Topsoil Nitrogen Research Articles

Distinct latitudinal patterns and drivers of topsoil nitrogen and phosphorus across urban forests in eastern China.

Nitrogen (N) and phosphorus (P) are the two most important macronutrients supporting forest growth. Unprecedented urbanization has created growing areas of urban forests that provide key ecosystem services for city dwellers. However, the large-scale patterns of soil N and P content remain poorly understood in urban forests. Based on a systematic soil survey in urban forests from nine large cities across eastern China, we examined the spatial patterns and key drivers of topsoil (0-20 cm) total N content, total P content, and N:P ratio. Topsoil total N content was found to change significantly with latitude in the form of an inverted parabolic curve, while total P content showed an opposite latitudinal pattern. Variance partition analysis indicated that regional-scale patterns of topsoil total N and P contents were dominated by climatic drivers and partially regulated by time and pedogenic drivers. Conditional regression analyses showed a significant increase in topsoil total N content with lower mean annual temperature (MAT) and higher mean annual precipitation (MAP), while topsoil total P content decreased significantly with higher MAP. Topsoil total N content also increased significantly with the age of urban park and varied with pre-urban soil type, while no such effects were found for topsoil total P content. Moreover, topsoil N:P ratio showed a latitudinal pattern similar to that of topsoil total N content and also increased significantly with lower MAT and higher MAP. Our findings demonstrate distinct latitudinal trends of topsoil N and P contents and highlight a dominant role of climatic drivers in shaping the large-scale patterns of topsoil nutrients in urban forests.

Soil chronosequence derived from landslides on the upper reach of Minjiang River, western China

Soil chronosequences derived from landslides with certain time series are the great avenue to elevate our understanding on the processes of pedogenesis, nutrient dynamics, and ecosystem evolution. However, the construction of reliable soil chronosequence from historical landslides remains intricate. Here, we presented a 22,000-year soil chronosequence from multiple landslides on the upper reach of Minjiang River, western China. The variation in a variety of pedogenesis indices and soil nutrients verified the reliability of the chronosequence. The silica-alumina ratio and silica sesquioxide ratio decreased significantly with soil age. This reflected the enrichment of Al/Fe/Ti oxides but the depletion of Si oxides with the soil development. Meanwhile, the values of the Chemical Index of Weathering and the Chemical Index of Alteration increased significantly with soil age, especially from 5 to 89 years. These variations were attributed to the soil weathering, which led to the destruction of soil minerals with the rapid loss of most of cations (e.g., K, Na, Ca, and Mg) during the soil development. The concentrations of carbon and nitrogen in topsoil increased with soil age, and the carbon accumulation rate slowed significantly from 5,500 to 22,000 years. The total phosphorus concentrations decreased with soil age, suggesting the gradual loss of soil phosphorus with soil development. The results indicate that the landslide chronosequence established on the upper reach of Minjiang River is reliable and delineates a long-term soil development process, which will provide a great platform for further improvement of biogeochemical theories and understanding sustainable vegetation restoration.

Autumn Tillage Reduces the Effect of Plant Cover on Topsoil Nitrogen Leaching

Keeping cover crops to reduce nitrogen leaching often conflicts with timing tillage operations before the soil becomes un-trafficable during winter, while leaving cover crops in the field until spring raises concerns over pre-emptive competition with the following crop. Therefore, farmers may resort to tilling their fields in autumn after letting cover crops remain in the fields for only a short period of time. We explore the effects of this practice in a laboratory lysimeter setting by analyzing the leaching of nitrate from intact topsoil cores. Cores were extracted from no-till (NT) plots and plots tilled in autumn (AuT), in areas kept bare (B) and with volunteer winter rye plant cover (V) after harvest. Nitrate breakthrough curves show that V significantly reduced N leaching by 61% relative to B in NT, but did not have a significant effect in AuT. Dissection of leached cores and undisturbed reference cores indicated a significant removal of mineral N from the soil during the lysimeter experiment for all treatments except V in NT. This indicates that volunteer cover removed a crucial amount of leachable N and suggests that tillage counteracted the effect of V in AuT, likely due to a combination of reduced uptake and re-mineralization of N in cover crop residue.

Evaluating the Capability of Satellite Hyperspectral Imager, the ZY1–02D, for Topsoil Nitrogen Content Estimation and Mapping of Farmlands in Black Soil Area, China

Soil nitrogen (N) content plays a vital role in agriculture and biogeochemical processes, ranging from the N fertilization management for intensive agricultural production to the patterns of N cycling in agroecological systems. While proximal sensing in laboratory settings can achieve ideal soil N estimation accuracy, the estimation and mapping by using remote sensing methods in a large spatial scale diplays low ability. A new hyperspectral imager with 166 spectral channels, the ZY1-02D, makes possible the detection of subtle but important spectral features of soil. This study aimed at exploring the capability of the ZY1-02D to estimate and map the topsoil N content of the black soil-covered farmlands in northeast China. To this aim, 646 soil samples from study sites were collected, processed, spectrally and geochemically measured for the soil N sensitive bands detection and partial least squares regression (PLSR) calibration and validation. The sensitive bands detection results showed an appealing regularity of the variability and stable tendency of the soil N sensitive spectral bands with the change of the sample size. Based on this, we compared the estimation capacity of the models developed with the full wavelength spectra and the models developed with the sensitive bands. The estimation based on ZY1-02D full wavelength spectral reflectance were robust, with R2 of 0.64 in validation. Further, the results of model developed with the sensitive bands showed better validation accuracy with R2 of 0.66 and were applied to create a map of topsoil N content of farmlands in the northeast China black soil area. The results demonstrated that sensitive bands modelling could enhance the accuracy of the estimation and simplify model, and what is more, showed the ideal capability of ZY1-02D for soil N content estimation at the regional scale.

Does restoring native forest restore ecosystem functioning? Evidence from a large‐scale reforestation project in the Scottish Highlands

Given the worldwide plans for extensive tree planting, we urgently need to understand how and where implementation will contribute to goals such as those for carbon sequestration. We used a long‐term, large‐scale native reforestation project in the Scottish Highlands to assess the response of carbon storage and other ecosystem functions to reforestation and grazing exclusion. We measured aboveground carbon, topsoil carbon, topsoil nitrogen, decomposition rates, soil invertebrate feeding activity, tree regeneration, and ground‐layer and moss height at 14 sites that are in the early stages of reforestation and fenced to exclude grazing. Reforestation areas were compared to unforested and mature forest areas that are both grazed and ungrazed, using 10 × 10 m plots. Aboveground carbon in the reforestation plots (1.4 kg/m2 [95% CI: 0.6, 2.6], average age 20 years since reforestation) was c. 8% of the mature forest plots (17.1 kg/m2 [13.1, 21.8]). Topsoil carbon was lower in the reforestation plots (18.78 kg/m2 [11.79, 25.78]) than in the unforested (29.82 kg/m2 [24.34, 35.29]) or mature forest (31.39 kg/m2 [22.91, 39.88]) plots. Responses of other functions to the reforestation and grazing interventions varied. Our results suggest that reforestation may trigger carbon loss from areas with high initial soil carbon even with low disturbance establishment, at least in the short term. Our work emphasizes where we lack knowledge: on the potential for long‐term re‐accumulation of soil carbon under semi‐natural native reforestation, soil carbon sequestration in the deeper soil layers, and the response of soil carbon to natural regeneration.

The Stratification of Organic Carbon and Nitrogen in Top Soils as Affected by the Management of Organic and Conventional Rice Cultivation

Organic and conventional management in rice cultivation have an impact on the nature of soil and the sustainability of agricultural system. This study aimed to determine the stratification of organic carbon and nitrogen in top soil from organic and conventional rice management. Top soil samples from organic and conventional rice management were taken before planting rice to find out the parameters of several soil characteristics. After rice was planted, top soil samples were taken at the depths of 0-4, 4-8, 8-12, 12-16, 16-20, 20-24 and 24-28 cm from organic and conventional rice fields, to determine the total organic carbon, total nitrogen and nitrate. The results show that organic rice management will provide better soil properties. Stratification of organic carbon and nitrogen was found in top soil from organic and conventional rice fields. Organic rice field appeared to have organic carbon content that was significantly higher than that of conventional rice field, and it is concentrated on top soil surface. The total nitrogen content in layers 0-4 cm and 4-8 cm in organic rice field was considerably higher than in conventional, but the content was different in layers 8-24 cm. Nitrate content was significantly different in top soil 12-16, 16-20 and 20-24 cm, significantly in top soil 8-12 cm, with nitrate in top soil of conventional rice field higher than in organic rice field. However, it was not significant in 0-4 cm and 4-8 cm top soils. This condition was influenced by organic and synthetic chemical fertilization, nitrification, denitrification and leaching.

Modelling soil nitrogen mineralisation in semi-mature pine stands of South Africa to identify nutritional limitations and to predict potential responses to fertilisation

Estimates of available nitrogen (based on topsoil nitrogen mineralisation rates) in semi-mature stands of Pinus radiata (D Don.) as well as pure species and hybrids of Pinus elliottii (Engelm.) in South Africa display a strong, significant, negative relationship with growth response to applied fertilisers in field experiments. This inexpensive technique can be incorporated in a fertiliser decision support system to minimise wasteful fertiliser applications. South African mid-rotation pine stands respond with high variability to nitrogen fertiliser supplements in the presence of phosphorus. We aimed to find a screening tool for stands that are responsive to fertilisation. The volume growth response relative to control plots (3 years after fertilisation with 200 kg ha−1 N in the presence of 100 kg ha−1 P) was determined across 14 pine fertiliser experiments in South Africa. These values were correlated to soil and other properties for each site and also to estimates of N availability and N mineralisation rates using the Soil Nitrogen Availability Predictor (SNAP) model. The relative volume growth response to fertilisation ranged with a factor from 0.05 to 0.96. No single result from standard soil analyses showed a strong positive or negative correlation with this growth response. However, highly significant negative correlations were observed between an estimate of N availability based on topsoil aerobic nitrogen mineralisation rates and the relative volume growth responses to fertilisation. The estimate of N availability derived from incubation studies may assist us to predict the magnitude of the response to N fertilisation (in the presence of P) with a fair degree of accuracy. The accuracy can be improved if the N availability estimate from aerobic incubation is used with other variables (pH and soil C content) in a multivariate regression to predict relative yield response to fertilisation.

Convergent and divergent responses of topsoil nitrogen and phosphorus content to nutrient addition in natural and restored alpine grasslands around the Qinghai Lake Basin

The availability and variation of soil nutrients are especially important for plant growth and soil carbon accumulation in the ongoing climate change. As a climate-sensitive region, the Qinghai Lake Basin (QLB) has experienced extensive land-use transitions. A three-year manipulative experiment was conducted in two grassland types around the QLB, including a natural alpine grassland (NG) and its adjacent restored grassland (RG), to examine the responses of soil nitrogen (N) and phosphorus (P) content to nutrient application with land-use. N addition continuously increased soil NO3−-N (SAN) content of NG in the whole experiment period, while displaying no detectable effect on SAN content of RG in the first experiment year. Nutrient addition presented no direct effects on soil total N (STN) content. However, N addition potentially promoted STN content indirectly by increasing SAN content, both in NG and RG. P addition significantly increased soil available P (SAP) content during the whole study period for both grasslands. Nevertheless, P addition significantly increased soil total P (STP) content of NG in the last two experiment years, while only elevating STP content of RG in the last experiment year. The results revealed that soil N and P content presented convergent and divergent responses to nutrient addition between NG and RG. STN and STP content were both positively related to growing season precipitation (GSP). SAN content was positively associated with growing season temperature in NG, and RG in N addition treatment. SAP content was consistently positively related to GSP in P addition treatment, but negatively related to GSP in the treatment without P addition, both in NG and RG. These findings highlight the importance of precipitation for soil nutrient accumulation, and imply that warming and increasing precipitation will be beneficial for the mineralization of soil N and P, respectively, in this semi-arid grassland ecosystem.

Trajectory of Topsoil Nitrogen Transformations Along a Thermo‐Erosion Gully on the Tibetan Plateau

AbstractPermafrost thaw, especially thermokarst formation, that is, ground collapse due to thawing of ice‐rich permafrost, is expected to alter soil gross nitrogen (N) transformations, which can regulate plant productivity and ecosystem carbon cycle. However, it remains unclear how thermokarst formation modifies soil N processes in permafrost ecosystems. Here 15N pool dilution techniques were used to evaluate changes in topsoil gross N transformations during various thaw stages (early, middle, and late stages) along a thermo‐erosion gully on the Tibetan Plateau. Structural equation modeling was then conducted to explore the relative importance of biotic and abiotic factors in affecting soil gross N transformations. The results showed that topsoil gross N mineralization (GNM) decreased at the three stages, reflecting declined inorganic N production after permafrost collapse. In contrast, topsoil gross nitrification increased only during the early stage. Additionally, the ratio of microbial N immobilization to GNM was enhanced during the middle and late stages, indicating a stronger microbial N limitation after thermokarst formation. The structural equation modeling analysis revealed that soil moisture played an important role in modulating gross N transformations. For GNM, decreased soil moisture had inhibiting effects via regulating the microbial biomass, microbial community, and enzyme activities along the thaw sequence. For gross nitrification, declined soil moisture exerted facilitating effects directly by improving oxygen availability and indirectly by modulating the abundances of ammonia‐oxidizing archaea and bacteria during the early stage. Overall, these results demonstrated that thermokarst formation altered soil N processes, potentially triggering interactions between ecosystem N and carbon cycles after permafrost thaw.

How long should the fully hillside-closed forest protection be implemented on the Loess Plateau, Shaanxi, China?

BackgroundRestoration of degraded forest ecosystem is crucial for regional sustainable development. To protect the country’s fragile and fragmented environment, the Chinese government initiated an ecological engineering project, the Natural Forest Protection Program, in seventeen provinces in China beginning in 1998. Fully hillside-closed forest protection (vegetation restoration naturally without any artificial disturbance) was one of vital measures of the Natural Forest Protection Program applied nation wide. Whether plant diversity, biomass and age structure of dominant tree species and soil nutrients in protected stands may become better with increase of protected period are still open problems.MethodsWe investigated community diversity, biomass of dominant tree species, age structures, and analyzed soil chemical properties of a Pinus tabulaeformis population at protected sites representing different protected ages at Huanglongshan Forest Bureau on the Loess Plateau, Shaanxi, China.ResultsPlant species richness of Pinus tabulaeformis community was significantly affected (p < 0.05) by forest protection and the effect attenuated with protection age. Shannon evenness index of plant species generally increased with protection age. Stands protected for 45 years had the highest tree biomass and considerable natural regeneration capacity. Contents of organic carbon, available phosphorus and available potassium in top soil increased in protected stands less than 45 years, however decreased significantly thereafter. Long-term forest protection also decreased the content of mineral nitrogen in top soil.DiscussionWe found that the richness of shrubs and herbs was significantly affected by forest protection, and evenness indices of tree, shrub and herb increased inconsistently with protected ages. Forest protection created more complex age structures and tree densities with increasing age of protection. Content of soil mineral nitrogen at 0–20 cm soil depth showed a decreasing trend in stands of up to 30 years. Soil available phosphorus and potassium contents were higher in stands with greater proportions of big and medium trees. Long-term protection (>45 years) of Pinus tabulaeformis stands in southeast Loess Plateau, China, may be associated with decreasing plant species richness, proportion of medium to large trees, dominant biomass of Pinus tabulaeformis and soil nutrients.

Environmental drivers of spatial patterns of topsoil nitrogen and phosphorus under monsoon conditions in a complex terrain of South Korea.

Nitrogen (N) and phosphorus (P) in topsoils are critical for plant nutrition. Relatively little is known about the spatial patterns of N and P in the organic layer of mountainous landscapes. Therefore, the spatial distributions of N and P in both the organic layer and the A horizon were analyzed using a light detection and ranging (LiDAR) digital elevation model and vegetation metrics. The objective of the study was to analyze the effect of vegetation and topography on the spatial patterns of N and P in a small watershed covered by forest in South Korea. Soil samples were collected using the conditioned latin hypercube method. LiDAR vegetation metrics, the normalized difference vegetation index (NDVI), and terrain parameters were derived as predictors. Spatial explicit predictions of N/P ratios were obtained using a random forest with uncertainty analysis. We tested different strategies of model validation (repeated 2-fold to 20-fold and leave-one-out cross validation). Repeated 10-fold cross validation was selected for model validation due to the comparatively high accuracy and low variance of prediction. Surface curvature was the best predictor of P contents in the organic layer and in the A horizon, while LiDAR vegetation metrics and NDVI were important predictors of N in the organic layer. N/P ratios increased with surface curvature and were higher on the convex upper slope than on the concave lower slope. This was due to P enrichment of the soil on the lower slope and a more even spatial distribution of N. Our digital soil maps showed that the topsoils on the upper slopes contained relatively little P. These findings are critical for understanding N and P dynamics in mountainous ecosystems.

Interannual Variability of Soil N and C Forms in Response to Snow—Cover duration and Pedoclimatic Conditions in Alpine Tundra, Northwest Italy

ABSTRACTIn alpine tundra the influence of snow-cover duration (SCD) and pedoclimatic conditions on soil nutrient forms during the growing season has received little attention. The hypothesis that SCD influences the soil temperature, which in turn can affect the annual changes in topsoil nitrogen (N) and carbon (C) forms, was tested for five growing seasons at three study sites in the alpine tundra of the NW Italian Alps. Among the pedoclimatic conditions studied (soil temperature, soil moisture, and number of freeze/thaw cycles), the mean soil temperature of the growing season was inversely correlated with the SCD (p < 0.01), which ranged from 216 to 272 days. Independently from the soil characteristics (e.g., degree of evolution), the microbial carbon (Cmicr) of the growing season was inversely correlated with the SCD and the mean soil temperature of the snow-covered season, suggesting the consumption of soil resources made by the Cmicr under the snowpack. During the growing season ammonium (N-NH4 +), dissolved organic carbon (DOC), and Cmicr were positively correlated with soil temperature and moisture. Path analysis shows that the interannual variability of topsoil N and C forms was significantly controlled by the pedoclimatic conditions recorded in both the snow-covered and the subsequent growing seasons, which in turn were influenced by SCD. Therefore, SCD played a fundamental role in terms of pedoclimatic conditions during the growing season, contributing to explaining the interannual variability of soil N and C forms, and may be a key factor for predicting the nutrient cycling in alpine tundra in the context of a changing climate.

Effect of Tillage and Straw Returning on Nitrogen Reserves in Summer Corn Topsoil

A field experiment with six treatments was conducted to study the nitrogen reserves in summer maize topsoil on the north China plain. Results showed that topdressing significantly increased topsoil nitrogen reserves. Summer corn topsoil nitrogen reserves were affected by several management measures. Shallow tillage, wheat straw no-returning and deep intertillage at the corn seedling stage significantly decreased topsoil nitrogen reserves, while wheat straw returning, no-tillage and biogas residue application during the wheat planting season significantly increased topsoil nitrogen reserves. The topsoil nitrogen reserve of Treatment 5 (straw returning + biogas residue + no-tillage + no-intertillage at the corn seedling stage) (biogas residue applied in the wheat season) increased by 629.55 kg/ha in the corn season. In Treatment 2 (straw returning + no-tillage + no-intertillage at corn seedling stage), topsoil nitrogen reserve increased by 445.2 kg/ha. Topsoil nitrogen storage showed the largest decrease in Treatment 3 (straw returning + no-tillage + intertillage at corn seedling stage), with a reduction of 1283.85 kg/ha. The topsoil N storage of Treatment 4 (straw returning + shallow (spin) tillage + no-intertillage at corn seedling) stage, Treatment 1 (straw no-returning + no-tillage + no-intertillage at corn seedling stage) and Treatment 3 (straw returning + no-tillage + intertillage at corn seedling stage) decreased by 935.7 kg/ha, 399.3 kg/ha and 351.9 kg/ha, respectively.

Soil attributes and plant production changes in a tropical littoral wetland

AbstractLake Naivasha is a freshwater lake in the East African Rift Valley. With continued lake level declines between 1980 and 2011, the newly exposed land areas were gradually taken for agricultural use. The resulting chronosequences allow for an analysis of the effects of land use duration on nutrient dynamics and agricultural production. Transects representing land use durations of 0–30 (cropland) and 15–30 years (pasture) were established on soils formed on alluvial deposits and lacustrine sediments. We assessed changes in topsoil nitrogen (N) stocks (t ha−1), ammonium mineralization potential (N‐supplying capacity), and plant‐available P with increasing durations of land use. An additional greenhouse experiment studied the responses of kikuyu grass (Cenchrus clandestinus) and maize (Zea mays) in potted topsoil collected from differnt land‐use types and chronosequence positions. With increasing duration of land use we noted a significant decline (P &lt; 5%) in soil N contents under both pasture and cropland uses, following a model of exponential decay. The N stocks decreased at 84 kg ha−1 a−1 and a decay rate constant of 0.019 a−1 in pasture soil within 15 years, and at 75 kg ha−1 a−1 with a decay rate‐constant of 0.013 a−1 in cropland soil within 30 years. While the ammonium‐N mineralization potential also decreased with land use duration, the trends were significant only in lacustrine pasture soils. Plant‐available P did not show any trends that were related to the duration of land use. Kikuyu grass and maize accumulated less dry matter and N as the duration of use increased. This biomass accumulation was significantly related to soil N. A continued mineralization of soil organic matter has possibly contributed to the observed soil N depletion over time. The continuous agricultural use of the littoral wetland zone of Lake Naivasha is likely to entail declining production potentials for both pastures and food crops.

Prediction of the presence of topsoil nitrogen from spaceborne hyperspectral data

Conventional methods of soil nitrogen extraction are time consuming, expensive and tedious. Remote sensing and Geographical Information System technologies can be used for the rapid and efficient prediction of the presence of soil nitrogen. However, studies are limited by and large to fields of larger and homogeneous units. This research concentrates on the prediction of topsoil nitrogen from harvested, scattered and small-sized agricultural fields of India using hyperspectral data. Spaceborne hyperspectral Hyperion data are used for the prediction of the presence of nitrogen. Multivariate partial least square regression method was used to predict the presence of nitrogen from reflectance. Reflectance data were pretreated using moving average and Savitzky–Golay filters which resulted in moderate prediction of R2 0.65 and 0.63 for calibration and validation, respectively. It can be inferred that Hyperion data can be effectively used for the prediction of the presence of soil nitrogen with a moderate level of accuracy even in case of scattered fields and fields of sizes approximately equal to the spatial resolution of the satellite.

Influence of the sewage irrigation on the agricultural soil properties in Tongliao City, China

Increasing shortages of fresh water has led to greater use of treated wastewater for irrigation of crops. This study evaluates the spatial variability of soil properties after irrigation with wastewater and freshwater. Geostatistical techniques were used to identify the variability of soil properties at the different sites. A set of physical and chemical soil properties were measured including total nitrogen (TN), total phosphorus (TP), organic matter (OM) and soil moisture. The TN concentration levels varied from 567 to 700 mg·kg−1, while OC levels ranged from 7.3 to 16.3 mg·kg−1 in wastewater-irrigated zones. The concentration levels of TP were between 371.53 and 402.88 mg·kg−1 for the wastewater-irrigated sites. Wastewater irrigation resulted in higher TN, TP and OM concentrations by 18.4%, 8% and 25%, respectively. The highest TN and OM occurred along the wastewater trunk. It was also observed that nitrogen concentrations correlate with the soil’s organic matter. The increase of salinity may be associated with the increase of pH, which might suggest that a reduction of pH will be beneficial for plant growth due to the decrease of salinity. The average concentrations of nitrogen in topsoil were higher than those in subsurface soils in irrigated areas. Such differences of the N profile might be due to variations in organic matter content and microbial populations. Consistent with TN and OM, soil C:N decreased significantly with an increase of depth. This phenomenon possibly reflects a greater degree of breakdown and the older age of humus stored in the deeper soil layers. The analysis of pH levels at different depths for the three sites showed that pH values for wastewater irrigation were slightly lower than the controlled sites at the same depths.

Mean residence time of global topsoil organic carbon depends on temperature, precipitation and soil nitrogen

Mean residence time (MRT) of topsoil organic carbon is one critical parameter for predicting future land carbon sink dynamics. Large uncertainties remain about controls on the variability in global MRT of soil organic carbon. We estimated global MRT of topsoil (0–20cm) organic carbon in terrestrial ecosystems and found that mean annual air temperature, annual precipitation, and topsoil nitrogen storage were responsible for the variability in MRT. An empirical climate and soil nitrogen-based (Clim&SN) model could be used to explain the temporal and spatial variability in MRT across various ecosystems. Estimated MRT was lowest in the low-latitude zones, and increased toward high-latitude zones. Global MRT of topsoil organic carbon showed a significant declining tendency between 1960 and 2008, particularly in the high-latitude zone of the northern hemisphere. The largest absolute and relative changes (0.2% per yr) in MRT of topsoil organic carbon from 1960 to 2008 occurred in high-latitude regions, consistent with large carbon stocks in, and greater degree of climate change being experienced by, these areas. Overall, global MRT anomalies (differences between MRT in each year and averaged value of MRT from 1960 to 2008) of terrestrial topsoil organic carbon were decreasing from 1960 to 2008. Global MRT anomalies decreased significantly (P<0.001) with the increase of global temperature anomalies, indicating that global warming resulted in faster turnover rates of topsoil organic carbon.

Spatial simulation of topsoil TN at the national scale in China

Based on 5336 typical soil profiles collected during the second national soil survey period,the correlation between topsoil total nitrogen(A horizon) and 11 environmental factors were analyzed and spatial distribution of topsoil nitrogen(TN) at national scale in China was simulated with the combination of multiple regression model and HASM model.Results indicated that,mean absolute error and mean relative error of the predicted value for 350 validation points were 0.67 g·kg-1 and 61.06%;compared with ordinary kriging method,the two errors were reduced by 0.05 g·kg-1 and 17.53% respectively.Besides,simulation result for northwest China,where the density of sample points was much smaller,was much closer to the actual situation.Thus,a combined method of multiple regression model and HASM model,which took the influence of environmental factors into account,can be used as an effective method for simulating spatial distribution of soil properties at a large scale.

Spatial variability of soil nitrogen by BP neural network interpolation

Precise information about the spatial variability of soil nitrogen is essential in developing soil regionalization management and fertilization. A total of 523 soil samples were taken from top soil (0-20 cm) in the yellow brown soil in Shucheng county, Anhui province for testing the spatial variability of soil nitrogen and determining appropriate number of samples and interpolation method. Spatial variability of topsoil nitrogen was obtained using BP neural network interpolation at various number of samples. Kriging was conducted to compare with BP neural network interpolation under the same condition. Compare of results of BP neural network interpolation with Kriging indicated that G value of BP neural network interpolation was 7.75% higher than Kriging interpolation at 100 samples, and RMSE value was 0.1 lower than Kriging interpolation at the same number of samples, if higher than the 200 samples, G and RMSE value of neural networks interpolation and Kriging interpolation were basically the same. With the increased number of samples, interpolation accuracy also increased, the growth rate of G and RMSE was flattening. It can be concluded that neural network interpolation is a potential approach to spatial variability of soil nitrogen at small sample and large-scale random sampling.

Controls and models for estimating direct nitrous oxide emissions from temperate and sub-boreal agricultural mineral soils in Europe

Based on a review of N2O field studies in Europe, major soil, climate and management controls of N2O release from agricultural mineral soils in the European Union have been identified. Data for these N2O emission drivers can easily be gathered from statistical services. Using stepwise multivariate linear regression analysis, empirical first order models of N2O emissions have been established which allow – in contrast to existing large-scale approaches – a regionally disaggregated estimation of N2O emissions at sub-national, national and continental level in the temperate and boreal climate regions of Europe. Arable soils showed lower mean and maximum emissions in oceanic temperate climate (“Temperate West”) than in pre-alpine temperate and sub-boreal climate (“Sub-boreal Europe”). Therefore, two separate regression models were developed. Nitrous oxide emissions from arable soils the Temperate West amount to an average flux rate below 2 kg N2O-N ha−1 yr−1 and rarely exceed 5 kg N2O-N ha−1 yr−1. They are modelled by the parameters fertiliser, topsoil organic carbon and sand content. In Sub-boreal European arable soils, N2O emissions vary in a much wider range between 0 and 27 kg N2O-N ha−1 yr−1 in dependence of available nitrogen, represented in the model by fertiliser and topsoil nitrogen content. Compared to existing methods for large scale inventories, the regression models allow a better regional fit to measured values since they integrate additional driving forces for N2O emissions. For grasslands, a fertiliser-based model was established which yields higher emission estimates than existing ones. Due to an extreme variability, no climate, soil nor management parameters could be included in the empirical grasslands model.