouwang) grown in two sites of blackland and were characterized by comparative sequence analyses of 16S rRNA, recA, atpD, nodC, and nifH genes, and whole genome. As a result, Rhizobium indigoferae, R. anhuiense, and R. croatiense as minor groups and three dominant novel Rhizobium species were identified based on their average nucleotide identity and DNA-DNA hybridization values to the type strains of relative species. This community composition of rhizobia associated with the common bean in the tested black soils was unique. Despite their different species affiliations, all of them were identified into the symbiovar phaseoli according to the phylogenies of symbiotic genes, nodC and nifH. While the phylogenetic discrepancies found in nodC, nifH evidenced that the evolutions of nodulation (nod) and nitrogen fixation (nif ) genes were partially independent. In addition, only one dominant rhizobial species was shared by the two common bean varieties grown in the two soil samples, implying that both the plant variety and the soil characteristics affected the compatibility between rhizobia and their hosts. These findings further enlarged the spectrum of common bean-nodulating rhizobia and added more information about the interactions among the soil factors, rhizobial species, and host plants in the symbiosis.

Differential Analysis of Biochar Effects on Soil Physicochemical Properties

For a long time, because of China’s large population and small per capita resource occupancy, the use of natural resources is unreasonable. Soil degradation problem due to the long-term irrational utilization of land resources is becoming more and more serious, which seriously damaging the ecological environment and hindering China’s modernization process. Facing the problem of soil remediation, biochar technology has become a research hotspot because of its advantages of green environmental protection, low cost, high efficiency, and wide application. And black soil in northeast China and southern region of red soil as important soil types of agroforestry in China, over the years have experienced serious soil degradation crisis. In this paper, black soil and red soil are selected as research objects to explore the impact of biochar on the physical and chemical properties of the two soils. This paper intends to use the methods of investigation and analysis, and comparison in many aspects. Through the study, it was found that the application of biochar had the same trend of influence on the organic carbon content and C/N ratio of the two soils, but the index of black soil increased more significantly. The change trend of soil bulk density and pH was also consistent with the application of biochar, and the difference was not significant. The effects of biochar applied to the two soils on greenhouse gas emissions were quite different. The soil health of black soil and red soil is of great significance in China’s agricultural production and life. This paper expects to bring reference value to the improvement of the overall soil function and the promotion of ecological restoration process of China’s biochar modification work for different soil types in the north and south, by comparing the impact of biochar on the physical and chemical properties of the two soils. A better soil improvement program can be obtained after comparative analysis, so as to provide suggestions on sustainable development and comprehensively promote ecological construction.

Residue dynamics of florpyrauxifen-benzyl and its effects on bacterial community structure in paddy soil of Northeast China

Florpyrauxifen-benzyl is an herbicide that has been developed in recent years. Its degradation mode in paddy soil environments is not clear. In this study, the degradation dynamics in paddy soil and water were studied by ultrahigh-performance liquid chromatography. Microbial degradation was the main degradation pathway. Using third-generation high-throughput sequencing technology, the changes in the soil bacterial community structure were studied. After 30 days of application, compared with the control group (F0), the abundance of Sphingomonas, Lysobacter, and Flavisolibacter in the recommended and repeated application groups (F1, F5 and F10) increased significantly, and uncultured bacterium and Terrimonas decreased significantly. Compared with the F0 and F1 groups, the species diversity of the F0 and F1 groups showed a significant increase over time. The species diversity of the F5 and F10 groups decreased significantly on Days 5 and 15. On Day 30, the recovery even exceeded that of the control group. Luteimonas and five other genera were positively correlated with herbicide residues, and Pseudolabrys and two other genera were negatively correlated. Repeated application showed a significant effect on the structure of the soil bacterial community, mainly showing a trend of a significant decrease in the initial stage and gradual recovery in the later stage. The results will guide the safe and rational use of florpyrauxifen-benzyl and provide a scientific basis for florpyrauxifen-benzyl dynamic supervision of environmental pollution and protection of black 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 of nitrogen storage in density and size fractions varied with tillage practices and cropping systems with residue return in black soil of Northeast China

AbstractCrop residue return can prevent the degradation of cropland caused by conventional tillage practice in Northeast China. Meanwhile, additional nitrogen (N) input from crop residue inevitably changes soil N pools. Our objectives were to evaluate soil N storage changes in soil physical fractions. The residue return treatments consisted of no‐tillage (NT) and moldboard plow (MP), combined with continuous maize (Zea mays L.) (MM) and maize–soybean [Glycine max (L.) Merr.] rotation (MS) cropping systems, that is, NTMM, NTMS, MPMM, MPMS; conventional tillage (removal of crop residue and deep plow) with continuous maize (CTMM) was included as a control. The concentration of total N (TN) in bulk soil and physical fractions (light fraction [LF], sand, silt, and clay) was measured. In 0‐to‐5‐cm layer, TN content was higher in NT than MP, whereas the result was opposite in 10‐to‐20‐cm layer. Thus, the stratification ratio (SR) of soil TN was greater under NT. The TN content in MM was greater than MS under both tillage practices with residue return. Residue return treatments increased soil N storage by 6.44–24.85% in 0–20 cm compared with CTMM. Continuous maize increased the N storage in all physical fractions, whereas the decrease of silt‐N storage was observed in MS. Overall, it was concluded that residue return could enhance soil N storage, whereas the distribution of N storage changes in LF and sand size fractions was influenced by tillage practice, and the distribution of N storage changes in silt size and clay size fractions was influenced by cropping system.

Maize/soybean intercropping improves stability of soil aggregates driven by arbuscular mycorrhizal fungi in a black soil of northeast China

Maize/soybean intercropping improves stability of soil aggregates driven by arbuscular mycorrhizal fungi in a black soil of northeast China

Evaluation of four primer sets for analysis of comammox communities in black soils.

Comammox, as a newly discovered ammonia oxidizer, urgently needs highly efficient and specific primers to detect its community structure and diversity. In this study, the performance of widely used primer set Ntsp-amoA 162F/359R and newly designed primer sets comamoA F/R, CA377f/C576r, and CB377f/C576r were evaluated, for high-throughput sequencing of comammox amoA genes in natural and arable soils sampled from two locations in the black soil region of northeast China. Results showed that, compared with the primer set comamoA F/R, primers Ntsp-amoA 162F/359R had more advantages in detecting comammox operational taxonomic unit (OTU) numbers, diversity, and community structure. The primer sets CA377f/C576r and CB377f/C576r had an advantage in detecting comammox sequences with low relative abundance. In addition, the results of the phylogenetic tree and the relative abundance of dominant OTUs showed that the comammox in the black soils of northeast China was dominated by Nitrospira Clade B. Furthermore, our study found that long-term land use reduced the alpha diversity of the comammox community, but lead to the convergent evolution of community structure. The Mantel test and canonical correspondence analysis indicated that soil NO3–-N content was the most important factor affecting the community structure of comammox. Our study provided experience accumulation for the selection of comammox primers for high-throughput sequencing in the black soil of northeast China.

Simulations and Experiments of Soil Temperature Distribution after 2.45 GHz Long-Term Microwave Treatment

Soil disinfection is an important agronomic measure to prevent soil-borne diseases, insects, weeds and other hazards. Based on the premise of being environmentally friendly, microwave soil disinfection can improve crop yield and quality in a pollution-free, residue-free and green way. The law of microwave soil heating is the theoretical basis of microwave soil disinfection. Therefore, in this paper, loess soil of North China and black soil of Northeast China are used as test materials to explore the law of soil heating under the action of microwaves. First, COMSOL Multiphysics software was used to simulate the temperature field change in the microwave-irradiated soil, and a simulation model of the temperature field of the microwave-irradiated soil was constructed to analyze the effective working range and temperature distribution characteristics of the microwave-irradiated soil. Second, using the 2.45 GHz microwave treatment, the following conditions were tested: soil moisture conditions of 10%, 15%, 20% and 23% (within the natural moisture content range). The loess and black soil were treated by microwave irradiation for 1~12 min, respectively (1 min/time increment). A single-factor experiment was designed to explore the influence of these factors on the soil heating law. The results show that the two soil surface temperatures are positively correlated with the soil moisture content, both of which satisfy Tsurface23% > Tsurface20% > Tsurface15% > Tsurface10%, and the surface temperature of black soil is higher than that of loess. According to the experimental results of the internal temperature distribution of loess and black soil irradiated by microwaves, the surface equations of “irradiation time–soil depth-soil temperature” and “irradiation time–soil moisture content–soil temperature” were constructed by surface fitting. When the irradiation time and moisture conditions are the same, the average temperature inside the irradiation area satisfies T¯α black soil > T¯α loess. The results of long-term microwave soil heating preliminarily confirmed the feasibility of microwave soil disinfection and the optimal conditions of microwave irradiation in loess of North China and Northeast black soil, which provides a certain reference for the study of soil-borne diseases inactivation at high temperature.

Ammonia oxidizing bacteria dominate soil nitrification under different fertilization regimes in black soils of northeast China

Although autotrophic ammonia oxidizing archaea (AOA) and bacteria (AOB) and comammox coexist in soils, their abundances and contributions to nitrification are not well addressed, especially in arable black soils. In this study, using the nitrification inhibitors acetylene and octyne, the contributions to nitrification potential provided by different ammonia oxidizers and heterotrophic nitrifiers in four long-term fertilization treatments, i.e., no fertilization (NoF), manure fertilization (M), chemical fertilization (CF), and chemical fertilization plus manure (CFM), were investigated in samples collected from the northern, middle and southern black soil regions of northeast China. The amoA gene abundances of AOA, AOB, comammox Clade A and comammox Clade B in these soils were quantified by qPCR. The results showed that the amoA gene abundances of the three ammonia oxidizers tended to increase from the northern to southern sites, while the opposite trend was observed in the ratios of AOA/AOB and comammox Clade B/Clade A; the different fertilization treatments significantly influenced the amoA abundances, and the effects varied with the ammonia oxidizers and across the sites. Autotrophic ammonia oxidizers accounted for 62%–100% of the gross soil nitrification potential across all soils. Among them, AOB dominated soil autotrophic nitrification in the fertilized soils, while no fertilization may have increased the nitrification potential provided by AOA plus comammox. Pairwise analysis showed that the amoA gene abundances of AOA and AOB were significantly and positively correlated with their respective nitrification-driven potentials. Correlation heatmaps indicated that soil pH and inorganic nitrogen content were the main soil factors related to nitrification activities and the abundances of the ammonia oxidizers. Our findings highlight that AOB are the dominant ammonia oxidizers contributing to nitrification in arable fertilized black soils, although AOA and comammox are highly abundant.

Test of Consolidation-Collapse Properties of the Black Soil of Northeast China Based on Burland Model

Organic matter is widely distributed in soils, which has remarkably influenced geotechnical engineering. The difference of the soil's structure, chemical constitution, and organic content leads to the distinction of mechanical property. The current research concentrates on the mechanical property of peaty soil and peat, and research on organic soil is rare. Several slope engineering issues show that the rainwater contact with the organic soil layer causes soil landslide, and the mechanism of landslide is that organic matter softens when it soaks the water under the vertical press. Studying the mechanical influence of organic soil with change in moisture content is meaningful because the moisture content of organic soil is much less than that of peat. This study mainly has the following content. The one-dimensional compression test with a variation of organic matter (F) and water (W) is selected to reveal the compression characteristics of organic soil. According to the analysis of the research consequence, the collapsibility with different organic contents and the same void ratio was further analyzed, and the research revealed the influence factor by analyzing the process of the collapse. Burland intrinsic compression theory, which reveals the soil's structure by analyzing the difference of undisturbed soil and remolded soil, was suitable for the initial moisture content of 1.5 to 2 times the liquid limit but not for organic soil with a moisture content lower than the liquid limit. Therefore, a modified model was provided to widen the range of liquid limit and present the phenomenon of collapse, and good prediction outcome can be obtained based on the linear-regression analysis model and the modified model. A black soil collapsibility model was established based on the experimental results, and it has good prediction outcome.

Deep incorporation of corn straw benefits soil organic carbon and microbial community composition in a black soil of Northeast China

Abstract‘Deep incorporation of corn straw’ (CSDI) is to concentrate the burial of corn straw into the subsurface soil layer (20–40 cm) and to break the plough pan, thereby creating a loosened plough layer (0–20 cm) and a fertile subsurface soil layer. However, its impacts on soil organic carbon (SOC) and the microbial community remain poorly understood. A field experiment was conducted to investigate the effects of 1‐year CSDI (CD1), 3‐year CSDI (CD3) and 5‐year CSDI (CD5) on soil aggregates and aggregate‐associated SOC, as well as bacterial and fungal community characteristics (examined by the high‐throughput gene sequencing method). The results demonstrated that SOC and soil fungal diversity were decreased by CD1, but increased by CD3 and CD5. Compared with the control, CD5 promoted 2–0.25 mm soil macroaggregation, significantly increased SOC by 8.94% and aggregate‐associated SOC by 5.96%–8.84%, consequently improving the physical protection of SOC by soil aggregates. CD3 and CD5 enhanced the richness and diversity of soil bacteria and fungi, and altered community composition. For soil bacteria, the relative abundance of Acidobacteria and Chloroflexi was increased, while that of Firmicutes, Gemmatimonadetes, Sphingomonas and Bacillus was decreased. For soil fungi, the relative abundance of Ascomycota, Zygomycota, Mortierella and Fusarium was greatly improved, but that of Basidiomycota was reduced. These obvious variations in microbial community structure were beneficial to straw degradation and SOC accumulation. Overall, the optimization of microbial community with CSDI plays a positive role in promoting soil organic matter, nutrient cycling and carbon sequestration, and thus improving soil fertility.

Effects of fertilization managements on nirK/nirS-type denitrifying bacterial community structures in upland black soils of Northeast China and suggestions for protecting black soil resource

Effects of fertilization managements on nirK/nirS-type denitrifying bacterial community structures in upland black soils of Northeast China and suggestions for protecting black soil resource

Carbon and nitrogen isotope constraints on source and variation of particulate organic matter in high-latitude agricultural rivers, Northeast China

The release of biospheric organic matter (OM) stored in the humus-rich black soils of Northeast China is highly susceptible to permafrost thaw and agriculturally induced erosion processes, and plays a disproportionate role in the global carbon cycle. However, the perturbations of global change and anthropogenic activities on riverine export of particulate organic carbon (POC) in the high-latitude agricultural areas remain poorly constrained. In the present study, this knowledge gap was filled by identifying the provenances of particulate organic matter (POM) and the erosional flux of POC from the rivers draining Northeast China. The elemental (POC%, PON% and C/N ratio) and isotopic (δ13C and δ15N) compositions of POM in suspended particulate matter (SPM) from the rivers in Northeast China (the Songhua River (SRB) and Liao River basins (LRB)) were analyzed. The results showed that during the wet season, the δ13C and δ15N values of POM in SPM were −25.8 ± 1.2‰ and 6.6 ± 2.2‰ respectively. Elemental and isotopic characteristics of the SPM samples and potential sources indicated that the sources of POM differed significantly among different sampling periods and sites. During the wet season, Soil OM was the primary POM contributor. Compared to the SRB, autochthonous OM made relatively larger contributions to POM in the LRB. During the dry season, for the SPM samples mainly from the LRB, the δ13C and δ15N values of POM were −22.7 ± 4.3‰ and 3.1 ± 2.4% respectively, suggesting that effluent detritus was the predominant source. The flux and yield of SPM revealed the seasonal and spatial variations of physical erosion rate that controls POC export. Seasonally, up to 61% of the annual SPM load and 58% of the annual POC flux of the SRB occurred in May and August due to thawing processes and increasing precipitation. Spatially, the lower reaches of the SRB had the highest SPM yield and contributed more than half of the annual SPM load of the SRB, likely attributable to the high intensity of agricultural activities. Globally, the POC% in SPM and POC yield of the SRB were larger than a series of the world's largest rivers under a given SPM condition, suggesting the high sensitivity of terrestrial OM export to erosion. These findings highlight the perturbation and mobilization of terrestrial OM in Northeast China under intensive agricultural activities and ongoing global climate change.

Quantifying influence of tillage practices on soil aggregate microstructure using synchrotron‐based micro‐computed tomography

AbstractStudying the internal structure of soil aggregates is an insightful way to improve the understanding of soil aggregation process. However, it is still not clear how the macroaggregate pore structure is influenced by the application of long‐term tillage practices. In this study, we aimed to determine the differences in macroaggregate pore structure among long‐term tillage practices using micro‐computed tomography (SR‐μCT). Soil samples were collected from no tillage (NT) and ridge tillage (RT) plots and surrounding fields under conventional tillage (CT) and uncultivated soils (CK). The results showed that the diameters of most pores were greater than 30 μm, but >100 μm pores had the greatest percentage of total macroaggregate porosities in all four soils, that is NT, RT, CT and CK. The CK soil had a higher aggregate porosity of <30 μm and 30–60 μm, as well as a lower porosity of >100 μm than the NT, RT and CT soils. Total porosities within soil macroaggregates in both CK and CT were significantly lower than those in RT and NT, but the porosities of 30–60 μm and 60–100 μm within soil macroaggregates in both CK and RT were no significance. There were no significant differences in pore parameters between CK and RT. The CK and RT had higher mean weight diameter (MWD) and aggregate‐associated SOC contents than CT. Therefore, the pore structure of RT was similar to CK with good soil structure. Overall, RT was more appropriate tillage system to protect soil aggregate structure in black soils of Northeast China.

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.

Optimization of Structure Parameters of the Grouser Shoes for Adhesion Reduction under Black Soil

The black soil of Northeast China has a strong adhesion ability because of its unique physical properties, and the soil often adheres to the surface of the grouser shoes of tracked vehicles during the operation. The adhesion performance depends largely on structure parameters of the grouser shoes. The grouser height, the grouser thickness, and the grouser splayed angle were selected as structure parameters. The adhesion force and adhesive soil mass were selected as indicators of adhesion performance. Therefore, the mathematical model between structure parameters and response indicators was established by the response surface method (RSM). The optimal parameters combination was that the grouser height was 20 mm, grouser thickness was 6.34 mm, and grouser splayed angle was 40.45°. The average data of verification experiments occurred when the adhesion force reached 1.11 kPa and adhesive soil mass reached 22.68 g. Compared with the average value of un-optimized experiment results, the adhesion force and adhesive soil mass reduced by 12.84% and 4.63%, respectively. The relative error of the predicted values and measured values was less than 5%, proving the reliability of the regression models. This study could provide a reference method for parameters optimization, and a new structure of the grouser shoes of tracked vehicles will be designed to reduce adhesion.

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.

Complex soil food web enhances the association between N mineralization and soybean yield – a model study from long-term application of a conservation tillage system in a black soil of Northeast China

Abstract. Long-term (10 years) application of conservation tillage following conversion from conventional tillage (CT) can achieve a new equilibrium in the soil environment, which is vital to reverse soil biodiversity declines and fulfil the goal of maintaining agroecosystem sustainability. However, in such a situation, how the soil community regulates nutrient cycling impacting crop yield is not well documented. Therefore, the relations between mineralized nitrogen (N) delivered by soil food web and soybean (Glycine max Merr.) yield were investigated after 14 years application of CT, reduced tillage (RT) and no tillage (NT) in a black soil (Typic Hapludoll) of Northeast China. We hypothesized that soil mineralizable N would increase with the complexity of the soil food web, and that the trophic groups involved in associating N mineralization with crop yield will vary with soil depth in the conservation tillage practice. During the soybean growing season, soil organisms, including bacteria, fungi, nematodes, mites and collembolans, were extracted and identified monthly from 0–5 and 5–15 cm soil depths to estimate the complexity of the food web indicated by the species richness and connectance indices, and to simulate the mineralized N using energetic food web modelling. The species richness and connectance of the food web at both soil depths were significantly affected by tillage practices, and their values decreased of the order of NT > RT > CT. A similar trend was also revealed for the simulated N mineralization, that is, the mineralized N released either from the functional feeding guilds or from the energy pathways of the food web were greater in RT and NT than in CT at both soil depths. Multiple linear regression analysis showed that soil organisms involved in coupling the mineralized N with soybean yield were different at different soil depths, in which fungal and root pathways at 0–5 cm and bacterial pathway at 5–15 cm were the driving factors for the supply of mineralized N to soybean in NT and RT soils. These results support our hypothesis and highlight the essential role of soil food web complexity in coupling N mineralization and crop yield after long-term application of conservation tillage. Additionally, the current modelling work provides basic hypotheses for future studies to test the impact of soil biodiversity or specific functional guilds on the fate of N in agro-ecosystems.