Biodegradability of soil water soluble organic carbon extracted from seven different soils

Water soluble organic carbon （WSOC） is considered the most mobile and reactive soil carbon source and its characterization is an important issue for soil ecology study. A biodegradability test was set up to study WSOC extracted from 7 soils differently managed. WSOC was extracted from soil with water （soil/water ratio of 1：2, W/V） for 30 min, and then tested for biodegradability by a liquid state respirometric test. Result obtained confirmed the finding that WSOC biodegradability depended on the both land use and management practice. These results suggested the biodegradability test as suitable method to characterize WSOC, and provided useful information to soil fertility.

Partitioning of water soluble organic carbon in three sediment size fractions:Effect of the humic substances

Water soluble organic carbon （WSOC） in sediments plays an important role in transference and transformation of aquatic pollutants. This article investigated the inherent mechanisms of how sediemnt grain size affect the partitioning coeffcient （k） of WSOC. Influences of NaOH extracted humic substances were particularly focused on. Sediments were sampled from two cross-sections of the middle Yellow River and sieved into three size fractions （〈 63 μm, 63-100 μm, and 100-300 μm）. The total concentration of WSOC in sediments （Cwsoc） and k were estimated using multiple water-sediment ratio experiments. Results showed that Cwsoc ranged from 0.012 to 0.022 mg/g, while k ranged from 0.8 to 3.9 L/kg. Correlations between the spectrum characteristics of NaOH extracted humic substances and k were analyzed. Strong positive correlations are determined between k and the aromaticity indicators of NaOH extracted humic substances in different sediment size fractions. Comparing with finer fractions （〈 63 μm）, k is higher in larger size fractions （63- 100 μm and 100-300 μm） related to higher aromaticity degree of NaOH extracted humic substances mostly. While negative relationship between k and the area ratio of fourier transform infrared spectroscopy （FT-IR） at 3400 and 1430 cm^-1 implied that the lowest k was related to the highest concentration of acidic humic groups in particles 〈 63 μm. WSOC in finer fractions （〈 63 μm） is likely to enter into pore water, which may further accelerate the transportation of aquatic contaminants from sediment to water.

Fluorescence characteristics of water soluble organic carbon in eastern China

Fluorescence excitation and average molecular weight of 46 water soluble organic matter (WSOC) samples extracted from 20 soil types in eastern China were determined. It was found all samples shared similar spectroscopy. A good linear relationship existed between total organic carbon and excitation in the range of 350 to 450 nm though the content of organic carbon and pH of the samples vary in a wide range. No significant correlation between relative excitation intensity and average molecular weight of WSOC and FA was found, but the partial correlation became significant with pH as the controlling factor for WSOC samples. The relative excitation intensity showed a general trend of increasing from south to north in the study area. The pH value might play an important role in regulating the fluorescent spatial variation of WSOC. S153 A

Effects of Long-Term Winter Planted Green Manure on Distribution and Storage of Organic Carbon and Nitrogen in Water-Stable Aggregates of Reddish Paddy Soil Under a Double-Rice Cropping System

In agricultural systems, maintenance of soil organic matter has long been recognized as a strategy to reduce soil degradation. Manure amendments and green manures are management practices that can increase some nutrient contents and improve soil aggregation. We investigated the effects of 28 yr of winter planted green manure on soil aggregate-size distribution and aggregateassociated carbon（C） and nitrogen（N）. The study was a randomized completed block design with three replicates. The treatments included rice-rice-fallow, rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass. The experiment was established in 1982 on a silty light clayey paddy soil derived from Quaternary red clay（classified as Fe-Accumuli-Stagnic Anthrosols） with continuous early and late rice. In 2009, soil samples were collected（0-15 cm depth） from the field treatment plots and separated into water-stable aggregates of different sizes（i.e., 〉5, 2-5, 1-2, 0.5-1, 0.25-0.5 and 〈0.25 mm） by wet sieving. The long-term winter planted green manure significantly increased total C and N, and the formation of the 2-5-mm water-stable aggregate fraction. Compared with rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass, the rice-rice-fallow significantly reduced 2-5-mm water-stable aggregates, with a significant redistribution of aggregates into micro-aggregates. Long-term winter planted green manure obviously improved C/N ratio and macro-aggregate-associated C and N. The highest contribution to soil fertility was from macro-aggregates of 2-5 mm in most cases.

Distribution characteristics of dissolved organic carbon in annular wetland soil-water solutions through soil profiles in the Sanjiang Plain,Northeast China

Overwhelming evidence reveals that concentrations of dissolved organic carbon （DOC） have increased in streams which brings negative environmental impacts. DOC in stream flow is mainly originated from soil-water solutions of watershed. Wetlands prove to be the most sensitive areas as an important DOC reserve between terrestrial and fluvial biogeosystems. This reported study was focused on the distribution characteristics and the controlling factors of DOC in soil-water solutions of annular wetland, i.e., a dishing wetland and a forest wetland together, in the Sanjiang Plain, Northeast China. The results indicate that DOC concentrations in soilwater solutions decreased and then increased with increasing soil depth in the annular wetland. In the upper soil layers of 0-10 cm and 10-20 cm, DOC concentrations in soil-water solutions linearly increased from edge to center of the annular wetland （R^2 = 0.3122 and R^2 = 0.443）. The distribution variations were intimately linked to DOC production and utilization and DOC transport processes in annular wetland soil-water solutions. The concentrations of total organic carbon （TOC）, total carbon （TC） and Fe（II）, DOC mobility and continuous vertical and lateral flow affectext the distribution variations of DOC in soil-water solutions. The correlation coefficients between DOC concentrations and TOC, TC and Fe（II） were 0.974, 0.813 and 0.753 respectively. These distribution characteristics suggested a systematic response of the distribution variations of DOC in annular wetland soil-water solutions to the geometry of closed depressions on a scale of small catchments. However, the DOC in soil pore water of the annular wetland may be the potential source of DOC to stream flow on watershed scale. These observations also implied the fragmentation of wetland landscape could bring the spatial-temporal variations of DOC distribution and exports, which would bring negative environmental impacts in watersheds of the Sanjiang Plain.

Factors controlling deep-profile soil organic carbon and water storage following Robinia pseudoacacia afforestation of the Loess Plateau in China

Background:Afforestation is a common and effective approach used for the restoration of degraded ecosystems worldwide.In China,Robinia pseudoacacia(RP)is among the main non-native tree species and has been widely planted in revegetation of the Loess Plateau.However,owing to uncertainties regarding soil water consumption and carbon sequestration,it is necessary to assess the suitability and sustainability of R.pseudoacacia in restoration.In this study,we aimed to analyse the dynamic effects of R.pseudoacacia forest on soil carbon storage(SCS)and soil water storage(SWS).Specifically,we investigated the association between soil water content(SWC)and soil organic carbon(SOC)and underlying factors in the 0-500-cm profile of a 10-to 50-year-old chronosequence.Results:The results obtained indicated that the dynamics of SWS and SCS on this time scale could be divided into an initial reduction phase(the initial 20 years after afforestation)and subsequent recovery(20-50 years after afforestation).Compared with in the abandoned land(AL),the net accumulation of SCS in R.pseudoacacia forest was 2.51 Mg·ha^(-1)at 50 years after afforestation,whereas there was a 398.76-mm deficit in SWS.Additionally,the natural succession of R.pseudoacacia forest has contributed to the continuous change in stand structure(e.g.vegetation cover(VC),understory vegetation coverage(UVC),and litter biomass(LB)).Conclusions:These findings indicate that vegetation restoration increases carbon sequestration while causing soil water deficit.Furthermore,stand density(SD)was established to make a predominant contribution to the dynamics of SWS and SCS via its effects in altering vegetation,soil,and litter characteristics.Therefore,high-density plantation forests in the Loess Plateau area should be appropriately thinned to reduce the density of forest stands on the basis of soil erosion control and wind and sand fixation,so as to increase carbon sink with lower water consumption,thus realizing the synergistic development of soil carbon sequestration and water connotation.

Effects of Soluble Organic N on Evaluating Soil N-Supplying Capacity

It is important to study the soluble organic N （SON） extracted during water-logged incubation for evaluating soil Nsupplying capacity. Soil initial SON and mineral N （Nmin）, cumulative soluble organic N and NH4＋-N in leachates during water-logged incubation, mineralization potentials of both easily decomposable N （ND） and resistant N （NR）, and their relationships with N uptake by crop in pot experiment were investigated by using 10 kinds of farmland soils with widely different physical and chemical properties on the Loess Plateau, China, and the effects of SON on evaluating soil Nsupplying capacity were studied. The results showed that the average content of initial SON （23.9 mg kg^-1） of 10 soils was 28.8% of initial total soluble N and 2.4% of soil total N. The percentage of cumulative SON in leaching total soluble N （118.1 mg kg^-1 was 46.4%, higher than the percentage of initial SON （28.8%）, and almost close to the percentage of cumulative NH4^＋-N in the leachates. ND had close correlation with total N, and the correlation coefficients were 0.92 （P 〈 0.01, excluding SON in estimating ND） and 0.88 （P 〈 0.01, including SON in estimating ND）, respectively. N mineralization potential and mineralization rate constant were different with the soil types. ND of Los-Orthic Entisols and Ust-Sandiic Entisols were lower than that of Eum-Orthrosols. Mineralization rate constant for the fast decomposable N-fraction （kD） decreased and the mineralization rate constant of resistant materials （kR） increased when SON was taken into account. Cumulative NH4^＋-N was a better evaluation index of soil N-supplying capacity, and it is not only suitable for the first season crops but also for two successive season crops. Cumulative SON alone was not a satisfactory index for the potential of mineralizable N. But it would be more accurate for ND in revealing the potential mineralizable N when SON was taken into account. Cumulative TSN, to some extent, could also be taken as an index for the potential mineralizable N. Cumulative NH4＋-N, total soluble N, and ND were good indexes for estimating soil potential mineralizable N, especially for soils of two successive season crops. And cumulative total soluble N and ND in evaluating the permanence of soil N-supply is of greater significance when SON was included.

Contents of soil organic carbon and nitrogen in water-stable aggregates in abandoned agricultural lands in an arid ecosystem of Northwest China

Soil organic matter content in water-stable aggregates（WSA） in the arid ecosystems（abandoned agricultural lands especially） of China is poorly understood. In this study, we examined the WSA sizes and stability, and soil organic carbon（OC） and nitrogen（N） contents in agricultural lands with abandonment ages of 0, 3, 12, 20, 30 and 40 years, respectively, in the Minqin Oasis of Northwest China. The total soil OC and N contents at depths of 0–20, 20–40 and 40–60 cm in abandoned agricultural lands were compared to those in cultivated land（the control）. Agricultural land abandonment significantly（P0.25 mm） as the age of agricultural land abandonment increased. The effect of abandonment ages of agricultural lands on MWD was determined by the changes of OC and N accumulation in WSA sizes ＆gt;2 mm. The total OC and N contents presented a stratification phenomenon across soil depths in this arid ecosystem. That is, both of them decreased significantly at depths of 0–20 and 40–60 cm while increased at the depth of 20–40 cm. The WSA sizes ＆lt;0.053 mm had the highest soil OC and N contents（accounting for 51.41%–55.59% and 42.61%–48.94% of their total, respectively）. Soil OC and N contents in microaggregates（sizes 0.053–0.25 mm） were the dominant factors that influenced the variations of total OC and N contents in abandoned agricultural lands. The results of this study suggested that agricultural land abandonment may result in the recovery of WSA stability and the shifting of soil organic matter from the silt＋clay（＆lt;0.053 mm） and microaggregate fractions to the macroaggregate fractions. However, agricultural land abandonment did not increase total soil OC and N contents in the short-term.

Difference in Organic Carbon Contents and Distributions in Particle-size Fractions between Soil and Sediment on the Southern Loess Plateau, China

The purpose of this study was to assess the effect of long-term cultivation and water erosion on the soil organic carbon （OC） in particle-size fractions. The study site is located at Nihegou Watershed in the Southern Loess Plateau, China. The soil at this site is loess with loose and silty structure, and contains macropores. The results showed that the OC concentrations in sediments and in the particle-size fractions of sediments were higher than those in soils and in the particle-size fractions of soils. The OC concentration was highest in the clay particles and was lowest in the sand particles. Clay particles possessed higher OC enrichment ability than silt and sand particles. The proportions of OC in the silt fractions of soil and sediment were the highest （mean value of 53.87% and 58.48%, respectively）, and the total proportion of OC in the clay and silt fractions accounted for 96% and 98% of the total OC in the soil and sediment, respectively. The loss of OC was highest in silt particles, with an average value of 0.16 Mg ha^-1 y^-1, and was lowest in the sand （0.003 Mg ha^-1 y^-l）. This result suggests that the fine particle-size fraction in the removed sediment may be an important indicator to assess soil OC losses.

Effects of degradation succession of alpine wetland on soil organic carbon and total nitrogen in the Yellow River source zone,west China

Wetland is an important carbon pool,and the degradation of wetlands causes the loss of organic carbon and total nitrogen.This study aims to explore how wetland degradation succession affects soil organic carbon(SOC)and total nitrogen(TN)contents in alpine wetland.A field survey of 180 soilsampling profiles was conducted in an alpine wetland that has been classified into three degradation succession stages.The SOC and TN contents of soil layers from 0 to 200 cm depth were studied,including their distribution characteristics and the relationship between microtopography.The results showed that SOC and TN of different degradation succession gradients followed the ranked order of Non Degradation(ND)>Light Degradation(LD)>Heavy Degradation(HD).SWC was positively correlated with SOC and TN(p<0.05).As the degree of degradation succession worsened,SOC and TN became more sensitive to the SWC.Microtopography was closely related to the degree of wetland degradation succession,SWC,SOC and TN,especially in the topsoil(0-30 cm).This result showed that SWC was an important indicator of SOC/TN in alpine wetland.It is highly recommended to strengthen water injection into the wetland as a means of effective restoration to reverse alpine meadow back to marsh alpine wetland.

Variation of soil organic carbon and bulk density during afforestation regulates soil hydraulic properties

Grain to Green program on arable land has been conducted for decades in semi-arid regions of North China.However,it remains uncertain how afforestation practices affect soil hydraulic properties(SHP).Two afforestation types,i.e.shrubland(SL)and woodland(WL),and the adjacent cropland(CL)were investigated to determine afforestation effects on SHP in this area.Disturbed and undisturbed soil cores were collected in three experimental sites.Soil field capacity(FC),wilting point(WP),and available water capacity(AWC)increased in SL compared to the CL.Soil saturated water content,however,decreased significantly in both SL and WL.Correlation and redundancy analysis identified that bulk density(BD)and soil organic carbon(SOC)were the main factors regulating SHP across different land uses.Lower saturated water contents in afforestation sites were likely driven by the higher BD,compared to the adjacent cropland.FC,WP,and AWC were positively correlated to SOC content.While afforestation may not increase the saturated water content of a landscape,our results indicate that it can improve soil water retention and could be an effective practice for soil and water conservation.

Soil Aggregates, Organic Matter, and Labile C and N Fractions after 37 Years of N, P and K Applications to an Irrigated Subtropical Soil under Maize-Wheat Rotation

Abstract： Physical, chemical and biological soil properties in surface （0-5 cm） and subsurface soil （5-15 cm） were determined in a field experiment conducted with seven treatments consisted of different combinations of fertilizer N （0, 100 and 200 kg N ha^-1）, P （0, 22 and 44 kg P2O5 ha^-1） and K （0, 41 and 82 kg K2O ha^-1） applied both to summer-grown maize （Zea mays L.） and winter-grown wheat （Triticum aestivum L.） crops continuously for 37 years under irrigated subtropical conditions. Application of N, P and K significantly increased water stable aggregates and had profound effects in increasing the mean weight diameter as well as the formation of macro-aggregates, which were highest in both surface （81%） and subsurface （74%） soil layers with application of 100 kg N ＋ 22 kg P2O5 ＋ 41 kg K2O ha^-1 （N100P22K41）. The N100P22K41 treatment also enhanced total organic C （TOC） from 4.4 g kg^-1 in no-NPK control to 4.8 g kg^-1in surface layer and from 3.3 to 4.1 g kg1 in subsurface layer leading to the 20% higher TOC stocks in 0-15 cm soil. The labile C and N fractions such as water soluble C, particulate and light fraction organic matter, potentially mineralizable N and microbial biomass were also highest under the optimized balanced application of N100P22K41. Relatively higher increase in all labile fractions of C and N as proportion of TOC and total N, respectively suggested that these are potential indicators to reflect changes in management practices long before changes in TOC and TN are detectable. These results demonstrated that optimized balanced application of N, P and K is crucial for improving soil health ensuring long-term sustainability of farming systems in semiarid subtropical soils.

Relationship Between Soil and Water Conservation Practices and Soil Conditions in Low Mountain and Hilly Region of Northeast China

The soil and water conservation practices of ecological restoration(ER),fish scale pit(FP),furrow and ridge tillage across the slope(FR),shrub strips(SS),and vegetation-covered ridge(VR)are characteristic of the Jixing small watershed of the low mountain and hilly region of Jilin Province,Northeast China.This study aims to elucidate the effects of soil and water conservation practices on soil conditions after the short-term implementation of practices.Soil samples were collected from five soil and water conservation sites(ER,FP,FR,SS,and VR)and two controls(BL and CT)to investigate their properties.To evaluate the influence of soil and water conservation practices on soil quality,an integrated quantitative index,soil quality index(QI),was developed to compare the soil quality under the different soil and water conservation practices.The results show that not all soil and water conservation practices can improve the soil conditions and not all soil properties,especially soil organic carbon(SOC),can be recovered under soil and water conservation practice in short-term.Moreover,the QI in the five soil and water conservation practices and two controls was in the following order:ER>VR>BL>FR>CT>SS>FP.ER exhibited a higher soil quality value on a slope scale.In the low mountain and hilly region of Northeast China,ER is a better choice than the conversion of farmlands to planted grasslands and woodlands early in the soil and water conservation program.

Short Term Leguminous Trees-Tillage Interactions and Their Effect on Soil-Water Content in a Semi-Arid Agroforestry Parkland

Agricultural activities that encourage slashing, burning and ploughing greatly affect the soil structure and soil organic matter on which soil water retention depends. In this study, we hypothesized that inclusion of rotational leguminous tree species improves soil water retention in a semi-arid conservation agriculture system. In a study done in Kibwezi, semi-arid eastern Kenya, results showed that the amount of water retained in the different soil strata from plots with different tree species and tillage practices was highly significant (P = 0.032). Plots with planting basins and Gliricidia sepium and Faidherbia albida tree species retained more water in both the upper and lower strata. Plots with G. sepium tree species under planting basins and zero tillage under F. albida had significantly higher soil organic carbon levels than plots that were managed under ridges and ploughing (P = 0.002). On the other hand, bulk density in plots with planting basins and zero tillage and ridges ranged between 1.35 g/cm3 and 1.53 g/cm3. Conventional tillage plots had bulk density values of 1.65 g/cm3 and 1.72 g/cm3 in the upper and lower strata respectively. The time-dependent nature of rotational leguminous tree species on soil organic matter and soil water retention in the semi-arid conservation agriculture system highlights the importance of considering these species for improving organic carbon and water retention for improved crop production.

Emission of organic carbon, elemental carbon and water-soluble ions from crop straw burning under flaming and smoldering conditions

Emissions from major agricultural residues were measured using a self-designed combustion system. Emission factors （EFs） of organic carbon （OC）, elemental carbon （EC）, and water-soluble ions （WSIs） （K＋, NH4＋, Na＋, Mg2＋, Ca2＋, Cl-, NO3-, SO42–） in smoke from wheat and rice straw were measured under flaming and smoldering conditions. The OC1/TC （total carbon） was highest （45.8% flaming, 57.7% smoldering） among carbon fractions. The mean EFs for OC （EFOC） and EC （EFEC） were 9.2 ± 3.9 and 2.2 ± 0.7 g/kg for wheat straw and 6.4 ± 1.9 and 1.1 ± 0.3 g/kg for rice straw under flaming conditions, while they were 40.8 ± 5.6 and 5.8 ± 1.0 g/kg and 37.6 ± 6.3 and 5.0 ± 1.4 g/kg under smoldering conditions, respectively. Higher EC ratios were observed in particulate matter （PM） mass under flaming conditions. The OC and EC for the two combustion patterns were significantly correlated （p 〈 0.01, R = 0.95 for wheat straw; p 〈 0.01, R = 0.97 for rice straw）, and a higher positive correlation between OC3 and EC was observed under both combustion conditions. WSIs emitted from flaming smoke were dominated by Cl- and K＋, which contributed 3.4% and 2.4% of the PM mass for rice straw and 2.2% and 1.0% for wheat straw, respectively. The EFs of Cl- and K＋ were 0.73 ± 0.16 and 0.51 ± 0.14 g/kg for wheat straw and 0.25 ± 0.15 and 0.12 ± 0.05 g/kg for rice straw under flaming conditions, while they were 0.42 ± 0.28 and 0.12 ± 0.06 g/kg and 0.30 ± 0.27 and 0.05 ± 0.03 g/kg under smoldering conditions, respectively. Na＋, Mg2＋, and NH4＋ were vital components in PM, comprising from 0.8% （smoldering） to 3.1% （flaming） of the mass. Strong correlations of Cl- with K＋, NH4＋, and Na＋ ions were observed in rice straw and the calculated diagnostic ratios of OC/EC, K＋/Na＋ and Cl-/Na＋ could be useful to distinguishing crop straw burning from other sources of atmospheric pollution.

水土保持碳汇内涵与测算方法

水土保持深刻改变着地表覆被和结构、土地利用方式和陆地生态系统结构等,是增强陆地碳汇能力的重要途径。以水土保持林草、工程和耕作措施为切入点,按照“机理阐述—模型构建—分类测算”的总体思路,阐明水土保持碳汇内涵,明确了水土保持碳汇途径,构建水土保持碳汇测算方法,估算全国水土保持碳汇量。结果表明:水土保持具有垂向碳增汇、横向保土固碳(减少侵蚀土壤横向输移导致的碳流失)与减蚀减碳(避免碳排放)的多重功能。2021年,全国现存水土保持措施垂向碳增汇总量为1.54亿t,对陆域碳汇的贡献约43.5%~56.5%,其中林草措施植被和土壤碳汇量超过95%。水土保持保土固碳作用显著,2021年全国水土保持措施保土固碳总量为3 040.86万t,且具有明显的累积效应和长效作用。总体来说,2021年水土保持碳增汇(不包括水土保持林草措施植被碳汇量和土壤碳汇量)和减碳量为5 115万~6 230万t CO_(2),约占到全国现有陆地生态系统碳中和总量的4%~6%,这一部分尚未纳入国家碳汇核算体系,其应是实现“双碳”目标的重要环节。

东北半干旱黑土区玉米秸秆还田方式对土壤水溶性有机碳含量及其组分的影响

为明确不同秸秆还田方式下土壤有机碳组分的变化特征,基于6 a秸秆还田长期定位试验,利用三维荧光光谱技术,对无秸秆还田(CK)、秸秆覆盖还田(FG)、秸秆翻埋还田(FM)处理下土壤有机碳(SOC)含量及水溶性有机碳(WSOC)含量及其结构特征进行分析。结果表明:(1)与CK相比,FM处理0~40 cm土层SOC含量提高7.87%~29.54%,FG处理0~30 cm土层SOC含量增加1.91%~18.61%,30~40 cm土层SOC含量降低7.67%;FM和FG处理0~40 cm土层土壤WSOC含量分别提升13.42%~39.42%和0.28%~26.34%。(2)通过WSOC三维荧光光谱发现,各土层CK(Ex/Em=300/34、Ex/Em=300/340、Ex/Em=240/340、Ex/Em=300/340)处理WSOC荧光特征峰为溶解性微生物代谢产物和类色氨酸蛋白质物质荧光峰;FM(Ex/Em=340/430、Ex/Em=340/430、Ex/Em=340/435、Ex/Em=340/435)和FG(Ex/Em=270/440、Ex/Em=270/435、Ex/Em=340/435、Ex/Em=340/430)处理为类腐殖酸类物质荧光特征峰,腐殖化程度较高,结构较为复杂;荧光区域积分表明,FM和FG处理类腐殖酸类物质(Ⅴ)和富里酸类物质(Ⅲ)的积分百分比分别较CK增加12.18%~27.39%、11.98%~30.72%和3.96%~5.73%、2.99%~5.40%。(3)土壤WSOC包含两个组分,C1(Ex/Em=340/435,270/435)组分为类腐殖酸类物质,C2(Ex/Em=290/345,240/345)组分为溶解性微生物代谢产物和类色氨酸蛋白质物质;F max值结果表明,0~40 cm土层的C1组分相对含量表现为FM>FG>CK,表明秸秆翻埋还田更有助于土壤中营养物质含量增加和形成更高分子量的有机物。综上,不同秸秆还田方式均可提升SOC和土壤WSOC含量,增加腐殖化程度,加强土壤的供肥能力,翻埋还田处理提升作用更为显著。

长期施用有机肥对半干旱区春小麦产量及其水分利用效率和土壤有机碳的影响

以国家土壤质量安定观测试验站黄绵土区的农田长期定位试验为研究对象,研究长期施用有机肥对半干旱区春小麦产量及其水分利用效率和有机碳的影响。结果表明,连续种植7年春小麦,施肥显著影响小麦产量及其水分利用效率,以化肥与有机肥配施(NPKM)处理效果最好,较单施化肥(NPK)、单施有机肥(OM)处理春小麦产量和水分利用效率分别增加了7.18%和7.82%、5.91%和3.83%;在定位施肥初期(前3年),NPKM和NPK处理的效果优于OM,在第4年三者无差异,而第5年及之后,NPKM和OM处理的效果明显好于NPK处理。长期NPKM和OM处理较NPK处理0~20 cm土层土壤有机碳含量分别显著增加了36.88%和31.98%,有机碳储量分别显著增加了31.17%~41.94%和27.80%~35.81%,表层0~10 cm的增加效果显著好于10~20 cm土层。不同施肥处理对0~20 cm土层土壤微生物生物量碳(MBC)的影响表现为NPKM>OM>NPK>CK,且差异显著,长期NPKM和OM处理较NPK处理土壤MBC分别显著增加了46.4%和28.7%,长期单施NPK处理可显著增加土壤MBC含量,但对有机碳影响不明显。综上所述,长期NPKM或OM处理可显著增加黄绵土小麦地土壤有机碳和MBC含量,增加有机碳储量,有利于农田土壤固碳增汇,提高小麦产量及其水分利用效率。

周期性水位波动对三峡水库消落带土壤有机碳含量和密度的影响

为探究水位波动对三峡水库消落带土壤有机碳的影响,在三峡水库消落带采集和测定了受不同水淹强度影响的石灰土、紫色土、黄壤及其植物样品,并运用Kruskal-Wallis非参数检验和基于冗余分析的典范分析等方法进行了研究。结果表明:周期性水淹增加了石灰土和紫色土的有机碳含量和密度,但降低了黄壤的有机碳含量和密度。此外,石灰土的有机碳分布还受地上生物量、土壤pH和土层深度的影响,紫色土的有机碳分布还受土层深度和地上生物量的影响,而黄壤的有机碳含量和密度则与地上生物量、土层深度和地下生物量有关。总之,周期性水位波动对消落带土壤有机碳影响深刻,但土壤类型分异了有机碳对水位波动的响应。