松嫩平原玉米带农田土壤氮密度时空格局

基于1980年吉林省第二次全国土壤普查剖面资料和2003—2006年的实测数据,估算了松嫩平原玉米带不同土壤类型农田表层(0—20 cm)土壤氮密度和储量,分析了该地区土壤氮密度的25a时空变化特征及其原因。结果表明,两个时期松嫩平原玉米带农田土壤氮密度的空间分布格局基本一致,中部高、边缘低,平均土壤氮密度变化不大,均为0.31 kg/m2,但25 a间不同土壤类型和土地利用方式的土壤氮密度变化趋势存在差异,暗棕壤、水稻土和沼泽土的氮密度上升,其它类型土壤的氮密度不变或下降,旱田的氮密度不变,水田的氮密度明显下降,25 a间研究区内的农田土壤总氮储量每年减少7.6×105kg。25 a间土壤氮密度的变化与1980年的初始值负相关,土壤氮密度的新稳定状态值为0.32 kg/m2。如保持1980年的土地利用方式和栽培耕作措施不变,该地区农田土壤总固氮潜力为5.18×106kg/a。但实际上,与固氮潜力相比,2005年该区农田土壤总氮储量偏低了1.20×108kg。因此,今后该区应多注重肥料的合理施用,加强农田管理,尤其是旱田改水田的管理。

Spatial and temporal variations of total nitrogen density in agricultural soils of the Songnen Plain Maize Belt

Nitrogen is a major nutrient for all living organism on Earth and plays a central role in regulating the composition, structure, and function of ecosystems. Most nitrogen within terrestrial ecosystems is stored in soil organic matter. Total nitrogen in soils is mostly correlated with soil organic carbon content. The enrichment experiments of carbon dioxide further indicate that nitrogen limitation directly influences carbon sequestration by terrestrial ecosystems. Increased nitrogen availability normally increases productivity and biomass accumulation in ecosystems. However, few studies have been conducted to calculate soil nitrogen density and storage and to analyze its tempo-spatial variations in the Songnen Plain Maize Belt.Based on the second national soil survey of Jilin Province conducted around 1980 and field measurements of nitrogen density taken in years from 2003 to 2006, this study was devoted to calculate the density and total storage of nitrogen in top soils (0-20 cm) of the Songnen Plain Maize Belt and investigate the spatial and temporal variations of nitrogen density and possible underlying factors during the period from 1980 to 2005, including land-use types, original nitrogen content, and soil organic carbon changes. The totals of soil nitrogen storage were (40.47 ± 1.67)×10⁸kg and (40.28 ± 1.35)×10⁸kg in 1980 and 2005, respectively. The spatial patterns of soil total nitrogen density were similar in 1980 and 2005, higher in the centre and lower in the edge parts. The average of soil total nitrogen density over the entire study area changed only marginally in 25 years, about 0.31 kg/m² in 1980 and 2005. However, the changes of soil total nitrogen density in 25 years varied with soils and land use types. Soil total nitrogen density increased in dark brown, paddy, and boggy soils. It did not change or even decreased in other soil types. Soil total nitrogen density changed a little in dry lands while it decreased obviously in paddy lands. The annual decrease rate of total nitrogen storage in top soils was 7.6×10⁵ kg/a. The change of soil total nitrogen density in 25 years was negatively correlated with its initial value in 1980, but positively correlated with the change of soil organic carbon density. Soil nitrogen sequestration potential was generally defined as the difference between the equilibrium value of soil nitrogen storage and its initial value. The new equilibrium value of soil total nitrogen density was 0.32 kg/m² in the study area. Without changes in land use and management after 1980, the soils of croplands in the study area has a potential of annually sequestrating nitrogen at the rate of 5.18×10⁶ kg/a. However, the total nitrogen storage in 2005 was 1.2×10⁸ kg lower than the potential of nitrogen sequestration. Actually, the application of nitrogenous fertilizer increased in the past 25 years according to the census data of Jilin Province. Therefore, reasonable fertilization should be practiced in this area. The management of croplands should be enhanced, especially for paddy lands converted from uplands.