Active Soil Organic Carbon Research Articles

Effects of intensive and extensive management on soil active organic carbon in bamboo forests of China

Aims Our objective was to determine the effects of intensive cultivation on soil organic carbon(SOC) in bam-boo(Phyllostachys heterocycla 'Pubescens') forests.Methods We used the reference land unit method and collected soil samples in intensively and extensively managed bamboo forests in the spring.Important findings Under intensive management,total organic carbon(TOC) decreased by 7.01% and 18.90% and readily oxidized carbon(ROC) decreased by 31.22% and 46.03% in 0-10 and 10-20 cm soil layers,respec-tively.Also,light fraction organic matter(LFOM) decreased 19.87% in the 0-20 cm soil layer.Soil organic car-bon under the two types of management decreased with increasing soil depth,but the ranges of decrease were dif-ferent.The vertical distribution of ROC under extensive management paralleled that of TOC,while both were different under intensive management.LFOM tended to accumulate in surface layers(0-20 cm).TOC,ROC and LFOM were strongly correlated with soil nutrients(p 0.01),and TOC was significantly related to available P(p 0.05).After intensive management,the percentage of ROC to TOC and activity of carbon pool significantly dropped by 26.01% and 50.52%(p 0.05),respectively,in the 0-10 cm soil layer and dropped by 35.51% and 54.41% respectively in the 10-20 cm soil layer.Therefore,a mixture of organic and inorganic manures with the proper ratio should be applied to promote SOC and improve biological and chemical soil activity.

Tillage Effects on Soil Active Organic Carbon in a Purple Paddy Soil

The effect of different tillage systems on the soil organic carbon (SOC), active organic carbon (AOC) and remaining organic carbon (ROC) were studied in a long-term experiment in Chongqing, China. The experiment included five tillage treatments, which are conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SH), no-till and ridge culture with rotation of rice and rape system (LM), no-till and plain culture with rotation of rice and rape system (XM) and tillage and ridge culture with rotation of rice and rape system (LF), respectively. The results showed that the content of SOC declined as the soil depth increased, and presented obvious surface enrichment phenomenon under the no-tillage systems. The order of SOC, AOC, ROC and ROC/SOC in the 0–60 cm soil layer under different tillage systems was LM (22.74 g kg-1) > DP (14.57 g kg-1) > XM (13.73 g kg-1) > LF (13.10 g kg-1) > SH (11.92 g kg-1), DP (3.67 g kg-1) > LF (3.49 g kg-1) > LM (3.28 g kg-1) > XM (3.17 g kg-1) > SH (2.69 g kg-1), LM (18.09 g kg-1) > DP (10.34 g kg-1) > XM (10.12 g kg-1) > LF (9.20 g kg-1) > SH (8.80 g kg-1) and LM (85%) > SH (78%) > XM 77%) > LF (75%) > DP (74%). Compared with other systems, LM significantly increased SOC, ROC and ROC/SOC, which indicated long-term LM system performed good effect for carbon sequestration.

Biodegradation and chemical characteristics of hot-water extractable organic matter from soils under four different vegetation types in the Wuyi Mountains, southeastern China

Water extractable organic carbon (WEOC) is the most active soil organic carbon and plays an important role in global C cycling. Our aim was to investigate the biodegradability and the chemical characteristics of hot-water extractable organic matter (HWEOM) from soils under different vegetation types, including evergreen broad-leaved forest (EBF), coniferous forest (CF), dwarf forest (DF) and alpine meadow (AM), across an altitude gradation in the Wuyi Mountains of southeastern China. We quantified the biodegradability in a 90 day incubation experiment by measuring the loss of hot-water extractable organic carbon (HWEOC) and calculated the sizes of labile and stable HWEOC pool and the respective decomposition rate constants by a double exponential model. We used UV and fluorescence spectroscopic techniques to characterize the structural properties of HWEOM and measured the contents of carbohydrates, phenols and hydrophilic carbon of HWEOM solution. The extent of HWEOC biodegradation was higher in EBF and DF soils with about 20% HWEOC loss, and the labile C accounted for 13–15% of the total HWEOC. HWEOC from CF soils was the least degradable with only 12% HWEOC loss. The estimated mean residence time of the labile HWEOC pool was 8–10 days, whereas that of the stable HWEOC pool ranged from 3 to 6 years. The biodegradability of HWEOC increased with decreasing soil C/N ratio, aromaticity and humification indices, proportion of phenols and increasing proportion of hydrophilic carbon.

Mineralization of active soil organic carbon in particle size fractions of a Brookston clay soil under no-tillage and mouldboard plough tillage

Soil organic matter is a heterogeneous mixture of organic substances with different compositions and stabilities. To enhance soil organic carbon (SOC) sequestration, it is helpful to understand the distribution of SOC among the soil particle size fractions, the stabilities of the SOC within each fraction, and the influence of management practices, such as tillage, on SOC mineralization. Hence, the objectives of this study were to determine the distribution and mineralization rate of active SOC in the sand (53-2000 µm), silt (2-53 µm) and clay (<2 µm) size fractions of a Brookston clay soil under a corn-soybean rotation and three tillage scenarios. The tillages included long-term (24 yr) mouldboard plough (MP83), long-term (24 yr) no-till (NT83) and short-term (10 yr) no-till (NT97). Bulk soil from the top 10 cm was dispersed into sand, silt and clay size fractions by applying ultrasound energy (750 J mL-1) to a 1:4 soil:water suspension. The sand, silt and clay fractions of the three tillages were aerobically incubated at 20°C and 30% moisture (wt/wt), and the CO2-C emissions were measured over 103 d. The SOC contents followed the order clay > silt > sand for all three tillages. On a whole-soil basis and averaged over the tillage treatments, 55.8% of the SOC was in the clay size fraction, 37.2% was in the silt fraction and 7.0% was in the sand fraction. Carbon mineralization rate in the incubated samples decreased over time, and was related to both particle size fraction and tillage practice. There was very good agreement between a first-order decay model (Ct= C1 + C0 (1-e-kt)) and measured SOC mineralization rates for all size fractions and tillages. The C mineralization data indicated that: (1) the SOC in the clay and sand fractions was more decomposable than the SOC in the silt fraction; and (2) the SOC associated with the clay and silt fractions was more readily decomposable under no-till than under mouldboard plough.

Dynamics of methane emission, active soil organic carbon and their relationships in wetland integrated rice-duck systems in Southern China

A randomized field experiment with three replicates was conducted in the subtropical region of China to investigate the effects of integrated rice-duck system (RD) on methane (CH4) emission, active soil organic carbon fractions and their relationships in 2007 and 2008, compared with conventional rice system (CK). Methane emissions were measured at 7–9 days intervals using a closed static chamber technique, and two fractions of active soil organic carbon, namely, dissolved organic carbon (DOC) and microbial biomass carbon (MBC), were analyzed simultaneously. Soil DOC and MBC in RD and CK had similarly distinct seasonal variation patterns within the 2 years. During this time DOC and MBC concentrations were low at the early growth stage, increased during panicle differentiation and heading period, and dropped during grain filling period of rice. CH4 emission fluxes from RD and CK followed a similar seasonal variation pattern both in 2007 and 2008. Two peaks of CH4 emission were observed, the first at the tillering stage, second at panicle differentiation and heading stage. The CH4 cumulative emission was reduced in RD by 19.3 and 19.6% in 2007 and 2008, respectively, compared with CK. Seasonal variation pattern of CH4 emission was regulated by soil DOC, MBC and soil temperature, all of which were significantly positively correlated with methane emissions. Improvement in soil redox status was the predominant reason for significant reduction of CH4 emission in RD. These results clearly indicate that integrated rice-duck system could be an effective mode of rice farming for decrease in methane emission in southern China.

Potential impacts of climate warming on active soil organic carbon contents along natural altitudinal forest transect of Changbai Mountain

Understanding soil carbon fractions and their responses to the global warming is important for improving soil carbon management of natural altitudinal forest ecosystem. In this study, the contents of soil total organic carbon (SOC), soil labile organic carbon (LOC), and microbial biomass carbon (MBC) in soil upper layers (0–20 cm) were measured along a natural altitudinal transect in the north slope of Changbai Mountain. The results showed that under natural conditions the contents of SOC and LOC were largest in Betula ermanii forest (altitude 1996 m), moderate in spruce-fir forest (altitude 1350 m), and smallest in Korean pine mixed broad-leaf tree forest (altitude 740 m). MBC contents in different forest ecosystems decreased in the order of Betula ermanii forest, Korean pine mixed broad-leaf tree forest, and dark coniferous forest. In addition, the responses of SOC, LOC, and MBC to soil warming were conducted by relocating intact soil cores from high- to low-elevation forests for one year. As expected, the soil core relocation caused significant increase in soil temperature but made no significant effect on soil moisture. After one year incubation, soil relocation significantly decreased SOC contents, whereas the contents of LOC, MBC, and the ratios of LOC to SOC and MBC to SOC increased.

Monitoring changes in soil organic carbon pools, nitrogen, phosphorus, and sulfur under different agricultural management practices in the tropics

Soil organic matter not only affects sustainability of agricultural ecosystems, but also extremely important in maintaining overall quality of environment as soil contains a significant part of global carbon stock. Hence, we attempted to assess the influence of different tillage and nutrient management practices on various stabilized and active soil organic carbon pools, and their contribution to the extractable nitrogen phosphorus and sulfur. Our study confined to the assessment of impact of agricultural management practices on the soil organic carbon pools and extractable nutrients under three important cropping systems, viz. soybean-wheat, maize-wheat, and rice-wheat. Results indicated that there was marginal improvement in Walkley and Black content in soil under integrated and organic nutrient management treatments in soybean-wheat, maize-wheat, and rice-wheat after completion of four cropping cycles. Improvement in stabilized pools of soil organic carbon (SOC) was not proportional to the applied amount of organic manures. While, labile pools of SOC were increased with the increase in amount of added manures. Apparently, green manure (Sesbania) was more effective in enhancing the lability of SOC as compared to farmyard manure and crop residues. The KMnO(4)-oxidizable SOC proved to be more sensitive and consistent as an index of labile pool of SOC compared to microbial biomass carbon. Under different cropping sequences, labile fractions of soil organic carbon exerted consistent positive effect on the extractable nitrogen, phosphorus, and sulfur in soil.

Effects of elevated CO2 concentration and nitrogen supply on biomass and active carbon of freshwater marsh after two growing seasons in Sanjiang Plain, Northeast China

An experiments were carried out with treatments differing in nitrogen supply (0, 5 and 15 g N/m2) and CO2 levels (350 and 700 micromol/mol) using OTC (open top chamber) equipment to investigate the biomass of Calamagrostis angustifolia and soil active carbon contents after two years. The results showed that elevated CO2 concentration increased the biomass of C. angustifolia and the magnitude of response varied with each growth period. Elevated CO2 concentration has increased aboveground biomass by 16.7% and 17.6% during the jointing and heading periods and only 3.5% and 9.4% during dough and maturity periods. The increases in belowground biomass due to CO2 elevation was 26.5%, 34.0% and 28.7% during the heading, dough and maturity periods, respectively. The responses of biomass to enhanced CO2 concentrations are differed in N levels. Both the increase of aboveground biomass and belowground biomass were greater under high level of N supply (15 g N/m2). Elevated CO2 concentration also increased the allocation of biomass and carbon in root. Under elevated CO2 concentration, the average values of active carbon tended to increase. The increases of soil active soil contents followed the sequence of microbial biomass carbon (10.6%) > dissolved organic carbon (7.5%) > labile oxidable carbon (6.6%) > carbohydrate carbon (4.1%). Stepwise regressions indicated there were significant correlations between the soil active carbon contents and plant biomass. Particularly, microbial biomass carbon, labile oxidable carbon and carbohydrate carbon were found to be correlated with belowground biomass, while dissolved organic carbon has correlation with aboveground biomass. Therefore, increased biomass was regarded as the main driving force for the increase in soil active organic carbon under elevated CO2 concentration.

Effects of water gradients on soil enzyme activity and active organic carbon composition under Carex lasiocarpa marsh

The responses of soil enzyme activity of freshwater marsh, microbial biomass carbon (MBC), dissolved organic carbon (DOC) and aboveground biomass to water gradients were studied with Carex lasiocarpa pot culture experiment. The relationships between soil enzyme activity and MBC, DOC and aboveground biomass were discussed. The water gradients were W1, 15 cm; W2, −5 cm; W3, −5–5 cm; W4, submerged. The results indicated that acid phosphatase, invertase and urease activities were decreased with the increase of water level, while catalase activity was increased with moisture content increasing. Drying-wetting alternation (W3) increased soil enzyme activities if compared with W1. MBC content followed the order of W3 > W1 > W2 > W4, and the activities of invertase, urease and catalase were significantly positively correlated with MBC ( p < 0.05). DOC content presented the order of W4 > W1 > W3 > W2, and the activities of urease and acid phosphatase were most significantly negatively correlated with DOC ( p < 0.01). In addition, drying-wetting alternation promoted the growth of Carex lasiocarpa. When water submerged plants, the growth of Carex lasiocarpa was significantly inhibited. The aboveground biomass was positively related to soil enzyme activities. There were close relationships between the activities of invertase, urease and catalase and the growth situation of Carex lasiocarpa.

A new model for soil organic carbon turnover using bomb carbon

A new model is presented that uses bomb carbon (14C enrichment) to calculate the turnover times of active soil organic carbon (SOC). The new approach overcomes major deficiencies of older models, particularly in respect to the 14C content of carbon input to SOC and of carbon output from SOC. Calculated turnover times of active carbon for ten European forest sites ranged from 4.0 to 15.1 years with a mean of 8.2 years. The model was successfully validated in soil incubation experiments, where the measured 14C content of (microbially) respired CO2 was on average 9.6% (ΔpM) higher than that of bulk SOC, but agreed considerably well with the modeled 14C content. Furthermore, we used the model's sensitivity tests to show that over long time periods (decades), soils can only sequester small amounts of carbon.

Radiocarbon Signatures of Turnover Rates in Active Soil Organic Carbon Pools

AbstractIdentifying turnover rates in active soil organic carbon (SOC) pools is a critical step toward the understanding of soil nutrient cycling and global C cycles. The mean residence times (MRT) of the dominating active SOC pools in surface soils are usually less than a few decades. This range of MRT is difficult to determine because it is too short for radiocarbon dating and too long for most tracer techniques. I developed a procedure to construct radiocarbon signatures for identifying MRT in active SOC pools based on the residue bomb 14C in the atmosphere. The radiocarbon signature is specific to the year when a soil sample is taken. The sensitivity of the radiocarbon signatures is a function of MRT and the time when a soil sample is taken. This method is sensitive to MRT of active SOC pools in a range from 1 to 80 yr at the present time. Using those radiocarbon signatures, the MRT of active SOC pools in the Morrow Plots (Urbana, IL) and Sanborn Field (Columbia, MO) were estimated at 67 and 34 yr, respectively.