Long‐term cropping systems and tillage management effects on soil organic carbon stock and steady state level of C sequestration rates in a semiarid environment

A calcareous and clayey xeric Chromic Haploxerept of a long‐term experimental site in Sicily (Italy) was sampled (0–15 cm depth) under different land use management and cropping systems (CSs) to study their effect on soil aggregate stability and organic carbon (SOC). The experimental site had three tillage managements (no till [NT], dual‐layer [DL] and conventional tillage [CT]) and two CSs (durum wheat monocropping [W] and durum wheat/faba bean rotation [WB]). The annually sequestered SOC with W was 2·75‐times higher than with WB. SOC concentrations were also higher. Both NT and CT management systems were the most effective in SOC sequestration whereas with DL system no C was sequestered. The differences in SOC concentrations between NT and CT were surprisingly small. Cumulative C input of all cropping and tillage systems and the annually sequestered SOC indicated that a steady state occurred at a sequestration rate of 7·4 Mg C ha⁻¹ y⁻¹. Independent of the CSs, most of the SOC was stored in the silt and clay fraction. This fraction had a high N content which is typical for organic matter interacting with minerals. Macroaggregates (>250 µm) and large microaggregates (75–250 µm) were influenced by the treatments whereas the finest fractions were not. DL reduced the SOC in macroaggregates while NT and CT gave rise to higher SOC contents. In Mediterranean areas with Vertisols, agricultural strategies aimed at increasing the SOC contents should probably consider enhancing the proportion of coarser soil fractions so that, in the short‐term, organic C can be accumulated. Copyright © 2010 John Wiley & Sons, Ltd.     

Tillage effects on soil aggregation and soil organic carbon profile distribution under Mediterranean semi‐arid conditions

In rainfed semi‐arid agroecosystems, soil organic carbon (SOC) may increase with the adoption of alternative tillage systems (e.g. no‐tillage, NT). This study evaluated the effect of two tillage systems (conventional tillage, CT vs. NT) on total SOC content, SOC concentration, water stable aggregate‐size distribution and aggregate carbon concentration from 0 to 40 cm soil depth. Three tillage experiments were chosen, all located in northeast Spain and using contrasting tillage types but with different lengths of time since their establishment (20, 17, and 1‐yr). In the two fields with mouldboard ploughing as CT, NT sequestered more SOC in the 0–5 cm layer compared with CT. However, despite there being no significant differences, SOC tended to accumulate under CT compared with NT in the 20–30 and 30–40 cm depths in the AG‐17 field with 25–50% higher SOC content in CT compared with NT. Greater amounts of large and small macroaggregates under NT compared with CT were measured at 0–5 cm depth in AG‐17 and at 5–10 cm in both AG‐1 and AG‐17. Differences in macroaggregate C concentration between tillage treatments were only found in the AG‐17 field at the soil surface with 19.5 and 11.6 g C/kg macroaggregates in NT and CT, respectively. After 17 yr of experiment, CT with mouldboard ploughing resulted in a greater total SOC concentration and macroaggregate C concentration below 20 cm depth, but similar macroaggregate content compared with NT. This study emphasizes the need for adopting whole‐soil profile approaches when studying the suitability of NT versus CT for SOC sequestration and CO₂ offsetting.     

Decadal Nitrogen Fertilization Decreases Mineral‐Associated and Subsoil Carbon: A 32‐Year Study

Crop residues and manure are important sources of carbon (C) for soil organic matter (SOM) formation. Crop residue return increases by nitrogen (N) fertilization because of higher plant productivity, but this often results only in minor increases of SOM. In our study, we show how N fertilization and organic C additions affected SOM and its fractions within a 32‐year‐long field‐experiment at Puch, Germany. Five organic additions, no‐addition (control), manure, slurry, straw and straw + slurry, were combined with three mineral N fertilization rates (no, medium and high fertilization), which resulted in 1·17–4·86 Mg C‐input ha^‐1 y^‐1. Topsoil (0–25 cm) SOM content increased with N fertilization, mainly because of the C in free light fraction (f‐LF). In contrast, subsoil (25–60 cm) SOM decreased with N fertilization, probably because of roots' relocation in Ap horizon with N fertilization at the surface. Despite high inputs, straw contributed little to f‐LF but prevented C losses from the mineral‐associated SOM fraction (ρ > 1·6 g cm^‐3) with N fertilization, which was observed without straw addition. Above (straw) and belowground (roots) residues had opposite effects on SOM fractions. Root C retained longer in the light‐fractions and was responsible for SOM increase with N fertilization. Straw decomposed rapidly (from f‐LF) and fueled the mineral‐associated SOM fraction. We conclude that SOM content and composition depended not only on residue quantity, which can be managed by the additions and N fertilization, but also on the quality of organics. This should be considered for maintaining the SOM level, C sequestration, and soil fertility. Copyright © 2016 John Wiley & Sons, Ltd.     

Response of organic matter to reduced tillage and animal manure in a temperate loamy soil

The impacts of tillage and organic fertilization on soil organic matter (SOM) are highly variable and still unpredictable, and their interactions need to be investigated under various soil, climate and cropping system conditions. Our work examined the effect of reduced tillage and animal manure on SOM stocks and quality in the 0–40 cm layer of a loamy soil under mixed cropping system and humid temperate climate. The soil organic carbon (SOC) and N stocks, particulate organic matter (POM), and C and N mineralization potential (301 days at 15 °C) were measured in a 8‐yr‐old split‐plot field trial, including three tillage treatments [mouldboard ploughing (MP), shallow tillage (ST), no tillage (NT)] and two fertilization treatments [mineral (M), poultry manure 2.2 t/ha/yr C (O)]. No statistically significant interactive effects of tillage and fertilization were measured except on C mineralization. NT and ST showed greater SOC stocks (41.2 and 39.7 t/ha C) than MP (37.1 t/ha C) in the 0–15 cm increment, while no statistical differences were observed at a greater depth. N stocks exhibited similar distribution patterns with regard to tillage effect. Animal manure, applied at a rate representative of typical field application rates, had a smaller impact on SOC and N stocks than tillage. The mean SOC and N stocks were higher under O than M, but the differences were statistically significant only in the 0–5 cm increment. MP showed lower C‐POM stocks than NT and ST in the 0–5 cm increment, whereas greater C‐POM stocks were measured under MP than under NT or under ST in the 20–25 cm increment. Organic fertilization had no impact on C‐POM or N‐POM stocks. In the 0–25 cm increment, NT showed a lower C and N mineralization potential than MP. Our work shows that the sensitivity of SOM to reduced tillage for the whole soil profile can be relatively small in a loamy soil, under humid‐temperate climate. However, POM was particularly sensitive to the differential effects of tillage practices with depth, and indicative of differentiation in total SOM distribution in the soil profile.     

Long‐term effects of soil management regimes on carbon contents and respiration rates of aggregate size fractions

This study investigated long‐term effects of soil management on size distribution of dry‐sieved aggregates in a loess soil together with their organic carbon (OC) and their respiratory activity. Soil management regimes were cropland, which was either abandoned, left bare fallow or cropped for 21 yr. Abandonment increased the abundance of macroaggregates (>2 mm) in the surface soil layer (0–10 cm) and reduced that of microaggregates (<0.25 mm) relative to Cropping, whereas the Fallow treatment reduced the abundance of macroaggregates at depths of 0–10 and 10–20 cm. All treatments yielded similar aggregate size distributions at a depth of 20–30 cm. The SOC content of aggregate size fractions in the surface soil from the Abandoned plots was greater (by 1.2–4.8 g/kg) than that of the corresponding fractions from the Cropped plots, but the opposite trend was observed in the subsurface soils. Conversely, the Fallow treatment reduced the SOC content of every aggregate size fraction. Smaller aggregates generally exhibited greater cumulative levels of C mineralization than larger ones. However, the bulk of the SOC losses from the soils via mineralization was associated with aggregates of >2 mm. Abandonment significantly increased the relative contribution of macroaggregates (>2 mm) to the overall rate of SOC loss, whereas the Fallow treatment significantly reduced the contribution of 0.25–2 mm aggregates to total SOC loss in the surface soil while substantially increasing their contribution in the subsurface soil.     

Natural 13C abundance and soil carbon dynamics under long‐term residue retention in a no‐till maize system

Residue retention and reduced tillage are both conservation agricultural practices that may enhance soil organic carbon (SOC) stabilization in soil. We evaluated the long‐term effects of no‐till (NT) and stover retention from maize on SOC dynamics in a Rayne silt loam Typic Hapludults in Ohio. The six treatments consisted of retaining 0, 25, 50, 75, 100 and 200% of maize residues on each 3 × 3 m plot from the crop of previous year. Soil samples were obtained after 9 yrs of establishing the experiment. The whole soil (0–10 and 10–20 cm of soil depths) samples under different treatments were analysed for total C, total N, recalcitrant C (NaOCl treated sample) and ¹³C isotopic abundance (0–10 cm soil depth). Complete removal of stover for a period of 9 yrs significantly (P < 0.01) decreased soil C content (15.5 g/kg), whereas 200% of stover retention had the maximum soil C concentration (23.1 g/kg). Relative distribution of C for all the treatments in different fractions comprised of 55–58% as labile and 42–45% as recalcitrant. Retention of residue did not significantly affect total C and N concentration in 10–20 cm depth. ¹³C isotopic signature data indicated that C₄‐C (maize‐derived C) was the dominant fraction of C in the top 0–10 cm of soil layer under NT with maize‐derived C accounting for as high as 80% of the total SOC concentration. Contribution of C₄‐C or maize‐derived C was 71–84% in recalcitrant fraction in different residue retained plots. Residue management is imperative to increase SOC concentrations and long‐term agro‐ecosystem necessitates residue retention for stabilizing C in light‐textured soils.     

菜地土壤有机碳分级以及总量变化的动态特征研究

Fertilisers significantly affect crop production and crop biomass inputs to soil organic carbon（SOC）. However, the long-term effects of fertilisers on C associated with aggregates are not yet fully understood. Based on soil aggregate and SOC fractionation analysis, this study investigated the long-term effects of organic manure and inorganic fertilisers on the accumulation and change in SOC and its fractions, including the C concentrations of free light fraction, intra-aggregate particulate organic matter（POM） and intra-aggregate mineral-associated organic matter（MOM）. Long-term manure applications improved SOC and increased the concentrations of some C fractions. Manure also accelerated the decomposition of coarse POM（cPOM） into fine POM（fPOM） and facilitated the transformation of fPOM encrustation into intra-microaggregate POM within macroaggregates. However, the application of inorganic fertilisers was detrimental to the formation of fPOM and to the subsequent encrustation of fPOM with clay particles, thus inhibiting the formation of stable microaggregates within macroaggregates. No significant differences were observed among the inorganic fertiliser treatments in terms of C concentrations of MOM, intra-microaggregate MOM within macroaggregate（imMMOM） and intra-microaggregate MOM（imMOM）. However, the long-term application of manure resulted in large increases in C concentrations of MOM（36.35%）, imMMOM（456.31%） and imMOM（19.33%） compared with control treatment.     

生物炭及秸秆长期施用对紫色土坡耕地土壤团聚体有机碳的影响

依托紫色土坡耕地长期施肥试验观测平台,研究生物炭、秸秆对紫色土坡耕地团聚体有机碳分布的影响。长期施肥试验处理包括不施肥(CK)、无机氮磷钾肥(NPK)、秸秆还田(RSD)、生物炭与无机氮磷钾配施(BCNPK)、秸秆与无机氮磷钾配施(RSDNPK)。利用湿筛法,进行土壤团聚体粒径分组,随后测定各粒径团聚体含量及其有机碳含量,并计算团聚体平均质量直径(MWD)和几何平均直径(GMD)。结果表明,RSD、RSDNPK和BCNPK处理的表层SOC含量比CK处理增加43.1%～90.5%,SOC储量提高65.1%～74.3%,其中RSDNPK处理、BCNPK处理较NPK处理SOC显著增加25.2%～33.1%(P0.05), SOC储量显著提高23.2%～30.0%(P0.05)。团聚体MWD和GMD均为RSD处理RSDNPK处理BCNPK处理NPK处理CK处理; RSD处理0.25～2 mm的团聚体含量高达45.5%,较CK处理提高57.7%;秸秆和生物炭配施处理(RSDNPK处理和BCNPK处理)0.25～2mm的团聚体含量为41.3%～45.7%,而0.053mm粒径团聚体含量却降低54.1%～55.4%。NPK处理、RSD处理与CK处理的增长趋势相似,呈随团聚体粒径减小,团聚体有机碳含量先增大后减小,继而再增大的趋势;而RSDNPK、BCNPK处理则呈随粒径减小团聚体有机碳含量增加的趋势。生物炭和秸秆的施用能显著提升土壤有机碳含量,增强土壤结构稳定性,但生物碳的施用对提升土壤有机碳含量效果优于秸秆的施用,秸秆的施用对稳定土壤结构效果更优,因此生物炭和秸秆的施用可作为紫色土耕地土壤肥力维持和提升的有效管理措施。     

Relationships between soil macroaggregation and humic carbon in a sandy loam soil following conservation tillage

Purpose

Humic substances are recalcitrant and might act as persistent binding agents to form macroaggregates. The focus of this study is in investigating the contribution of humic carbon (HC) to soil aggregation in response to various tillage and residue managements.

Materials and methods

Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution and stability and HC fractions including humic acid (HA) and fulvic acid (FA). The contribution of HC to aggregation was divided into three special effects including positive effect (PE), negative effect (NE), and combined effect (CE), and these effects were measured using aggregate fractionation techniques.

Results and discussion

As well as to promote structural stability, HC bounds predominantly with the silt + clay fraction and secondarily with microaggregates to form larger aggregates. The PE increased with increasing aggregate size, whereas the NE followed the opposite pattern. A positive CE was observed for large and small macroaggregates, whereas the CE for microaggregates and the silt + clay fraction was negative. Compared to continuous tillage, reduced- and no-tillage decreased the PE for large and small macroaggregates by 1.58–30.98% at the 0–20 cm depth, and straw returning also slightly decreased the corresponding PE relative to straw removing. By contrast, a significantly higher NE for small macroaggregates at the 0–10 cm depth while 6.33–81.11% decreases in CE for large and small macroaggregates at the 0–10 cm depth as well as for large macroaggregates at the 10–20 cm depth, were observed under reduced- and no-tillage. The extraction of HC significantly reduced the aggregate stability and reduced- and no-tillage effectively limited its decrease magnitude. Small macroaggregates and microaggregates made larger contributions to soil HC accumulation than did other fractions. An averagely increased contribution from large or small macroaggregates was observed under both reduced-/no-tillage and straw returning at the 0–20 cm depth. A significant and positive relationship was found between the mass proportion of macroaggregates and the HC accumulation in 0–20 cm soil. Large macroaggregates had significantly higher HA/FA ratios than small macroaggregates, and reduced- and no-tillage significantly increased these ratios both in large and in small macroaggregates. The CE for large or small macroaggregates was also significantly negatively correlated with their HA/FA ratios.

Conclusions

Overall, the HC accumulation in soil is likely to play a key role in macroaggregation, but conservation tillage might decrease the contribution magnitude of HC to large or small macroaggregation through increasing the corresponding HA/FA ratios.

     

The effects of irrigation and cultivation on the quality of desert soil in central Iran

Cultivation of irrigated desert soils in Central Iran is one way of utilizing under‐exploited land to produce more food. This study explores the value of soil quality indicators as measures when converting desert to croplands. Soil samples from unfarmed desert, wheat and alfalfa sites in the Abarkooh Plain (Central Iran) were taken from 0–10, 10–20 and 20–30 cm depths. Soil quality indicators including organic carbon, total nitrogen, carbohydrate, particulate organic carbon (POC) in aggregate fractions, and aggregate water‐stability were determined. The desert soils contained organic carbon of 0·26–0·56 g kg⁻¹, total nitrogen of 0·05–0·08 g kg⁻¹ and carbohydrate of 0·03–0·11 g kg⁻¹ at 0–30 cm depth. Across this depth, the contents of organic carbon, total nitrogen and carbohydrate in wheat were about 3–7, 2–3 and 6–26‐times higher than those of desert soils, respectively. These values for alfalfa were 5–12, 3–4 and 7–35 times, respectively. The POC (near zero in desert soils) and generally other soil quality indicators showed greater improvement in alfalfa than in wheat fields. The results indicated a significant decrease in proportion of the fraction <0·05 mm in cultivated soils, whereas the proportion of the large aggregate size classes (2–4 and 1–2 mm) was increased by irrigation and cultivation. A significant improvement in aggregate water‐stability was observed in cultivated soils. At all depths, a large portion of the total soil organic carbon was stored in the fractions <0·05 mm for desert and macroaggregates (0·25–2 mm) for cultivated soils. Copyright © 2010 John Wiley & Sons, Ltd.     

Potential of mine land reclamation for soil organic carbon sequestration in Ohio

Soils are an effective sink for carbon storage and immobilization through biomass productivity and enhancement of soil organic carbon (SOC) pool. The SOC sink capacity depends on land use and management. Degraded lands lose large amounts of C through SOC decomposition, erosion, and leaching. Thus, restoration of disturbed and degraded mine lands can lead to increase in biomass productivity, improved soil quality and SOC enhancement and sequestration. Reclamation of mined lands is an aggrading process and offers significant potential to sequester C. A chronosequence study consisting of 0‐, 5‐, 10‐, 15‐, 20‐ and 25‐year‐old reclaimed mine soils in Ohio was initiated to assess the rate of C sequestration by pasture and forest establishment. Undisturbed pasture and forest were used as controls. The SOC pool of reclaimed pasture sites increased from 15·3 Mg ha⁻¹ to 44·4 Mg ha⁻¹ for 0–15 cm depth and from 10·8 Mg ha⁻¹ to 18·3 Mg ha⁻¹ for 15–30 cm depth over the period of 25 years. The SOC pool of reclaimed forest sites increased from 12·7 Mg ha⁻¹ to 45·3 Mg ha⁻¹ for 0–15 cm depth and from 9·1 Mg ha⁻¹ to 13·6 Mg ha⁻¹ for 15–30 cm depth over the same time period. The SOC pool of the pasture site stabilized earlier than that of the forest site which had not yet attained equilibrium. The SOC sequestered in 0–30 cm depth over 25 years was 36·7 Mg ha⁻¹ for pasture and 37·1 Mg ha⁻¹ for forest. Copyright © 2000 John Wiley & Sons, Ltd.     

Effect of straw amendment modes on soil organic carbon,nitrogen sequestration and crop yield on the North‐Central Plain of China

We quantified the effects of different straw return modes on soil organic carbon (SOC), total nitrogen content (TN) and C:N ratios in a wheat/maize double‐cropping agricultural system by analysing their content in different soil aggregate sizes and density fractions under four modes of straw return: (a) no return/retention of wheat and maize straw (Control); (b) retention of long wheat stubble only (Wheat Stubble); (c) retention of long wheat stubble and return of chopped maize straw (Mixed); and (d) return of chopped wheat and maize straw (Both Chopped). The Mixed and Both Chopped straw return modes produced the highest crop yields. Relative to the Control, SOC stock was 9.6% greater with the Mixed treatment and 14.5% greater with the Both Chopped treatment, whereas the Wheat Stubble treatment had no effect on SOC. Mixed and Both Chopped significantly enhanced TN stock relative to the Wheat Stubble and Control treatments. Compared with the Control, the Mixed and Both Chopped treatments increased the mass proportions of large macroaggregates and reduced the silt plus clay fraction; Mixed and Both Chopped caused a significant increase in SOC and TN in large and small macroaggregates; the Mixed treatment significantly increased SOC content in the coarse and fine intra‐aggregate particulate organic matter (iPOM) density fractions of large macroaggregates, whereas Both Chopped increased SOC in the coarse iPOM, fine iPOM and mineral‐associated organic matter (mSOM) density fractions of both large and small macroaggregates; and Mixed and Both Chopped enhanced TN content in coarse iPOM and fine iPOM within small macroaggregates. Although the Mixed treatment was slightly less effective at improving C sequestration in agricultural fields than the Both Chopped treatment, the Mixed treatment may nonetheless be the optimal plant residue management mode in terms of minimizing time and labour due to its ability to improve soil structure, maintain organic carbon levels and provide a means of sustainable crop production in intensive wheat/maize double‐cropping systems.     

Effects of intercropping and drought on soil aggregation and associated organic carbon and nitrogen

Drought has significant effects on soil physicochemical properties and thereby crop productivity. Intercropping is a traditional agricultural practice with a good ecological effect and can improve soil structure. However, the effects of intercropping on soil aggregate distribution and associated organic carbon (OC) and nitrogen (N) compared with monoculture under drought remains unclear. Therefore, a two-year controlled rainfall field (i.e., 30–40 days of 100% rainfall reduction during crop growth) was carried out to examine the effects of intercropping and short-term drought on soil aggregate stability and associated OC and N in Northeast China. Results showed that soil OC and N were predominant in macroaggregates (2–0.25 mm), accounting for 39%–51% of SOC, 36%–51% of N at 0–10 cm depth, and 44%–67% of SOC, 43%–66% of N at 10–20 cm depth. After 2 years of a rainfall reduction treatment, large macroaggregates (>2 mm) increased by 84.7% at 0–10 cm and the aggregate stability improved. There was no difference in the mass of aggregates between monoculture and intercropping, but short-term drought increased >0.25 mm aggregates and stability in intercropping soil at 0–10 cm depth. Moreover, drought significantly increased bulk soil OC in 10–20 cm but decreased the OC and N concentrations in large macroaggregates and silt + clay fractions (<0.053 mm) in 0–10 cm. Compared with the monoculture, intercropping enhanced OC and N concentrations in aggregates, and decreased soil C/N ratio. Therefore, these findings provide insights into how intercropping and short-term drought interactively influence soil aggregation, and C and N processes.     

Soil carbon sequestration in sub‐Saharan Africa: a review

Restoration of degraded soils is a development strategy to reduce desertification, soil erosion and environmental degradation, and alleviate chronic food shortages with great potential in sub‐Saharan Africa (SSA). Further, it has the potential to provide terrestrial sinks of carbon (C) and reduce the rate of enrichment of atmospheric CO₂. Soil organic carbon (SOC) contents decrease by 0 to 63 per cent following deforestation. There exists a high potential for increasing SOC through establishment of natural or improved fallow systems (agroforestry) with attainable rates of C sequestration in the range of 0·1 to 5·3 Mg C ha⁻¹ yr⁻¹. Biomass burning significantly reduces SOC in the upper few centimeters of soil, but has little impact below 10 to 20 cm depth. The timing of burning is also important, and periods with large amounts of biomass available generally have the largest losses of SOC. In cultivated areas, the addition of manure in combination with crop residues and no‐till show similar rates of attainable C sequestration (0 to 0·36 Mg C ha⁻¹ yr⁻¹). Attainable rates of SOC sequestration on permanent cropland in SSA under improved cultivation systems (e.g. no‐till) range from 0·2 to 1·5 Tg C yr⁻¹, while attainable rates under fallow systems are 0·4 to 18·5 Tg C yr⁻¹. Fallow systems generally have the highest potential for SOC sequestration in SSA with rates up to 28·5 Tg C yr⁻¹. Copyright © 2005 John Wiley & Sons, Ltd.     

Five-year warming does not change soil organic carbon stock but alters its chemical composition in an alpine peatland

Climate warming may promote soil organic carbon(SOC) decomposition and alter SOC stocks in terrestrial ecosystems, which would in turn affect climate warming. We manipulated a warming experiment using open-top chambers to investigate the effect of warming on SOC stock and chemical composition in an alpine peatland in Zoigê on the eastern Tibetan Plateau, China. Results showed that 5 years of warming soil temperatures enhanced ecosystem respiration during the growing season, promoted above-and be...     

长期施肥对浙江稻田土壤团聚体及其有机碳分布的影响

以浙江省稻田长期定位试验站为依托,研究长期不同施肥措施对土壤团聚体及其有机碳分布的影响。研究结果表明,与不施肥对照(CK)相比,栏肥与化肥配施(NPKOM)、单施栏肥(OM)、秸秆与化肥配施(NPKRS)和单施秸秆(RS)处理均显著提高了2 mm和2~0.25 mm水稳定性大团聚体的含量和团聚体平均重量直径(p0.05),强化了团聚体对土壤有机碳的物理保护作用。此外,长期有机无机配施(NPKOM和NPKRS)处理显著提高了各个粒级团聚体中有机碳含量,并且显著增加水稳定性大团聚体有机碳的贡献率,而长期单施化肥和单施秸秆处理并未有效增加土壤总有机碳含量。不同施肥处理下,2~0.25 mm粒级团聚体有机碳占土壤总有机碳的34.2%~48.6%,是土壤有机碳的主要载体。利用傅立叶变换红外光谱(FT-IR)技术对2~0.25 mm和0.053 mm团聚体进行结构表征,发现长期单施有机肥或者有机无机配施下芳香族C较CK提高29.9%~45.2%,较NPK处理提高22.3%~36.6%,提高了土壤有机碳的芳构化。在有机碳积累方面,施用有机肥,尤其是栏肥与化肥配施,同时强化了团聚体对有机碳的物理保护以及促进了化学抗性有机碳组分的积累,是加强稻田土壤有机碳库积累的合理施肥模式。     

Impact of 47 Years of No Tillage and Stubble Retention on Soil Aggregation and Carbon Distribution in a Vertisol

Aggregation often provides physical protection and stabilisation of soil organic carbon (C). No tillage (NT) coupled with stubble retention (SR) and nitrogen (N) fertiliser application (90 N, 90 kg N ha⁻¹ application) can help improve soil aggregation. However, information is lacking on the effect of long‐term NT, SR and N fertiliser (NT, SR + N) application on soil aggregation and C distribution in different aggregates in vertisols. We analysed the soil samples collected from 0‐ to 30‐cm depth from a long‐term (47 years) experiment for soil aggregation and aggregate‐associated C and N. This long‐term field experiment originally consisted of 12 treatments, having plot size of 61·9 × 6·4 m, and these plots were arranged in a randomised block design with four replications, covering an area of 1·9 ha. Soil organic C concentrations as well as stocks were significantly higher under the treatment of NT, SR + N only in 0–10 cm compared with other treatments such as conventional tillage, stubble burning + 0 N (no N application) and conventional tillage, SR + 0 N. Mineral‐associated organic C (MOC) of <0·053 mm was 5–12 times higher (r  = 0·68, p  < 0·05, n  = 32) compared with particulate organic C (POC) (>0·053 mm) in the 0‐ to 30‐cm layer. We found that NT, SR + N treatment had a positive impact on soil aggregation, as measured by the mean weight diameter (MWD) through wet sieving procedure, but only in the top 0‐ to 10‐cm depth. MWD had significant positive correlation with water stable aggregates (r  = 0·67, p  < 0·05). Unlike MWD, water stable aggregates were not affected by tillage and stubble management. Large macroaggregates (>2 mm) had significantly higher organic C and N concentrations than small macroaggregates (0·25–2 mm) or microaggregates (0·053–0·25 mm). We also found that N application had a significant effect on MWD and soil organic C in vertisols. It is evident that better soil aggregation was recorded under NTSR90N could have a positive influence on soil C sequestration. Our results further highlight the importance of soil aggregation and aggregate‐associated C in relation to C sequestration. Copyright © 2016 John Wiley & Sons, Ltd.     

Long‐term non‐flooded mulching cultivation influences rice productivity and soil organic carbon

A field experiment was conducted for 10 years to examine the long‐term effects of non‐flooded mulching cultivation on rice yield and soil organic carbon on Chengdu Plain, south‐west China. Compared with traditional flooded cultivation (TF), non‐flooded plastic film mulching (PM) resulted in a 14% higher average rice (Oryza sativa L.) yield. However, non‐flooded straw mulching (SM) decreased the average rice yield by 11% compared with TF. After 10 years, PM led to similar or higher (SM) soil organic carbon (SOC) and total soil N (TN) in the top 5 cm of the soil profile compared with TF. No differences were found among the three cultivation systems in SOC or total N at 5–12 and 12–24 cm soil depths. Small macroaggregates (0.25–2 mm) were predominant in the top 5 cm of the soil (58–63% of whole soil) across the three cultivation systems. However, the proportion of large macroaggregates (>2 mm) from SM and PM was significantly larger than from TF in the top 5 cm of the soil. Non‐flooded mulching cultivation led to increased C and N contents in large macroaggregates and mean weight diameter of aggregates in the 0–5 cm soil depth. This suggests that non‐flooded mulching cultivation increased soil aggregation concomitant with soil C stabilization within the improved soil structure.     

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.     

Long-term effects of mineral and organic fertilization on soil organic matter fractions and sorghum yield under Sudano-Sahelian conditions

Abstract. Knowledge of changes in soil organic matter (SOM) fractions resulting from agricultural practice is important for decision‐making at farm level because of the contrasting effects of different SOM fractions on soils. A long‐term trial sited under Sudano‐Sahelian conditions was used to assess the effect of organic and inorganic fertilization on SOM fractions and sorghum performance. Sorghum straw and kraal manure were applied annually at 10 t ha^?1, with and without urea at 60 kg N ha^?1. The other treatments included fallowing, a control (no fertilization), and inorganic fertilization only (urea, 60 kg N ha^?1). Fallowing gave significantly larger soil organic carbon and nitrogen (N) levels than any other treatment. Total soil SOM and N concentrations increased in the following order: urea only < straw < control < straw+urea < manure with or without urea < fallow. Farming had an adverse effect on SOM and N status; however, this mostly affected the fraction of SOM >0.053 mm (particulate organic matter, POM). The POM concentrations in the control, straw and urea‐only treatments were about one‐half of the POM concentrations in the fallow treatment. POM concentrations increased in the following order: urea only < control < straw with or without urea < manure with or without urea < fallow. The fraction of SOM <0.053 mm (fine organic matter, FOM) was greater than POM in all plots except in fallow and manure+urea plots. Total N concentration followed the same trend as SOM, but cultivation led to a decline in both POM‐N and FOM‐N. Crop yield was greatest in the manure plots and lowest in the straw, control and urea‐only plots. Results indicate that under Sudano‐Sahelian conditions, SOM, POM and FOM fractions and crop performance were better maintained using organic materials with a low C/N ratio (manure) than with organic material with a high C/N ratio (straw). Urea improved the effect of straw on crop yield and SOM concentration.