| As an important commodity grain base in China,Heilongjiang Province has a large arable land area and fertile black soil,which has a pivotal position in national food security.In recent years,in response to the construction of high-standard farmland,Heilongjiang Province has vigorously promoted the standardization and transformation of gridded fields,and moderately merged smaller gridded fields;carried out land leveling to convert dry land into standardized paddy fields,but the remediated plots are relatively scattered and difficult to monitor centrally,and there is little analysis of crop growth change patterns after land remediation and a lack of relevant theoretical research,which cannot meet the needs of long-term tracking and monitoring and precise management after land remediation.Relying on the favorable conditions of concentrated and continuous farmland,combined with the rapidly developing remote sensing technology,it is feasible to carry out long-term crop growth monitoring and accurate management of paddy fields after land remediation based on remote sensing means,which is the first to be implemented under farm conditions in Northeast China.In this study,the standardized transformation plot of dry to water grassland located in Youyi Farm and the standardized transformation plot of grassland in Daxing Farm in Heilongjiang Province were selected as the study area,and a method of monitoring and partitioning the quality of grassland after land remediation through object-oriented partitioning based on the vegetation index of rice maturity was realized by combining crop yield,soil nutrients and topographic changes.We analyzed the changes of plot size,topography,soil nutrients and crop yield after land remediation through visitation survey and data collection;clarified the relationships between topography changes,soil nutrients,yield and crop growth after land remediation in two types of land remediation methods,relying on Sentinel-2 and Planet satellite images,and analyzed the multi-year fertility Normalized Difference Vegetation Index(NDVI).Based on Sentinel-2 and Planet satellite images,we analyzed the transfer matrix of Normalized Vegetation Index(NDVI),clarified the spatial and temporal changes of crop growth before and after land remediation,and used the object-oriented partitioning method to accurately manage the paddy fields after land remediation,and made suggestions on the process of land remediation and improving the efficiency of arable land use after remediation.are as follows:(1)The 2 land improvement projects have significant effects on the size of cultivated plots,soil nutrients and topography,and the standardized transformation of gridded fields has the advantages of significant cost savings and efficiency;protection of arable land and strong risk resistance;and significant quality and yield improvement,which are affirmed by farms and growers.(2)On the one hand,by digging the soil profile of the dryland to standardized gridded field plots,we found that the soil occurrence layer stratification was obvious and there were significant differences in different soil depths;on the other hand,by differencing the DEM before and after the dryland to standardized gridded field to quantify the soil disturbance of the land remediation project,we found that the degree of soil disturbance during the remediation process had a significant relationship with crop growth,with the highest correlation of 0.723,and the greater the degree of soil disturbance,the worse the crop growth.The greater the soil disturbance,the worse the crop growth,but the correlation between small soil disturbance and crop growth was not significant.Analysis of the 25 m grid sampling data of soil alkaline nitrogen in the standardized transformation plots of the gridded fields revealed that there was spatial variability in soil alkaline nitrogen after remediation of the study plots,and the variability was more caused by structural factors;therefore,it can be clarified that the land remediation project had a significant impact on soil structural stability in the study area.(3)The correlation analysis of multi-year full-fertility rice NDVI after land remediation with post-land remediation yield,post-land remediation DEM difference and post-land remediation soil alkaline nitrogen revealed that all of them had the highest correlation with rice NDVI at maturity in September,with 0.587,0.645 and 0.723,respectively,so September is the best window for monitoring the effect of land remediation based on fertility NDVI.(4)Through comparative analysis of the growth of the trumpet stage of corn in the three years before the dry field and the growth of rice in the two years after the dry field,it is found that The crop growth pattern changed greatly before and after the standardization of dry land,Crop growth spatial variability increases;Through comparative analysis of the growth of rice in the first 3 years and the last 3 years after the standardized transformation of field,Before the standardized transformation of field,the crop growth is more uniform,The coefficient of variation was all less than 0.1,Is a weak degree of variation;After the standardized transformation of field,the uniformity of crop growth is reduced,There were significant differences in crop growth within the plot,But as the remediation went passed,After remediation,the spatial variability of crop growth has decreased.(5)In the partitioning of precision management for dryland conversion to standardized gridded fields,by partitioning NDVI of different spatial resolution images at the field scale and evaluating the partitioning by DEM difference;partitioning based on DEM difference and NDVI at the gridded field scale and evaluating the partitioning by NDVI.In terms of precise management partitioning for standardized transformation of gridded fields,the effect was evaluated by multi-year precise management partitioning at the field scale and based on NDVI;the partitioning was performed on NDVI of different spatial resolution images at the gridded field scale and evaluated based on soil alkali-dissolved nitrogen data.The results of the above zoning experiments all proved that the spatial variability of crop growth,soil nutrients and topographic changes within the zoning area can be effectively reduced by precision management zoning,and the zoning effect based on high spatial resolution images is not necessarily better than that of low spatial resolution when the number of zoning areas is close,but it is more detailed in the delineation of zoning details.And on this basis,the paddy fields after land remediation are judged as heavily degraded area,lightly disturbed area and stable enhancement area,and corresponding countermeasures are proposed according to the different zoning.The results describe the spatial and temporal changes of crop growth in paddy fields before and after land remediation,and prove the feasibility of precise management zoning of paddy fields at field scale and gridded field scale after land remediation based on remote sensing,providing a theoretical basis for long-term tracking and monitoring,soil improvement and variable management of paddy fields after land remediation,helping to improve land use efficiency and providing a new idea for precision agriculture development. |
