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Climate factors, considered significant factors in regulating soil organic carbon (SOC), are not equally important at all spatial scales. However, the scale which provides the optimal relationship between climate and SOC and how that relationship varies at multiple scales are still unclear. Thus, it is crucial to study the relationship between climate factors and SOC at multiple scales when attempting to accurately predict the SOC pool and evaluate the influence of climate change on global carbon cycling. The objective of this research is to examine the scale effect of climate factors on SOC content in the Uplands of Northeast China. The relationship between climate factors and SOC content at the regional, provincial, city, and county scales was evaluated at 0–20 and 0–100 cm using correlation and regression analysis. Data for the study in the Uplands of Northeast China were examined using 1,022 profiles obtained from the Second National Soil Survey of China. A nested sampling scheme was adopted at four scales for this research. Differences exist in the degree of correlation and relative importance of temperature and precipitation at different scales. Temperature is the main climate factor controlling SOC content at the regional scale. At the provincial scale, temperature is also the main climate factor controlling SOC content in the Uplands of Heilongjiang and Eastern Inner Mongolia. SOC content in Jilin and Liaoning is influenced jointly by temperature and precipitation. Additionally, obvious regional differences occurred in the relationship between climate factors and SOC content at the provincial scale. Although this scale differs from those by other researchers, similar results have been reported in China, Spain, and the USA. The reasons might be attributed to the differences in soil type, ecosystem, and topographic position. At both the city and county scales, weak or no relation was observed between climate factors and SOC content. Climate factors have limited ability to explain SOC content variability given that SOC is affected by multiple factors which were not taken into account by this research. Therefore, multiple scales should be considered when the feedback relationship between global climate change and SOC content is studied. The relationship between climate factors and SOC content weakens with decreasing scale, especially from the provincial to city scale. The main climate factors controlling SOC content vary with different scales. The provincial scale is optimal for studying the relationship between climate factors and SOC content in the Uplands of Northeast China. Seasonal change of temperature and precipitation may also influence SOC. Thus, it is necessary to consider climate factors at multiple timescales. Moreover, further studies focusing on the scale effect of other factors (including climate) on SOC content variability will be carried out at different scales to determine the main factors controlling SOC content. [ABSTRACT FROM AUTHOR]

urate simulation of soil organic carbon (SOC) dynamics is vitally important in researching the carbon cycle in terrestrial ecosystems. Especially, the application of SOC model at the regional scale has major implications for regional and global carbon cycling. This paper addresses the regional simulation for SOC in the surface layer (0~15 cm) of paddy soils in Wuxi and Changzhou, Jiangsu Province, China from 1982~2000 by linking a model of agro-ecosystem SOC dynamic simulation with GIS data on the basis of 100 × 100 m grids. The dataset includes soil profile descriptions and chemical data of 187 paddy soil samples in the Second National Soil Survey of China in 1982 and 352 paddy soil samples taken in 2000. Soil maps at a scale of 1:50,000 were used for the simulation. Results showed that the area of differences between simulated and observed SOC in 2000 (in the range of −3.6 to 3.6 Mg C ha) accounted for 50.6% of the total area. Also, when a 10% and 20% simulated increase, and a 10%, 20% and 30% simulated decrease in harvested crop straw and manure amendments were simulated to test the sensitivity of the model, simulated SOC would range from 10.26 to 50.40 Mg C ha with a standard deviation of 1.6 and 2.5, respectively. It is indicated that a key factor controlling SOC is the amount of residue and manure inputs. As for the assessment model suitability based on soil textures, soil types, and parent materials, the model seemed to perform better for clayey soils, groundwater-related paddy soils and soils derived from alluvial parent material than for loamy soils, surface water-related paddy soils and soil derived from loess material. [ABSTRACT FROM AUTHOR]

Abstract  Balances of major nutrients such as nitrogen (N), phosphorus (P), and potassium (K) in small-scale farming systems are of critical importance to nutrient management and sustainable agricultural development. Mass balances of N, P, and K and some of their influencing factors were studied for two years from July 2003 to July 2005 on small-scale vegetable-farming systems in two contrasting peri-urban areas (Nanjing and Wuxi) of the Yangtze river delta region of China. This balance approach considered organic fertilizer inputs (cow manure, pig manure, and human biosolids), inorganic fertilizer inputs (urea, composite fertilizer, and phosphates), irrigation water, and atmospheric deposition; and considered outputs by vegetables. Input via organic fertilizers was significant for all element balances in the Nanjing area. Inorganic and organic fertilizer, particularly inorganic fertilizer, contributed major nutrient inputs to the system in the Wuxi area. Compared with nutrient output by vegetables, there were significant surpluses of N and P on two vegetable farm systems. Furthermore, N surplus in the Nanjing area was higher than that in the Wuxi area with an inverse relationship to P surplus. In contrast, the general trend of K balances was negative on both sites; hence, the nutrient use efficiency was significantly lower for N and P than K. The nutrient imbalance may be attributed to the differences between fertilizer types and management modes driven by social economic status differences among farmer households. The large N and P net excess creates an environmental threat because of potential losses to ground or surface waters, whereas negative K balance creates soil fertility risks. The results highlight researchers’ and farmers’ need to develop rational fertilization technology to optimize nutrient management on vegetable farmlands to promote sustainable agricultural development in peri-urban areas. [ABSTRACT FROM AUTHOR]