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1.
Microbial biomass, β-glucosidase and β-glucosaminidase activities, and availability, storage, and age of soil organic C were investigated after 26 years of conversion from sugarcane (Saccharum officinarum) to forest (Eucaliptus robusta or Leucaena leucocephala), pasture (mixture of tropical grasses), and to vegetable cropping (agriculture) in a vertisol in Puerto Rico. Soil organic C (SOC) at 0–100 cm was similar under Leucaena (22.8 kg C/m2), Eucalyptus (18.6 kg C/m2), and pasture (17.2 kg C/m2), which were higher than under agriculture (13.0 kg C/m2). Soil organic N (SON) at 0–100 cm was similar under the land uses evaluated which ranged from 1.70 (under agriculture) to 2.28 kg N/m2 (under Leucaena forest). Microbial biomass C (MBC) and N (MBN) of the 0–15-cm soil layer could be ranked as: pasture > Leucaena = Eucalyptus > agriculture. The percentages of SOC and SON present as MBC and MBN, respectively, were nearly 1% in pasture and less than 0.50% in forest under Leucaena or Eucalyptus and agricultural soil. The activity of β-glucosidase of the 0–15-cm soil layer could be ranked as: Leucaena = Eucalyptus > pasture > agriculture; while β-glucosaminidase activity was ranked as: Eucalyptus > Leucaena = pasture > agriculture. The soil δ 13C changed from 1996 to 2006 in forest under Eucalyptus (18.7‰ to 21.2‰), but not under Leucaena (20.7‰ to 20.8‰). The soil under Leucaena preserved a greater proportion of old C compared to the forest under Eucalyptus; the former had an increased soil mineralizable C from the current vegetation inputs. The soil under agriculture had the lowest enzyme activities associated with C cycling, lowest percentage of SOC as MBC, highest percentage of SOC present as mineralizable C, and highest percentage of MBC present as mineralizable C compared to the other land uses.  相似文献   

2.
The conversion of tropical forests to agricultural land use is considered as a major cause for a decline in soil organic carbon (SOC) stocks. However, the extent and impact of different land uses on SOC stock development is highly uncertain, especially for tropical Africa due to a lack of reliable data. Interactions of SOC with the soil mineral phase can modify the susceptibility of SOC to become mineralized. Pedogenic Fe‐, Al‐oxides and clay potentially affect SOC stabilization in highly weathered soils typically found in the humid tropics. The aim of our study was to determine the impact of different land uses on SOC stock on such soils. For that purpose, 10 pedologically similar, deeply weathered acidic soils (Acrisols, Alisols) in the Eastern Usambara Mountains (Amani Nature Reserve, NE Tanzania) under contrasting land use were sampled to a depth of 100 cm. The calculated mean SOC stocks were 17.5 kg C m?2, 16.8 kg C m?2, 16.9 kg C m?2, and 20.0 kg C m?2 for the four forests, two tea plantations, three croplands, and one homegarden, respectively. A significant difference in mean SOC stock of 1.3 kg C m?2 was detected between forest and cropland land use for the 0–10 cm depth increment. No further significant impacts of land use on SOC stocks were observed. All soils have a clearly clay‐dominated texture. They are characterized by high content of pedogenic oxides with 29 to 47 g kg?1 measured for the topsoils and 36 to 65 g kg?1 for the subsoils. No positive significant relationship was found between SOC and clay content. Statistically significant positive relationships existed between oxalate‐extractable Fe, Al, and SOC content for cropland soils only. Compared to data published in literature the SOC stocks determined in our study were generally high independent of the established land use. It appears that efficient SOC stabilization mechanisms are counteracting the higher disturbance regime under agricultural land use in these highly weathered tropical soils.  相似文献   

3.
The objective of this work was to evaluate the C and N stocks and organic‐C fractions in soil under mixed forest stands of Scots pine (Pinus sylvestris L.) and Sessile oak (Quercus petraea [Matt.] Liebl.) of different ages in NE Germany. Treatments consisted of pure pine (age 102 y), and pine (age 90–102 y) mixed with 10‐, 35‐, 106‐, and 124‐y‐old oak trees. After sampling O layers, soils in the mineral layer were taken at two different depths (0–10 and 10–20 cm). Oak admixture did not affect total organic‐C (TOC) and N stocks considering the different layers separately. However, when the sum of TOC stocks in the organic and mineral layers was considered, TOC stocks decreased with increasing in oak age (r2 = 0.58, p < 0.10). The microbial C (CMB) was not directly correlated with increase of oak age, however, it was positively related with presence of oak species. There was an increase in the percentage of the CMB‐to‐TOC ratio with increase of oak‐tree ages. On average, light‐fraction C (CLF) comprised 68% of the soil TOC in upper layer corresponding to the highest C pool in the upper layer. CLF and heavy‐fraction C (CHF) were not directly affected by the admixture of oak trees in both layers. The CHF accounted on average for 30% and 59% of the TOC at 0–10 and 10–20 cm depths, respectively. Despite low clay contents in the studied soils, the differences in the DCB‐extractable Fe and Al affected the concentrations of the CHF and TOC in the 10–20 cm layers (p < 0.05). Admixture of oak in pine stands contributed to reduce topsoil C stocks, probably due to higher soil organic matter turnover promoted by higher quality of oak litter.  相似文献   

4.
Forests represent an important resource for mitigating the greenhouse effect, but which is the contributions of the different forest types in sequestering and keeping soil C for a longer time is still uncertain, particularly in the Mediterranean area. The aim of this work is to quantify the soil organic C (SOC) stock in the 0–30 and 0–100?cm depths of mineral soil, according to the main forest types—conifers, broadleaf and evergreen broadleaf—and the different climatic zones of Spain, using a database comprising records of 1,974 pedons. Conifers and broadleaf forests show a trend in SOC stock distribution, with the stocks decreasing with increasing Mediterranean conditions. On average, in the 0–30?cm depth, the soils under broadleaf store the highest amount of SOC (5.9?±?0.1?kg?m?2), followed by conifers (5.6?±?0.1?kg?m?2) and evergreen broadleaf soils with an amount always lower (3.4?±?0.2?kg?m?2). Climate and forest cover are the principal factors in determining the amount of SOC stored in Spanish forests. The significantly higher amount of SOC found in conifers and broadleaf forests than the evergreen broadleaf forests leads us to hypothesize a decrease in the SOC if climate change will increase drought periods with a consequent expansion of this latter forest type. Correlations between the SOC stocks under the different forest types, climate and soil features support the major role of climate and vegetation in controlling SOC sequestration in the Mediterranean area, while the effect of texture is less pronounced. Assigning a precise SOC stock to the different forest types, according to each climatic zone, would notably help to obtain an accurate SOC estimate at national level and for future assessments of the status of this large C reservoir.  相似文献   

5.
The Brazilian Cerrado is a large and expanding agricultural frontier, representing a hotspot of land-use change (LUC) from natural vegetation to farmland. It is known that this type of LUC impacts soil organic matter (SOM) dynamics, particularly labile carbon (C) pools (living and non-living), decreasing soil health and agricultural sustainability, as well as increasing soil greenhouse gas (GHG) emissions, and accelerating global climate change. In this study, we quantified the changes in the quantity and quality of SOM and GHG fluxes due to changes in land use and cropland management in the Brazilian Cerrado. The land uses studied were native vegetation (NV), pasture (PA) and four croplands, including the following management types: conventional tillage with a single soybean crop (CT), and three no-tillage systems with two crops cultivated in the same year (i.e., soybean/sorghum (NTSSo), soybean/millet (NTSMi) and maize/sorghum (NTMSo)). Soil and gases were sampled in the rainy season (November, December and January) and dry season (May, July and September). The highest soil C and nitrogen (N) stocks (6.7 kg C m−2 and 0.5 kg N m−2, 0–0.3-m layer) were found under NV. LUC reduced C stocks by 25% in the CT and by 10% in the PA and NT. Soil N stocks were 30% lower in the PA and NTMSo and 15% lower in the croplands with soybean compared to NV. δ13C values clearly distinguished between the C-origin from NV (−25‰) and that from other land uses (−16‰). Soil (0–0.1 m) under NV also presented higher labile-C (625 g C m−2), microbial-C (70 g C m−2) and microbial-N (5.5 g N m−2), whereas other land uses presented values three times lower. GHG emissions (expressed as C-equivalent) were highest in the NV (1.2 kg m−2 year−1), PA (1.3 kg m−2 year−1) and NTMSo (0.9 kg m−2 year−1) and were positively related to the higher SOM turnover in these systems. Our results suggest that in order to maintain SOM, it is necessary to adopt “best” management practices, that provide large plant residue inputs (above- and belowground). This can be seen as a pathway to achieving high food production with low GHG emissions.  相似文献   

6.
The brigalow clay soils of central Queensland in eastern Australia contain large quantities of nitrate-N in the subsoil beneath shallow rooting cultivated crops. A laboratory incubation study was conducted to determine whether nitrate accumulation at depth beneath these crops was due to in situ nitrogen mineralization. Intact soil cores, 5 cm long and 5 cm diameter, were obtained at four depths to 120 cm beneath cultivated black gram (Vigna mungo) and green panic (Panicum maximum var trichoglume) permanent pasture and incubated for 12 weeks at 60% water-filled pore space and 25°C. Net mineralization of organic N occurred in all soil cores obtained from under black gram with values ranging from 4.3 to 9 mg N kg?1 soil at 12 weeks. Beneath the pasture, net mineralization had not commenced by the end of 12 weeks. Potentially available nitrogen (Na) ranged from 1.2 to 62.7 kg N ha?1 under black gram, and from 10.2 to 136.9 kg N ha?1 under pasture. A significant relationship was observed between Na and total N beneath both crops, and between Na and total C under the pasture. Leaching of N mineralized in the surface layers of soil appears to be the main avenue of nitrate build-up in the subsoil beneath black gram, with subsoil mineralization making only a partial contribution to the accumulated nitrate pool.  相似文献   

7.
The production and composition of leaf litter, soil acidity, exchangeable nutrients, and the amount and distribution of soil organic matter were analyzed in a broad‐leaved mixed forest on loess over limestone in Central Germany. The study aimed at determining the current variability of surface‐soil acidification and nutrient status, and at identifying and evaluating the main factors that contributed to the variability of these soil properties along a gradient of decreasing predominance of European beech (Fagus sylvatica L.) and increasing tree‐species diversity. Analyses were carried out in (1) mature monospecific stands with a predominance of beech (DL 1), (2) mature stands dominated by three deciduous‐tree species (DL 2: beech, ash [Fraxinus excelsior L.], lime [Tilia cordata Mill. and/or T. platyphyllos Scop.]), and (3) mature stands dominated by five deciduous‐tree species (DL 3: beech, ash, lime, hornbeam [Carpinus betulus L.], maple [Acer pseudoplatanus L. and/or A. platanoides L.]). The production of leaf litter was similar in all stands (3.2 to 3.9 Mg dry matter ha–1 y–1) but the total quantity of Ca and Mg deposited on the soil surface by leaf litter increased with increasing tree‐species diversity and decreasing abundance of beech (47 to 88 kg Ca ha–1 y–1; 3.8 to 7.9 kg Mg ha–1 y–1). The soil pH(H2O) and base saturation (BS) measured at three soil depths down to 30 cm (0–10 cm, 10–20 cm, 20–30 cm) were lower in stands dominated by beech (pH = 4.2 to 4.4, BS = 15% to 20%) than in mixed stands (pH = 5.1 to 6.5, BS = 80% to 100%). The quantities of exchangeable Al and Mn increased with decreasing pH and were highest beneath beech. Total stocks of exchangeable Ca (0–30 cm) were 12 to 15 times larger in mixed stands (6660 to 9650 kg ha–1) than in beech stands (620 kg ha–1). Similar results were found for stocks of exchangeable Mg that were 4 to 13 times larger in mixed stands (270 to 864 kg ha–1) than in beech stands (66 kg ha–1). Subsoil clay content and differences in litter composition were identified as important factors that contributed to the observed variability of soil acidification and stocks of exchangeable Ca and Mg. Organic‐C accumulation in the humus layer was highest in beech stands (0.81 kg m–2) and lowest in stands with the highest level of tree‐species diversity and the lowest abundance of beech (0.27 kg m–2). The results suggest that redistribution of nutrients via leaf litter has a high potential to increase BS in these loess‐derived surface soils that are underlain by limestone. Species‐related differences of the intensity of soil–tree cation cycling can thus influence the rate of soil acidification and the stocks and distribution of nutrients.  相似文献   

8.
Abstract

To determine the rates of increase in C and N stocks in the soil and organic layers following afforestation in Andisols, we measured C and N densities in the organic and soil layers at depths of 0–5, 5–15 and 15–30?cm, together with a chronosequence analysis of 4-year-old, 14-year-old and 23-year-old Japanese cedar (Cryptomeria japonica) and 4-year-old, 12-year-old and 25-year-old Hinoki cypress (Chamaecyparis obtusa) plantations. The short-term changes in C and N were confirmed by repeated sampling 5?years after the first sampling. Tree growth, biomass accumulation and organic layers were much greater in Japanese cedar than in Hinoki cypress plantations. Soil C density (kg?m?3) increased and bulk density decreased with stand age in the surface layer (0–5?cm). The average soil C accumulation rate was 22.9?g?C?m?2?year?1 for Japanese cedar and 21.1?g?C?m?2?year?1 for Hinoki cypress. Repeated sampling showed that the rate of increase in C in the surface soil was relatively slow in young stands and that soil C density (kg?m?3) in the subsurface soil did not change over a 5-year period. Although N accumulated in the tree biomass and organic layers, the soil N density (kg?m?3) did not change after afforestation. Although the andic properties of the soil and differences in the planted species did not influence the rate of increase in soil C, soil C density was expected to increase to a concentration greater than 80?g?kg?1, possibly because of the large C accumulation capacity of Andisols.  相似文献   

9.
The effects of atmospheric nitrogen (N) deposition on carbon (C) sequestration in terrestrial ecosystems are controversial. Therefore, it is important to evaluate accurately the effects of applied N levels and forms on the amount and stability of soil organic carbon (SOC) in terrestrial ecosystems. In this study, a multi‐form, small‐input N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station from 2007 to 2011. Three N fertilizers, NH4Cl, (NH4)2SO4 and KNO3, were applied at four rates: 0, 10, 20 and 40 kg N ha?1 year?1. One hundred and eight soil samples were collected at 10‐cm intervals to a depth of 30 cm in 2011. Contents and δ13C values of bulk SOC were measured, as well as three particle‐size fractions: macroparticulate organic C (MacroPOC, > 250 µm), microparticulate organic C (MicroPOC, 53–250 µm) and mineral‐associated organic C (MAOC, < 53 µm). The results show that 5 years of N addition changed SOC contents, δ13C values of the bulk soils and various particle‐size fractions in the surface 10‐cm layer, and that they were dependent on the amounts and forms of N application. Ammonium‐N addition had more significant effects on SOC content than nitrate‐N addition. For the entire soil profile, small additions of N increased SOC stock by 4.5% (0.43 kg C m?2), while medium and large inputs of N decreased SOC stock by 5.4% (0.52 kg C m?2) and 8.8% (0.85 kg C m?2), respectively. The critical load of N deposition appears to be about 20 kg N ha?1 year?1. The newly formed C in the small‐input N treatment remained mostly in the > 250 µm soil MacroPOC, and the C lost in the medium or large N treatments was from the > 53 µm POC fraction. Five years of ammonium‐N addition increased significantly the surface soil POC:MAOC ratio and increased the instability of soil organic matter (SOM). These results suggest that exogenous N input within the critical load level will benefit C sequestration in the alpine meadow soils on the Qinghai–Tibetan Plateau over the short term.  相似文献   

10.
Integrated crop–livestock management systems (ICLS) have been increasingly recommended in Brazilian agroecosystems. However, knowledge of their effect on soil organic carbon (SOC) and total nitrogen (TN) concentrations and stocks is still limited. The study was undertaken to evaluate the effects of ICLS under two tillage and fertilization regimes on SOC and TN concentrations and stocks in the 0–30 cm soil layer, in comparison with continuous crops or pasture. The following soil management systems were studied: continuous pasture; continuous crop; 4 years’ crop followed by 4 years’ pasture and vice-versa. The adjacent native Cerrado area was used as a control. Under the rotation and continuous crop systems there were two levels of soil tillage (conventional and no-tillage) and fertility (maintenance and corrective fertility). The stock calculations were done using the equivalent soil mass approach. The land use systems had a significant effect on the concentrations of SOC and TN in the soil, but no effect was observed for the soil tillage and fertilizer regimes. For these two latter, some significant discrepancies appeared in the distribution of SOC and TN concentrations in the 0–30 cm layer. Carbon storage was 60.87 Mg ha−1 under Cerrado, and ranged from 52.21 Mg ha−1 under the ICLS rotation to 59.89 Mg ha−1 with continuous cropping. The decrease in SOC stocks was approximately 8.5 and 7.5 Mg ha−1, or 14 and 12%, for continuous pasture and ICLS respectively. No-tillage for 10 years after the conversion of conventional tillage to no-tillage under the continuous crop system, and 13 years of conventional tillage in continuous cropping did not result in significant changes in SOC stocks. The SOC and TN stocks in surface layers, using the equivalent soil mass approach rather than the equivalent depth, stress the differences induced by the calculation method. As soil compaction is the principal feature of variability of stocks determinations, the thickness should be avoid in these types of studies.  相似文献   

11.
Land use change (LUC) is known to have a large impact on soil organic carbon (SOC) stocks. However, at a regional scale, our ability to explain SOC dynamics is limited due to the variability generated by inconsistent initial conditions between sample points, poor spatial information on previous land use/land management history and scarce SOC inventories. This study combines the resampling in 2003–2006 of an extensive soil survey in 1950–1960 with exhaustive historical data on LUC (1868–2006) to explain observed changes in the SOC stocks of temperate forest soils in the Belgian Ardennes. Results from resampling showed a significant loss of SOC between the two surveys, associated with a decrease in variability. The mean carbon content decreased from 40.4 to 34.5 g C kg?1 (10.6 to 9.6 kg C m?2), with a mean rate of C change (ΔSOC) of ?0.15 g C kg?1 year?1 (?0.023 kg C m?2 year?1). Soils with high SOC content tended to loose carbon while conversely soils with low SOC tended to gain carbon. Land use change history explained a significant part of past and current SOC stocks as well as ΔSOC during the last 50 years. We show that the use of spatially explicit historical data can help to quantitatively explain changes in SOC content at the regional scale.  相似文献   

12.
Mineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl2) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO3– concentrations. The soil contained more mineral N in autumn (64–133 kg N ha?1 to 120 cm) than in spring (51–96 kg N ha?1), with NO3– comprising 70–77%. No NO3– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l?1 as NO3– initially but < 1 mg N l?1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l?1 during winter. Losses of NO3– were small in surface runoff (0–2 kg N ha?1 year?1). In 1995, 9–19 kg N ha?1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha?1 in 1995 and 4–10 kg N ha?1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha?1 year?1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha?1 year?1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha?1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.  相似文献   

13.
Hedgerows have the potential to influence ecosystem function in livestock‐grazed pasture. Despite this, they are often ignored when quantifying farmland ecosystem service delivery. In this study, we assess the contribution of hedgerows to the ecosystem function of carbon (C) storage, with a particular emphasis on soil organic carbon (SOC). We measured SOC stock (kg C m?2), on an equivalent soil mass basis, at 0–0.15 m depth in pasture adjacent to 38 hedgerows (biotic) and 16 stone walls or fences (abiotic controls) across ten farms in the county of Conwy, Wales, UK. Pasture SOC stock (~7 kg C m?2) was similar adjacent to biotic and abiotic field boundaries, positively associated with soil moisture and negatively with soil bulk density (BD). For biotic boundaries, two further variables were significantly associated with SOC stock, distance from hedgerow (decrease in SOC stock) and slope orientation (upslope SOC stock greater than downslope). For pasture adjacent to hedgerows, a model combining the aforementioned variables (BD, soil moisture, distance from hedgerow, slope orientation) explained 78% of variation in SOC stock. This study demonstrates that whilst hedgerows do have subtle positive effects on SOC stock in adjacent pasture, SOC storage adjacent to field boundaries is influenced more by soil moisture content and BD than field boundary type.  相似文献   

14.

Purpose

Small but highly bioactive labile carbon (C) and nitrogen (N) pools are of great importance in controlling terrestrial C and N fluxes, whilst long-term C and N storage is determined by less labile but relatively large sizes of C and N pools. Little information is available about the effects of global warming and grazing on different forms of C and N pools in the Qinghai?CTibet Plateau of China. The aim of this study was to investigate the effects of warming and grazing on the sizes of different soil labile C and N pools and N transformation in this region.

Materials and methods

A free-air temperature enhancement system in a controlled warming?Cgrazing experiment had been implemented since May 2006. Infrared heaters were used to manipulate temperature, and a moderate grazing intensity was simulated by Tibetan sheep. After 3 years?? warming, soil samples were taken from the four treatment plots: no warming with no grazing; no warming with grazing; warming with no grazing; and warming with grazing. Concentrations of inorganic N in the 40?Ccm soil profiles were measured by a flow injection analyser. Microbial biomass C (MBC) and microbial biomass N (MBN) were measured by the fumigation?Cextraction method, and soluble organic C (SOC) and soluble organic N (SON) were determined by high-temperature catalytic oxidation. Total N (TN), C isotope composition (??13C) and N isotope composition (??15N) were determined using an isotope ratio mass spectrometer. Net N transformation under low temperature was studied in a laboratory incubation experiment.

Results and discussion

Warming and grazing treatments affected soil C and N pools differently, and these effects varied with soil depth. Warming significantly increased TN, MBC, MBN, and SON and decreased ??13C at the 10?C20 and 20?C30 cm soil depths, whilst grazing generally decreased SON at the 10?C20 and 20?C30 cm, and MBC at 20?C30 cm. At the 0?C10 cm depth, neither warming nor grazing alone affects these soil parameters significantly, indicating that there could be considerable perturbation on the soil surface. However, grazing alone increased NO 3 ? ?CN, total inorganic N, SOC and ??15N at the 0?C10 cm depth. Incubated at 4°C, warming (particularly with grazing) led to net immobilization of N, but no-warming treatments led to net N mineralization, whilst nitrification was strong across all these treatments. Correlations between MBC and SOC, and TN and MBN or SON were positive. However, SON was less well correlated with TN and MBN compared with the highly positive correlations between SOC and MBC.

Conclusions

It is clearly demonstrated that warming and grazing affected labile C and N pools significantly, but differently after 3 years?? treatments: Warming tended to enlarge labile C and N pools through increased litter inputs, whilst grazing tended to increase inorganic N pools, decrease SON and accelerate N cycling. Grazing might modify the mode that warming affected soil C and N pools through its strong impacts on microbial processes and N cycling. These results suggested that interactive effects of warming and grazing on C and N pools might have significant implications for the long-term C and N storage and productivity of alpine meadow ecosystem in the Qinghai?CTibet Plateau of China.  相似文献   

15.
Managing soil carbon requires accurate estimates of soil organic carbon (SOC) stocks and its dynamics, at scales able to capture the influence of local factors on the carbon pool. This paper develops a spatially explicit methodology to quantify SOC stocks in two contrasting regions of Southern Spain: Sierra Norte de Sevilla (SN) and Cabo de Gata (CG). Also, it examines the relationship between SOC stocks and local environmental factors. Results showed that mean SOC stocks were 4·3 kg m−2 in SN and 3·0 kg m−2 in CG. Differences in SOC in both sites were not significant, suggesting that factors other than climate have a greater influence on SOC stocks. A correlation matrix revealed that SOC has the highest positive correlation with clay content and soil depth. Based on the land use, the largest SOC stocks were found in grassland soils (4·4 kg m−2 in CG and 5·0 kg m−2 in SN) and extensive crops (3·0 kg m−2 in CG and 5·0 kg m−2 in SN), and the smallest under shrubs (2·8 kg m−2 in CG and 3·2 kg m−2 in SN) and forests soils (4·2 kg m−2 in SN). This SOC distribution is explained by the greatest soil depth under agricultural land uses, a common situation across the Mediterranean, where the deepest soils have been cultivated and natural vegetation mostly remains along the marginal sites. Accordingly, strategies to manage SOC stocks in southern Spain will have to acknowledge its high pedodiversity and long history of land use, refusing the adoption of standard global strategies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

16.

Purpose

So far, the soil organic carbon (SOC) literature is dominated by studies in the humid environments with huge stocks of vulnerable carbon. Limited attention has been given to dryland ecosystems despite being often considered to be highly sensitive to environmental change. Thus, there is insufficient research about the spatial patterns of SOC stocks and the interaction between soil depth, ecohydrology, geomorphic processes, and SOC stocks. This study aimed at identifying the relationship between surface characteristics, vegetation coverage, SOC, and SOC stocks in the arid northern Negev in Israel.

Materials and methods

The study site Sede Boker is ideally suited because of well-researched but variable ecohydrology. For this purpose, we sampled five slope sections with different ecohydrologic characteristics (e.g., soil and vegetation) and calculate SOC stocks. To identify controlling factors of SOC stocks on rocky desert slopes, we compared soil properties, vegetation coverage, SOC concentration, and stocks between the five ecohydrologic units.

Results and discussion

The results show that in Sede Boker, rocky desert slopes represent a significant SOC pool with a mean SOC stock of 0.58?kg?C?m?2 averaged over the entire study area. The spatial variability of the soil coverage represents a strong control on SOC stocks, which varies between zero in uncovered areas and 1.54?kg?C?m?2 on average in the soil-covered areas. Aspect-driven changes of solar radiation and thus of water availability are the dominant control of vegetation coverage and SOC stock in the study area.

Conclusions

The data indicate that dryland soils contain a significant amount of SOC. The SOC varies between the ecohydrologic units, which reflect (1) aspect-driven differences, (2) microscale topography, (3) soil formation, and (4) vegetation coverage, which are of greatest importance for estimating SOC stocks in drylands.  相似文献   

17.
Irrigation of grazed pasture significantly increases plant and animal production, which may in turn increase soil organic carbon (SOC), depending on the balance between primary production and below‐ground allocation of C on the one hand, and the decomposition and export of C from the soil on the other. To evaluate the effect of irrigation on SOC we sampled a grazed pasture field experiment maintained under different irrigation treatments for 62 years. The dry‐land treatment in this experiment only received rainfall at an average of 740 mm year?1. The 10 and 20% irrigation treatments involved application of 100 mm of irrigation when the soil reached 10 and 20% gravimetric moisture content, respectively. The 10 and 20% irrigation treatments received average total annual irrigation inputs of 260 and 770 mm year?1, respectively. The 10 and 20% irrigation treatments increased pasture production by 44 and 74%, respectively, compared with that from the dry‐land. Analysis of soils taken to 1‐m depth revealed that amounts of SOC were not significantly different between the dry‐land (125.5 Mg ha?1) and 10% irrigation (117.8 Mg ha?1) treatments, but these were significantly greater than the 20% irrigation treatment (93.0 Mg ha?1). At 50–100 cm, SOC was also less (34%) for the 20% irrigation treatment than for the 10% irrigation treatment. The relative quantities of carbon (C) and nitrogen (N) in the light fraction (LF) at all soil depths decreased successively from dry‐land to the 20% irrigation treatment, suggesting that wetter soil conditions accelerated decomposition of the LF fraction, a comparatively labile SOC fraction. The C‐to‐N ratio of the bulk soil was also less for the 20% irrigation treatment, indicating more decomposed SOM in the irrigated than in the dry‐land treatment. There were no significant differences in the microbial biomass between the three different irrigation treatments, but the respiration rate (CO2 production) of soil organisms in the 20% irrigation treatment was consistently greater than in the other two treatments. It was concluded that large increases in plant productivity as a result of irrigation had either no effect or significantly reduced SOC stocks under grazed pasture. The reduced SOC content observed in the 20% irrigation treatment was attributed to a combination of increased C losses in animal products and drainage associated with greater stocking, together with accelerated decomposition of organic C resulting from elevated soil moisture maintained throughout the growing season.  相似文献   

18.
The Grain to Green Program in China which began in 1999 led to the conversion of 0.64 million ha of cropland to grassland on steep sloping landscapes. However, the pattern of natural vegetation succession following cropland has not been well represented in previous regional syntheses of land use change effects on soil organic carbon (SOC). A chronosequence study focusing on the vegetation succession and soil carbon stocks was conducted in the center of the Loess Plateau. The chronosequence included fields of 0, 2, 5, 8, 9, 10, 12, 15 and 25 years of self‐restoration after cropland abandonment, as well as a natural grassland reference. Plant coverage, species richness and plant biomass increased significantly with time of cropland abandonment. Over time, the species composition more nearly resembled a natural grasslands community. Cropland abandonment replenished SOC stocks by 3.6 kg C m−2 during the 25‐year self‐restoration, but the SOC accumulation was restricted to the upper soil profiles (0–60 cm). SOC accumulation rate was 88 g C m−2 y−1 in 0–30 cm and 55 g C m−2 y−1 in 30–60 cm soil depth, respectively. These carbon stocks were still significantly lower than those found in the natural grassland soil. Our results suggest that the recovery of plant communities and SOC stocks appears to be slow in this semiarid environment without revegetation effort along with appropriate field management, although the post‐agricultural soils have a high potential for carbon sequestration. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
Tillage practices can potentially afect soil organic carbon (SOC) accumulation in agricultural soils. A 4-year experiment was conducted to identify the influence of tillage practices on SOC sequestration in a double-cropped rice (Oryza sativa L.) field in Hunan Province of China. Three tillage treatments, no-till (NT), conventional plow tillage(PT), and rotary tillage(RT), were laid in a randomized complete block design. Concentrations of SOC and bulk density(BD) of the 0-80 cm soil layer were measured, and SOC stocks of the 0-20 and 0-80 cm soil layers were calculated on an equivalent soil mass(ESM) basis and fixed depth (FD) basis.Soil carbon budget(SCB) under diferent tillage systems were assessed on the basis of emissions of methane(CH4) and CO2 and the amount of carbon (C) removed by the rice harvest. After four years of experiment, the NT treatment sequestrated more SOC than the other treatments. The SOC stocks in the 0-80 cm layer under NT (on an ESM basis) was as high as 129.32 Mg C ha 1,significantly higher than those under PT and RT (P < 0.05). The order of SOC stocks in the 0-80 cm soil layer was NT > PT > RT,and the same order was observed for SCB; however, in the 0-20 cm soil layer, the RT treatment had a higher SOC stock than the PT treatment. Therefore, when comparing SOC stocks, only considering the top 20 cm of soil would lead to an incomplete evaluation for the tillage-induced efects on SOC stocks and SOC sequestrated in the subsoil layers should also be taken into consideration. The estimation of SOC stocks using the ESM instead of FD method would better reflect the actual changes in SOC stocks in the paddy filed, as the FD method amplified the tillage efects on SOC stocks. This study also indicated that NT plus straw retention on the soil surface was a viable option to increase SOC stocks in paddy soils.  相似文献   

20.
The net effect of agriculture on soil carbon is not yet fully understood. While a number of studies on shallow profiles have been published, evidence suggests that carbon stock changes occur in deeper layers. In this study we analyzed the effect of agriculture in the Cerrado soil C looking at changes in seven different profile depths from 0 to 100 cm in a commercial grain farm. We also used isotopic techniques to distinguish between the original Cerrado C3 carbon and the C4 carbon derived from the grasses used in agriculture. At 0–5 cm depth C stocks significantly decreased with cultivation time. The C stock did not change significantly when it was calculated using the 0–10, 0–20, 0–30, 0–50 or 0–75 cm profile (p > 0·05) but increased with cultivation time when the profile considered was 0–100 cm (p < 0·05). A two‐source isotope model revealed that there was a significant increase in carbon derived from C4 grasses for all depths with cultivation time. Annual carbon sequestration rates for the upper 100 cm of soil were 1·1 Mg C ha−1 year−1 for total carbon and 0·8 Mg C4 C ha−1 year−1 for C4 carbon. The oldest area, with 23 years of cultivation, had a soil C stock increase compared to the native Cerrado soil of 17·6%. These findings suggest that commercial grain farms practices may increase soil C stock compared to native Cerrado soil, if a more complete soil profile down to 100 cm is used to assess C stocks. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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