Conversion of cropland into grassland: Implications for soil organic‐carbon stocks in two soils with different texture

Soil organic‐carbon (SOC) stocks are expected to increase after conversion of cropland into grassland. Two adjacent cropland and grassland sites—one with a Vertisol with 23 y after conversion and one with an Arenosol 29 y after conversion—were sampled down to 60 cm depth. Concentrations of SOC and total nitrogen (N_tot) were measured before and after density fractionation in two light fractions and a mineral‐associated fraction with C adsorbed on mineral surfaces. For the soil profiles, SOC stocks and radiocarbon (¹⁴C) concentrations of mineral associated C were determined. Carbon stocks and mineral‐associated SOC concentrations were increased in the upper 10 cm of the grassland soil compared to the cropland. This corresponded to the root‐biomass distribution, with 59% and 86% of the total root biomass at 0–5 cm soil depth of the grasslands. However, at the Arenosol site, at 10–20 cm depth, C in the mineral‐associated fraction was lost 29 y after the conversion into grassland. Over all, SOC stocks were not significantly different between grassland and cropland at both sites when the whole profile was taken into account. At the Arenosol site, the impact of land‐use conversion on SOC accumulation was limited by low total clay surface area available for C stabilization. Subsoil C (30–50 cm) at cropland of the Vertisol site comprised 32% of the total SOC stocks with high ¹⁴C concentrations below the plowing horizon. We concluded that fresh C was effectively translocated into the subsoil. Thus, subsoil C has to be taken into account when land‐use change effects on SOC are assessed.     

Land‐Use Type Effects on Soil Organic Carbon and Microbial Properties in a Semi‐arid Region of Northeast Brazil

Land‐use change is one of the most important anthropogenic environmental change drivers affecting the biodiversity and functioning of ecosystems. However, there is limited knowledge of the consequences for soil processes in many regions around the globe. The Brazilian semi‐arid ecosystem known as Caatinga has experienced the transformation from native forest into agricultural land, with heretofore unknown effects on soil processes and microbial properties. The aim of this study was to evaluate the impact of five land‐use changes (to maize and cowpea cropland, grape orchard, and cut and grazed pasture) on total organic C (TOC) and total N (TN) stocks and soil microbial properties of Ultisol from Caatinga. Soil samples (0–10 and 10–20 cm depth) were collected during the wet and dry periods. Split–split plot analysis of variance was used to test the effects of land use, soil depth, season and the interaction between land‐use and soil depth on soil microbial properties, TOC and TN stocks. Land‐use effects were more pronounced in the top soil layer than in the lower layer, while the pattern was less consistent in soil microbial properties. Land conversion from native forest to cropland may cause C losses from the soil, but conversion to pastures may even increase the potential of soils to function as C sinks. Grazed pastures showed not only high C and N stocks but also the highest soil microbial biomass and lowest respiratory quotients, all indications for elevated soil C sequestration. Thus, grazed pastures may represent a land‐use form with high ecosystem multifunctionality in Caatinga. Copyright © 2014 John Wiley & Sons, Ltd.     

Soil organic carbon and nitrogen fractions and water‐stable aggregation as affected by cropping and grassland reclamation in an arid sub‐alpine soil

This paper investigates effects of cropping abandonment and perennial grass growing on soil organic C and N pools and aggregate stability, by comparing soils under native grassland, crop cultivation, perennial grass growing and cropping abandonment, in degraded cropland at a sub‐alpine site in north‐western China. The pools of total and particulate organic C (115 and 37 Mg ha⁻¹) in the 0–30 cm soil layer of native grassland were reduced by 31 and 54% after 30 years of crop cultivation. After 4 years of conversion from cropland to perennial grass growing total and particulate organic C pools were increased by 29 and 56%, whereas 4 year cropping abandonment increased particulate organic C by 36%. Rapid increases in total and particulate N were also found in perennial grass growing and cropping abandonment soils. The native grassland soil and soils of cropping abandonment and perennial grass growing had higher carbohydrate C concentrations in the 0–10 cm layer than the cropped soil. The rapid recovery of particulate organic fraction and carbohydrates in the re‐vegetated soils were probably due to higher plant biomass inputs and lower organic matter decomposition compared with those in the cropped soil. Aggregate stability of the 0–30 cm soil layer was significantly decreased by crop cultivation but showed a good recovery after 4 year re‐vegetations. This study suggests that reduction of soil organic matter and aggregate stability under crop cultivation may be remedied by cropping abandonment or perennial grass growing. Copyright © 2008 John Wiley & Sons, Ltd.     

Changes in carbon and nitrogen of Chernozem soil along a cultivation chronosequence in a semi‐arid grassland

Changes in the carbon (C) stock of grassland soil in response to land use change will increase atmospheric CO₂, and consequently affect the climate. In this study we investigated the effects of land use change on soil organic C (SOC) and nitrogen (N) along a cultivation chronosequence in the Xilin River Basin, China. The chronosequence consisted of an undisturbed meadow steppe, a 28‐year‐old cropland and a 42‐year‐old cropland (abbreviated as Steppe, Crop‐28 Y and Crop‐42Y, respectively). Crop‐28Y and Crop‐42Y were originally created on the meadow steppe in 1972 and 1958, respectively. The soil samples, in ten replications from three depth increments (0–10, 10–20 and 20–30 cm), were collected, respectively, in the two cropland fields and the adjacent undisturbed steppe. Bulk density, SOC, total N and 2 m KCl‐extractable mineral N including ammonium and nitrate were measured. Our results showed that the greatest changes in the measurements occurred in the 0–10 cm soil depth. The SOC stock in the upper 30‐cm soil decreased by 9.83 Mg C ha⁻¹ in Crop‐28Y and 21.87 Mg C ha⁻¹ in Crop‐42Y, which indicated that approximately 10 and 25% of the original SOC of the steppe had been emitted over 28 and 42 years, respectively. Similarly, the total N lost was 0.66 Mg N ha⁻¹ and 1.18 Mg N ha⁻¹, corresponding to approximately 9% and 16%, respectively, of the original N at the same depth and cropping duration as those noted for SOC. The mineral N concentration in the soil of both the two croplands was greater than that in the steppe soil, and the ammonium‐N was less affected by cultivation than the nitrate‐N. The extent of these changes depended on soil depth and cropland age. These effects of cultivation were much greater in the top 10 cm of soil than in deeper soil, and also greater in Crop‐42Y than in Crop‐28Y. The findings are significant for assessing the C and N sequestration potential of the land use changes associated with grassland conversion, and suggest that improved management practices are needed to sequester SOC and total N in the cropped soil in a semi‐arid grassland.     

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.     

Effect of land‐use on soil nutrients and microbial biomass of an alpine region on the northeastern Tibetan plateau,China

Land‐use patterns affect the quantity and quality of soil nutrients as well as microbial biomass and respiration in soil. However, few studies have been done to assess the influence of land‐use on soil and microbial characteristics of the alpine region on the northeastern Tibetan plateau. In order to understand the effect of land‐use management, we examined the chemical properties and microbial biomass of soils under three land‐use types including natural grassland, crop‐field (50 + y of biennial cropping and fallow) and abandoned old‐field (10 y) in the area. The results showed that the losses of soil organic carbon (SOC) and total nitrogen (TN) were about 45 and 43 per cent, respectively, due to cultivation for more than 50 y comparing with natural grassland. Because of the abandonment of cultivation for about a decade, SOC and TN were increased by 27 and 23 per cent, respectively, in comparison with the crop field. Microbial carbon (ranging from 357·5 to 761·6 mg kg⁻¹ soil) in the old‐field was intermediate between the crop field and grassland. Microbial nitrogen (ranging from 29·9 to 106·7 mg kg⁻¹ soil) and respiration (ranging from 60·4 to 96·4 mg CO₂‐C g⁻¹ C_mic d⁻¹) were not significantly lower in the old‐field than those in the grassland. Thus it could be concluded that cultivation decreased the organic matter and microbial biomass in soils, while the adoption of abandonment has achieved some targets of grassland restoration in the alpine region of Gansu Province on the northeastern Tibetan plateau. Copyright © 2010 John Wiley & Sons, Ltd.     

SOIL ORGANIC CARBON STOCK AND FRACTIONS IN RELATION TO LAND USE AND SOIL DEPTH IN THE DEGRADED SHIWALIKS HILLS OF LOWER HIMALAYAS

The proportional differences in soil organic carbon (SOC) and its fractions under different land uses are of significance for understanding the process of aggregation and soil carbon sequestration mechanisms. A study was conducted in a mixed vegetation cover watershed with forest, grass, cultivated and eroded lands in the degraded Shiwaliks of the lower Himalayas to assess land‐use effects on profile SOC distribution and storage and to quantify the SOC fractions in water‐stable aggregates (WSA) and bulk soils. The soil samples were collected from eroded, cultivated, forest and grassland soils for the analysis of SOC fractions and aggregate stability. The SOC in eroded surface soils was lower than in less disturbed grassland, cultivated and forest soils. The surface and subsurface soils of grassland and forest lands differentially contributed to the total profile carbon stock. The SOC stock in the 1.05‐m soil profile was highest (83.5 Mg ha⁻¹) under forest and lowest (55.6 Mg ha⁻¹) in eroded lands. The SOC stock in the surface (0–15 cm) soil constituted 6.95, 27.6, 27 and 42.4 per cent of the total stock in the 1.05‐m profile of eroded, cultivated, forest and grassland soils, respectively. The forest soils were found to sequester 22.4 Mg ha⁻¹ more SOC than the cultivated soils as measured in the 1.05‐m soil profiles. The differences in aggregate SOC content among the land uses were more conspicuous in bigger water‐stable macro‐aggregates (WSA > 2 mm) than in water‐stable micro‐aggregates (WSA < 0.25 mm). The SOC in micro‐aggregates (WSA < 0.25 mm) was found to be less vulnerable to changes in land use. The hot water soluble and labile carbon fractions were higher in the bulk soils of grasslands than in the individual aggregates, whereas particulate organic carbon was higher in the aggregates than in bulk soils. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of nitrogen deposition on soil organic carbon fractions in the subtropical forest ecosystems of S China

Experiments were conducted between 2003 and 2008 to examine how N additions influence soil organic C (SOC) and its fractions in forests at different succession stages in the subtropical China. The succession stages included pine forest, pine and broadleaf mixed forest, and old‐growth monsoon evergreen broadleaf forest. Three levels of N (NH₄NO₃)‐addition treatments comprising control, low‐N (50 kg N ha^–1 y^–1), and medium‐N (100 kg N ha^–1 y^–1) were established. An additional treatment of high‐N (150 kg N ha^–1 y^–1) was established in the broadleaf mixed forest. Soil samples were obtained in July 2008 for analysis. Total organic C (TOC), particulate organic C (POC, > 53 μm), readily oxidizable organic C (ROC), nonreadily oxidizable organic C (NROC), microbial biomass C (MBC), and soil properties were analyzed. Nitrogen addition affected the TOC and its fractions significantly. Labile organic‐C fractions (POC and ROC) in the topsoil (0–10 cm) increased in all the three forests in response to the N‐addition treatments. NROC within the topsoil was higher in the medium‐N and high‐N treatments than in the controls. In the topsoil profiles of the broadleaf forest, N addition decreased MBC and increased TOC, while no significant effect on MBC and TOC occurred in the pine and mixed forests. Overall, elevated N deposition increased the availability of labile organic C (POC and ROC) and the accumulation of NROC within the topsoil irrespective of the forest succession stage, and might enhance the C‐storage capacity of the forest soils.     

Soil Organic Carbon and Inorganic Carbon Accumulation Along a 30‐year Grassland Restoration Chronosequence in Semi‐arid Regions (China)

Carbon accumulation is an important research topic for grassland restoration. It is requisite to determine the dynamics of the soil carbon pools [soil organic carbon (SOC) and soil inorganic carbon (SIC)] for understanding regional carbon budgets. In this study, we chose a grassland restoration chronosequence (cropland, 0 years; grasslands restored for 5, 15 and 30 years, i.e. RG5, RG15 and RG30, respectively) to compare the SOC and SIC pools in different soil profiles. Our results showed that SOC stock in the 0‐ to 100‐cm soil layer showed an initial decrease in RG5 and then an increase to net C gains in RG15 and RG30. Because of a decrease in the SIC stock, the percentage of SOC stock in the total soil C pool increased across the chronosequence. The SIC stock decreased at a rate of 0·75 Mg hm⁻² y⁻¹. The change of SOC was higher in the surface (0–10 cm, 0·40 Mg hm⁻² y⁻¹) than in the deeper soil (10–100 cm, 0·33 Mg hm⁻² y⁻¹) in RG5. The accumulation of C commenced >5 years after cropland conversion. Although the SIC content decreased, the SIC stock still represented a larger percentage of the soil C pool. Moreover, the soil total carbon showed an increasing trend during grassland restoration. Our results indicated that the soil C sequestration featured an increase in SOC, offsetting the decrease in SIC at the depth of 0–100 cm in the restored grasslands. Therefore, we suggest that both SOC and SIC should be considered during grassland restoration in semi‐arid regions. Copyright © 2016 John Wiley & Sons, Ltd.     

Nitrogen pools and turnover in arable soils under different durations of organic farming: I: Pool sizes of total soil nitrogen,microbial biomass nitrogen,and potentially mineralizable nitrogen

Soil organic matter contents, soil microbial biomass, potentially mineralizable nitrogen (N) and soil pH values were investigated in the Ap horizons of 14 field plots at 3 sites which had been under organic farming over various periods. The objective was to test how these soil properties change with the duration of organic farming. Site effects were significant for pH values, microbial biomass C and N, and for potentially mineralizable N at 0—10 cm depth. The contents of total organic C, total soil N, and potentially mineralizable N tended to be higher in soils after 41 versus 3 years of organic farming, but the differences were not significant. Microbial biomass C and N contents were higher after 41 years than after 3 years of organic farming at 0—10 cm depth, and the pH values were increased at 10—27 cm depth. Nine years of organic farming were insufficient to affect soil microbial biomass significantly. Increased biomass N contents help improve N storage by soil micro‐organisms in soils under long‐term organic farming.     

Land use effects on the dynamics of soil C, N and microbes in the water-wind erosion crisscross region of the northern Loess Plateau, China

The water-wind erosion crisscross region of the northern Loess Plateau in China is under constant pressure from severe erosion due to its windy and dry climate and intensive human activities. Identifying sustainable land use patterns is key to maintaining ecosystem sustainability in the area. Our aim was to appraise the impacts of different land use regimes on the dynamics of soil total organic C(TOC), total N(TN), and microbes in a typical watershed in the northern Loess Plateau to identify sui...     

Soil carbon pools of reclaimed minesoils under grass and forest landuses

Minesoils are characterized by low soil organic matter and poor soil physicochemical environment. Mine soil reclamation process has potential to restore soil fertility and sequester carbon (C) over time. Soil organic C (SOC) pool and associated soil properties were determined for reclaimed minesoils under grass and forest landuses of varied establishment year. Three grassland sites of 30, 9, and 1 years after reclamation (G30, G9, and G1) and two forest sites, 11 years after reclamation (RF) and undisturbed stand of 40 years (UF), were selected within four counties (Morgan, Muskingum, Noble, and Coshocton) of southeastern Ohio. Soil bulk density (BD) of reclaimed forest (RF) soil was significantly higher than undisturbed forest (UF) soils within 10–40 cm soil depth profile. Reclamation process increased soil pH from slightly acidic to alkaline and decreased the soil EC in both landuses. Among grassland soils, significant changes in SOC and total soil N contents were observed within 0–10 cm soil depth. SOC contents of G30 (29.7 Mg ha⁻¹) and G9 (29.5 Mg ha⁻¹) were significantly higher than G1 soils (9.11 Mg ha⁻¹). Soil N content was increased from G1 (0.95 Mg ha⁻¹) to G9 (2.00 Mg ha⁻¹) site and then the highest value was found under G30 (3.25 Mg ha⁻¹) site within 0–10 cm soil depth. UF soils had significantly higher SOC and total N content than RF soils at 0–10 and 10–20 cm soil depths. Copyright © 2009 John Wiley & Sons, Ltd.     

Soil organic‐matter stocks and characteristics along an Alpine elevation gradient

Mountain regions are known to be especially vulnerable to climatic changes; however, information on the climate sensitivity of alpine ecosystems is still scarce to date. In this study, we investigate the impacts of climate and vegetation composition on soil organic‐matter (SOM) stocks and characteristics along an elevation gradient (900 to 1900 m asl) in the Austrian Limestone Alps. The soils classified as Leptic Histosols, i.e., organic soils directly overlying the calcareous bedrock. Soil organic‐carbon stocks (SOC; mean ± standard deviation) to bedrock increased in the low‐elevation forest sites from 19 ± 3 kg m^–2 (900 m asl) to 31 ± 3 kg m^–2 (1300 m asl), reached a maximum (38 ± 5 kg m^–2) in the shrubland at 1500 m asl, but decreased again in the high‐elevation grassland sites (26 ± 3 kg m^–2 at 1700 m asl and 13 ± 3 kg m^–2 at 1900 m asl). Thermogravimetic measurements and Fourier‐transform infrared spectroscopy (FTIR) suggest that the upper soil layers were dominated by more labile organic compounds, whereas more persistent materials increased with depth. Along the studied climosequence, the aliphatic FTIR band (2920 cm^–1) was lower in the low‐elevation forest sites compared to the high‐elevation grassland sites. Most other FTIR bands did not change with altitude, but were related to specific site conditions, such as vegetation composition and associated differences in soil pH. Our results demonstrate that differences in SOM stocks and characteristics are not consistently related to variations in climatic conditions along the studied elevation gradient, but are strongly affected by the vegetation composition, their C input and litter quality. This, in turn, is expected to shift in response to climate change.     

Carbon stock assessment and soil carbon management in agricultural land‐uses in Thailand

The organic carbon pool in agricultural land‐uses is capable of enhancing agricultural sustainability and serving as a potential sink of atmospheric carbon dioxide. A study was carried out to estimate and map carbon stock of different agricultural land‐uses in a sub‐watershed of Thailand and to assess the land‐use sustainability with respect to carbon management. A quadrat sampling methodology was adopted to estimate the biomass and its carbon content of 11 different land‐uses in the study area. Existing soil data were used to calculate the soil carbon. GIS was used for integrating biomass carbon, soil carbon and carbon stock mapping. Roth carbon model was used to project the soil carbon of present land‐uses in the coming 10 years and based on which the sustainability of land‐uses was predicted. The total carbon stock of agricultural land‐uses was estimated to be 20·5 Tg, of which 41·49 per cent was biomass carbon and 58·51 per cent was soil carbon. Among the land‐uses, para rubber had the highest average biomass C (136·34 Mg C ha⁻¹) while paddy had the lowest (7·08 Mg C ha⁻¹). About four‐fifths of agricultural land‐uses in the watershed are sustainable in maintaining the desired level of soil carbon in coming 10 years while one‐fifths are unstable. Such information on carbon stock could be valuable to develop viable land‐use options for agricultural sustainability and carbon sequestration. Copyright © 2007 John Wiley & Sons, Ltd.     

Soil carbon sequestration in China through agricultural intensification,and restoration of degraded and desertified ecosystems

The industrial emission of carbon (C) in China in 2000 was about 1 Pg yr⁻¹, which may surpass that of the United States (1ċ84 Pg C) by 2020. China's large land area, similar in size to that of the United States, comprises 124 Mha of cropland, 400 Mha of grazing land and 134 Mha of forestland. Terrestrial C pool of China comprises about 35–60 Pg in the forest and 120–186 Pg in soils. Soil degradation is a major issue affecting 145 Mha by different degradative processes, of which 126 Mha are prone to accelerated soil erosion. Total annual loss by erosion is estimated at 5ċ5 Pg of soil and 15ċ9 Tg of soil organic carbon (SOC). Erosion‐induced emission of C into the atmosphere may be 32–64 Tg yr⁻¹. The SOC pool progressively declined from the 1930s to 1980s in soils of northern China and slightly increased in those of southern China because of change in land use. Management practices that lead to depletion of the SOC stock are cultivation of upland soils, negative nutrient balance in cropland, residue removal, and soil degradation by accelerated soil erosion and salinization and the like. Agricultural practices that enhance the SOC stock include conversion of upland to rice paddies, integrated nutrient management based on liberal use of biosolids and compost, crop rotations that return large quantities of biomass, and conservation‐effective systems. Adoption of recommended management practices can increase SOC concentration in puddled soil, red soil, loess soils, and salt‐affected soils. In addition, soil restoration has a potential to sequester SOC. Total potential of soil C sequestration in China is 105–198 Tg C yr⁻¹ of SOC and 7–138 Tg C yr⁻¹ for soil inorganic carbon (SIC). The accumulative potential of soil C sequestration of 11 Pg at an average rate of 224 Tg yr⁻¹ may be realized by 2050. Soil C sequestration potential can offset about 20 per cent of the annual industrial emissions in China. Copyright © 2002 John Wiley & Sons, Ltd.     

滇中尖山河小流域不同土地利用类型土壤活性有机碳分布特征

土壤活性有机碳对土地利用方式最为敏感,定量分析不同土地利用方式对土壤活性有机碳分布特征的影响对流域的土壤碳循环研究具有重要意义。从滇中尖山河小流域坡耕地、荒草地、林地、园地4种不同土地利用类型角度,系统地分析了0—10,10—20,20—30 cm土层土壤有机碳（SOC）、微生物有机碳（MBC）、易氧化有机碳（EOC）及可溶性有机碳（DOC）的分布特征及其相关性。结果表明:不同土地利用类型下土壤SOC,MBC,EOC,DOC整体均表现为园地 > 林地 > 坡耕地 > 荒草地;4种土地利用类型MBC,EOC,DOC整体上随着土层深度的增加而逐渐降低,且主要分布在0—20 cm土层,在20—30 cm土层含量较低（低于30%）;4种土地利用类型下SOC和MBC,EOC,DOC呈极显著正相关关系,MBC,EOC,DOC两两之间也表现出极显著正相关。综上,退耕还林以及在荒草地种植人工林可作为提高土壤有机碳及活性有机碳含量的有效措施,并将在减少流域水土流失和面源污染、改善土壤质量、恢复土壤肥力等方面起到重要作用。     

Microbial biomass nitrogen pool in soils from a warm temperate grassland,and from deciduous and evergreen forests in Chiba,central Japan

We evaluated the status of the microbial biomass N pool in grassland, and in deciduous and evergreen forest soils in Chiba, central Japan. Microbial biomass N, a labile fraction of total N in the soil, ranged from 6.96 g N m^-2 (15 cm depth) in the grassland to 24.8 g in the deciduous and 20.7 g in the evergreen soils, on a landscape basis. Thus the pattern in the grassland and in the forest soils differed. The N flush measured by a fumigation-incubation method indicated that in the grassland soil microbial biomass N was underestimated by a factor of 2.6 compared with the results from a fumigation-extraction method, because of heavy N immobilization in the microbial biomass. This was in contrast to results from the forest soils, which did not immobilize N. Thus, the forest soils were in a steady-state condition compared with the grassland which formed a seral phase in the ecological succession. Simple correlation coefficients indicated a significant positive relationship between biomass N and organic C in the soil and the N concentration in the litter, the main component of organic matter in the soils of the three ecosystems.     

黄土丘陵区不同土地利用方式对土壤微生物量碳氮磷的影响

为探讨植被区与土地利用方式对土壤微生物量的影响,在陕西省延河流域森林区、森林草原区和草原区采集5种土地利用方式下的土壤剖面样品(0-10cm,10-30cm),并对其微生物量碳(SMBC)、微生物量氮(SMBN)和微生物量磷(SMBP)及土壤理化性质进行了分析。结果表明,微生物量磷的含量在3个植被区中均是在农地、撂荒地中相对较高,微生物量碳、氮在森林区表现为:乔木林地>农地在森林草原区表现为:灌木林地>天然草地>乔木林地>农地>撂荒地在草原区表现为:天然草地>乔木林地>灌木林地>农地>撂荒地。相同土地利用方式下,土壤养分和微生物量在森林区最高,森林草原区次之,草原区最低。相关分析表明,微生物量碳、氮、磷、代谢熵、微生物量碳氮比与土壤养分相关性极为密切。因此,土壤微生物量能够作为评价土壤质量的生物学指标。不同植被区不同土地利用方式对土壤质量的改善作用不同,林地和天然草地作用效果好,对土壤微生物量的提高有明显的促进作用。     

Soil microbial biomass and activity: the effect of site characteristics in humid temperate forest ecosystems

Microbial biomass, respiratory activity, and in‐situ substrate decomposition were studied in soils from humid temperate forest ecosystems in SW Germany. The sites cover a wide range of abiotic soil and climatic properties. Microbial biomass and respiration were related to both soil dry mass in individual horizons and to the soil volume in the top 25 cm. Soil microbial properties covered the following ranges: soil microbial biomass: 20 µg C g^–1–8.3 mg C g^–1 and 14–249 g C m^–2, respectively; microbial C–to–total organic C ratio: 0.1%–3.6%; soil respiration: 109–963 mg CO₂‐C m^–2 h^–1; metabolic quotient (qCO₂): 1.4–14.7 mg C (g C_mic)^–1 h^–1; daily in‐situ substrate decomposition rate: 0.17%–2.3%. The main abiotic properties affecting concentrations of microbial biomass differed between forest‐floor/organic horizons and mineral horizons. Whereas microbial biomass decreased with increasing soil moisture and altitude in the forest‐floor/organic horizons, it increased with increasing N_tot content and pH value in the mineral horizons. Quantities of microbial biomass in forest soils appear to be mainly controlled by the quality of the soil organic matter (SOM), i.e., by its C : N ratio, the quantity of N_tot, the soil pH, and also showed an optimum relationship with increasing soil moisture conditions. The ratio of C_mic to C_org was a good indicator of SOM quality. The quality of the SOM (C : N ratio) and soil pH appear to be crucial for the incorporation of C into microbial tissue. The data and functional relations between microbial and abiotic variables from this study provide the basis for a valuation scheme for the function of soils to serve as a habitat for microorganisms.     

Soil Property Changes After Conversion from FOrest to Pasture in Mount Sacinka,Artvin, Turkey

Turkey's forests have been continuously facing conversion into both agriculture and pasturelands, causing not only degradation and fragmentation of forested lands but also negative changes in soil properties that have not been thoroughly investigated. In order to determine possible changes in some physical and hydrophysical soil parameters along with the dispersion ratio between natural coppice forests and the neighbouring forest‐to‐grassland converted areas, a foothill of Mount Sacinka in Artvin was chosen as a research area. Besides land use, possible effects of elevation change on soil properties due to the mountainous and moderately steep landscape of the region were also taken into consideration. The soil samples were analysed for soil texture, permeability, field capacity, bulk density, organic matter, pH and dispersion ratio. The results indicated that whereas permeability (43·05 mm h⁻¹ in forest and 18·82 mm h⁻¹ in pasture), field capacity (43·45% in forest and 38·08% in pasture) and organic matter (6·36% in forest and 5·34% in pasture) values turned out to be higher in forest soils, bulk density (0·91 g cm⁻³ in forest and 1·06 g cm⁻³ in pasture) and pH (5·89 in forest and 6·55 in pasture) values were low in grassland soils, meaning that conversion has negative effects on soil properties. Additionally, the mean dispersion ratios of 27·55% and 33·58% for forest and pastureland soils, respectively, indicated soil erosion problems in both land uses. In addition, as for elevation effect, forest soils especially showed better characteristics at higher elevations with high permeability, field capacity and organic matter and low pH and dispersion ratio. Copyright © 2015 John Wiley & Sons, Ltd.