[Evaluation of carrying capacity and spatial pattern matching on urban-rural construction land in the Poyang Lake urban agglomeration, China]. / çŽ¯é„±é˜³æ¹–åŸŽå¸‚ç¾¤åŸŽä¹¡å»ºè®¾ç”¨åœ°çš„æ‰¿è½½èƒ½åŠ›è¯„ä»·åŠç©ºé—´æ ¼å±€åŒ¹é .

Land carrying capacity is one of the important research fields for land management and sustainable use. Urban-rural construction land is an essential component of land use type, the rationality of whose structure and layout is crucial to the sustainable use of land. Here, we executed the evaluation of the suitability of urban-rural construction land development, accounted the bearable critical threshold of urban-rural construction land, calculated the bearable abundance of urban-rural construction land, and compared with the current urban-rural construction land, analyzed the matching of the space layout, and then obtained the remaining development intensity of each county (city or district) of the Poyang Lake urban agglomeration. The results showed that the most suitable, more suitable, less suitable and unsuitable area about the evaluation results of urban-rural construction land development suitability were 3130.62, 2477.29, 867.03 and 29509.14 km2, respectively. The bearable critical threshold of urban-rural construction land (developable strength) was 16.6%, and the value of each county (city, district) was 7.7%-100%. The abundance of urban-rural construction land in each county (city, district) was mainly 0.15-1.30. The remaining development intensity was 12.3%, and the spatial matching degree was 0.76. The remaining develo-pment intensity of each county (city, district) was 4.9%-53.5%, and the spatial matching degree of each county (city, district) was 0.11- 1.00, with a wide range. Our results would help to clarify the relationship between the current development status and the rational development status, which could provide a basis for the refined management of urban-rural construction land and the regulatory policies' formulation of spatial pattern optimization.

[Spatial and Temporal Variability of Soil C-to-N Ratio of Yugan County and Its Influencing Factors in the Past 30 Years].

The soil carbon-to-nitrogen (C/N) ratio of soils is a sensitive indicator of soil quality and an indicator for assessing the carbon and nitrogen nutrition balance of soils. Its variation is significant in reflecting the carbon and nitrogen cycling of soils. An accurate knowledge of how the C/N ratio varies spatially and temporally and the driving factors at county scale is of great significance to the extrapolation of balanced fertilization based on soil C/N ratio regulation as well as to the protection of the ecological environment. This study was based on 200 points of surface soil samples (0-20 cm) collected during the second National Soil Survey in 1982 and 423 points of surface soil samples (0-20 cm) collected during the soil test-based formulated fertilization project in 2012 in Yugan County. Combined with the soil parent material, soil type, farmland-use type, terrain factors, pH, straw incorporation pattern, and nitrogen fertilizer rate over the past 30 years, spatial and temporal variability characteristics of the soil C/N ratio were analyzed by using ordinary kriging methods, and the effects of the influencing factors were quantified by regression analysis. The results indicated that the mean value of the C/N ratio was 10.05 and 11.18 in 1982 and 2012, respectively. The coefficient of variation was 19.40% and 25.04%, respectively, which suggested the soil C/N ratio had moderate variability in the study area. The ratios of nugget to sill were 15.91% and 71.25% in 1982 and 2012, respectively. This means that the leading factor from the structural factors (parent material and soil type) into the stochastic factors (nitrogen fertilizer rate and straw incorporation pattern). In the past 30 years, most of the regional soil C/N ratio increased significantly especially the eastern region. The spatial variability of soil C/N in 1982 was mainly affected by soil parent material, soil type, terrain factor, and pH, with the degree of influence of each variable at 17.3%, 14.2%, 7.4%, and 2.3%. In 2012, the spatial variability was mainly affected by soil parent material, soil type, farmland-use type, terrain factor, straw incorporation pattern, and nitrogen fertilizer rate, with the degree of influence of each variable of 8.7%, 23.5% 28.2%, 12.2%, 12.6%, and 42.3%, respectively. To maintain the steady growth of the soil C/N ratio, it is suggested that the return of carbon be incorporated with the input of nitrogen, such as incorporating crop residues into the soil and inputting more organic fertilizers into the soil in future farming practices.

[Spatial Variability of C-to-N Ratio of Farmland Soil in Jiangxi Province].

Spatial variability of soil carbon-to-nitrogen ratio (C/N) at the provincial scale was analyzed using ordinary kriging methods. The effects of the factors influencing C/N were quantified by regression analysis based on 16,582 points of surface soil samples (0-20 cm) collected during the project of soil-test-based formulated fertilization in Jiangxi Province in 2012. The results showed that soil C/N ranged from 2.98 to 52.67, with an average of 11.72. The coefficient of variation was 25.17%, suggesting moderate variability. The nugget-to-sill ratio was 88.44%, meaning that the stochastic factors played a more important role in the spatial variability of soil C/N between the structural and stochastic factors. The spatial distribution of soil C/N was relatively smooth and the high-value areas were mainly distributed in Pengze County-Jiujiang City, Shangli County-Pingxiang City, and Lean County-Fuzhou City. The terrain factors, farmland-use type, parent material, soil type, and the level of nitrogen fertilizer had significant impacts on the spatial variability of soil C/N (P<0.05), but the degree of influence was different for each factor. Soil C/N indicated a significant positive Pearson's correlation with elevation and the slope of slope (P<0.05). The terrain factors explained 0.3% of the spatial variability of soil C/N and the farmland-use could explain 1.4%. The explanatory power of soil groups, subgroups, and soil family were 2.7%, 3.6%, and 5.5% respectively. The level of nitrogen fertilizer could explain 33.4% of the spatial variability of soil C/N, which showed that the amount of nitrogen fertilizer was the main factor that controls the spatial distribution of soil C/N.