Under the background that the black land degradation is becoming more and more serious, based on the survey data of 680 farmers in the black soil area of Jilin Province, the paper examines the impact of value perception and policy tools on farmers' black land conservation tillage behavior, and explores its mechanism and internal logic. The results show that: value perception has a significant impact on farmers' black land conservation tillage behavior, and the driving effect of policy making on their behavior is limited. However, through its regulatory role, policies can enhance the promotion of benefit perception on farmers' black land conservation tillage behavior, weaken the inhibitory effect of risk perception on farmers' black land conservation tillage behavior, and significantly increase the positive impact of value perception on decision-making of farmers' black land conservation tillage behavior. Therefore, in the process of enhancing farmers' black land conservation tillage behavior, giving full play to the internal incentive role of farmers' value perception, strengthening the external driving force of policy tools, and grasping the regulatory role of policy making on value perception is of great significance to promote farmers' participation in black land conservation tillage behavior.

From the perspective of supply and demand of water resources for cultivated land use, this paper comprehensively considered cultivated land use type, crop planting structure, crop growing period and other conditions, combined with the data from the national meteorological stations in Heilongjiang province, and explored the water demand for cultivated land use and effective water supply on the micro scale. Based on this, the spatio-temporal dynamics of land and water resources matching in different growing periods from 1990 to 2018 were analyzed. The results show that: the cultivated land structure of Heilongjiang had been changing from 1990 to 2018, and the phenomenon of changing from dryland to paddy was the most common from 2010 to 2018; the demand for water was greater in the early and middle stages of crop growth compared with the later stage. The water demand increases year by year, which is consistent with the change of paddy proportion, and the migration law of areas with high water demand is highly consistent with the phenomenon of dryland converting to paddy in the same period. From 1990 to 2018, the matching degree of land and water resources in each growth period of crops decreased first and then increased. Most high-value areas of land and water resources matching are distributed in the interface between high-value areas of effective precipitation and dryland areas. It can be seen that natural precipitation is still the main source of water for cultivated crops. In recent years, the matching degree of land and water resources in the southern part of the Sanjiang Plain decreased obviously, and the unit yield of grain declined. It is suggested to reduce the quantities of dryland-to-paddy conversion projects in this area. At the same time, the matching level of land and water resources and the unit yield of grain in the western part of the Songnen Plain increased year by year, so the dryland-to-paddy conversion project can be carried out appropriately.

Ground substrate, which can nurture the basic materials that support various natural resources, is the basic material formed by the natural action. Different types of ground substrates, such as rock, gravel, sand, soil, and mud, form the surface substratum layer through the organic combination of water, gas and biomass by natural action, and nurture and support each other with the surface cover layer, which maintains the normal operation of the earth's surface ecosystem and provides production, ecological and living services for human beings. As a type of invaluable natural resources, the black soil in Northeast China is a special ground substrate layer that supports and nurtures large areas of arable soil and forest soil, and serves a production and ecological service function that cannot be ignored. More and more attention has been paid to the rational utilization and development of black soil resources at home and abroad. Through the pilot survey of black soil ground substrate in Baoqing, the content, index elements and technical requirements for the survey were constructed, and the "four-in-one" survey and evaluation of black soil ground substrate quantity, quality, structure and function were carried out. On the basis of the understanding of the current situation of black soil resources in Baoqing, we proposed some suggestions on the evaluation of the rationality and development suitability of black soil resources. The comprehensive survey and evaluation of the suitability of black soil resources based on the ground substrate is of great and far-reaching significance to the scientific and rational protection and use of black soil resources.

The ecological degradation of cultivated land poses a serious threat to the sustainable development of black soil regions. Clarifying the law of the spatial and temporal differentiation is an important scientific proposition to improve the productivity of black soil cultivated land and achieve sustainable agricultural development. Taking Fujin, a typical city of black soil in Northeast China as the research area, based on the environmental stress and ecological restoration caused by external disturbance changes in cultivated land, the remote sensing-driven multi-source environmental stress monitoring model, the improved CRITIC model, and the optimized InVEST model are used to clarify the results of the interaction between the environmental stress and ecological restoration, revealing the spatio-temporal differentiation of the ecological degradation of cultivated land in the study area from 2000 to 2020. Results showed that: (1) The exogenous environmental stress intensity of cultivated land is overall low, showing a spatial and temporal differentiation pattern with the intensity being high in the east, west, and north, while low in the middle and south. (2) The endogenous ecological restoration intensity of the cultivated land is higher than the stress intensity, showing a spatial and temporal differentiation pattern with a west-east-central gradient attenuation. (3) A total of 968.12 km² of cultivated land has experienced ecological degradation, which is concentrated in the eastern and central parts of the study area and sporadically distributed in other parts. The study clarified the interaction effect between multi-source environmental stress and multi-source ecological restoration, realized the dynamic sensitivity measurement of each cultivated land plot to various environmental stresses and ecological resilience, and further characterized the ecological degradation process and the measurement results, which is consistent with the actual cultivated land use intensity. The results provide theoretical reference and technical support for the accurate diagnosis of ecologically degraded cultivated land in black soil regions.

The mollisol region is one of the main grain-producing bases in China, especially the long gentle slopes. Unfortunately, more than 80% of farmland there was suffering from soil erosion, but the variation of soil erosion along the long gentle slopes was still unclear, which will make it more difficult to control soil erosion and protect soil resources. Therefore, the aim of this study was to find the variation law of soil erosion along the gentle slopes. Three gentle slopes (a straight slope, a concave slope and a compound slope ) in Keshan Farm No. 5 were selected as the objects. Soil samples were collected at 30 m intervals along the slopes in early May, 2019. Then the ¹³⁷Cs-activity was measured to evaluate the soil erosion and deposition rates, and to measure soil organic carbon as a parameter of cultivated land soil quality. Wavelet analysis was employed to quantify the variation of soil erosion along the gentle slopes and the response of cultivated land soil quality parameters. The results showed that: (1) The annual average erosion rates of straight slope, composite slope and concave slope are 3040 t·km^-2·a^-1, 3395 t·km^-2·a^-1 and 4220 t·km^-2·a^-1, respecctively. (2) The main changing periods of the whole straight gentle slope, the concave gentle slope, and the compound gentle slope were 380 m, 250 m, and 300 m, respectively. (3) There was a significant negative correlation between soil SOC content and soil erosion rate, and the spatial distribution of soil SOC along the slope length was opposite to that of soil erosion rate, indicating that soil erosion is a key driving factor for soil degradation. Conclusions of this study can help to formulate the targeted soil and water conservation measures for the realization of soil nutrient management along long gentle slope and provides theoretical guidance for soil erosion control of the long gentle cultivated slopes in the mollisol region of Northeast China.

Soil denitrification is one of the important processes of soil nitrogen cycling, which is closely related to soil nitrogen loss and greenhouse gas emissions. The relation between communities and the release of N₂O was analyzed in this study. The results showed that regardless the fertilization treatments, nirK type denitrifying bacteria had higher diversity than nirS type denitrifying bacteria, which were more susceptible to soil physical and chemical properties. Application of chemical fertilizer decreased soil nutrient content, the diversity of denitrifying bacteria and the release of N₂O, while organic fertilizer (F+M and F+2M) application significantly increased the soil denitrification. Therefore, application of chemical fertilizer is not conducive to maintaining the fertility of black soil. Although the combined application of chemical fertilizer and organic fertilizer can improve soil fertility, the potential negative environmental effects can not be ignored. So, we suggested that the protection of black soil should actively promote the planting and breeding integrated mode, construct the recyclable agricultural system; appropriately apply organic fertilizers, regulate the activities of soil microbials; improve the relevant institutions, create new norms of scientific managements, and finally construct the multi-directional patterns for the protection of farmland in black soil region of Northeast China.

The effects of soybean continuous cropping (CS), maize continuous cropping (CM), corn-soybean rotation (MS), corn-corn-soybean (MMS) and corn-soy-soybean (MSS) on soil nitrogen fixing bacteria abundance and community structure were analyzed by fluorescence quantitative PCR and high-throughput sequencing. The results showed that soil organic matter (SOM), total phosphorus (TP), available nitrogen (AN) and available phosphorus (AP) contents in rotation were significantly higher than those in continuous cropping. The abundance of nitrogen-fixing bacteria in rotation was significantly higher than that in CM and significantly lower than that in CS. The diversity of NITR Ogen-fixing bacteria in MMS and MSS was significantly higher than that in CM. Total nitrogen (TN) was the main driving factor for the change of nitrogen-fixing bacteria community structure. Planting system indirectly affected the abundance and diversity of nitrogen-fixing bacteria through soil chemical properties. These results indicate that MSS and MMS are more conducive to the propagation of soil nitrogen-fixing bacteria in the semi-arid area of Western Jilin province, which can provide scientific basis for rational planting and nitrogen regulation from the perspective of microbiology.