Agricultural reclamation in coastal zones is effective for mitigating population pressure on the food supply. Soil properties are important factors influencing crop production in reclaimed coastal lands. This study aims to investigate the impacts of time and land use trajectories on soil physicochemical properties after reclamation. We sampled soils in areas that were reclaimed in 1999, 1998, 1991, 1989, 1986, 1981, and 1979 and determined some soil physicochemical properties such as electrical conductivity with a 1:5 soil:water ratio (EC1:5), exchange sodium percentage (ESP), sodium adsorption ratio (SAR), pH, organic matter (OM), total nitrogen (TN), alkaline hydrolyzable nitrogen (AN), cation exchange capacity (CEC), total phosphorus (TP), available phosphorus (TP) and soil particle size ratio. We analyzed their correlation with land use and the time since reclamation using one-way analysis of variance (ANOVA) and principal component analysis (PCA). The results showed that soil physicochemical properties changed significantly after agricultural reclamation. Soil EC1:5, ESP, and SAR declined rapidly, and OM, TN, and AN increased rapidly during the 29 years after reclamation. The soil particle size ratio was not significantly correlated with reclamation time. The land-use trajectories identified after reclamation had obvious effects on soil physicochemical properties. Aquaculture ponds were superior to cultivated land in terms of decreasing soil salinity but were inferior in terms of soil nutrient accumulation. In the future, more attention should be given to the environmental effects of agricultural reclaimed soils.

Urban fringe is an active expanding belt, indicating urban-rural interaction processes. Previous studies have attempted to define urban fringe as the transitional area between urban and rural areas, but there is a lack of quantitative analysis of the periphery boundaries. We developed a novel, the Spatial Segmentation Model (SSM), to detect the extent of urban fringe via calculating the share of the built-up land. Within the urban fringe, we statistically compared the number of built-up patches in each direction and described four urban expanding patterns (stable, sprawling, leaping, and mixing patterns) indicated by the empirical analysis. The results show that this model can reliably detect the urban fringe and could reveal urban growth characteristics. We find the spatial territory changes are highly relative with transport infrastructures in Harbin. Meanwhile, the roads density in the urban core are higher than in the urban fringe. Especially for city roads, roads density in the urban core is more than 4 times higher than in the urban fringe. The growth of the urban fringe is closely related to the development of social economies as well as the space policies and development plans designed by governments. Similar to the post-industry cities worldwide, Harbin should take action to address population decline. Effective land-use and suitable urban growth strategies play an important role in alleviating urban shrinkage. Thus, understanding the dynamics, urban expanding patterns, and driving factors in the urban fringe can help us form a basis for future urban development.

The multi-function characteristics of cultivated land have been widely recognized by researchers in China and globally, and it is important to provide a theoretical basis and practical reference for future research on the evaluation and zoning of cultivated land quality based on a space–function–environment perspective. Spearman rank correlation analysis and cluster analysis were used to categorize cultivated land by its quality. This study developed a theoretical evaluation framework of the space–function–environment quality for cultivated land and constructed a total of 23 indicators of cultivated land quality in three dimensions. The framework was applied to a case study that evaluated and zoned cultivated land quality based on a space–function–environment perspective. The results showed that the synergies and tradeoffs among spatial quality, functional quality and environmental quality, and the influences of the three on cultivated land quality are mutually restricted and act together. The cultivated land in Qujiang District can be divided into five types of areas according to the cold and hot spot analysis results of the secondary indexes of cultivated land spatial quality, functional quality and environmental quality. Based on these results, different protection schemes are proposed for different cultivated land qualities.

Agricultural land reclamation of coastal tidal land (CTL) with organic amendments may modulate the soil properties, and therefore promote crop growth. However, the linkages between soil nutrient contents, pools, stoichiometry, and crop growth under the supplement of organic amendments in CTL is limited. In this study, six treatments including the control (CK), organic manure (OM), polyacrylamide plus organic manure (PAM + OM), straw mulching plus organic manure (SM + OM), buried straw plus organic manure (BS + OM), and bio-organic manure plus organic manure (BM + OM) were conducted to explore these linkages in newly reclaimed CTL in Jiangsu Province, eastern China. The results showed that the application of different soil reclamation treatments increased soil nutrient contents, pools, and modulated their stoichiometric ratio, which thus promoted the growth of oat. Soil under all reclamation treatments increased the contents of surface soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP), and the BM + OM treatment had the highest increase, which increased by 11.7–182.4%, 24.3–85.7%, 3.2–29.4%, respectively. The highest soil C pools were observed in the oat heading stage (36.67–41.34 Mg C ha⁻¹), whereas the soil N and P pools were more stable during the oat growth period. Similarly, the highest surface soil C/N and C/P were observed in the oat heading stage (11.23–14.67 and 8.97–14.21), whereas the N/P in surface soil increased compared with the CK treatment during the oat growth period, with the exception of the filling stage. Land reclamation treatments significantly promoted oat growth by changing soil C, N, and P contents, pools, and stoichiometry, among which soil SOC, TN, TP, C/P, and N/P are more closely related to oat growth (p < 0.05).

Urbanization and industrialization in developing countries has contributed to great changes in rural settlements, which presents an increasing threat to rural sustainability. Spatiotemporal changes in rural settlements at the county level are significant to land use planning and are not clear in the highly urbanized regions. This study considered Jiangsu, one of the most urbanized provinces of China, as an example and investigated the spatial variation in rural settlements and their socioeconomic driving factors during the period of 2000–2020 using mixed geographic weighted regression. The results showed that the area of rural settlements in the highly urbanized province expanded from 2000 to 2015 following a decrease in the rural population, but then began to decrease from 2015. There were obvious spatial differences in the rural settlements in the counties of Jiangsu Province. The area of rural settlements in the different counties maintained a positive association with the rural population and cropland but had a negative correlation with the rural production value in 2000. By 2020, the area of rural settlements was only positively associated with the rural population. The correlation between the area of rural settlements and rural population continually decreased from 2000 to 2020. The area of rural settlements had no significant association with the area of urban settlements. The expansion of rural settlements mainly occurred at the expense of cropland. The decrease in the rural settlements was accompanied by an increase in the urban settlements and an expansion of cropland. The policy implications arising from this study are presented to provide guidance for rural development at the county level and ensure rural sustainability.