Variability Of Soil Organic Matter Research Articles

Realistic soil C sink estimate in dry forests of western Argentina based on humic substance content

Due to high temporal variation of soil organic matter in arid regions, estimates of annual sequestered C might be overestimate. We assessed the soil stable organic matter (humic substances) in the transitional area between Dry Chaco and Monte eco-regions in western Argentina, as an approach to estimate realistic soil C sink. Soil samples were taken during wet and dry seasons in four sites along precipitation gradient. In each site three soil cover situations (under tree, under shrubs and on bare soils) were sampled (n = 5) and the quantity and type of residues (tree and shrub leaves, woody material, grasses and forbs) were recorded. Soil organic matter and humic substances (humic and fulvic acids) content were analyzed and non-humic substances were calculated by the differences between organic matter and humic substances. Soil humic substance proportion respect to SOM was low (20%) in all sites and it did not correspond with the precipitation gradient. Non-humic substances were lower in wet season indicating high C lability. The most important factors that affected soil humic substance content were the type and quantity of organic residues and soil cover type. Our results suggest that previous C sink estimations in Argentina dry forest probably are overestimated.

Variations of Soil Organic Matter and Nutrients in Degenerated Wetland in Response to Ecological Restoration in Shuangtaizi Estuary, Northeast China

The aim of the research is to study the changes of soil properties during the process of wetland restoration, and evaluate the results or effect of wetland restoration. Soil samples were collected from both restored and unrestored wetlands in Shuangtaizi estuary, and then we compared seasonal changes of soil properties in these two areas. The results indicated a significant increase of NH4-N, whereas TP(total phosphorous) declined slightly in restored wetland. In addition, significant seasonal variations of SOM(soil organic matter) and nutrients were exhibited in restored and unrestored wetlands especially in July and August. Meanwhile, we found that C/P ratio in restored wetland increased in summer and reduced in September. All these have suggested that soil properties and nutrients proportions were changed after the restoration, which would be more conductive for soil ecological function.

Spatial Distribution of Soil Organic Matter and Nutrients in the Pear Orchard Under Clean and Sod Cultivation Models

The soil organic matter and nutrients are fundamental for the sustainability of pear production, but little is known about the spatial distribution of soil organic matter and nutrients in a pear orchard. With the soil of the pear (cv. Dangshansu on P. betulifolia Bunge. rootstock) orchard under clean and sod cultivation models as test materials, the experiment was conducted to evaluate spatial variability of soil organic matter (SOM), total nitrogen (STN), total phosphorus (STP), total potassium (STK), available nitrogen (SAN), and available potassium (SAK) in and between rows at different soil depths (0–60 cm). The SOM, STN, STP, STK, SAN and SAK of the different soil layers under the two tillage models were different in the vertical direction. The SOM, STN, STP and SAN in the 0–20 cm soil layer were higher than those in the 20–40 and 40–60 cm soil layers. The STK of 40–60 cm soil layer was higher than that in the 0–20 and 20–40 cm soil layers. The STK increased with the depth of soil in the vertical direction in the clean cultivated pear orchard. Variability of the SOM, STN, STP, STK, SAN and SAK of sample sites in between rows of the same soil layer was found in the pear orchard soil in the horizontal direction under clean and sod cultivation management systems, except that STK of all sites did not show the difference in identical soil layers in the pear orchard under clean cultivation. The sod cultivation model improved the SOM, STN, and STK in the 0–20 cm soil layer in the pear orchard, and the three components increased by 12.8, 12.7 and 7.3% compared to clean cultivation, respectively. The results can be applicable to plan collection of orchard soil samples, assess orchard soil quality, and improve orchard soil management practices.

江苏省土壤有机质变异及其主要影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 江苏省土壤有机质变异及其主要影响因素 DOI: 10.5846/stxb201205200749 作者: 作者单位: 土壤与农业可持续发展国家重点实验室中国科学院南京土壤研究所,土壤与农业可持续发展国家重点实验室中国科学院南京土壤研究所,土壤与农业可持续发展国家重点实验室中国科学院南京土壤研究所,土壤与农业可持续发展国家重点实验室中国科学院南京土壤研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 科技部国际科技合作资助项目(2010DFB24140);中国科学院战略性先导科技专项(XDA05050500)子课题 (XDA05050503) Variability of soil organic matter and its main factors in Jiangsu Province Author: Affiliation: Institute of Soil Science, Chinese Academy of Sciences,Institute of Soil Science, Chinese Academy of Sciences,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤有机质在陆地生态系统中具有重要作用,是估算土壤碳储量、评价土壤肥力和质量的重要指标。从省域尺度上分析土壤有机质的分布和变异,及其影响因素,对节能减排和土壤的可持续利用具有重要的指导意义。以江苏省第二次土壤普查的1519个土壤剖面数据为基础,分析了江苏省表层(0-20 cm)土壤有机质分布、变异及其影响因素。结果表明,全省土壤有机质平均含量为(16.55±8.49) g/kg,变异系数为51.36%,属中等变异水平。不同土壤类型有机质含量差异较大,沼泽土最高,为31.60 g/kg,棕壤最低,为8.69 g/kg;自然土壤的有机质含量变异程度大于耕作土壤。年均温、年均降雨量、成土母质、土地利用、土壤质地和土壤pH对全省土壤有机质含量变异的综合能解释能力为52.6%。土壤质地和年均温是有机质含量变异的主要影响因素,土壤质地对其变异的影响大于年均温,二者能够独立解释其变异的32.0%和23.4%。 Abstract:In the terrestrial ecosystems, soil organic matter (SOM) plays an important role in estimating soil C sequestration potential, soil fertility and quality, etc. In this study, Jiangsu Province was chosen as an example in eastern China and a total of 1519 soil profiles were collected from the Second National Soil Survey of Jiangsu Province. And furthermore, the variability of SOM in the surface layer (0-20 cm) of Jiangsu Province was analyzed; and its main factors, too, by means of variance analysis and regression analysis. The results show that the SOM content of the region varied in the range of (16.55±8.49) g/kg, with a coefficient of variation of 51.36%, both belonging to a moderate level. SOM content of different types varies widely, with the maximum value of 31.60 g/kg in boggy soil, and with the minimum value of 8.69 g/kg in brown soil. The variation degree of SOM in natural soil was higher than that in cultivated soil. Analysis of variance suggests that mean annual temperature (MAT), mean annual precipitation (MAP), parent material, land use, soil texture and pH significantly affected the variability of SOM in Jiangsu Province. All these 6 natural factors can explain 52.6% variability of SOM. Soil texture and MAT are the main factors controlling variability of SOM. The effect of soil texture on SOM variation is stronger than that of MAT, and two factors can independently explain about 32.0% and 23.4% variability of SOM, respectively. 参考文献 相似文献 引证文献

Vegetation and Topographic Control on Spatial Variability of Soil Organic Carbon

Soil organic carbon (SOC) is one of the most important parameters affecting the hydraulic characteristics of natural soils. Despite being rather easy to measure, SOC is known to be highly variable in space. In this study, vegetation, climate, and morphology factors were used to reproduce the spatial distribution of SOC in the mineral horizons of forest and grassland areas in north-western Italy and the feasibility of the approach was evaluated. When the overall sample (114 samples) was analyzed, average annual rainfall and elevation were significant descriptors of the SOC variability. However, a large part of the variability remains unexplained. Two stratification criteria were then adopted, based on vegetation and topographic properties. We obtained an improvement of the quality of the estimates, particularly for grasslands and forests in the absence of local curvatures. These results indicate that the spatial variability of soil organic matter is scarcely reproducible at the regional scale, unless an a-priori reduction of the heterogeneity is applied. A discussion on the feasibility of applying stratification criteria to deal with heterogeneous samples closes the paper.

Spatial Variation in Soil Organic Matter, Available Phosphorus, and Potassium under Semi-arid Conditions: Research Station Management Implications

Natural ecosystems are characterized by variability in space and, to a lesser extent, in time. Soil types and properties vary on landscape and field scales. Such variability is either inherent or human-induced and influences crop management. Variability at the plot level impinges on field experimentation. In this study at the main station, Tel Hadya, of the International Center for Agricultural Research in the Dry Areas (ICARDA), we intensively sampled four large field plots and analyzed the samples for soil organic matter (SOM), available Olsen phosphorus (P), and extractable potassium (K). Variability parameters were established for each property, as well as semivariograms. Contour maps for each plot were drawn by kriging. Despite the history of uniform management in each plot, large residual spatial variability was evident for each parameter. Although such variability is generally disregarded by agronomists and crop scientists and is generally believed to be eliminated by an alternate year of uniform cropping (i.e., “homogenization”), the residual persistent variability in these parameters cause variation in crop growth and need to be considered in designing experimental treatments, especially with regard to plot size and orientation. Although P and K variability can be masked by uniform fertilizer application, the effects of SOM persist for several years and thus can influence nutrient availability and soil moisture under such dryland conditions. Systematic soil sampling can help in reducing variability at trial sites, but background variability cannot be eliminated completely in natural bodies such as soils.

Comparison of Geographically Weighted Regression and Regression Kriging for Estimating the Spatial Distribution of Soil Organic Matter

Soil organic matter (SOM) is an important component of soils, and knowing the spatial distribution and variation of SOM is the premise for sustainably utilizing soils. The objective of this study was to compare geographically weighted regression (GWR) with regression kriging (RK) for estimating the spatial distribution of SOM using field-sample data in SOM and auxiliary data in correlated environmental variables (e.g., elevation, slope, ferrous minerals index, and Normalized Difference Vegetation Index). Results showed that GWR was a relatively better method and could provide promising results for SOM prediction in comparison with RK. The map interpolated by GWR showed similar spatial patterns influenced by environmental variables and the nonapparent effect of data outliers, but with higher accuracies, compared to that interpolated by RK.

Carbon distribution in top‐ and subsoil horizons of two contrasting Andisols under pasture or forest

Volcanic ash soils display distinctive morphological, physical and chemical properties and they contain several times more organic matter than non‐volcanic soils. So far, there are few studies of soil organic matter (SOM) distribution in different chemically and physically protected carbon pools of soil horizons of volcanic soils. The aim of this study was to determine the SOM distribution (and its δ13C and δ15N composition) in different chemical and physical fractions at various depth horizons of two Andisols under pasture or rain forest in southern Chile. We used the amount of humus‐complexes (Cp) extracted with Na pyrophosphate as a measure of C stabilized by aluminum (Alp) and iron (Fep) in combination with density fractionation to separate particulate organic matter as free (fPOM), occluded (oPOM) and organic matter associated with the mineral fraction (MF). The results showed that soil SOM stock (0–40 cm) in the pasture soil was 166 Mg C ha−1 (11.7 Mg N ha−1) and in the forest soil 100 Mg C ha−1 (4.1 Mg N ha−1). The SOM variation was explained largely by the differences in Cp, Alp and Fep. About 34% of total soil C was found as Cp in both oPOM and MF in the topsoil, whereas 33–53% was found in the subsoil horizons. The oPOM fraction was more important in the forest soil and generally decreased in the subsoil where these fractions were enriched with δ13C and δ15N. Our results emphasize the importance of the humus complex and oPOM formation as the SOM stabilization mechanism in the forest Andisol, whereas under pasture organo‐mineral interaction, including the formation of humic‐metal complexes, is the most important stabilization mechanism. A conceptual model is lacking to demonstrate the major areas of uncertainty within known mechanisms and factors that explain the distribution of SOM through soil profiles in Andisols.

Organic Matter Dynamics in Soils Regenerating from Degraded Abandoned Rubber Plantation in Orogun Area of the Rainforest Zone of Southern Nigeria

The area of secondary forest (SF) regenerating from degraded abandoned rubber ( Hevea brasiliensis ) plantation is increasing in the rainforest zone of south southern Nigeria; however, the build-up of soil organic matter following abandonment is not well understood. This study examined the build-up of soil organic matter in a mature forest and three secondary forest fields aged 1, 5 and 10 years of age following the abandonment of degraded rubber ( Hevea brasiliensis ) plantation in Orogun in a part of the rainforest zone of south southern Nigeria. This is in order to ascertain the rate of build-up of organic matter in the soil during the course of forest regeneration from degraded abandoned rubber plantation ( Hevea brasiliensis ). There was a progressive increase in organic matter content of the soil with increasing age of the secondary forest. Organic matter increase was more rapid in the topsoil (0-10cm) than the subsoil (10-30cm): the level of organic matter in the topsoil reached 92.94% of the level of organic matter in the mature forest topsoil by the tenth year and 84.62% of the level of organic matter in the mature forest subsoil by the tenth year. The concentration of organic matter in the topsoil is higher than the subsoil. Reviews of the reported trends in soil organic matter build up during forest establishment after agricultural use show no common trend. This study showed a great variation in soil organic matter build up even within the same locality. Keywords: Organic matter, Rubber plantation, Degraded, Orogun, South Southern Nigeria, Secondary forest.

喀斯特峰丛洼地不同森林表层土壤有机质的空间变异及成因

基于动态监测样地(200 m × 40 m)的网格(10 m × 10 m)取样,以农作区为对照,用地统计学方法研究了喀斯特峰丛洼地人工林、次生林和原生林3类典型森林生态系统表层土壤(0-15 cm)有机质的空间变异,通过主成分分析和相关分析,探讨了其生态学过程和机制。结果表明:喀斯特峰丛洼地土壤有机质很高,沿着农作区-人工林-次生林-原生林的恢复梯度,土壤有机质显著提高,变异系数逐步增大;农作区和3类森林土壤表层有机质均具有良好的空间自相关性;农作区试验半变异函数<em>C₀/</em>(<em>C₀</em>+<em>C</em>)值为26.5%,呈中等程度的空间相关性;3类森林的<em>C₀/</em>(<em>C₀</em>+<em>C</em>)值为9.0%-22.6%,呈强烈的空间相关性;农作区和人工林土壤有机质呈单峰分布,次生林呈凹型分布,原生林呈凸型分布;不同森林的主导因子不同,农作区的主导因子为主要土壤养分,人工林为地形和物种多样性,次生林为森林结构和物种多样性,原生林为地形和物种多样性,且同一因子在不同森林与土壤表层有机质的正负作用关系和相关程度也不同。因此,农作区和3类森林应根据其土壤表层有机质的空间变异及主要影响因子制定相应的固碳措施。;The spatial variability of surface soil (0-15 cm) organic matter in plantation, secondary forest, and primary forest in depressions between hills in a karst region was examined using farmland as a control. The ecological processes and mechanisms behind this variability were also discussed. Eighty sample plots of 10 m × 10 m were established in 200 m × 40 m farmland, plantation, secondary fores, and primary forest plots in depressions between karst hills. Geostatistics was used to analyze the spatial pattern of surface soil organic matter in the plots and principal component analysis and correlation analysis were used to analyze the relationships with other factors. The soil organic matter content in the depressions between karst hills was high. Along the restoration gradient from farmland > plantation > secondary forest > primary forest, the surface soil organic matter content significantly increased and the coefficients of variation also increased. The vegetation in primary forest was well preserved and soil organic matter was up to 118 g/kg, 3.76 times that of farmland. The coefficients of variation of soil organic matter in the farmland and three forest types were 19.4%-48.5%. There was a fine spatial autocorrelation in the surface soil organic matter in the farmland and the three forest types. The farmland and plantation forest were strongly influenced by humans and therefore more balanced. This meant the correlogram range was large and the maximum correlogram coefficient Moran's I was 0.460 in the farmland and 0.780 in the plantation. The natural restoration time of the secondary forest was 22 years. Here there were more, but unevenly distributed, vegetation types meaning the correlogram range was smaller and Moran's I coefficients fluctuated considerably. In the primary forest, however, the disturbance was low and vegetation intact. This meant the correlation was mainly affected by the topography. The best fitting models for semi-variation of secondary forest soil organic matter function in Karst peak-cluster depressions are the exponential model and the Gaussian model. The resulting <em>R</em>² values of 0.926-0.971 demonstrate how well they reflected the soil organic matter spatial structure characteristics. The value of <em>C₀/</em>(<em>C₀</em>+<em>C</em>) of the surface soil organic matter in farmland was 26.5%, indicating a medium spatial correlation. The values of <em>C₀/</em>(<em>C₀</em>+<em>C</em>) in the three forest types ranged from 9.0% to 22.6%, suggesting strong spatial correlations. The spatial pattern of surface soil organic matter in farmland and plantation presented a unimodal distribution: in secondary forest it had a concave distribution and in primary forest it had a convex distribution. Soil nutrient content was the largest influencing factor on the variation in the farmland, topography and species diversity were the largest influencing factors in the plantation and primary forest, and forest structure and species diversity were the largest influencing factors in the secondary forest. Even when considering the same factor in the three forest types, the functions and correlations differed. Therefore, the corresponding strategies of fixing carbon should take the spatial variability of surface soil organic matter and its largest influencing factors in farmland and the three forest types into account.

Conservation agriculture in dry areas of Morocco

Moroccan agriculture is characterized by the co-existence of both modern and smallholder traditional agriculture. Both types of agriculture are under degradative processes due to mis-use of tillage implements, mis-management of crop residues and inappropriate links between grain and livestock productions. From the research conducted over the last three decades, the vast majority of beneficial tillage effects are transient. Conversely, the harmful effects of conventional tillage (CT) systems are long-lasting, if not permanent. The present paper aims at evaluating major achievements in conservation or no-tillage agriculture (CA or NT) research conducted in dry areas of Morocco and presenting important ways to implement these achievements within the Moroccan rural society. CA has been introduced in response to issues of soil conservation, drought mitigation and soil quality management. NT systems have resulted in reduced soil erosion, greater soil water conservation, improved soil quality and stable and higher crop yields. Changes in crop production practices due to shifting to NT or CA systems and retention of crop residues at or near the surface produced progressive qualitative and quantitative variations in soil organic matter. This can allow agriculture to contribute to country's efforts to reduce and control greenhouse gas emissions. These effects benefited both farmers and society in terms of higher returns and efficiencies. Under NT, benefits from improved agriculture's environmental performance must be added to remunerations of reducing costs of production and improving well-being of farmers. The other strong benefits that CA brings come from the opportunity for early sowing and savings in time, machinery and fuel. Even though, many agronomic, socio-economic and environmental benefits accrue from NT and increasing crop diversity; lack of incentives from the government and social factors encourage the continued use of CT systems. CA systems were sufficiently tested in research stations but found limited adoption in farm communities. The shift in the late nineties to more on-farm research did not result in the envisaged breakthroughs, mainly due to poor research-extension linkages and several social and technical barriers. Consequently, in order to realize durable agricultural growth, there is a huge challenge to out- and up-scale CA in Morocco through linkage of all stakeholders (farmers, developers, researchers, industrials and policy makers). This paper fulfills information gaps and presents a thorough discussion on constraints to CA adoption as well.

Spatial prediction of soil organic matter using terrain indices and categorical variables as auxiliary information

Soil organic matter (SOM) is one of the most important indicators of the soil quality. Accurate information about the spatial variation of SOM is critical to sustainable soil utilization and management. Although utilizing spatially correlated auxiliary information to improve the prediction accuracy of soil properties has been widely recognized in pedometrics, not all studies have taken account of the influence of categorical variables (e.g., land use types, soil texture and soil genetic types) and did not systematically analyze the relationship between auxiliary variables and soil properties to be predicted. This paper aimed to examine whether inclusion of categorical variables can improve the accuracy of SOM prediction based on systematical analyses of variability. The least-significant difference (LSD) method and Pearson correlation analysis were used to systematically and quantitatively analyze the relationship between SOM and other environment variables (terrain indices, land use types, soil texture and soil genetic types). Spatial distribution of SOM was predicted by multiple linear stepwise regressions, ordinary Kriging and regression Kriging. Results indicated that spatial distribution of SOM was mainly affected by terrain indices, soil texture and soil genetic types. The root mean squared error of predictions based on elevation, which is used frequently as an auxiliary variable, was reduced when categorical variables were added as predictors. Our study suggested that introduction of categorical variables, such as soil genetic types, improved the prediction accuracy for a given prediction method. At the same time, systematic and exploratory analyses of the relationship between variables to be predicted and auxiliary was also important to ensure good predictions.

Refining Soil Organic Matter Determination by Loss-on-Ignition

Wet oxidation procedure, i.e., Walkley-Black (WB) method, is a routine, relatively accurate, and popular method for the determination of soil organic matter (SOM) but it is time-consuming, costly and also has a high potential to cause environmental pollution because of disposal of chromium and strong acids used in this analysis. Therefore, loss-on-ignition (LOI) procedure, a simple and cheap method for SOM estimation, which also avoids chromic acid wastes, deserves more attention. The aims of this research were to study the statistical relationships between SOM determined with the LOI (SOM LOI) and WB (SOM WB) methods to compare the spatial variability of SOM in two major plains, Shahrekord and Koohrang plains, of Chaharmahal-va-Bakhtiari Province, Iran. Fifty surface soil samples (0–25 cm) were randomly collected in each plain to determine SOM using the WB method and the LOI procedure at 300, 360, 400, 500 and 550 °C for 2 h. The samples covered wide ranges of soil texture and calcium carbonate equivalent (CCE). The general linear form of the regression equation was calculated to estimate SOM LOI from SOM obtained by the WB method for both overall samples and individual plains. Forty soil samples were also randomly selected to compare the SOM and CCE before and after ignition at each temperature. Overall accuracy of the continuous maps generated for the LOI and WB methods was considered to determine the accordance of two procedures. Results showed a significant positive linear relationship between SOM LOI and SOM WB. Coefficients of determination ( R 2) of the equations for individual plains were higher than that of the overall equation. Coefficients of determination and line slopes decreased and root mean square error (RMSE) increased with increasing ignition temperature, which may be due to the mineral structural water loss and destruction of carbonates at higher temperatures. A temperature around 360 °C was identified as optimum as it burnt most organic carbon, destroyed less inorganic carbon, caused less clay structural water loss, and used less electrical energy. Although the trends of SOM in the kriged maps by the two procedures accorded well, low overall accuracy was observed for the maps obtained by the two methods. While not suitable for determination where high accuracy is required, determination of organic carbon through LOI is likely suitable for exploratory soil surveys where rough estimation of organic matter is required.

Soil Organic Carbon Accumulation in Intensively Managed Phyllostachys praecox Stands

Area of bamboo forest (Phyllostachys praecox) has rapidly increased in southern China during the last 20 years due to its high economic value. Aims of this study were to analyse the temporal and spatial variations of soil organic matter (SOM) in heavily winter mulched bamboo stands and to estimate potential for carbon sequestration. Total of 60 soil profiles with 0–15 years of bamboo plantation were sampled from three towns in Lin’an County. Results showed that with increased plantation years, SOM decreased slightly at the beginning (1–5 years), and then rose up steadily. Based on the average of the three locations, the highest SOM content of 75.82 g/kg was the surface layer (0–10 cm) of the 15 years. As plantation year increased, the variation of SOM in the surface layer (0–10 cm) was represented by a parabolic shape, and in the second layer (10–20 cm), it was a similar mode, but less vigorous. Soil organic carbon (SOC) storage significantly increased during 5 to 15 years after it reached full production, and the calculated annual SOC increment in 0–40 cm soil profile was about 6.3 t C/ha/year. Therefore, extended Phyllostachys praecox forests can be considered as one option for countering CO2 emissions and regional climate change.

Assessment of properties of Tunisian agricultural waste composts: Application as components in reconstituted anthropic soils and their effects on tomato yield and quality

Organic soil improvers are mainly used for their potential for preventing soil losses. This study investigates the physicochemical properties of six different organic soil improvers and their effects on the properties and productivity of reconstituted anthropic soils during short-term application compared to farm manure. Treatment materials were obtained from Tunisian agricultural waste composts (almond shell (AS), sesame bark (SB), olive cake (OC), olive mill wastewater sludge (OMWS) and poultry manure (PM)) as well as mixtures of compost–manure (CM). The characterization of soil conditioners shows that (i) nitrogen contents are higher in olive wastes and PM-based composts; (ii) carbon/nitrogen ratio (C/N) and the organic matter (OM) contents are in the ranges of 14.1–29.7 and 19.3–64.5%, respectively; (iii) the electrical conductivity (EC) is higher in manure (M) and compost–manure mixture (4.8–10.4 mS/cm) and (iv) pH values are alkaline (8.2–8.8). Treatments were applied as components of a reconstituted soil at a rate of 14 kg/m 2. Except for the manures, the mixtures of soil and treatment material (in a ratio of 600 L/28 kg) were placed in metallic basins to form the reconstituted anthropic soil. Plot areas of 2 m 2 were used for each treatment and 2 × 2 m 2 for the control. An assessment of the geochemical properties of soils during the cultivation period reveals variations in soil organic matter (SOM) contents as well as pH and EC values. Soil productivity is determined by quantitative and qualitative comparison of tomato fruits obtained from each plot amended with manure-treated soil.

Land use and soil organic matter in South Africa 2: A review on the influence of arable crop production

The decline of soil organic matter as a result of agricultural land use was identified for a review with the ultimate aim of developing a soil protection strategy and policy for South Africa. Such a policy is important because organic matter, especially the humus fraction, influences the characteristics of soil disproportionately to the quantities thereof present. Part 1 of this review dealt with the spatial variability of soil organic matter and the impact of grazing and burning under rangeland stock production. In this second part of the review, the impact of arable crop production on soil organic matter is addressed. A greater number of studies have addressed the degradation of soil organic matter that is associated with arable crop production than the restoration. However, cropping under dryland has been found to result in significant losses of soil organic matter, which is not always the case with cropping under irrigation. Restoration of soil organic matter has been very slow upon the introduction of conservational practices like zero tillage, minimal tillage, or mulch tillage. Reversion of cropland to perennial pasture has also been found to result in discouragingly slow soil organic matter restoration. Although increases or decreases in soil organic matter levels have occurred in the upper 300 mm, in most instances this took place only in the upper 50 mm. The extent of these changes was dependent inter alia on land use, soil form and environmental conditions. Loss of soil organic matter has resulted in lower nitrogen and sulphur reserves, but not necessarily lower phosphorus reserves. Depletion of soil organic matter coincided with changes in the composition of amino sugars, amino acids and lignin. It also resulted in a decline of water stable aggregates which are essential in the prevention of soil erosion. Although much is known about how arable crop production affects changes in soil organic matter, there are still uncertainties about the best management practices to maintain and even restore organic matter in degraded cropland. Coordinated long-term trials on carefully selected ecotopes across the country are therefore recommended to investigate cultivation practices suitable for this purpose.

Temporal and spatial variability of soil organic matter and total nitrogen in a typical oasis cropland ecosystem in arid region of Northwest China

Soil degradation resulted from unreasonable land use has been a serious problem in the arid region of Northwest China. This paper seeks to understand the relationship between topsoil properties and farming practices for land management targeting at improving soil quality in this region. The temporal and spatial variation of soil organic matter (SOM), total nitrogen (STN) were analyzed with classical statistics and geostatistics methods in Linze County, Gansu Province, an typical oasis agricultural area in arid region of northwest China, as affected by farming practices using the data from 1982 to 2008. The results of classical statistics indicated that the average SOM and STN concentrations were 12.78 ± 4.38 g kg−1 and 0.72 ± 0.21 g kg−1 in 1982, 13.76 ± 4.02 g kg−1 and 0.81 ± 0.20 g kg−1 in 2008, respectively. The net carbon and nitrogen increased at an average rate of 0.104 Mg C ha-1 year−1 (1 Mg = 106g) and 0.014 Mg N ha−1 year−1 in the past 26 years. Geostatistical analyses showed that the spatially related areas of SOM and STN were expanded by effect of farming practices. The spatial distributions of SOM and STN contents were influenced by regional soil parent materials. Temporal variation maps of SOM revealed a change trend was closely related to the amount of the application of organic manures. It was concluded that the applications of chemical fertilizers were effective for increasing of STN, and the continuous applications of chemical fertilizers combining with applications of organic manures (approximately 45 m3 ha−1) every other year were helpful in accumulating soil organic carbon.

Sensitivity of digital soil maps based on FCM to the fuzzy exponent and the number of clusters

Fuzzy c-means clustering (FCM) has been used frequently in digital soil mapping. One of the key issues in applying FCM is the determination of the appropriate classification parameters of the fuzzy exponent (m) and the number of clusters (c). To determine the optimal selection of appropriate m and c values, in this study, we first used two simulated datasets to demonstrate the sensitivity of three commonly used validity functions to m and c. These two simulated datasets contained overlapping clusters and hierarchical clusters, respectively. The three studied validity functions were fuzzy performance index (FPI), compactness and separation (S) and a derivative of the objective function with respect to the fuzzy exponent (−[(δJE/δm)c0.5]). Then, a case study mapping soil organic matter (SOM) based on memberships from FCM clustering terrain attributes was conducted to investigate the sensitivity of soil maps to m and c. The results of the study on the simulated datasets showed that the three validity functions were sensitive in differing degrees to the structures of the clustered datasets under a wide range of m, but the sensitivities and the range of m were different for different validity functions and depended on the clustered datasets. The results from the case study of the soil mapping showed that soil maps based on FCM clustering were sensitive to m and c, but only the spatial variations of SOM presented on the maps were significantly sensitive to c. Furthermore, mapping accuracy was slightly sensitive to m and c. It is concluded that there was a range of optimal m over which digital soil maps did not change very much, but this was not certain for c, given that the spatial variation presented on the maps changed significantly with c.

Effects of land use on the level, variation and spatial structure of soil enzyme activities and bacterial communities

The aim of this study was to evaluate the long-term influence of contrasting rural land use types on the level, plot-scale variation and horizontal spatial structure of decomposition activities and the bacterial community in soil. Experimental data were collected in the southern boreal zone from topsoil layers of adjacent spruce forest, unmanaged meadow (former field) and organically cultivated field that all shared the same soil origin. The forest soil was sampled separately for the organic and mineral layers. A geostatistical design comprising 50 sampling points per plot area of 10 × 10 m2 was used. The measured microbiological characteristics included eight different hydrolytic soil enzyme activities involved in C, P and S cycles, bacterial 16S rDNA length heterogeneity profiles (LH-PCR) and total DNA yield as a relative estimate of microbial biomass.Effects of land use were pronounced on both the bacterial community structure and soil enzyme activities. Soil organic matter (SOM) content predicted well the major differences in soil enzyme activities and microbial biomass. Highest enzyme activities were generally found in the forest organic soil whereas the underlying mineral soil showed significantly lower activities with a pattern similar to those of the other mineral soils, especially the cultivated field. Bacterial LH-PCR fingerprints were distinct but at the same time remarkably similar between field and meadow soils whereas the forest organic layer differed clearly from the mineral soils. Within-plot variation of soil microbiological characteristics was best explained by the variation of SOM. Relative standard deviations of soil microbiological characteristics typically decreased in the order: forest organic layer ≈ forest mineral layer > meadow > field. However, bacterial fingerprints showed lowest variation within the meadow. Most of the microbiological variables studied showed no or only weak spatial structure at the scale sampled.

Temporal variation of soil organic matter content and potential determinants in Tibet, China

Understanding temporal variations in soil organic matter (SOM) is important because SOM improves soil, sustains soil productivity, and sequesters carbon. The Tibetan Plateau plays a critical role in climate change at both regional and global scales. Thus, the main objective of this study was to investigate temporal variations in SOM content in Tibetan soils as an important indicator of climate change. SOM content data were obtained from soil surveys conducted in the 1980s and resampled in the 2000s. In this study, SOM content data from the A horizon of the soil profile were compared over time, and a paired t-test was conducted to verify differences between the two datasets. The results reveal that SUM content in the A horizon decreased significantly. To determine the causes of SOM content decreases in the A horizon, soil samples were grouped into ten soil types, four land-use types, and seven physiogeographical units. SUM content in four soil types (felty soils, cambisols in the World Reference Base (WRB) for soil resources; cold calcic soils, cambisols in the WRB; bog soils, gleysols in the WRB; and meadow soils, umbric gleysols/haplic phaeozem in the WRB), pasture, and broad valleys and basins of the south Tibetan zone of montane shrubby steppe decreased significantly in the A horizon. Based on the analysis of some known realities, this change should be attributed to pasture degradation resulting from overgrazing and climate warming. (C) 2011 Elsevier B.V. All rights reserved.