Contour Farming Suitability of the Black Soil Region in Northeast China and Its Spatial Characteristics

Contour farming technology plays a key role in reducing soil erosion,enhancing water use efficiency,and fostering sustain-able agricultural development,Despite being a straightforward yet efficacious farming technique,it has not seen widespread implement-ation in China.Considering the deteriorating quality of arable lands in the Black Soil Region of Northeast China(BSR-NEC),it is ne-cessary to investigate spatial patterns and identify suitable areas for contour farming in this region.To achieve this objective,spatial autocorrelation and grouping analysis methods were employed to classify the land into four categories of suitability for contour farming:highly suitable,moderately suitable,generally suitable,and unsuitable.The results reveal that:1)the contour farming suitable area in BSR-NEC covers 89861.32 km^(2),accounting for 21.59%of arable land as of 2020.Heilongjiang Province owns the largest suitable area of 32853.68 km^(2),and Inner Mongolia has the highest proportion of 28.89%.2)In terms of the spatial distribution,regions with higher suitability for contour farming are concentrated in the Da Hinggan Mountains region,particularly Nenjiang City(Heilongjiang Province),which has the highest area of 2593.07 km^(2).Areas with a high proportion of suitable arable lands for contour farming are mainly found in the Da Hinggan Mountains and Changbai Mountains regions,with Ergun City(Inner Mongolia)having the highest pro-portion at 47.2%.Regions with higher suitability and proportion are concentrated in the Da Hinggan Mountains region,primarily cover-ing the Inner Mongolia and Heilongjiang.3)Regarding spatial clustering,both the area and proportion of suitable contour farming areas exhibit noticeable clustering effects,though not entirely consistent.4)Group analysis results designate 148 counties in BSR-NEC as highly suitable areas,predominantly located in the Changbai Mountains region,Liaodong Peninsula,Hulun Buir Plateau,and the north and south regions of the Da Hinggan Mountains.The zoning of suitable areas for contour farming in BSR-NEC informs the strategic de-velopment of policies and measures,allowing for the implementation of targeted policies in distinct areas suitable for contour farming.This provides a valuable reference for promoting contour farming technology more effectively and efficiently.re effectively and effi-ciently.

Trade-off and Synergy of Rural Functions Under County Depopulation in the Typical Black Soil Region of Northeast China

As the population continues to shrink in the black soil region of Northeast China since 2000,it is critical to master the impact of population shrinkage on rural functions to realize rural revitalization and sustainable development.In this study,we focused on the impacts of depopulation on the evolution and interrelationship of rural subfunctions.Based on the rural function indexes system,the TOPSIS(Technique for Order Preference by Similarity to an Ideal Solution)method,spatial analysis method,and mathematical statistics analysis method were used to summarize the spatial and temporal characteristics of rural function development,as well as the effect of population shrinkage in the typical black soil region of Northeast China.The results showed that depopulation varied in the extent and duration between the forested region and plain areas,which both impacted the trajectories of rural subfunctions evolution.For the economic development function and ecological conservation function,the effect of continuous slight depopulation was beneficial,while the effect of rapid depopulation was adverse,which was exactly opposite to the agricultural production function.All forms of population shrinkage were conducive to the development of the social security function.With the deepening population shrinkage,depopulation mainly promoted the collaborative development between subfunctions in this study,except the relationship between agricultural production and social security function.But effects of depopulation on the interrelationship of rural subfunctions varied between the forested region and plain areas in some cases.The results provided evidence for the cognition that population shrinkage had complicated effects on rural subfunctions.

Evaluation and Driving Force Analysis of Cultivated Land Quality in Black Soil Region of Northeast China

Cultivated land is an important natural resource to ensure food,ecological and economic security.The cultivated land quality evaluation(CQE)is greatly significant for protecting and managing cultivated land.In this study,320 counties in the black soil region of Northeast China(BSRNC)represent the research units used to construct the CQE system measuring the soil properties(SP),cultivated land productivity(CLP),ecological environment(EE)and social economy(SE).The total of 19 factors were selected to calculate the integrated fertility index(IFI)and divided into grades.Simultaneously,we used the coupling coordination degree model to comprehensively analyze the spatial pattern of the cultivated land quality(CLQ)in the BSRNC,and use the structural equation model(SEM)to analyze the driving mechanism.The results show the following:1)The CLQ of 262 counties in the BSRNC is in a state of coupling and coordination,and the coupling and coordination degree presents a spatial distribution pattern of‘high in the southwest and northeast,low in the northwest and southeast’.The coordinated development degree of 271 counties is between 0.4 and 0.6,which is in a transitional state between coordination and disorder.2)The CLQ in the BSRNC is generally good,with an average grade of 3.High-quality cultivated land accounts for 58.45%of all counties,middle-and upper-quality cultivated land accounts for 27.05%,and poor-quality cultivated land accounts for 14.49%.3)The SEM analysis shows that the SP,CLP,EE,and SE all influence the CLQ.Among them,the SP has the largest driving force on the CLQ,while the SE has the smallest driving force on it.The results confirm that the main factors affecting the evaluation results are crop productivity level,normalized difference vegetation index,ratio vegetation index,difference vegetation index,and organic carbon content.When implementing protection measures in counties with a low CLQ,considering a balanced coordination of multiple systems and reasonably controlling the quality degradation are important.This study provides the current situation and driving factors of the CLQ in the BSRNC and will play an important role in black soil governance and utilization.

Changes of spring wind erosion based on wind erosion climate factor in the black soil region of Northeast China

The dry and windy climate and low ground cover in spring in the black soil region of Northeast China make the soil strongly affected by wind erosion,which seriously threatens the food security and ecological security of this region.In this paper,based on the daily observation data of 124 meteorological stations in study area from 1961 to 2020,seasonal and monthly wind erosion climate factor(C)in spring(March to May)were calculated by using the method proposed by the Food and Agriculture Organization of the United Nations(FAO),the wind erosion characterization in spring were systematically analyzed based on C by various statistical analysis methods.The results showed that in the past 60 years,spring wind erosion climate factor(CSp)and monthly C of the whole region and each province(region)all showed highly significant decreasing trend,but they began to show rebounded trend in the middle or late 2000s.CSp of the study area showed a significant upward trend since 2008 with an increase of 4.59(10a)^(-1).The main contributors to this upward trend are the changes of C in March and in April.For the four provinces(regions),CSp in Heilongjiang,Jilin,Liaoning and eastern Inner Mongolia all showed rebounded since 2008,2011,2008 and 2009,respectively.The rebounded trend of CSp in eastern Inner Mongolia was the most obvious with a tendency rate of 11.27(10a)^(-1),and its mutation occurred after 1984.The rebound trend of CSp in Heilongjiang Province takes the second place,with a trend rate of 4.72(10a)^(-1),but there’s no obvious time mutation characteristics.The spatial characteristics of CSpand monthly C are similar,showing decreasing characteristics centered on the typical black soil belt of Northeast China.Compared with 1961-1990,in the period from 1991 to 2020,the proportion of high value areas(CSp>35,monthly C>10)has decreased to varying degrees,while the proportion of low value areas(CSp≤10,monthly C≤4)has increased.The trends of seasonal and monthly C in 82.2%~87.7%of the stations show significant decreases at 95%confidence level.CSp is closely related to wind speed at 2m height,temperature difference,minimum temperature and precipitation in the same period,of which the correlation between CSp and wind speed is the strongest,indicating that the main control factor for CSp in the study area is wind speed,but the impact of the change of temperature and precipitation on CSp cannot be ignored.

Effect of farmland shelterbelts on gully erosion in the black soil region of Northeast China

The black soil region of northeast China is one of the most important grain-producing areas in China. Increasingly severe gully erosion in this region has destroyed much farmland and reduced grain production. We analyzed SPOT5 imagery from 2007 and TM imagery from 2008 to describe the distributions of gullies and farmland shelterbelts in Kedong County and to assess the effect of farmland shelterbelts on gully erosion. The ima- gery revealed 2311 gullies with average density of 418.51 m km-2, indicating very serious gully erosion. With increasing slope gradient there was an inverse trend between gully density and shelterbelt density, indicating that farmland shelterbelts can prevent gully erosion. The defense effect of farmland shelterbelts against gullyerosion varied with distance： for distances 〈120 m, the defense effect was consistent and very strong; for distances of 120-240 m, a weak linear decrease was found in the defense effect; and for distances 〉240 m, the defense effect of the shelterbelts was significantly weaker. We recommend an optimal planting density of farmland shel- terbelts for the prevention of gully erosion at 1100-1300 m km-2.

Study on Relative Soil and Water Conservation Benefits of Ridge Tillage in Different Terrain Conditions in the Black Soil Area of Northeast China

Ridge tillage, which is a very common and important tillage measure in the black soil area of northeast China, has some soil and water conservation bene- fits, but has little attention. It is very important to explore the spatial distribution of the ridge direction of the arable land and its soil and water conservation benefits in different terrain conditions in the black soil area. So Binxian County of Heilongjiang Province was selected as the study area, and 168 field investigation units were ex- tracted by stratified sampling method and investigated. According to equations of slope gradient factor and slope gradient in ridge direction, and based on the soft- ware of Arcmap, SPSS and Excel, the investigation data of soil and water loss in Binxian County were analyzed and counted, The results show that in plain, hilly and mountainous areas, the average ground slope gradients are 1.92°, 6.20° and 8.27° respectively, and the average slope gradients along ridge direction are 1.33°, 4.52°and 6.45° respectively, which account for about 70%, 73% and 78% of the average ground slope gradients in the same terrain condition; the relative quantities of soil erosion in the present ridge tillage condition account for about 55%, 69% and 67% respectively of that in down-slope ridge tillage conditions, so the present ridge tillage has obviously relative soil and water conservation benefits. Based on these results, the reasons of the present ridge tillage status were analyzed, and some reform measures were proposed. The results could not only help to comprehend the spatial distribution and soil and water conservation benefits of ridge tillage in the black soil area of Northeast China, but also provide scientific references for the layout of local soil and water conservation measures.

Using ^(137)Cs Tracer Technique to Evaluate Erosion and Deposition of Black Soil in Northeast China

Soil and water losses through erosion have been serious in the black soil region of Northeast China. Therefore, a sloping cultivated land in Songnen Plain was selected as a case study to： 1） determine the ^137Cs reference inventory in the study area; 2） calculate erosion and deposition rates of black soil on different slope locations; 3） conduct a sensitivity analysis of some model parameters; and 4） compare overall outputs using four different models. Three transects were set in the field with five slope locations for each transect, including summit, shoulder-slope, back-slope, foot-slope, and toe-slope. Field measurements and model simulation were used to estimate a bomb-derived ^137Cs reference inventory in the study area. Soil erosion and deposition rates were estimated using four ^137Cs models and percentage of ^137Cs loss/gain. The ^137Cs reference value in the study area was 2 232.8 Bq m^-2 with ^137Cs showing a clear topographic pattern, decreasing from the summit to shoulder-slope, then increasing again at the foot-slope and reaching a maximum at the toe-slope, Predicted soil redistribution rates for different slope locations varied. Among models, the Yang Model （YANG-M） overestimated erosion loss but underestimated deposition. However, the standard mass balance model （MBM1） gave predictions similar to a mass balance model incorporating soil movement by tillage （MBM2）. Sensitivity analysis of the proportion factor and distribution pattern of ^137Cs in the surface layer demonstrated the impact of ^137Cs enrichment on calculation of the soil erosion rate. Factors influencing the redistribution of fallout ^137Cs in landscape should be fully considered as calculating soil redistribution rate using ^137Cs technique.

Study on the Method of Soil Productivity Assessment in Black Soil Region of Northeast China

The objective of this paper is to investigate a simple and practical method for soil productivity assessment in the black soil region of Northeast China. Firstly, eight kinds of physicochemical properties for each of 120 soil samples collected from 25 black soil profiles were analyzed using cluster and correlation analysis. Subsequently, parameter indices were calculated using physicochemical properties. Finally, a modified productivity index （MPI） model were developed and validated. The results showed that the suitable parameters for soil productivity assessment in black soil region of Northeast China were soil available water, soil pH, clay content, and organic matter content. Compared with original productivity index （PI） model, MPI model added clay content and organic matter content in parameters while omitted bulk density. Simulation results of original PI model and MPI model were compared using crop yield of land block where investigated soil profiles were located. MPI model was proven to perform better with a higher significant correlation with maize yield. The correlation equation between MPI and yield was： Y= 3.2002Ln（MP/）＋ 10.056, R^2 = 0.7564. The results showed that MPI model was an effective and practical method to assess soil productivity in the research area.

Effects of Tillage Management on Infiltration and Preferential Flow in a Black Soil, Northeast China

The impacts of no-tillage （NT） and moldboard plough （MP） managements on infiltration rate and preferential flow were characterized using a combined technique of double-ring device and dye tracer on a black soil （Mollisols） in Northeast China. The ob- jective of this study is to evaluate how tillage practices enhance soil water infiltration and preferential flow in favor of soil erosion con- trol in the study area. The steady infiltration rates under NT management are 1.6 and 2.1 times as high as those under MP management in the 6th and 8th years of the tillage management in place, while the infiltrated water amounts under NT management are 1.4 and 2.0 times as high as those under MP management, respectively. The depth of methylene blue penetrated into NT soil increases from 43 cm in the 6th year to 57 cm in the 8th year, which are 16 cm and 19 em deeper than those in MP soil, respectively. The results of morphol- ogic image show that more biological macro-pores occur in NT soil than in MP soil. These macro-pores play a key role in enhancing preferential flow in NT soil, which in turn promotes water infiltration through preferential pathways in NT soil. The results are helpful to policy-making in popularizing NT and have the implications for tillage management in regard to soil erosion control in black soil region of China.

Using CropSyst to Simulate Spring Wheat Growth in Black Soil Zone of Northeast China

Available water and fertilizer have been the main limiting factors for yields of spring wheat, which occupies a large area of the black soil zone in northeast China; thus, the need to set up appropriate models for scenario analysis of cropping system models has been increasing. The capability of CropSyst, a cropping system simulation model, to simulate spring wheat growth of a widely grown spring cultivar, 'Longmai 19', in the black soil zone in northeast China under different water and nitrogen regimes was evaluated. Field data collected from a rotation experiment of three growing seasons (1992-1994) were used to calibrate and validate the model. The model was run for 3 years by providing initial conditions at the beginning of the rotation without reinitializing the model in later years in the rotation sequence. Crop input parameters were set based on measured data or taken from CropSyst manual. A few cultivar-specific parameters were adjusted within a reasonable range of fluctuation. The results demonstrated the robustness of CropSyst for simulating evapotranspiration, aboveground biomass, and grain yield of 'Longmai 19' spring wheat with the root mean square errors being 7%, 13% and 13% of the observed means for evapotranspiration (ET), grain yield and aboveground biomass, respectively. Although CropSyst was able to simulate spring production reasonably well, further evaluation and improvement of the model with a more detailed field database was desirable for agricultural systems in northeast China.

Dynamics of soil organic carbon following land-use change:insights from stable C-isotope analysis in black soil of Northeast China

Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent.Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C_4) and from natural vegetation (C_3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C_4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg^(-1) on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment.The increase in the percentage of C_4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C_4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment.

Analysis on Status and Development Trend of Wind Erosion in Black Earth Region of Northeast China

In this paper,areas and main factors of wind erosion in black earth region of Northeast China were systematically analyzed,as well as the development trend of wind erosion in black earth region of Northeast China.In addition,development trend of wind erosion in black earth region of Northeast China was analyzed from the aspects of the geographic position,climatic change law in recent 40 years and effects of northeast sand land desertification on wind erosion in black earth region,which had provided references for the research and prevention of wind erosion in soil of black earth region of Northeast China.

Temporal and Spatial Change of Soil Organic Matter and pH in Cultivated Land of the Songliao Plain in Northeast China during the Past 35 Years

Soil organic matter(SOM)and pH are not only an important part of soil fertility,but also a source of nutrients for plants and an energy source for the life activities of soil microorganisms(Huang,2000).Moreover,soil organic matter(SOM)has a great impact on soil properties and can improve soil fertility and buffering performance.

Erosion effect on the productivity of black soil in Northeast China

Continuous soil erosion has caused serious land degradation in the black soil area of Northeast China. The primary objective of this study was to determine the effects of accelerated erosion on soil productivity, as measured by soybean (Glycine max L. Merr.) yields. Eight erosion levels, 0, 10, 20, 30, 40, 50, 60, and 70 cm, were simulated by imitating the integrated process of natural erosion and tillage activity. Each erosion level had two sub-treatments: conventional fertilization and no fertilization. Soil erosion was found to affect survival probability and to cause remarkable reductions in the Leaf Area Index (LAI), plant height, pod number, biomass, and yield. Soybean yield was exponentially decreased with the increase of soil erosion depth. Compared to erosion depth of 0 cm, erosion levels of 10, 20, 30, 40, 50, 60, and 70 cm experienced reductions in soybean yield by 28.8%, 37.8%, 43.5%, 52.6%, 53.1%, 52.9%, and 64.1% respectively when fertilized whereas the reductions at those levels were 32.6%, 42.2%, 53.0%, 54.0%, 65.8%, 69.7%, and 72.6%, respectively, when unfertilized. At the erosion depths of 10, 20, 30, 40, 50, 60, and 70 cm, the yield reductions per 10 cm of soil eroded when fertilized were 28.8%, 18.9%, 14.5%, 13.2%, 10.6%, 8.8%, and 9.2%, averaged 14.9%, but when unfertilized they were 32.6%, 21.1%, 17.7%, 13.5%, 13.2%, 11.6%, and 10.4%, averaged 17.1%. The results also showed that chemical fertili zers could enhance the yields of eroded soil, but could not recover the yields to the pre-erosion level. Additionally, the results indicated that the primary reason for the decrease in soybean yield with increasing erosion depth was the loss of soil organic matter, soil N and P. These results may aid in selecting effective soil erosion control strategy, forecasting land degradation, establishing soil erosion tolerance, and evaluating the economic cost of soil erosion in the black soil region in Northeast China.

Assessing soil thickness in a black soil watershed in northeast China using random forest and field observations

Soil thickness determines the soil productivity in the black soil region of northeast China,which is important for national food security.Existing information on the spatial variation of black soil thickness is inadequate.In this paper,we propose a model framework for spatial estimation of the black soil thickness at the watershed scale by integrating field observations,unmanned aerial vehicle variations of topography,and satellite variations of vegetation with the aid of random forest.We sampled 141 sample profiles over a watershed and identified the black soil thickness based on indices of the mollic epipedon.Topographic variables were derived from a digital elevation model and vegetation variables were derived from Landsat 8 imagery.Random forest was used to determine the relationship between black soil thickness and environmental variables.The resulting model explained 61%of the black soil thickness spatial variation,which was more than twice that of traditional interpolation methods(ordinary kriging,universal kriging and inverse distance weighting).Topographic variables contributed the most toward explaining the thickness,followed by vegetation indices.The black soil thickness over the watershed had a clear catenary soil pattern,with thickest black soil in the low depositional areas and thinnest at the higher elevations that drain into the low areas.The proposed model framework will improve estimates of soil thickness in the region of our study.

Soil loss tolerance in the black soil region of Northeast China

Soil loss tolerance （/） is the maximum rate of annual soil erosion that is tolerated and still allows a high level of crop productivity to be sustained economically and indefinitely. In the black soil region of Northeast China, an empirically determined, default Tvalue of 200 （t/km2.a） is used for designing land restoration strategies for different types of soils. The ob- jective of this study was to provide a methodology to calculate a quantitative T for different black soil species. A field investigation was conducted to determine the typical soil profiles of 21 black soil species in the study area and a quantitative methodology based on a modified soil productivity index model was established to calculate the Tvalues. These values, which varied from 68 t/km2.a to 358 t/km2-a, yielded an average Tvalue of 141 t/km2.a for the 21 soil species. This is 29.5% lower than the current national standard T value. Two significant factors that influenced the T value were soil thickness and vulnerability to erosion. An acceptable reduction rate of soil productivity over a planned time period of 1% is recommended as necessary for maintaining long-term sustainable soil productivity. Compared with the cur- rently used of regional unified standard T value, the proposed method, which determines T using specific soil profile indices, has more practical implications for effective, sustainable management of soil and water conservation.

典型黑土区不同保护性耕作方式对玉米生长发育及产量形成的影响

实施保护性耕作对保护东北黑土和保障国家粮食安全具有重要意义。为明确东北典型黑土区保护性耕作对玉米产量的影响及其关键因素,开展了连续3年大田定位试验,设常规垄作秸秆不还田(CK)、免耕秸秆全量粉碎覆盖(T1)、免耕留高茬全量秸秆覆盖(T2)、少耕秸秆全量条带覆盖(T3)共4个处理,分析了不同处理对土壤理化特性及玉米生长发育、产量及其构成因素的影响。结果表明,与CK相比,保护性耕作处理(T1、T2和T3)0~20 cm耕层土壤有机质含量呈增加趋势;保护性耕作显著提高了播种至出苗期耕层土壤含水量,T1、T2和T3处理分别提高7.8%~30.4%、9.0%~18.7%和17.3%~20.0%,但显著降低土壤温度,分别降低2.56~3.11℃、2.02~2.27℃、0.94~1.93℃;分别延迟玉米出苗时间5~7 d、4~6 d和2 d;T3处理3年平均出苗率较CK增加3.2%,T1和T2处理出苗率分别降低4.3%和4.7%;T1、T2和T3处理均降低了苗期株高整齐度和植株干物质积累,但T3处理降低幅度明显小于T1和T2处理,6叶期之后干物质积累降低幅度逐渐减小;T1和T2处理显著降低玉米产量,降幅分别为7.5%~15.6%和5.5%~12.9%,T3处理产量与CK差异不显著。结构方程模型(SEM)揭示,保护性耕作通过调节土壤含水量和温度,间接影响玉米出苗时间、出苗率、穗数和百粒重,进而影响产量,也可通过直接影响出苗质量和产量构成因素进而影响产量。在东北典型黑土区,少耕秸秆全量条带覆盖(T3)不仅有利于提高土壤有机质含量,而且还有利于平衡土壤水分和温度矛盾,缩短出苗时间、提高出苗质量、高产稳产,是该区域适宜的保护性耕作方式。

“双碳”目标下东北黑土区耕地利用生态效率时空格局与演变趋势

[目的]探究东北黑土区耕地利用生态效率的时空格局和演变趋势,将碳源与碳汇融入耕地利用过程,这对于实现黑土减排增效和“双碳”目标至关重要。[方法]基于超效率SBM模型、核密度估计、探索性空间数据分析和空间插值工具等方法,系统考察了2006—2020年东北黑土区耕地利用生态效率的时空特征与演进规律。[结果]黑土区耕地利用生态效率历经波动上升、显著下降和迅速回升3个阶段,总体处于较高发展水平,北部边缘城市的效率值明显高于中南部地区,基期和末期区间两极分化局势尤为显著,整体发展严重失衡;黑土区耕地利用生态效率全局空间相关特性并不明显,大致呈现“边缘—中心”空间扩散格局,由南北两端高值集聚向内及四周递减,而后形成多个块状高值区和低值分布带,规模集聚优势未能得到充分发挥;多数城市均存在不同程度的投入与产出冗余,劳动力和化肥冗余问题较为严重,碳排放冗余是造成黑土区耕地利用生态效率损失的普遍因素。[结论]优化要素配置和污染减排治理成为黑土利用重点改善方向,也是提升黑土区耕地利用生态效率的关键路径。

东北半干旱黑土区玉米秸秆还田方式对土壤水溶性有机碳含量及其组分的影响

为明确不同秸秆还田方式下土壤有机碳组分的变化特征,基于6 a秸秆还田长期定位试验,利用三维荧光光谱技术,对无秸秆还田(CK)、秸秆覆盖还田(FG)、秸秆翻埋还田(FM)处理下土壤有机碳(SOC)含量及水溶性有机碳(WSOC)含量及其结构特征进行分析。结果表明:(1)与CK相比,FM处理0~40 cm土层SOC含量提高7.87%~29.54%,FG处理0~30 cm土层SOC含量增加1.91%~18.61%,30~40 cm土层SOC含量降低7.67%;FM和FG处理0~40 cm土层土壤WSOC含量分别提升13.42%~39.42%和0.28%~26.34%。(2)通过WSOC三维荧光光谱发现,各土层CK(Ex/Em=300/34、Ex/Em=300/340、Ex/Em=240/340、Ex/Em=300/340)处理WSOC荧光特征峰为溶解性微生物代谢产物和类色氨酸蛋白质物质荧光峰;FM(Ex/Em=340/430、Ex/Em=340/430、Ex/Em=340/435、Ex/Em=340/435)和FG(Ex/Em=270/440、Ex/Em=270/435、Ex/Em=340/435、Ex/Em=340/430)处理为类腐殖酸类物质荧光特征峰,腐殖化程度较高,结构较为复杂;荧光区域积分表明,FM和FG处理类腐殖酸类物质(Ⅴ)和富里酸类物质(Ⅲ)的积分百分比分别较CK增加12.18%~27.39%、11.98%~30.72%和3.96%~5.73%、2.99%~5.40%。(3)土壤WSOC包含两个组分,C1(Ex/Em=340/435,270/435)组分为类腐殖酸类物质,C2(Ex/Em=290/345,240/345)组分为溶解性微生物代谢产物和类色氨酸蛋白质物质;F max值结果表明,0~40 cm土层的C1组分相对含量表现为FM>FG>CK,表明秸秆翻埋还田更有助于土壤中营养物质含量增加和形成更高分子量的有机物。综上,不同秸秆还田方式均可提升SOC和土壤WSOC含量,增加腐殖化程度,加强土壤的供肥能力,翻埋还田处理提升作用更为显著。

东北黑土区生态系统服务权衡与协同

东北黑土区作为我国最大的商品粮基地,土地退化问题日趋严峻,严重影响了生产—生态功能的协同发展。采用CASA(Carnegie-Ames-Stanford Approach)、降水贮存量法、修正的通用土壤流失方程(Revised Universal Soil Loss Equation,RUSLE)和修正的风蚀方程(Revised Wind Erosion Equation,RWEQ)量化了东北黑土区供给、水源涵养、土壤保持和防风固沙4种关键生态系统服务并分析了其时空演化特征,采用残差分析法厘定了气候变化与人类活动因素对供给服务的贡献率,从栅格尺度和县域尺度刻画了不同地区、不同主导驱动因素下生态系统服务间的权衡与协同特征。结果显示:(1)近20年东北黑土区供给、水源涵养和防风固沙服务量总体上小幅提升,县域数量分别占96.6%、76.9%和75.4%,其中内蒙古东部和黑龙江的供给服务量、黑龙江和吉林的水源涵养量以及辽宁的防风固沙量增势明显。土壤保持量总体上小幅下降,县域数量占60.7%,特别是吉林下降趋势最明显。(2)东北黑土区供给服务变化主要受气候变化与人类活动的共同促进作用。人类活动是主导驱动因素,总体贡献率为62.65%,县域数量占76.6%。(3)东北黑土区供给与水源涵养、防风固沙之间主要表现为协同关系,约有88.67%和77.14%的县域表现为协同,而供给与土壤保持之间主要表现为权衡关系,县域数量占比为68.25%,人类活动因素加重了各服务之间的权衡作用。研究有助于明晰东北黑土区生态系统服务的主要矛盾,科学合理、有针对性的制定生态保护修复相关政策,对提升东北生态功能以及保障国家粮食安全具有重要意义。