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1.
Cropland (CP), native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L. ) (ST), and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China. Total organic carbon (TOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), total N (TN), nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2--N), ammonium nitrogen (NH4+-N), total P, and available P (AP) were measured. The results showed that SOC in NG, ST and BT were 12.7%, 27.7% and 34.8% higher than that of the cropland, respectively. LFOC, light fraction (LF) dry matter, ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland. Cropland had the highest TN, the sum of NO3--N and NO2--N, TP and AP due to the use of chemical fertilizers. TOC significantly correlated with LFOC, HFOC and C/N. LFOC significantly correlated with dry matter of the LF and C/N. TN, the sum of NO3--N and NO2--N and AP were significantly negatively correlated with TOC and LFOC. Therefore, land use conversion from cropland to shrub land, or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.  相似文献   

2.
黄淮海平原小麦-玉米轮作制度下的地下水NO3-N污染研究   总被引：5，自引：0，他引：5  
The North China Plain, where summer corn (Zea mays L.) and winter wheat (Triticum aestivum L.) are the major crops grown, is a major agricultural area in China. Permeable soils make the region susceptible to groundwater pollution by NO3-N, which is applied to fields in large amounts of more than 400 kg NO3-N ha-1as fertilizer. A field experiment was established in 2002 to examine the relationship among N fertilization rate, soil NO3-N, and NO3-N groundwater contamination. Two adjacent fields were fertilized with local farmers' N fertilization rate (LN) and double the normal application rate (HN), respectively, and managed under otherwise identical conditions. The fields were under a traditional summer corn/winter wheat rotation. Over a 22-month period, we monitored NO3-N concentrations in both bulk soil and soil pore water in 20-40 cm increments up to 180 cm depth. We also monitored NO3-N concentrations in groundwater and the depth of the groundwater table. No significant differences in soil NO3-N were observed between the LN and HN treatment. We identified NO3-N plumes moving downward through the soil profile. The HN treatment resulted in significantly higher groundwater NO3-N, relative to the LN treatment, with groundwater NO3-N consistently exceeding the maximum safe level of 10 mg L-1, but groundwater NO3-N above the maximum safe level was also observed in the LN treatment after heavy rain. Heavy rain in June, July, and August 2003 caused increased NO3-N leaching through the soil and elevated NO3-N concentrations in the groundwater. Concurrent rise of the groundwater table into NO3-Nrich soil layers also contributed to the increased NO3-N concentrations in the groundwater. Our results indicate that under conditions of average rainfall, soil NO3-N was accumulated in the soil profile. The subsequent significantly higherthan-average rainfalls continuously flushed the soil NO3-N into deeper layers and raised the groundwater table, which caused continuous groundwater contamination with NO3-N. The results suggest that under common farming practices in the North China Plain, groundwater contamination with NO3-N was likely, especially during heavy rainfalls, and the degree of groundwater contamination appeared to be proportional to the N application rates. Decreasing fertilization rates, splitting fertilizer inputs, and optimizing irrigation scheduling had potential to reduce groundwater NO3-N contamination.  相似文献   

3.
淹水稻田氮的损失   总被引：29，自引：3，他引：29  
A field microplot experiment was conducted during the tillering stage of paddy rice to investigate nitrogen(N) Iosses from flooded rice fields following fertilizer application. After application of ammonium bicarbonate, most of nitrogen in the flood water was present as NH4-N and its concentration varied widely with time. Concentrations of both NO3-N and NO2-N in the floodwater were low due to the weakened nitrification. Under flooded anaerobic reducing conditions, soil solution concentrations of NO3-N and NH4-N were nothigh, ranging from 0.6 mg L-1 to 4.8 mg L-1, and decreased with soil depth. However, the ground water wasstill contaminated with NO3-N and NH4-N. Rainfall simulation tests showed that the N losses via runoff inrice fields were closely related to the time intervals between fertilizer applications and rainfall events. Whena large rain fell for a short period after fertilizer application, the N losses via runoff could be large, which could have a considerable effect on surface water quality. Both irrigation and N fertilizer application must be controlled and managed with great care to minimize N losses via runoff from agricultural land.  相似文献   

4.
结合统计和数字地形数据的可视化方法预测土壤深度   总被引：2，自引：0，他引：2  
F. M. ZIADAT 《土壤圈》2010,20(3):361-367
Information about the spatial distribution of soil attributes is indispensable for many land resource management applications; however, the ability of soil maps to supply such information for modern modeling tools is questionable. The objectives of this study were to investigate the possibility of predicting soil depth using some terrain attributes derived from digital elevation models (DEMs) with geographic information systems (GIS) and to suggest an approach to predict other soil attributes. Soil depth was determined at 652 field observations over the Al-Muwaqqar Watershed (70 km2) in Jordan. Terrain attributes derived from 30-m resolution DEMs were utilized to predict soil depth. The results indicated that the use of multiple linear regression models within small watershed subdivisions enabled the prediction of soil depth with a difference of 50 cm for 77% of the field observations. The spatial distribution of the predicted soil depth was visually coincided and had good correlations with the spatial distribution of the classes amalgamating three terrain attributes, slope steepness, slope shape, and compound topographic index. These suggested that the modeling of soil-landscape relationships within small watershed subdivisions using the three terrain attributes was a promising approach to predict other soil attributes.  相似文献   

5.
This paper introduces briefly two remote sensing case studies on land use in the subtropic region of China. One is on slope land use in the Yangtze River Three Gorges area. This is a large area of 60497 km2. First of all, geometric correction and supervised classification were conducted for ten scenes of Landsat-5 TM or MSS images. The resolution of the processed images is 50 m × 50 m on ground. By the classification the land use/cover categories in this area were discriminated. Then the croplands including rice fields and upland fields were extracted from the land use/cover maps. Simultaneously the slope grade maps were prepared based on the topographic maps. Overlaying the slope grade maps and the cropland maps, the area and percentage of the croplands in different slope grades were determined. This case study indicated that 71.5% of the uplands was situated on the slope above 150 and 25% on the slope above 250 in this area. It is dangerous, and urgent cultivation or engineering measures should be taken. Another case study is on soil erosion in Linshan County of Guangxi Province. Airphoto interpretation and supervised classification of a Landsat TM image were carried out for discriminating land cover/use categories in an area of 3 557.8 km2. And the soil erosion intensity grades were determined according to the land cover/use maps and slope maps. It wad discovered that the land suffering soil erosion accounted for 2404.0 km2, 67.6% of the total area of the county. Necessary measures to control soil erosion should be taken also.  相似文献   

6.
黄河三角洲耕地变化及其驱动力的卫星遥感分析   总被引：11，自引：5，他引：11  
Taking Kenli County in the Yellow River Delta, China, as the study area and using digital satellite remote sensing techniques, cultivated land use changes and their corresponding driving forces were explored in this study. An interactive interpretation and a manual modification procedure were carried out to acquire cultivated land information. An overlay method based on classification results and a visual change detection method which was supported by land use maps were employed to detect the cultivated land changes. Based on the changes that were revealed and a spatial analysis between cultivated land use and related natural and socio-economic factors, the driving forces for cultivated land use changes in the study area were determined. The results showed a decrease in cultivated land in Kenli County of 5321.8 ha from 1987 to 1998, i.e., an average annual decrement of 483.8 ha, which occurred mainly in the central paddy field region and the northeast dry land region. Adverse human activities, soil salinization and water deficiencies were the driving forces that caused these cultivated land use changes.  相似文献   

7.
上海郊区园艺土壤氮素的生物形成动态变化   总被引：3，自引：0，他引：3  
Dissolved organic nitrogen (DON) represents a significant pool of soluble nitrogen (N) in soil ecosystems. Soil samples under three different horticultural management practices were collected from the Xiaxiyang Organic Vegetable and Fruit Farm, Shanghai, China, to investigate the dynamics of N speciation during 2 months of aerobic incubation, to compare the effects of different soils on the mineralization of 14C-labeled amino acids and peptides, and to determine which of the pathways in the decomposition and subsequent ammonification and nitrification of organic N represented a significant blockage in soil N supply. The dynamics of N speciation was found to be significantly affected by mineralization and immobilization. DON, total free amino acids, and NH4+-N were maintained at very low levels and did not accumulate, whereas NO3--N gradually accumulated in these soils. The conversion of insoluble organic N to low-molecular-weight (LMW) DON represented a main constraint to N supply, while conversions of LMW DON to NH4+-N and NH4+-N to NO3--N did not. Free amino acids and peptides were rapidly mineralized in the soils by the microbial community and consequently did not accumulate in soil. Turnover rates of the additional amino acids and peptides were soil-dependent and generally followed the order of organic soil > transitional soil > conventional soil. The turnover of high-molecular-weight DON was very slow and represented the major DON loss. Further studies are needed to investigate the pathways and bottlenecks of organic N degradation.  相似文献   

8.
A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH4+-N + NO3--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH4+-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH4+-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH4+-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH4+-N fixation or volatilization in the soil during the fertigation process.  相似文献   

9.
High quality, agricultural nutrient distribution maps are necessary for precision management, but depend on initial soil sample analyses and interpolation techniques. To examine the methodologies for and explore the capability of interpolating soil properties based on neural network ensemble residual kriging, a silage field at Hayes, Northern Ireland, UK, was selected for this study with all samples being split into independent training and validation data sets. The training data set, comprised of five soil properties: soil pH, soil available P, soil available K, soil available Mg and soil available S,was modeled for spatial variability using 1) neural network ensemble residual kriging, 2) neural network ensemble and 3) kriging with their accuracies being estimated by means of the validation data sets. Ordinary kriging of the residuals provided accurate local estimates, while final estimates were produced as a sum of the artificial neural network (ANN) ensemble estimates and the ordinary kriging estimates of the residuals. Compared to kriging and neural network ensemble,the neural network ensemble residual kriging achieved better or similar accuracy for predicting and estimating contour maps. Thus, the results demonstrated that ANN ensemble residual kriging was an efficient alternative to the conventional geo-statistical models that were usually used for interpolation of a data set in the soil science area.  相似文献   

10.
黄土高原小流域土壤有机碳空间变异性研究   总被引：12，自引：0，他引：12  
Soil organic carbon (SOC) has great impacts on global warming, land degradation and food security. Classic statistical and geostatistical methods were used to characterize and compare the spatial heterogeneity of SOC and related factors, such as topography, soil type and land use, in the Liudaogou watershed on the Loess Plateau of North China. SOC concentrations followed a log-normal distribution with an arithmetic and geometric means of 23.4 and 21.3 g kg-1, respectively, were moderately variable (CV = 75.9%), and demonstrated a moderate spatial dependence according to the nugget ratio (34.7%). The experimental variogram of SOC was best-fitted by a spherical model, after the spatial outliers had been detected and subsequently eliminated. Lower SOC concentrations were associated with higher elevations. Warp soils and farmland had the highest SOC concentrations, while aeolian sand soil and shrublands had the lowest SOC values. The geostatistical characteristics of SOC for the different soil and land use types were different. These patterns were closely related to the spatial structure of topography, and soil and land use types.  相似文献   

11.
Core lysimeters containing undisturbed coarse sandy soil (from grassland) were amended with a high rate of anaerobically digested sewage sludge (equivalent to >1,000 t ha–1). Water, at a rate equivalent to the mean weekly rainfall for the soil, was applied to amended and control lysimeters for 30 weeks and the leachate analysed for anions and cations. Lysimeters were also destructively sampled at intervals throughout the experiment and soil samples were analysed for extractable NH4+-N, NO3–-N and PO43–-P. Ammonium N leached for about 11 weeks from the amended lysimeters, then abruptly stopped. A similar amount of NO3–-N leached, but leaching was continuing when the experiment finished. The control lysimeters leached as much NO3–-N as those that were amended, but no NH4+-N. The amended lysimeters also leached NO2–-N. Negligible PO43–-P, but large amounts of SO42– were leached from the amended lysimeters. Concentrations of extractable NH4+-N and PO43–-P were very high in the amended soils, but NO3–-N concentrations remained low throughout the experiment, indicating that nitrification rates were low and/or that denitrification rates were high.  相似文献   

12.
The aim of this study was to investigate how electromagnetic induction can be used to improve the characterization of N dynamics in a 1.2 ha pasture. The soil apparent electrical conductivity (ECa) was measured by electromagnetic induction using an EM38DD. At 116 locations, soil samples were taken according to a clustered sampling design, three times during one winter, and analyzed for the NO3––N content in the topsoil (0–60 cm). Management zones were delineated using a fuzzy k-means classification of the interpolated ECa measurements. Two ECa zones were found, reflecting mainly differences in soil texture. Since the mean NO3––N content was different for the two ECa zones (24 and 65 kg/ha in November 2002), the residuals were interpolated using stratified simple kriging. This allowed evaluating the NO3– dynamics during the winter in both zones; one ECa zone showed a higher risk for NO3– losses than the other calling for a site-specific N management. As a validation, NO3––N was interpolated using ordinary kriging without stratification. This resulted in similar zones confirming the usefulness of the ECa measurements to assess N-specific management zones, even within small fields.  相似文献   

13.
Micro-spatial analysis of nitrate (NO3), an environmental contaminant partially attributed to nitrogen fertilization, can be useful for estimating its distribution in soils. A study was conducted to determine the micro-spatial distribution of soil NO3 using kriging and cokriging in a drip-irrigated and nitrogen-fertilized field. One hundred soil samples were collected in a regular grid pattern from a 10 m × 20 m plot, and analyzed for soil NO3 and pH. The effect of reduced sample size on NO3 estimation was also evaluated. The pH data indicated the soils were slightly acidic to neutral with log[NO3] values ranging from 1.66 to 2.95. These parameters were inversely related; which was probably an attribute of soil nitrification process. Sample variograms and cross-variograms suggested that the spatial distribution of pH and log[NO3] could be described by linear models in the area studied, as indicated by small MSE (mean sum error), and RKV (reduced kriging variance) values close to 1. Contour maps based on kriging and cokriging estimates indicated greater homogeneity of the variables in the south-north direction than the east-west, except for zones of high NO3 and low pH in the north-central edge and north-east corner of the grid area. Cokriging of log[NO3] estimation, using pH data, improved MSE, MSSE (mean sum square error), MKV (mean kriging variance), RKV, CEE (correlation between estimated data and error), CEM (correlation between estimated and measured data) by 46, 31, 30, 22, 96, and 98%, respectively, as compared to kriging. Lower cokriging variance for any estimated log[NO3] value, as compared to the kriging analysis, indicated that cokriging provided more accurate estimates. With reduced sample observations (n) for NO3 similar conclusions were obtained; and the estimation accuracy was maintained up to n >70. Cokriging analysis with reduced n also curtailed the analytical cost, and facilitated NO3 estimation by means of pH, which was measured at a cheaper cost.  相似文献   

14.
Soil erosion is a threat to the water quality constituents of sediments and nutrients and can cause long-term environmental damages. One important parameter to quantify the risk of soil loss from erosion is the crop and cover management factor (C-factor), which represents how cropping and management practices affect the rates and potential risk of soil erosion. We developed remotely sensed data-driven models for dynamic predictions of C-factor by implementing dynamic land cover modeling using the SWAT (Soil and Water Assessment Tool) model on a watershed scale. The remotely sensed processed variables included the enhanced vegetation index (EVI), the fraction of photosynthetically active radiation absorbed by green vegetation (FPAR), leaf area index (LAI), soil available water content (AWC), slope gradient (SG), and ratio of area (AR) of every hydrologic response unit (HRU) to that of the total watershed, comprising unique land cover, soil type, and slope gradient characteristics within the Fish River catchment in Alabama, USA between 2001 and 2014. Linear regressions, spatial trend analysis, correlation matrices, forward stepwise multivariable regression (FSMR), and 2-fold cross-validation were conducted to evaluate whether there were possible associations between the C-factor and EVI with the successive addition of remotely sensed environmental factors. Based on the data analysis and modeling, we found a significant association between the C-factor and EVI with the synergy of the environmental factors FPAR, LAI, AWC, AR, and SG (predicted R2 (Rpred2) = 0.51; R2 = 0.68, n = 3 220, P < 0.15). The results showed that the developed FSMR model constituting the non-conventional factors AWC (Rpred2 = 0.32; R2 = 0.48, n = 3 220, P < 0.05) and FPAR (Rpred2= 0.13; R2 = 0.28, n = 3 220, P = 0.31) was an improved fit for the watershed C-factor. In conclusion, the union of dynamic variables related to vegetation (EVI, FPAR, and LAI), soil (AWC), and topography (AR and SG) can be utilized for spatiotemporal C-factor estimation and to monitor watershed erosion.  相似文献   

15.
Small scale digital soil mapping in Southeastern Kenya   总被引：1，自引：0，他引：1  
Digital soil mapping techniques appear to be an interesting alternative for traditional soil survey techniques. However, most applications deal with (semi-)detailed soil surveys where soil variability is determined by a limited number of soil forming factors. The question that remains is whether digital soil mapping techniques are equally suitable for exploratory or reconnaissance soil surveys in more extensive areas with limited data availability. We applied digital soil mapping in a 13,500 km2 study area in Kenya with the main aim to create a reconnaissance soil map to assess clay and soil organic carbon contents in terraced maize fields. Soil spatial variability prediction was based on environmental correlation using the concepts of the soil forming factors equation. During field work, 95 composite soil samples were collected. Auxiliary spatially exhaustive data provided insight on the spatial variation of climate, land cover, topography and parent material. The final digital soil maps were elaborated using regression kriging. The variance explained by the regression kriging models was estimated as 13% and 37% for soil organic carbon and clay respectively. These results were confirmed by cross-validation and provide a significant improvement compared to the existing soil survey.  相似文献   

16.
Soil nitrogen mineralization as affected by water and temperature interactions   总被引：10，自引：0，他引：10  
Summary The hypothesis that water and temperature interact to influence the rate of soil N mineralization was studied in laboratory incubation experiments with two contrasting soils. Small sample rings (10 mm tall, 50 mm diameter) were packed to uniform bulk density with 1–2 mm aggregates of Plano silt loam and Wacousta silty clay loam. Samples were brought to five different water potentials (–0.1, –0.33, –0.5, –1.0, –3.0 bars) using pressure-plate techniques, and the undisturbed sample rings were then incubated at 10–35°C for 3, 10 or 14 days. The concentration of soil exchangeable NH4 +-N and NO3 –-N was measured at the end of each incubation period on replicate samples. The Q10 of N mineralization was approximately 2 for all tested water potentials. Soil N mineralization was linearly related to water content or log water potential, but no water-temperature interaction was evident. The Q10 was constant with water content, and the scaled water content-N mineralization relationship was constant with temperature. We recommend the use of scaling approaches for assessing interactive effects between water and other environmental factors on N turnover in soils.  相似文献   

17.
人为活动对云南纳帕海湿地土壤碳氮变化的影响   总被引：22，自引：0，他引：22       下载免费PDF全文
以纳帕海湿地原生沼泽作为参照 ,选择人为干扰下的沼泽化草甸 ,草甸和排干湿地开垦的耕地作为研究对象 ,研究人为干扰对纳帕海湿地土壤碳氮变化的影响。两年的定位研究结果表明 :沼泽土壤C/N值较高 ;人为干扰下纳帕海湿地土壤空间结构上土壤有机质 0～ 2 0cm表层与 2 0～ 4 0cm下层相差 4倍 ,水平分布上则随人为干扰加强、沼泽化过程减弱而降低 ,下降幅度高达 2 2 .92 %～ 6 9.6 4 %;土壤全氮及其空间分布呈现与有机质相同趋势 ,两者相关系数r=0 .98;NH 4 N、NO-3 N与全氮和水解氮相关系数分别为r=- 0 .74、r=- 0 .6 5 ,r=- 0 .81、r=- 0 .76。表明了纳帕海湿地沼泽土壤较低的矿化量和对碳的固定及较大的氮累积量 ,以及人为活动干扰后湿地土壤碳氮养分的释放变化。  相似文献   

18.
Summary A roller bed and rotary end-over-end shaker were compared for the extraction of mineral N from a variety of soil types; both were equally efficient with an optimum extraction time of 30 min. However, the roller bed permitted a greater operational capacity, a faster throughput of samples, and easier identification of sample bottles compared with the end-over-end shaker. More NH4 +-N and NO3 –-N (P<0.001) was recovered from soil by 2 M KCl than by any other extractant, in a soil: extractant ratio of 1 to 5 (w:v), except water, which was equally efficient at removing NO3 –-N from soils.  相似文献   

19.
Availability and leaching of dissolved inorganic N (DIN = NH4+ + NO3-) in soil were measured in a periodically flooded forest of the Central Amazon floodplain (várzea) during one terrestrial phase. Special emphasis was on the effects of a legume and a non-legume tree species. NH4+-N accounted for more than 85% of DIN even at the end of the terrestrial phase although it decreased throughout the experimental period. While extractable NO3–-N was always low in the soil (less than 15% of DIN), the amount of leached NO3–-N was in the same range as NH4+-N. Under the legume trees mean DIN contents of the topsoil were higher than under the non-legume trees. DIN leaching from the topsoil (0–20 cm) was significantly higher under the legume trees than at the other sites, also indicating a higher N availability. Therefore, despite considerable leaching legume trees may be an important source of N supporting a high biomass production of the várzea forest.  相似文献   

20.
Summary The chloroform fumigation-incubation method (CFIM) was used to measure the microbial biomass of 17 agricultural soils from Punjab Pakistan which represented different agricultural soil series. The biomass C was used to calculate biomass N and the changes occurring in NH4 +-N and NO3 –-N content of soils were studied during the turnover of microbial biomass or added C source. Mineral N released in fumigated-incubated soils and biomass N calculated from biomass C was correlated with some N availability indexes.The soils contained 427–1240 kg C as biomass which represented 1.2%–6.9% of the total organic C in the soils studied. Calculations based on biomass C showed that the soils contained 64–186 kg N ha–1 as microbial biomass. Immobilization of NCO3 –-N was observed in different soils during the turnover of microbial biomass and any net increase in mineral N content of fumigated incubated soils was attributed entirely to NH4 +-N.Biomass N calculated from biomass C showed non-significant correlation with different N availability indexes whereas mineral N accumulated in fumigated-incubated soils showed highly significant correlations with other indexes including N uptake by plants.  相似文献   

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