黄土高原丘陵区不同土地利用方式对土壤理化性质的影响

对晋西北黄土高原丘陵区持续利用30年的小叶锦鸡儿人工林、农田、杨树林、小叶锦鸡儿和杨树的混交林地以及撂荒地的土壤理化性状进行了研究。结果表明,不同土地利用方式对土壤理化性质影响很大。小叶锦鸡儿和杨树的混交林以及小叶锦鸡儿人工林可以降低土壤容重,提高土壤酶活性、有机质和全N含量,从而改善土壤肥力。混交林和小叶锦鸡儿人工林的土壤培肥作用高于杨树纯林。粗放的农业耕作措施提高土壤容重,降低土壤养分含量,使土壤退化。撂荒地一定程度上可以起到培肥土壤的作用。在黄土高原丘陵区,种植小叶锦鸡儿人工林以及小叶锦鸡儿和杨树的混交林是较好的生态重建和植被恢复方式。     

Assessment of soil quality in different ecosystems (with soils of Podolsk and Serpukhov districts of Moscow oblast as examples)

The values of the soil-ecological index and microbiological parameters (the carbon of microbial biomass C_mic, its ratio to the total organic carbon C_mic/C_org, and basal respiration) were determined for the soddy-podzolic, soddy-gley, bog-podzolic, meadow alluvial, and gray forest soils under different land uses (forest, fallow, cropland, and urban areas) in the Podolsk and Serpukhov districts of Moscow oblast (237 and 45 sampling points, respectively). The soil sampling from the upper 10 cm (without the litter horizon) was performed in September and October. To calculate the soil-ecological index, both soil (physicochemical and agrochemical) and climatic characteristics were taken into account. Its values for fallow, cropland, and urban ecosystems averaged 70.2, 72.8, and 64.2 points (n = 90, 17, and 24, respectively). For the soils of forest ecosystems, the average value of the soil-ecological index was lower (54.4; n = 151). At the same time, the micro-biological characteristics of the studied forest soils were generally higher than those in the soils of fallow, cropland, and urban ecosystems. In this context, to estimate the soil quality in different ecosystems on the basis of the soil-ecological index, the use of a correction coefficient for the biological properties of the soils (the C_mic content) was suggested. The ecological substantiation of this approach for assessing the quality of soils in different ecosystems is presented in the paper.     

Ecological study on the dynamics of soil organic matter and its related properties in shifting cultivation systems of Northern Thailand

Abstract

There is a large number of hill people in northern Thailand, who practices shifting cultivation. In order to analyze the soil ecological problems involved in the transition from traditional shifting cultivation to more intensive upland farming, the authors carried out comparative studies on the dynamics of organic matter and its related properties in soils both in the traditional shifting cultivation systems adopted by Karen people and more intensive upland farming practiced by Thai and Hmong people in the area. The contents of organic matter and available N in the surface 10 cm layers of soil from the fields continuously cultivated were lower than those in soils under prolonged fallow (more than 10 y) or natural forest. Based on the rate of soil respiration, the amount of organic matter decomposed within 1 y was estimated to reach nearly 10% of that stored in the upper 50 cm layers of the soil profile in the upland crop fields. These results indicate that the organic matter-related resources markedly decreased under continuous cropping. The contents of C, N, and P in the microbial biomass of the surface 10 cm layers of soil ranged from 0.37 to 2.09 mg C g^?l soil, from 22.7 to 188 µg N g^?l soil, and from 6.1 to 65.7 µg P g^?l soil, respectively. Since the contents of microbial C, N, and P in the surface soils were generally higher under prolonged fallow and natural forests than in the fields continuously cultivated, the microbial activity and/or the amounts of C, N, and P available for biological activity seemed to have declined under continuous upland farming. The incubation experiment to assess the N mineralization pattern showed two remarkable characteristics: 1) there was an initial time lag until active mineralization of N occurred in the soils from young fallow forest and 2) the soil burning effect was observed after burning in the fields under prolonged fallow. The active process of nitrification after N mineralization was always associated with a sharp fall in soil pH, suggesting that soil acidification was promoted and basic cations were lost from the soils. In conclusion, rapid deterioration of the soil organic matter-related properties in cropping fields can be considered to be one of the ecological reasons why upland fields must be returned to fallow again a few years after forest reclamation in traditional shifting cultivation systems. Therefore, in alternative farming systems with more intensive land use, it is essential to apply organic materials into soils to decrease the rate of soil degradation, or to improve the soil fertility, in avoiding soil acidification along with nitrification.     

The effects of agricultural use on the structure and physical properties of three soil types

This investigation was carried out to determine the influence of the use of soils on their morphological structure and properties. Three soil types (i.e. Haplic Phaeozem derived from loess, Orthic Luvisol derived from loess and Orthic Luvisol derived from sandy loam) were involved. In each soil unit, profiles lying at a small distance from one another were taken for detailed examination. The main difference between the soils within each unit was the use to which they were put. The following soils were selected for evaluation: (A) soil from natural forest habitat; (B) soil cultivated in farms with a very low level of mechanisation; (C) soil cultivated in farms which had been completely mechanised for many years; (D) soil used for many years in a vegetable garden, similar to hortisol.

In the selected profiles the morphological features, soil structure in all genetic horizons, granulometric composition, humus content, pH, density, air and water capacity and air permeability were analysed.

It was found that the transition from forest soil management to agricultural use leads not only to the formation of an arable-humus horizon and to changes in structure but also to changes of the physico-chemical properties of soils. Soils under agricultural use manifest a lower level of acidification than forest soils, as well as a different distribution of organic matter. In all agricultural soils, increased compaction of humus horizons was observed, compared with the corresponding horizons of forest soils, as well as changes in other physical features. The use of heavy machines over many years in field operations results in increased density of the soil and deterioration of soil structure. This effect is greater in soils with low colloids and organic matter contents.     

Long‐term changes of aggregate‐associated and labile soil organic carbon and nitrogen after conversion from forest to grassland and cropland in northern Turkey

Soil management systems can have great effect on soil chemical, physical and biological properties. Conversion of forest to grassland and cropland can alter C and N dynamics. The objective of this study was to evaluate the changes in aggregate‐associated and labile soil organic C and N fractions after conversion of a natural forest to grassland and cropland in northern Turkey. This experiment was conducted on plots subject to three different adjacent land uses (forest, grassland and cropland). Soil samples were taken from 0–5, 5–15 and 15–30 cm depths from each land use. Some soil physical (soil texture, bulk density), chemical (soil pH, soil organic matter, lime content, total organic C and N, inorganic N, free and protected organic C) and biological (microbial biomass C and N, mineralizable C and N) properties were measured. The highest and lowest bulk densities were observed in grassland (1.41 g cm⁻³) and cropland (1.14 g cm⁻³), respectively. Microbial biomass C and total organic C in forest were almost twice greater than grassland and four‐times greater than cropland. Cultivation of forest reduced total organic N, mineralizable N and microbial biomass N by half. The great portion of organic C was stored in macroaggregates (>250 µm) in all the three land uses. Free organic C comprised smaller portion of soil organic C in all the three land uses. Thus, this study indicated that long‐term conversion of forest to grassland and cropland significantly decreased microbial biomass C, mineralizable C and physically protected organic C and the decreases were the greatest in cropland. Copyright © 2011 John Wiley & Sons, Ltd.     

An ecological analysis of soil sarcodina at Dongzhaigang mangrove in Hainan Island,China

The community structure of soil sarcodina in three different habitats within a typical mangrove forest in Dongzhaigang, Hainan, China was investigated with qualitative and quantitative analyses. The three habitats were Site A (bare land without vegetation), Site B (artificially planted mangroves) and Site C (natural mangroves). The abundance, species diversity, dominance and community similarity index of soil sarcodina in fresh and air-dried soils with different physical/chemical properties were comparatively analyzed. Statistical analyses showed that the sarcodina abundance was positively correlated with moisture, salinity, organic matter (OM), total nitrogen (TN), total phosphorus (TP) and sulfate (SO₄^2?) of the mangrove soil, but the correlation coefficients with pH and total potassium (kalium, TK) were negative. The abundance and diversity index of sarcodina followed the order of Site A < Site B < Site C in both fresh and air-dried soils; Site B showed the highest community similarity with Site C; whereas, Sites A and C had the smallest community similarity in both fresh and dried samples from these three different habitats.     

Effects of edaphic factors on the tree stand diversity in a tropical forest of Sierra Madre del Sur, Mexico

Two sites with similar environmental parameters, except for the edaphic factor, were selected in the mountainous tropical forest of southern Mexico. Site 1 was established on an Alisol; site 2, on a Phaeozem. Representative soil profiles were examined on each of the sites, and topsoil was sampled on a regular grid pattern. The soil of site 2 was richer in organic matter and major nutrients and had a less acid reaction than the soil of site 1. The species diversity of the trees at site 2 (30 species) was higher than that at site 1 (17 species). The species compositions of the trees were different on the two soils: there were only six species in common for both sites. The coefficients of species similarity on the sites were low. We concluded that the presence of different soils within the same type of forest ecosystem increases its ??-diversity. The examination of edaphic preferences of the species showed that Alstonia longifolia and Thouinidium decandrum preferred rich soils, Inga punctata and Ocotea sinuata preferred poor soils, and Cupania dentata and Hamelia patens did not display preferences in the studied range of soil properties. Thus, the spatial variability of the soil properties affect the spatial pattern of tree species in the studied tropical forest ecosystems.     

Effect of tillage and rotation on organic carbon forms of chernozemic soils in Saskatchewan

The effects of selected tillage and rotation systems on soil organic carbon and its fractions were studied on Chernozemic soils in south‐western and east‐central Saskatchewan. After practicing a no‐till fallow unfertilized‐wheat rotation for 7 years on an Orthic Brown Chernozem in south‐western Saskatchewan, total soil organic carbon (TOC) in the 0 – 5 cm and 5 – 10 cm layers was slightly lower than the tillage fallow‐unfertilized wheat comparable treatment. However, light fraction of organic carbon (LFOC) was similar in the two treatments. Comparison of the tillage fallow‐unfertilized wheat to a treatment involving conversion to a fertilized continuous cropping system for 10 years showed TOC increased slightly in the two depths and LFOC increased by 24 % and 29 % in the 0 – 5 cm and 5 – 10 cm layer, respectively, of the continuous cropping treatment. Microbial biomass carbon (MB‐C) was increased significantly at the 5 – 10 cm depth. After conversion of fallow‐wheat to alfalfa as perennial forage for 10 years, TOC increased by 80 % and 27 %, LFOC by 245 % and 286 %, and HFOC by 63 % and 20 % at 0 – 5 cm and 5 – 10 cm depths, respectively, compared to the tilled cereal‐fallow system. Meanwhile, water soluble organic carbon (WSOC) was not affected but MB‐C increased significantly. In an Orthic Black Chernozem in east‐central Saskatchewan, the depletion and restoration of organic carbon was observed when native sod was changed into cropland and then back to grassland. For example, the TOC of cropland under cereal‐fallow rotation for 62 years decreased by 42 % and 33 % at 0 – 5 cm and 5 – 10 cm depths, respectively, compared to native sod. The LFOC decreased by 79 % and 74 % in the layers, and reductions in WSOC and MB‐C were even greater. After cropland was re‐seeded to grassland for 12 years, the concentration of total organic carbon was increased by 16 % and 22 % while the mass of organic carbon was the same as the cropland in the two layers. The LFOC and MB‐C amounts in the grass seed‐down were double that of the cropped land, but the amounts of TOC, LFOC, and MB‐C in grass seed‐down were still significantly lower than the native sod.     

Labile pools of organic matter and microbial biomass in the surface soils under shifting cultivation in northern Thailand

In order to analyze the N mineralization process under shifting cultivation in northern Thailand, labile pools of soil organic matter were studied, which were considered to be the factors contributing to the N mineralization process. Organic C, (organic + NH₄ ⁺)-N, and hexose-C were extracted from fresh soils in the surface 0–5 cm layers with a 0.5 M K₂S₀. solution at 110°C in an autoclave (fraction A) or at room temperature with a reciprocal shaker (fraction B), and analyzed as labile pools of organic matter. In the traditional shifting cultivation system, the content of organic C in fraction A in the fallow fields for 8 to 15 y was 3,710 mg kg^-1 while that in the fallow fields for 1 y and 3 to 5 y was 2,640 and 2,600 mg kg^-1, respectively. A high correlation was observed between the contents of the labile pool in fraction A and total soil organic matter. The ratio of the pool in fraction A to total soil organic matter apparently remained constant through the input-output balance in the pool. The content of the labile pool in fraction B was the highest among the fields cultivated for 1 y after the slash and burn practice and it decreased in the course of the fallow period. The content of organic C was 548 mg kg^-1 in the fields cultivated for 1 y and 235 mg kg^-1 in the fallow fields for 8-15 y, respectively. There was a reverse relation between the contents of the pool in fraction B and microbial biomass. Therefore, the origin of the pool in fraction B was attributed to the microbial debris associated mainly with a decrease in the soil moisture content in the dry season. On the other hand, in the relatively intensive cultivation system, there was no significant difference in the contents of the labile pools both in fractions A and B among the land use stages, suggesting that the preservation mechanism of these pools, which was observed in the traditional cultivation system, did not operate well in the intensive system. In alternative farming systems in future, it will be essential to apply organic materials to soils to supply organic matter and to maintain the microbial biomass.     

Land‐use effects on the distribution of soil organic carbon within particle‐size fractions of volcanic soils in the Transmexican Volcanic Belt (Mexico)

The aim of this study was to determine the effect of land‐use and forest cover depletion on the distribution of soil organic carbon (SOC) within particle‐size fractions in a volcanic soil. Emphasis was given to the thermal properties of soils. Six representative sites in Mexico were selected in an area dominated by Andosols: a grassland site, four forested sites with different levels of degradation and an agricultural site. Soils were fractionated using ultrasonic energy until complete dispersion was achieved. The particle‐size fractions were coarse sand, fine sand, silt, clay and particulate organic matter from the coarse sand sized fraction (POM‐CS) and fine sand (POM‐FS). Soil organic carbon decreased by 70% after forest conversion to cropland and long‐term cultivation; forest cover loss resulted in a decrease in SOC of up to 60%. The grassland soil contained 45% more SOC than the cropland one. Soil organic carbon was mainly associated with the silt‐size fraction; the most sensitive fractions to land‐use change and forest cover depletion were POM followed by SOC associated with the silt and clay‐sized fractions. Particulate organic matter can be used as an early indicator of SOC loss. The C lost from the clay and silt‐sized fractions was thermally labile; therefore, the SOC stored in the more degraded forest soils was more recalcitrant (thermally resistant). Only the transformation of forest to agricultural land produced a similar loss of thermally stable C associated with the silt‐sized fraction.     

Soil capability as a predictor of cropland change in Alberta,Canada from 1988 to 2010

Understanding the mutual influences between cropland use and soil characteristics is important in anticipating and planning for food production, environmental protection and resource sustainability. Numerous studies focus on the relationship between crop rotations and soil characteristics at a microscale, but fewer studies focus on the relationships between soil capability and cropland use and change at a medium scale. We explore how soil capability has influenced cropland changes over 22 yr, using statistical and land use transition analysis. Landsat images from the years 1988, 2002 and 2010 were used to map cropland changes by soil capability class within a pilot site in Alberta, Canada. Between the late 1980s and 2010: (i) the area of annual crops increased substantially while that of forest and summer‐fallow decreased; (ii) changes in cropland use among annual crops, perennial crops and summer‐fallow differed substantially depending on soil capability; and (iii) a transition from annual crops and summer‐fallow to perennial crops was more likely on land of poorer soil capability, whereas the transition from perennial crops and summer‐fallow to annual crops was more likely on land with higher soil capability. The changes in land use practices identified in this study indicate that producers are actively intensifying production on their best land to optimize profitability while simultaneously reducing the intensity of production on poorer land for either financial or environmental reasons, or both.     

Evidence that stable C is as vulnerable to priming effect as is more labile C in soil

A significant fraction of soil organic carbon, named stable organic carbon (C) pool, has residence times longer than centuries and its vulnerability to land use or climatic changes is virtually unknown. Long-term bare fallows offer a unique opportunity to isolate the stable organic pool of soils and study its properties. We investigated the vulnerability of the stable organic C pool to fresh organic matter inputs by comparing the mineralization in a long-term bare fallow soil with that of an adjacent arable soil, containing stable C as well as more labile C. For this, we amended or not the soil samples with two different ¹³C-labelled fresh organic matter (straw or cellulose). In all cases we found a positive priming effect (i.e. an increased mineralization of soil organic carbon) when fresh organic matter was added. By comparing the results obtained on both soils, we estimated that half of the “primed” C in the arable soil due to straw addition as fresh organic matter, originated from the stable C pool. Our results suggest that under such conditions, which frequently occur, the stable pool of soil organic matter may largely contribute to soil extra-CO₂ emissions due to priming effect. Consequently, the C storage potential of this pool may be modified by changes in land use and/or biomass production that might change the priming of the mineralization of the stable pool of soil organic carbon.     

Soil‐organic‐matter stability in sandy cropland soils is related to land‐use history

Sandy cropland soils in NW Europe were found to contain unusually high organic‐carbon (OC) levels, and a link with their land‐use history has been suggested. This study's aim was to assess the discriminating power of physical and chemical fractionation procedures to yield information on soil‐organic‐matter (OM) stability for these soils. In relict‐ and cultivated‐heathland soils, much higher proportions of 6% NaOCl treatment–resistant but 10% HF–soluble OC (MOC) and N (32.2% and 29.9%) were measured compared to a set of “permanent"‐cropland soils without a history of heathland land use (11.9% and 8.5%). Also, the proportions of 6% NaOCl– and 10% HF treatment–resistant OC and N in the relict and cultivated heathlands (19.2% and 12.0%) were higher than in the permanent‐cropland soils (17.7% and 5.7%). Stepwise multiple linear‐regression yielded a significant relationship between the annual mineralization (g C [100 g OC]^–1), soil OC (g C kg^–1) content, and %MOC: Annual mineralization = 4.347 – 0.087 soil OC – 0.032 %MOC (R² = 0.65). Combinations of incubation experiments for quantification of the labile soil OM pool with chemical fractionation may thus yield meaningful data for development of soil‐organic‐matter models with measurable pools, but their applicability will be limited to specific combinations of former land use with soil, climate, and current management.     

Changes in soil properties related to different land uses in part of the Nigerian semi-arid Savannah

Abstract. Changes in soil physical and chemical properties associated with different land uses including natural savannah were compared in Nigeria. The study was conducted on large unreplicated sites. There was a significant coarsening of texture, depletion of organic matter and nutrients and increase in bulk density under Eucalyptus camaldulensis and Mangifera indica (mango) plantations, and also under arable and fallow conditions compared with under natural vegetation. The soil conditions were slightly better under Mangifera than under Eucalyptus , and in the fallow land than the arable land and tree plantations, but the differences were mostly non-significant. The land uses studied were less efficient than the natural savannah in protecting the soil from loss of organic matter and nutrients by offtake or surface washing. The options open to Nigerian smallholder fanners are discussed in relation to sustaining soil fertility and productivity.     

Soil organic carbon as affected by land use in young and old reclaimed regions of a coastal estuary wetland,China

Soil organic carbon (SOC) and selected soil properties were measured in fringe and ditch marshes and cropland of old and young reclaimed areas in a subtropical estuary in China in order to investigate the effects of land use and reclamation history on SOC. The results show that after the conversion of wetlands to cropland, a longer reclamation history (>20 yr) resulted in greater soil bulk density, salinity, clay and silt, and lower soil moisture, SOC and sand content, whereas a shorter reclamation history (<20 yr) induced smaller values for soil pH, moisture and sand. Ditch marshes had greater average SOC in the top 50 cm than fringe marshes and cropland. SOC decreased generally down soil profiles from 0 to 50 cm in depth, except for the obvious accumulation of SOC in deeper soils from old fringe and young ditch marshes. Ditch marshes had the greatest SOC densities in the top 50 cm in both regions compared to the other land uses. SOC densities in the top 50 cm were less in croplands than in fringe marshes in the young region, while there were no significant differences between them in the older one. Except for cropland, SOC densities in the top 50 cm of the fringe or ditch marshes in the old region were not significantly different from those in the young region. SOC in both regions was reduced by 13.53 × 10⁴ t (12.98%) in the top 50 cm of the marshes after conversion to cropland, whereas the regional SOC storage increased by 29.25 t when ditch marshes were included. The results from regression analysis show that bulk density and soil moisture significantly influenced SOC. The total SOC stored in both ditch marshes and croplands was higher compared to fringe marshes. The regional SOC storage in the top 50 cm was not reduced after reclamation due to C accumulation in the ditch marshes. The regional effects of cultural practices should be taken into account in devising strategies for managing soils in coastal wetlands, particularly in the developing world.     

Influence of land use on soil properties in a forest region of Southern Nigeria

Abstract. To assess the effect of different land uses on soil properties, five land use types (fallow, Gmelina , arable, secondary forest and cocoa plots) on a sandy loam Alfisol (Typic Kandiudalf) were compared in terms of surface (0–15 cm) soil pH, exchangeable acidity, K, Ca and Mg, extractable P, total N, organic matter, gravimetric moisture, temperature and bulk density. There were significant differences ( P ≤ 0.05- P ≤ 0.001) between the land use types for all the properties except exchangeable acidity and moisture. All the land use types differed significantly from each other in at least four properties. Fallow and secondary forest differed in nine properties, fallow and cocoa in seven and fallow and Gmelina in six. In terms of the number of properties with high variability (CV ≥ 35%), the order was arable, secondary forest and cocoa (4) > Gmelina (3) > fallow (1).     

定边县板凳滩移民区土壤发生特性与系统分类研究

通过对陕西省定边县板凳滩移民区2 500hm2未利用地的调查及不同深度剖面土样的分析,研究了不同地形和不同植被下土壤的发生特性及系统分类。项目区内土壤没有完整的发生层次;土壤颜色、结构和养分在剖面层次上无明显差异;土壤有机质含量较低,最高1.7871g/kg,最小0.201 7g/kg;土壤碳酸钙无明显的淋溶淀积,剖面中无淀积层;颗粒组成以2～0.02mm粒级的砂粒为主;土壤CEC集中分布在2.5～5cmol/kg,保肥性能差。通过诊断层和诊断特征分析,研究区土壤共分属1个土纲,1个亚纲,2个土类和4个亚类,其中剖面Ⅱ1属于弱盐潮湿砂质新成土,剖面Ⅱ5属于钠质潮湿砂质新成土,剖面Ⅲ4属于石灰潮湿砂质新成土,剖面Ⅵ4属于石灰干润砂质新成土。研究结果可为移民区的土壤资源综合评价、土壤适宜性评价及农、林、牧业合理布局提供依据。     

银川市黄河滩地土壤性状空间分布特征与肥力质量评价

为阐明银川市黄河滩地土壤性质的空间分布特征,分析不同用地类型(荒地、林地、耕地、退耕地)之间土壤性质的差异,通过均匀取样法实地采集银川市黄河滩地耕层土壤样品92份,采用地统计学和模糊数学法对土壤容重、孔隙度、田间持水量等物理性质和pH、电导率、可溶性盐、有机质、全氮、全磷、全钾、碱解氮、有效磷、速效钾、硝态氮、铵态氮等化学性质的空间分布特征进行了分析和综合评价。结果表明:银川市黄河滩地表层土壤容重在1.07～1.52 g/cm³,田间持水量为18.18%～31.16%,总孔隙度介于33.60%～49.83%,毛管孔隙度在26.67%～36.43%,非毛管孔隙度为5.6%～17.00%;土壤均为盐碱土,氮、磷元素含量偏低,其余养分含量处于中等水平;不同用地类型之间,林地的物理特征表现最优,退耕地土壤pH显著高于耕地(P<0.05),电导率、可溶性盐和铵态氮含量均表现为退耕地显著高于其他3种用地类型(P<0.05),全磷含量表现为林地显著低于其他3种用地类型(P<0.05),有效磷含量表现为耕地和退耕地显著高于林地和荒地(P<0.05),其余理...     

Soil microbiological and biochemical properties for assessing the effect of agricultural management practices in Estonian cultivated soils

A set of soil microbiological and biochemical properties was used to assess the influence of agricultural practices such as rotation, usage of pesticides, and fertilizers on the three most widespread soil types (Calcaric Regosols, Calcaric Cambisols and Stagnic Luvisols) in the fields of horticultural farms throughout Estonia. Microbial biomass, dehydrogenase and alkaline phosphatase activity were significantly higher in Calcaric Regosols, whereas measured soil chemical parameters showed practically no difference among soil types. Multivariate exploratory analysis of soil biochemical and microbiological parameters clearly distinguished soils with different management practices when the effect of soil type was taken into account in data analysis. Activity of dehydrogenase, potential nitrification, N-mineralisation, and microbial biomass contributed most strongly to the differentiation of soils from differently managed fields. Soils managed according to organic farming principles were generally characterized by elevated microbiological parameter values, but at the same time the variation of those parameters among soils from these fields was also highest. The application of organic manure positively affected microbial biomass, N-mineralisation, potential nitrification, dehydrogenase and acidic phosphatase activity. Data analysis indicated that the amount of mineral nitrogen fertilizers added over time has a stronger effect on microbial biomass than the amount added in a given year. Legume-based crop rotation increased soil respiration and microbial biomass.     

Soil Aggregate and Organic Carbon Stability under Different Land Uses in the North China Plain

Soil aggregates and organic matter are considered to be important indicators of soil quality. The objective of this study was to determine land-use effects on the distribution of soil organic carbon (SOC) associated with aggregate-size fractions. Bulk soil samples were collected from incremental soil depths (0–10, 10–20 20–40, 40–70, and 70–100 cm) under three land-use types: fruit tree orchards established in 1987, cropland, and forage field. Soil samples collected from these plots were analyzed for aggregate stability after wet sieving into four aggregate-size classes (>2000, 250–2000, 53–250, and <53 μm), and the concentration of SOC was determined in each size fraction. Cropland and forage field soils were significantly more alkaline than the fruit tree soil. Bulk densities were greater in cropland and forage field (1.40–1.52 g cm^?3) than in fruit tree orchards (1.33–1.37 g cm^?3). The total weight of soil aggregates varied in the order of forage field > cropland > fruit tree orchard. Aggregate stability was greater in cropland and forage field than under fruit tree orchards. Soil organic C decreased with increasing soil depth but was greater under fruit tree orchards than others and was mainly concentrated in the topsoil layer (0–20 cm). Sieved fraction (<53 μm) had a greater SOC concentration, regardless of soil depth or land use. Our data supported the hypothesis that perennial vegetation (fruit tree orchard) and the proportion of aggregates with diameter <53 μm are suitable indicators of SOC accumulation and may therefore have a greater potential for SOC sequestration than the cropland.