Soil Region Of Northeast China Research Articles

Response of soil erosion resistance to straw incorporation amount in the black soil region of Northeast China

Straw incorporation has been considered as an effective environmental management application to improve soil erosion resistance (SER) and organic carbon sequestration. SER is useful to evaluate soil erosion subjected to concentrated flow. Nevertheless, few studies have been performed to examine how SER varied with the amount of straw incorporation on sloping croplands in high latitude and cool regions. In the current study, the fixed bed scouring tests were conducted in a large hydraulic flume using undisturbed soil samples taken from Hebei small watershed in the black soil region of Northeast China. The response of SER to different straw incorporation amounts (0, 1.125, 2.25, 4.5, 6.75, 9.0 and 13.5 t ha−1) was quantified after three months of straw decomposition. The major influencing factors and the corresponding mechanisms were determined. The findings demonstrated that rill erodibility firstly decreased exponentially with straw incorporation amount (R2 = 0.93), while it slightly increased when straw incorporation amount was more than 9.0 t ha−1. Critical shear stress firstly increased logarithmically (R2 = 0.90) and then slightly decreased when the amount exceeded 9.0 t ha−1. Compared to the treatment of 0 t ha−1, rill erodibility reduced by 17.0%–92.8% and critical shear stress increased by 59.6%–127.2% across different treatments of straw incorporation. Rill erodibility had significant and negative correlations with soil organic matter content, aggregate stability, cohesion, root mass density, straw mass density and straw decomposition amount. The key mechanisms for promoting SER were derived by the direct and indirect effects of straw incorporation and its decomposition on soil physicochemical properties and crop roots. The amount of 9.0 t ha−1 was recommended as the optimum amount of straw incorporation in croplands in Northeast China. These findings are useful to understand how soil erosion resistance responds to the amount of straw incorporation and make rational environmental management policy for semi-humid and cool regions.

Soil surface roughness of sloping croplands affected by land degradation degree and residual of incorporated straw

Changes in soil surface roughness (SSR) are not only closely associated with the characteristics of the underlying surface but also play a vital role in hydrological and soil erosion processes. SSR of degraded croplands is likely affected by the residual of incorporated straw, however, few studies have been focused on this topic. This study was conducted to investigate the changes in SSR of sloping croplands with different land degradation degrees under straw incorporated and without straw incorporated treatments, and determine the dominant factors attributing to these changes in the black soil region of Northeast China. SSR was determined by a photogrammetry technique and the dominant influencing factors were identified by redundancy analysis. The results showed that SSR were decaying by land degradation. Compared to non-degraded croplands, SSR of light, moderate and heavy degraded croplands decreased by 10.4 %, 11.3 %, 23.3 % and 13.8 %, 16.7 %, 31.9 % for straw incorporated and without straw incorporated treatments, respectively. The improvement of SSR was mediated by residual of incorporated straw. Compared to the treatment of without straw incorporation, SSR of straw incorporated treatment increased by 29.4 %, 30.5 %, 32.7 %, and 33.3 % for non, light, moderate and heavy degraded croplands, respectively. Change in SSR was modulated by soil properties, crop characteristics, and residual of incorporated straw. Change of SSR was dominantly controlled by water-stable aggregate (WSA), penetration resistance (PR), soil organic matter (SOM), structure stability index (SSI), mean weight diameter (MWD), root mass density (RMD), litter mass density (LMD) and amount of incorporated straw residual. The increase in SSR was linear with SSI, SOM, RMD and LMD, and logarithmic with MWD and WSA. The measured SSR could be well estimated by WSA, SOM, PR and RMD (R2 = 0.82). SSR could affect hydrological and erosion processes of croplands by reducing sediment connectivity and increasing land surface storage of runoff. The results of this study are helpful in understanding the spatial heterogeneity of SSR at the hillslope scale.

Impact of Winter Cover Crops on Total and Microbial Carbon and Nitrogen in Black Soil

Winter cover crops have been shown to promote the accumulation of microbial biomass carbon and nitrogen, enhance nutrient cycling, reduce erosion, improve ecosystem stability, etc. In the black soil area of Northeast China, Triticum aestivum L., Medicago sativa L., Vicia villosa Roth., Triticum aestivum L. and Medicago sativa L. mixed planting, Triticum aestivum L. and Vicia villosa Roth. mixed planting, and winter fallow fields (CK) were selected to investigate the effects of winter cover crops on soil total carbon and nitrogen and microbial biomass carbon and nitrogen. The results showed that (1) after seasonal freeze-thaw, the rate of change in SOC (−2.49~6.50%), TN (−1.54~5.44%), and C/N (−1.18~1.16%) was less than that in SMBC (−80.91~−58.33%), SMBN (−65.03~332.22%), and SMBC/SMBN (−45.52~−90.03%); (2) winter cover crops not only alleviated the negative effects of seasonal freeze-thaw, which reduces SMBC and qMBC, but also increased SMBN and qMBN; (3) there was an extremely significant (p < 0.01) positive correlation between SOC and TN, a significant (p < 0.05) negative correlation between SMBC and SMBN, and there was no significant correlation between SOC and SMBC or between TN and SMBN; (4) alkali-hydrolysable nitrogen had the greatest impact on SOC and TN, while the soil’s saturation degree had the greatest impact on SMBC and SMBN; and (5) the Triticum aestivum L. monoculture was the most effective in conserving soil microbial carbon and nitrogen. In conclusion, winter cover crops can mitigate the reduction in soil microbial biomass carbon caused by seasonal freeze-thaw and also increase the soil microbial nitrogen content in the black soil region of Northeast China, of which Triticum aestivum L. monoculture showed the best performance.

Effect and Mechanism of Root Characteristics of Different Rice Varieties on Methane Emissions

Methane (CH4), which is an important component of the greenhouse gases from paddy ecosystems, is a major contributor to climate change. CH4 emissions from paddy ecosystems are closely related to the rice root system; however, how the rice root system affects CH4 emissions remains unclear. We conducted a field experiment in 2023 at the Heping Irrigation District Rice Irrigation Experiment Station in Qing’an County, Heilongjiang Province. The field experiment used five local rice varieties with similar fertility periods to observe rice root morphology and physiology indexes, CH4 emission fluxes, and cumulative CH4 emissions. A structural equation model (SEM) was established to investigate the effects of root characteristics on the CH4 emissions from rice and understand the potential mechanisms of these effects. The results showed that the seasonal patterns of CH4 emission fluxes were similar in different rice varieties, and that, during the tillering to heading–flowering stages, the cumulative CH4 emissions accounted for 89.8–92.6% of the total cumulative CH4 emissions of rice. Significant negative correlations were observed between CH4 emission fluxes and root volume, root dry weight, root oxidation activity (ROA), and root radial oxygen loss (ROL) (r = −0.839, −0.885, −0.401 and −0.934, p < 0.05), while there were significant positive correlations between root diameter; malic acid, citric acid, and succinic acid contents; and CH4 emission fluxes (r = 0.407, 0.753, 0.797, and 0.685, p < 0.05). The SEM showed that CH4 emission fluxes were directly influenced by ROL and organic acid contents, while the other root indicators had indirect effects by modulating ROL and organic acid contents. ROL and root volume had the largest total effect, indicating that ROL and root volume were the most significant root physiological and morphological indicators affecting CH4 emission fluxes. This study provides theoretical support and reference data for achieving sustainable agricultural development in the black soil region of Northeast China.

Short‐term conservation tillage degrades soil infiltration properties in the black soil region of Northeast China

AbstractSoil infiltration properties (SIPs) are crucial soil hydraulic parameters for hydrological and erosion models as they regulate the movement of water and nutrients within the soil. Tillage practice can significantly impact the hydrological and erosional processes of sloping farmland by changing SIPs through altering soil structure. Nevertheless, knowledge regarding the effects of short‐term conservation tillage on SIPs is unclear, which greatly limits the management of soil and water resources of sloping farmland. This study aimed to clarify the potential impact and underlying mechanisms of short‐term implementation of conservation tillage on SIPs under three typical tillage management types: conventional downslope tillage (DT), conservation contour tillage (CT), and no‐tillage (NT) in the black soil region of Northeast China. SIPs of initial infiltration rate (IIR), steady infiltration (SIR), and hydraulic conductivity (Ks) were determined by a field disc infiltration experiment under pressure heads (h) of −3, −1.5, and 0 cm. The results revealed that short‐term implementation of conservation tillage management degraded SIPs, with a significant difference observed between DT and NT. In comparison to DT, the mean SIPs of IIR, SIR, and Ks of CT decreased by 27.5%, 31.2%, and 28.6%, and the corresponding reduced values of NT were 54.1%, 65.0%, and 65.5%, respectively. SIPs were significantly correlated with soil texture, bulk density (BD), capillary porosity (CP), total porosity (TP), field capacity (FC), saturated water content (SSWC), and organic matter content (SOM). Among these influencing factors, the variations in SIPs among different tillage management and soil layers were primarily influenced by differences in clay and gravel contents, FC, and SSWC and SSWC played the most critical role. These results highlight the substantial impacts and clarify the mechanisms of short‐term conservation tillage on SIPs, which is helpful for understanding the potential effect of short‐term conservation tillage management on hydrology and erosional processes, thereby improving the sustainable utilization of arable land.

Disentangling slope‐scale spatial variability of saturated hydraulic conductivity in the black soil region of northeast China using noise‐assisted multivariate empirical mode decomposition

AbstractReliable estimates of saturated hydraulic conductivity (Ks) are usually difficult to obtain, as Ks is regulated by a variety of soil processes acting at different spatial scales that may obscure each other's impacts. We hypothesized that these scale‐specific relationships could be well characterized with the aid of the noise‐assisted multivariate empirical mode decomposition (NA‐MEMD), thereby serving as a solid foundation for an accurate Ks prediction. The objective was to evaluate whether the incorporation of NA‐MEMD could improve the estimation of Ks based on the multiscale associations it unraveled. On a typical slope transect of 860 m in the black soil region of northeast China, Ks, mollic epipedon thickness, bulk density, soil organic carbon content, total (ϕ) and effective porosities (ϕe), and particle size distribution were investigated at every 20 m. Prior to NA‐MEMD, Ks was most strongly correlated with ϕe, and the linear regression models based on ϕe solely were satisfactory for Ks estimation at the scale of investigation. Adding other predictors significantly improved Ks prediction in calibration, but impaired it in validation. Upon decomposition by NA‐MEMD, Ks was found to be significantly associated with each attribute at two scales of oscillation at least. Summing up the estimates of each Ks component derived from the properties at the equivalent oscillation scales, the results outperformed the traditional multiple linear regressions made at the investigation scale, when the same sets of predictors were used. The application of NA‐MEMD, moreover, could save the tedious measurements of ϕe and ϕ. Excluding these two porosity‐related properties, Ks estimates obtained by incorporating NA‐MEMD were statistically similar or even better than those involving them before NA‐MEMD. These findings demonstrate the great potential of NA‐MEMD in untangling scale‐dependent relationships of Ks with various processes and hold important implications for future estimations of Ks and other hydraulic properties in the black soil region of northeast China and similar regions.

Winter Cover Crops Affect Aggregate-Associated Carbon, Nitrogen and Enzyme Activities from Black Soil Cropland

The thinning, leaning, and hardening of arable land in the black soil region of Northeast China has brought serious challenges to the sustainable development of agriculture. It is of great significance to explore suitable conservation tillage for the conservation and sustainable utilization of black soil resources actively. The topsoil of the cropland in the northeastern part of the Songnen Plain with winter fallow (CK), planted alfalfa, and planted winter wheat was used as the research object to analyze the changes in the soil aggregate composition, nutrients, and enzyme activities before and after freeze–thaw, respectively, and to investigate the effect of winter cover crops on the improvement of the quality of the black soil cropland. Compared with the winter fallow field, (1) planting alfalfa significantly increased the mechanical stability of 1–2 mm and 0.25–1 mm particle size aggregates (about 3 times and 25 times over), and planting winter wheat increased the water stability of 0.25–1 mm particle size aggregates significantly (2.7 times over); (2) planting alfalfa and winter wheat increased the soil C/N ratio of >2 mm and 1–2 mm particle size aggregates, and the increment in the C/N ratio in >2 mm particle size aggregates remarkably increased, by 203.6% and 362.7%, respectively; (3) planting alfalfa significantly enhanced the soil invertase activity and urease activity in >2 mm and 0.25–1 mm particle size aggregates, and planting winter wheat significantly enhanced the catalase activity in 0.25–1 mm particle size aggregates. In conclusion, planting winter cover crops during the winter fallow period can maintain and promote the mechanical and water stability of medium and large (0.25–1 mm,1–2 mm) soil aggregates, increase the carbon content and C/N ratio of larger (1–2 mm, >2 mm) aggregates, and enhance the enzyme activity of small and medium (0.25–1 mm, <0.25 mm) aggregates to varying degrees. The results of the study can provide a reference for the promotion of basic research on and technology for winter cover crops in the black soil region.

Integrated Use of GIS and USLE Models for LULC Change Analysis and Soil Erosion Risk Assessment in the Hulan River Basin, Northeastern China

The Hulan River Basin is located in the black soil region of northeast China. This region is an important food-producing area and the susceptibility of black soil to erosion increases the risk of soil erosion, which is a serious environmental problem that affects agricultural productivity, water supply, and other important aspects of the region. In this paper, the changes in LULC (land use and land cover) in the basin between 2001 and 2020 were thoroughly analysed using GIS (geographic information system) and USLE (universal soil loss equation) models. The soil erosion risk in the Hulan River Basin between 2001 and 2020 was also studied and soil erosion hot spots were identified to target those that remained significant even under the implementation of soil conservation measures. Precipitation data were used to obtain the R factor distribution, LULC classification was adopted to assess the C factor distribution, soil data were employed to estimate the K factor distribution, DEM (Digital Elevation Model) data were used to generate an LS factor map, and slope and LULC data were considered to produce a P factor distribution map. These factors were based on the model parameters of the USLE. The findings of LULC change analysis over the last 20 years indicated that, while there have been nonobvious changes, agricultural land has continued to occupy the bulk of the area in the Hulan River Basin. The increase in areas used for human activities was the most notable trend. In 2001, the model-predicted soil erosion rate varied between 0 and 120 t/ha/yr, with an average of 4.63 t/ha/yr. By 2020, the estimated soil erosion rate varied between 0 and 193 t/ha/yr, with an average of 7.34 t/ha/yr. The Hulan River Basin was classified into five soil erosion risk categories. Most categories encompassed extremely low-risk levels and, over the past 20 years, the northeastern hilly regions of the basin have experienced the highest concentration of risk change areas. The northeastern hilly and mountainous regions comprised the risk change area and the regions that are most susceptible to erosion exhibited a high concentration of human production activities. In fact, the combined use of GIS and USLE modelling yielded erosion risk areas for mapping risk classes; these results could further assist local governments in improving soil conservation efforts.

Influences of conservation tillage on soil macrofaunal biodiversity and trophic structure in the Mollisol region of Northeast China

Tillage regimes directly impact soil disturbance and crop residue levels in the field, subsequently affecting soil macrofauna abundance and diversity, crucial for maintaining soil health and ecosystem functionality. The present study aimed to investigate the effects of different tillage regimes (no-tillage (NT), conventional tillage (CT) and reduced-tillage (RT)) on soil properties and macrofaunal communities in a typical black soil region of Northeast China. Our study revealed that, in comparison to CT and RT, NT significantly enhanced soil macrofauna biodiversity and brought about modification in the community composition. Additionally, it reduced changes in the soil physical–chemical properties. Furthermore, the choice of tillage regimes impacted the trophic structure of soil macrofauna, manifesting in great density and species richness of herbivores and predators in NT plots with crop residue retention when compared to those managed with tillage. Overall, soil organic carbon (SOC) and pH played pivotal roles in regulating the soil macrofaunal community. The alternations observed in the soil macrofaunal community represented a comprehensive response to tillage practices and residue return, which in turn influenced soil properties and microenvironments, including food resources and microhabitats. Therefore, our findings indicated that conservation tillage exerted a notable influence on the soil macrofaunal community. This underscores the significance of soil environments and properties in molding the structure and composition of the soil macrofaunal community. The study will enhance comprehension of soil management practices and advocate for diversity within soil macrofaunal communities.

Modified biochar reduces the greenhouse gas emission intensity and enhances the net ecosystem economic budget in black soil soybean fields

Long-term high intensity utilization leads to the degradation of black soil in Northeast China and the serious loss of organic carbon. Biochar has great potential for improving the carbon storage capacity of agroforestry ecosystems and reducing greenhouse gas (GHG) emissions. However, the effectiveness of biochar application depends on pedoclimatic factors, and few studies have explored the effects of biochar and its modified biochars on the net ecosystem economic benefit (NEEB) of black soil farmland. To increase the environmental benefits of carbon sequestration and emission reduction and to improve farmer profits, this study modified biochars by physical, chemical and biological methods, and studied the effects of different types of modified biochars on soil properties, crop yield and GHG emissions in black soil farmland through field experiments. The NEEB of different treatments was evaluated by combining carbon cost, yield benefit and biochar cost. A total of 6 treatments were used in the experiment: normal fertilization (CK), fertilization + raw biochar (BC), fertilization + physically modified biochar (PBC), fertilization + acid-modified biochar (HBC), fertilization + magnetically modified biochar (MBC), and fertilization+ biologically modified biochar (BBC) treatments. Compared with the control (CK), the application of biochar increased the content of soil organic matter by 18.76–42.57% and improved the soil fertility. The raw biochar had no significant effect on soybean yield and increased the global warming potential by 41.18%. Soybean yields significantly increased with decreasing GHG emission intensity when modified biochars were applied. Due to the high cost of biochar and the current low carbon price, the effect of biochar on crop yield is crucial for increasing the NEEB. The NEEB in the HBC treatment was the highest, 57.86% higher than that in the CK treatment and was an effective strategy for increasing crop yield while reducing GHG emissions. The results of this study could provide a theoretical basis and technical support for soybean farmland carbon sequestration, emission reduction, soil improvement and yield improvement in the black soil region of Northeast China.

Measurement of cultivated land ecosystem resilience in black soil region of Northeast China under the background of cultivated land protection policy in China: Case study of Qiqihar City

Scientific understanding and measurement of cultivated ecosystem resilience is crucial for the protection of cultivated land represented by black soil and the sustainable development of cultivated land ecosystem. In this study, we took Qiqihar, a typical black soil region, as the study area and divided the cultivated land ecosystem into two subsystems, black soil ecology and human socioeconomic. And we constructed a “policy background - generation process - system composition” measurement element screening model (PGSM) to establish the subsystem index systems. Cultivated land ecosystem resilience in 2020 was measured by the Pressure-State-Response (PSR) model and the multiscale fusion model. The results showed that the resilience of the black soil ecological subsystem (54.27) in Qiqihar is higher than that of the socioeconomic subsystem (49.01), and their spatial distribution trends were opposite. The overall resilience of cultivated land ecosystem was moderately low (51.64) but spatially heterogeneous. Cultivated land resource endowment and human activities pressure had the greatest impact on the subsystem. Socioeconomic input was the primary problem in regional resilience. Based on these findings, we made suggestions for cultivated land protection in black soil regions. This study contributes to the scientific and comprehensive measurement of the cultivated land ecosystem resilience and provides reference for sustainable management of black soil systems in China and globally.

Temporal variability of saturated hydraulic conductivity on a typical black soil slope of northeast China

Saturated hydraulic conductivity (Ks) is highly variable in both space and time. Compared to its spatial variability, however, the temporal Ks variability has rarely been studied or taken into account in the hydrological modelling. The objectives were to characterize the slope-scale temporal variability of Ks and to diagnose the primary factors regulating Ks variation during the growing season. In the black soil region of northeast China, a typical slope farmland dominated by silt loam was selected and divided into five sections with respect to soil erosion. Soil samples were collected in each section at approximately every 3 weeks during the maize growing season, and Ks, bulk density (BD), land surface roughness, wet-aggregate stability (WAS), soil organic carbon content (SOC), clay and sand contents (SAND) were investigated. Mainly owing to root growth, precipitation and agricultural management, strong temporal variability of Ks was observed in each of the five sections, as the corresponding coefficients of variation all exceeded 35 %. Using the redundancy analysis (RDA) and classical correlation analyses, the primary variables controlling Ks distribution varied among sections, i.e., precipitation (P) and SAND in the erosive section and BD in the others. The predominance of BD was also manifested when performing RDA and structural equation modelling (SEM) over the entire slope covering all five sections.The other significant factors included SAND, SOC, P and WAS, in the decreasing order of direct path coefficient. In addition, these factors also indirectly affected Ks through their influence on BD and/or other factors. These findings demonstrate the strong temporal variability of Ks throughout the maize growing season and intricate interactions of Ks with related factors, and have important implications for hydrological modelling and agricultural production in the black soil region of northeast China and other similar regions.

Assessment of the cultivated land quality in the black soil region of Northeast China based on the field scale.

In some developing countries, particularly China, a significant number of individual farmers manage small field scale of cultivated land. However, the existing research on cultivated land quality assessment mainly focuses on large-scale regions, establishing comprehensive index systems from a macro perspective, while lacking evaluations customized to individual farmers, who constitute a crucial component in agricultural production, and a demand-driven field-scale assessment of cultivated land quality. Therefore, we developed a field-scale index system that meets the needs of individual farmers in the black soil region of Northeast China. Additionally, we proposed a machine learning model for field-scale cultivated land quality assessment. The experimental results showed that our model achieved an [Formula: see text] value of 0.9660 and an [Formula: see text] of [Formula: see text] under fourfold cross-validation, which represents an improvement of 5.19% and a reduction of 1.13%, respectively, relative to the XGBoost model. Ultimately, we conducted obstacle factor diagnosis, aiming to assist individual farmers in identifying the existing issues in their cultivated land fields. This study not only provides guidance to individual farmers but also addresses the research gap in cultivated land quality assessment by offering an individual farmer demand-driven index system for field-scale studies.

Investigating the Soil Wind Erosion in the Black Soil Region of Northeast China Based on <sup>137</sup>Cs Tracer Method

Investigating the Soil Wind Erosion in the Black Soil Region of Northeast China Based on <sup>137</sup>Cs Tracer Method

Temporal and spatial distribution and development of permanent gully in cropland in the rolling hill region (phaeozems area) of northeast China

The cropland in the Songnen phaeozems area (SPA) experiences an extensive gully erosion in the black soil region of northeast China. This study investigates the historical trends, current status, and future trajectories of permanent gully (PG) development, aiming to reveal the mechanisms behind PG development and protect the black soil. We selected nine study areas, totalling 378 km2, across three latitudinal zones in the SPA with slopes of 0–1 %, 1–3 %, and 3–5 %. The results revealed a consistent rise in gully density over time in the SPA, with values increasing from 0.87 km/km2 in 1970 to 0.94 km/km2 in 2010, and 1.32 km/km2 in 2021. Conversely, the ground lacerative degree significantly decreased from 0.025 km2/ km2 in 1970 to 0.010 km2/ km2 in 2010, and rebounding slightly to 0.019 km2/ km2 in 2021. The development rate of PG in the northern area was higher than that in the middle and southern areas, with steeper slopes (3–5 %) having more PGs compared to gentler slopes. The average rate of gully area extension increased with increasing gully level. From 1970 to 2010, the area of PG experienced a decline attributed to extensive gully management. However, subsequent decade (2010–2021) experienced a more rapid PG development, resulting in an annual cropland loss of 0.097 %. The northern area has consistently exhibited the fastest PG development rate in 1970–2021. It is noteworthy that managing gullies through reclamation after filling PG has resulted in the re-generation of secondary gullies in the same locations, which developed more rapidly than natural gullies. The reclamation after filling PG, without improvement of field drainage systems, contributes to an accelerated development rate of PG in cropland. Despite significant reductions in the total area and length of PGs through large-scale gully management, the notable increase in the development rate of gullies warrantsattention in the SPA of northeast China. Furthermore, the global community should take caution with inappropriate gully management measures because they not only prove ineffective but aggravate gully erosion.

Effect of long‐term strip tillage on soil macropore structure in cool black soil region of Northeast China

AbstractSoil pore structure is essential for storing and transporting water, and it can be affected by different tillage practices. Strip tillage (ST) is an innovative technology aimed at addressing the challenge of reduced crop yield caused by no‐tillage (NT) in the cool black soil region of Northeast China. Nevertheless, what remains unclear is the influence of ST on soil pore structure in the cool black soil region. After conducting a 14‐year long‐term positioning experiment, this study investigated the variations in spatial distribution patterns of soil macropores under ST practice using X‐ray computed microtomography (μCT). The research also examined, the response of soil organic carbon (SOC) and soil bulk density to ST compared to conventional tillage (CT). This finding revealed that ST significantly increased the macroporosity (>25 μm) at 0–20 cm depths in comparison with CT. The detailed analysis of soil pore size distribution revealed a significant increase in macroporosity of the >2000 μm pore sizes in 0–10 cm layer by 144.79% because of ST. Furthermore, ST significantly increased pore connectivity at the 0–10 cm depth by 3.37% and pore fractal dimension at the 10–20 cm depth by 13.42%. Meanwhile, there was a significant correlation among the changes in soil bulk density, SOC content, macroporosity, pore connectivity, and pore tortuosity, indicating soil bulk density and SOC have a substantial impact on the pore structure. Overall, the implementation of ST leads to a significant enhancement in soil pore structure, improving the understanding of the regulatory mechanism of ST in the cool black soil region of Northeast China. This research aids in advancing the conservation and sustainable utilization of black soil.

Effect of straw incorporation on controlling runoff and soil erosion in cropland with different land degradation degrees

AbstractStraw incorporation plays a vital role in regulating runoff and soil erosion of cropland. However, the benefits of straw incorporation to control runoff and soil erosion on croplands under different degradation degrees have not been fully clarified. This study was performed to investigate the benefits of straw incorporation to reduce runoff and soil erosion under different degradation degrees and determine its dominant influencing factors. The event runoff and soil erosion were measured from late May to late September 2022 using 16 runoff plots (9 m in length and 3.3 m in width) in the black soil region of Northeast China. The results showed that straw incorporation significantly reduced runoff and soil erosion on croplands with different degradation intensities. Compared to croplands without straw incorporation, runoff and soil erosion of straw incorporation decreased by 48. 8%, 40.0%, 30.9%, 25.5%, and 55.2%, 48.8%, 40.8%, and 36.5% for croplands of no, light, moderate, and strong degradation intensities, respectively. The roles of straw incorporation in controlling runoff and erosion decreased with rainfall intensity. Compared to light rainfall, runoff reduction ratio and erosion reduction ratio of moderate and heavy rainfalls reduced by 19.5%–61.3% and 27.5%–64.4%. The benefit of straw incorporation to control runoff and erosion was limited on strong degraded cropland or under heavy storm. Moreover, soil hydrological properties and crop growth characteristics decreased by land degradation and improved by straw incorporation, which inevitably affected runoff and soil erosion. Soil bulk density, maximum rainfall intensity of 30‐min, saturated water content, precipitation, rainfall intensity, saturated hydraulic conductivity, and total porosity were the dominant factors affecting the roles of straw incorporation in controlling runoff and erosion on degraded croplands. The results of this study are helpful to prevent land degradation or recover the functions of degraded lands in semi‐humid region.

[Short-term effect of different returning methods of maize straw on the temperature of black soil plough layer].

Clarifying the effect of different maize straw returning methods on soil temperature is crucial for optimizing the management of farmland straw and the efficient utilization of heat resources in the black soil region of Northeast China. To investigate the impacts of straw returning methods on soil temperature, we conducted a field experiment with four treatments during 2018 and 2020, including plough tillage with straw returning (PTSR), rotary tillage with straw returning (RTSR), no-tillage with straw returning (NTSR), and a control treatment of conventional ridge tillage without straw returning (CT). We measured soil temperature and water content at the 5 cm, 15 cm and 30 cm soil layer, and the straw coverage rate during the 3-year maize growth period. We further analyzed the differences of soil temperature in different soil layer under different treatments, accumulated soil temperature and growing degree-days (GDD) above 10 ℃, daily dynamics of soil temperature, the production efficiency of air accumulated temperature among different treatments, and explored factors causing the difference of soil temperature and the production efficiency of air accumulated temperature. Our results showed that different treatments mainly affected soil temperature from the sowing to emergence stage (S-VE) of maize. The daily average soil temperature showed a trend of CT>PTSR>RTSR>NTSR. The differences of soil temperature under different treatments showed a decreasing trend as growth process advanced and soil depth increased. Compared with the CT treatment, soil temperature at 5 cm depth was decreased by 0.86, 1.84 and 3.50 ℃ for PTSR, RTSR, and NTSR treatments, respectively. NTSR significantly reduced the accumulated temperature of ≥10 ℃ in different soil layers and GDD. The accumulated temperature ≥ 10 ℃ at the 5, 15, and 30 cm soil layers decreased by 216.2, 222.7, and 165.1 ℃·d, and the GDD decreased by 201.9, 138.7 and 123.9 ℃·d, respectively. In addition, production efficiency of air accumulated temperature decreased by 9.7% to 15.6% for NTSR. Conclusively, PTSR and RTSR had significant impacts on topsoil temperature during the maize growing period from sowing to emergence, but did not affect the accumulated soil temperature and the production efficiency of air accumulated temperature. However, NTSR significantly reduced topsoil temperature and production efficiency of air accumulated temperature.

Variation Characteristics and Expression State of Nitrogen and Phosphorus Metering Ratio of Rice in Black Soil under Film Mulching and Irrigation Methods

In order to investigate the effects of film mulching and water-saving methods on soil inorganic nitrogen, nitrogen content of rice organs, nitrogen-phosphorus metering ratio, and nutrient limitation during rice yield formation, two water-saving irrigation methods and black biodegradable film mulching were adopted. The effects of water-saving film mulching on NH4+-N and NO3−-N in 0 to 60 cm soil, nitrogen accumulation and ratio, and nitrogen-phosphorus metering ratio in rice organs were analyzed. The nitrogen-phosphorus-limiting state of rice growth under water-saving film mulching was determined. The results showed that water-saving and film mulching methods could weaken the leaching of NH4+-N and NO3−-N and enhance the nitrogen uptake of rice. The water-saving method of mulching could reduce the metering ratio of nitrogen and phosphorus in rice organs. The panicle maturity process had been in a state of nitrogen limitation, and the effect was gradually enhanced. The nitrogen and phosphorus metering ratio of panicles was positively correlated with NH4+-N accumulation in the 0 to 60 cm soil layer and nitrogen accumulation of rice organs, and negatively correlated with soil NO3−-N accumulation under film mulching and water-saving methods. The correlation between stems and leaves’ nitrogen and phosphorus metering ratios and influencing factors was basically opposite to that of panicles’ nitrogen and phosphorus metering ratio. This study can provide a reference for the formulation of a fertilization system under film mulching in the black soil region of northeast China.

Legacy of herbicides in water from Hailun City, Northeast China: Occurrence, source, and ecological risk assessment

Herbicides (HBCs) are extensively used in modern agriculture. However, their potential negative impacts on environmental media have emerged as a significant environmental concern. In this study, we employed positive matrix factorization (PMF) to identify the potential sources of HBCs. Furthermore, we utilized a multi-matrix ecological risk model to assess the risks associated with HBCs in both surface water and groundwater in the black soil region of Northeast China. The findings revealed that the levels of ∑15HBCs in surface water and groundwater ranged from 585.84 to 6466.96 ng/L and 4.80 to 11,774.64 ng/L, respectively. The PMF results indicated that surface runoff and erosion accounted for 50% of the total HBCs in water, serving as the primary sources. All tested HBCs exhibited acute risk values within acceptable levels. The risk index for the ∑15HBCs was categorized as “moderate risk” in 31% of the surface waters and 13% of the groundwaters. However, 4% of the groundwater sampling sites reached the “high risk” level. The chronic risk quotient of ∑15HBCs in surface water and groundwater was 92% and 62% at the “high risk” level, respectively. Interestingly, non-carcinogenic HBCs contributed more significantly to the ecotoxicology of the aquatic system than carcinogenic HBCs. This study provides comprehensive information on the legacy of HBCs in water bodies and emphasizes the potential risks posed by HBCs to aquatic systems. The results obtained from this study could help relevant management authorities in developing and implementing effective regulations to mitigate the ecological and environmental risks associated with HBCs.