The impact of agroforestry combined with water harvesting on soil carbon and nitrogen stocks in central Chile evaluated using the ICBM/N model

Soil organic carbon (SOC) and total nitrogen (N) stocks in an agroforestry system with water harvesting were analysed in a field experiment and the results compared with those of other crop management systems in the Mediterranean zone of central Chile. Agroforestry with water harvesting showed higher positive effects on N stocks, mainly in the upper soil layer, than the other crop management systems. However, soil analysis revealed a lack of differences between treatments, a fact that might be related mainly to the short study time (12 years) and the high spatial variability in these soil properties at the experimental site. In addition, the Introductory Carbon Balance Model that simulates N processes (ICBM/N) was evaluated for simulating trends in SOC and N stocks in the field experiment. Soil data collected between 1996 and 2008 in the field experiment and primarily literature data sets were used to test ICBM/N and its performance was evaluated by considering uncertainty in model inputs using Generalised Likelihood Uncertainty Estimation (GLUE) methodology. The GLUE estimates (5% and 95%) and measured SOC and N stocks were in satisfactory agreement. The observed SOC and N stocks were bracketed by the uncertainty bands in 70% and 80% of the simulations, respectively. Sensitivity analysis showed the model to be most sensitive to C parameters, such as the humification coefficient (h). The results of this study show that ICBM/N can be an effective tool for estimating SOC and N stocks from agroforestry combined with water harvesting systems in the Mediterranean zone of central Chile over the medium term. However, they also indicate that additional data sets are needed to redefine the parameter distributions in the model and thus to predict trends in SOC and N stocks in the future.     

秸秆还田配施化肥对稻-油轮作土壤酶活性及微生物群落结构的影响

秸秆还田是农业生态系统提高土壤肥力和维持作物生产力的有效管理措施.为了研究秸秆还田配施化肥对巢湖地区稻-油轮作农田土壤养分含量、酶活性和微生物群落的影响,开展连续4 a （2016~2020年）的田间定位试验,设置无秸秆+无施肥（CK）、常规施肥（F）、秸秆还田+常规施肥（SF）和秸秆还田+常规施肥减20%（SDF）这4个处理,探究不同处理下影响土壤酶活性与细菌、真菌群落发生变化的关键环境因子.结果表明,秸秆还田配施化肥较常规施肥处理能够提高土壤养分含量,SF处理的土壤养分含量最高.与F相比,SF处理的水稻季土壤有机质（OM）和全磷（TP）含量显著提高了7.94%和24.07%（P<0.05）,油菜季碱解氮（AN）含量显著提高了13.62%（P<0.05）.SF较F处理的土壤磷酸酶和脲酶在水稻季显著提高了28.54%和24.13%,在油菜季显著提高了38.97%和30.70%,而SDF处理的4种土壤酶中仅脲酶活性较F处理显著提高,水稻季和油菜季分别提高了20.31%和24.33%（P<0.05）.秸秆还田对水稻季土壤细菌的Chao1和Shannon指数有所增加,油菜季则有所减少,而对真菌群落的Chao1和Shannon指数均增加.对于微生物群落结构而言,SF和SDF较F处理的变形菌门相对丰度在水稻季分别增加了8.22%和7.88%,油菜季分别增加了18.53%和5.68%.与F相比,SF和SDF处理的绿弯菌门相对丰度在水稻季分别增加了12.00%和11.25%,油菜季分别增加了15.02%和8.43%.水稻季SF和SDF处理的担子菌门较F相比相对丰度显著提高了70%和43.42%（P<0.05）,油菜季SF和SDF处理的子囊菌门与F相比显著提高了69.79%和43.72%（P<0.05）.综上,秸秆还田配施化肥可提高土壤养分含量,土壤脲酶和磷酸酶对秸秆还田的响应更为敏感,稻-油轮作农田土壤的细菌群落构成发生改变主要受土壤TP和速效磷（AP）影响,而土壤OM、AN和pH则是引起真菌群落构成变化的主要环境因子,因而秸秆还田有利于提高农田土壤肥力和维护生态系统健康.     

秸秆还田对江西农田土壤固碳影响的模拟分析

秸秆还田等农田管理措施能有效地增加土壤碳储量,从而有利于减缓大气CO₂浓度的上升趋势。论文基于环境政策综合气候模型(EPIC),采用千烟洲生态试验站和鹰潭生态试验站农田监测场长期观测数据,验证和优化了EPIC模型参数,同时利用1990-2010年江西省气象资料以及土壤清查资料,模拟分析了4种秸秆还田(CR)比例情景下2010-2030年江西省水稻田土壤的固碳潜力。研究结果表明,无秸秆还田 (CR0%)和秸秆还田25%(CR25%)两种处理下耕作层土壤有机碳储量分别下降21.3%和6.5%,秸秆还田50%(CR50%)和100%(CR100%)处理下土壤有机碳储量分别增加5.4%和11.9%;相对CR0%情景而言,CR25%、CR50%、CR100% 情景下江西省水稻田土壤总固碳潜力分别为6.43、14.92和25.26 TgC(1 Tg = 10⁶ t)。研究结果表明,通过合理的调控措施,采用保护性耕作(秸秆还田)是提高水稻田土壤固碳能力的一种有效途径。     

Crop residue removal and fertilizer N: Effects on soil organic carbon in a long-term crop rotation experiment on a Udic Boroll

Biofuels can be produced by converting cellulose in crop residues to ethanol. This has recently been viewed as a potential supplement to non-renewable energy sources, especially in the Americas. A 50-yr field experiment was analyzed to determine the influence of (i) removing approximately 22% of the above-ground wheat (Triticum aestivum L.) residue each crop year, and (ii) N and P fertilization on soil carbon (C) in the top 15 cm depth of a fallow–wheat–wheat (F–W–W) rotation. The study was conducted from 1958 to 2007 on a clay soil, at Indian Head in sub-humid southeast Saskatchewan, Canada. Soil C concentrations and bulk densities were measured in the 0–7.5 and 7.5–15 cm depths in 1987, 1996 and 2007 and soil C changes were related to C inputs estimated from straw and root yields calculated from regressions relating these to grain yields. Two soil organic matter models [the Campbell model and the Introductory Carbon Balance Model (ICBM)] were also used to simulate and predict the effects of the treatments on soil C change over time, and to estimate likely soil C change if 50% or 95% of above-ground residues were harvested each crop year. Crop residue removal reduced cumulative C inputs from straw and roots over the 50-yr experiment by only 13%, and this did not significantly (P > 0.05) reduce soil C throughout the experiment duration. However, after 50 yr of applying N fertilizer at recommended rates, soil C increased significantly by about 3 Mg ha⁻¹ compared to the non-fertilized treatment. The simulated effect of removing 50% and 95% of the above-ground residues suggested that removing 50% of the straw would likely have a detectable effect on the soil C, while removing 95% of the straw certainly would. Measurements and model simulations suggest that adoption of no-tillage without proper fertilization will not increase soil C. Although it appears that a modest amount of residue may be safely removed from these Udic Borolls (Black Chernozems) without a measurable effect on soil C, this would only be feasible if accompanied by appropriate fertility management.     

Integrated nutrient management and waste recycling for restoring soil fertility and productivity in Japanese mint and mustard sequence in Uttar Pradesh, India

Supplementing the nutrient requirement of crops through organic manures plays a key role in sustaining soil fertility, and crop productivity and reducing use of fossil fuels. Field experiments were conducted for 2 years at two different locations (i.e. Lucknow and Pantnagar) in Uttar Pradesh, India. The objectives of the study were to assess the herb and essential oil yields of Japanese mint (Mentha arvensis cv. Hy 77), and its nutrient accumulation under single and combined applications of organic manures and inorganic fertilizers (NPK). Changes in physical and chemical characteristics of the soils (Fluvisols, Mollisols) were also determined. Eight treatments comprising different combinations of NPK through inorganic fertilizers and farm yard manure (FYM) were compared. The distilled waste of mint after extraction of essential oil was recycled to soils in the plots to supplement the nutritional requirement of the succeeding mustard crop (Brassica juncea cv. Pusa Bold). Herb and essential oil yield of mint were significantly higher with combined application of organic and inorganic sources of nutrients as compared to single applications. Accumulation of N and P was at par under full inorganic and combined supply whereas, K accumulation was higher with the former. Soil organic C and pH after harvest of mint did not significantly differ among the treatments, but the level of mineralizable N, Olsen-P and NH₄OAc extractable K were higher in soil with integrated supply of nutrients. Significant increase in soil water stable aggregates, organic C, available NPK and microbial biomass, and decrease in soil bulk density were observed with waste recycling over fertilizer application. These benefits were reflected in the seed and stubble yield of mustard which succeeded mint. This study indicates that combined application of inorganic fertilizers with organics helps in increasing the availability of nutrients and crop yield and provides a significant effect to the succeeding crop. Similarly, recycling crop residues reduces the need for fossil fuel based fertilizer, and helps in sustaining and restoring soil fertility in terms of available nutrients and major physical and chemical characteristics of the soil.     

Carbon Management in Agricultural Soils

World soils have been a major source of enrichment of atmospheric concentration of CO₂ ever since the dawn of settled agriculture, about 10,000 years ago. Historic emission of soil C is estimated at 78 ± 12 Pg out of the total terrestrial emission of 136 ± 55 Pg, and post-industrial fossil fuel emission of 270 ± 30 Pg. Most soils in agricultural ecosystems have lost 50 to 75% of their antecedent soil C pool, with the magnitude of loss ranging from 30 to 60 Mg C/ha. The depletion of soil organic carbon (SOC) pool is exacerbated by soil drainage, plowing, removal of crop residue, biomass burning, subsistence or low-input agriculture, and soil degradation by erosion and other processes. The magnitude of soil C depletion is high in coarse-textured soils (e.g., sandy texture, excessive internal drainage, low activity clays and poor aggregation), prone to soil erosion and other degradative processes. Thus, most agricultural soils contain soil C pool below their ecological potential. Adoption of recommend management practices (e.g., no-till farming with crop residue mulch, incorporation of forages in the rotation cycle, maintaining a positive nutrient balance, use of manure and other biosolids), conversion of agriculturally marginal soils to a perennial land use, and restoration of degraded soils and wetlands can enhance the SOC pool. Cultivation of peatlands and harvesting of peatland moss must be strongly discouraged, and restoration of degraded soils and ecosystems encouraged especially in developing countries. The rate of SOC sequestration is 300 to 500 Kg C/ha/yr under intensive agricultural practices, and 0.8 to 1.0 Mg/ha/yr through restoration of wetlands. In soils with severe depletion of SOC pool, the rate of SOC sequestration with adoption of restorative measures which add a considerable amount of biomass to the soil, and irrigated farming may be 1.0 to 1.5 Mg/ha/yr. Principal mechanisms of soil C sequestration include aggregation, high humification rate of biosolids applied to soil, deep transfer into the sub-soil horizons, formation of secondary carbonates and leaching of bicarbonates into the ground water. The rate of formation of secondary carbonates may be 10 to 15 Kg/ha/yr, and the rate of leaching of bicarbonates with good quality irrigation water may be 0.25 to 1.0 Mg C/ha/yr. The global potential of soil C sequestration is 0.6 to 1.2 Pg C/yr which can off-set about 15% of the fossil fuel emissions.     

Long-term changes in soil fertility in organic arable farming systems in England,with particular reference to phosphorus and potassium

Organic farming has undergone significant expansion in Europe over the last decade and it is often seen as a sustainable alternative to intensive agricultural systems. If it is to be truly sustainable, it must maintain levels of soil fertility sufficient for economic crop production in the long-term, whilst also protecting the environment. This paper presents results comparing soils managed organically for at least 15 years, with soils under conventional management, on four arable farms in England. There were no significant differences in total soil organic matter, total nitrogen or C:N ratio between the conventionally and organically managed soils. However, concentrations of extractable potassium and phosphorus were significantly lower in soils managed organically. The largest difference between the conventional and organic fields in potassium concentration was on the oldest organic farm. These results support the argument that organic mixed arable systems are mining reserves of potassium and phosphorus, built up during conventional management, and that changes to organic management practices to increase inputs of potassium and phosphorus are required, if long-term declines in soil fertility, and thus, yields are to be avoided.     

Potential and sustainability for carbon sequestration with improved soil management in agricultural soils of China

Arable land soils generally have lower organic carbon (C) levels than soils under native vegetation; increasing the C stocks through improved management is suggested as an effective means to sequester CO₂ from the atmosphere. China's arable lands, accounting for 13% of the world's total, play an important role in soil C sequestration, but their potential to enhance C sequestration has not yet been quantitatively assessed. The C sequestration by agricultural soils is affected by many environmental factors (such as climate and soil conditions), biological processes (crop C fixation, decomposition and transformation), and crop and soil management (e.g. tillage and manure application). Estimation of the C sequestration potential requires the quantification of the combined effects of these factors and processes. In this study, we used a coupled remote sensing- and process-based ecosystem model to estimate the potential for C sequestration in agricultural soils of China and evaluated the sustainability of soil C uptake under different soil management options. The results show that practicing no-tillage on 50% of the arable lands and returning 50% of the crop residue to soils would lead to an annual soil C sequestration of 32.5 Tg C, which accounts for about 4% of China's current annual C emission. Soil C sequestration with improved soil management is highly time-dependent; the effect lasted for only 20–80 years. Generally, practicing no-tillage causes higher rate and longer sustainability of soil C sequestration than only increasing crop residue into soils. The potential for soil C sequestration varied greatly among different regions due to the differences in climate, soil conditions and crop productivity.     

Organic inputs for soil fertility management in tropical agroecosystems: application of an organic resource database

Organic resources play a critical role in both short-term nutrient availability and longer-term maintenance of soil organic matter in most smaller holder farming systems in the tropics. Despite this importance, there is little predictive understanding for the management of organic inputs in tropical agroecosystems. In this paper, an organic resource database (ORD) is introduced that contains information on organic resource quality parameters including macronutrient, lignin and polyphenol contents of fresh leaves, litter, stems and/or roots from almost 300 species found in tropical agroecosystems. Data on the soil and climate from where the material was collected are also included, as are decomposition and nutrient release rates of many of the organic inputs. Examples of uses of ORD are provided in the paper: (1) nutrient contents (including median values and ranges) and other resource quality parameters of farmyard manure and crop residues are compared to that of alternative nutrient sources such as different plant parts and plant types; (2) nutrient stocks found in farm boundary hedges are estimated and evaluated as a source of nutrients for soil fertility management; (3) hypotheses regarding the indices and critical values of N, lignin, and polyphenol contents for predicting N release rates are tested; (4) organic materials for soil fertility management experiments are selected. This database, when coupled with models and decision support tools, will help advance organic matter management for soil fertility improvement from an empirical to a predictive practice.     

Farmers’ nutrient management practices in indigenous cropping systems in southern Cameroon

With increasing population densities, food production needs to be increased. A common response of farmers is to shorten fallow periods, which can lead to a decline in crop yields, due to incomplete nutrient replenishment. However, whether farmers change their management of soil and nutrients according to the fallow length is not known. A survey was carried out in southern Cameroon in 1995 to establish factors determining farmers’ nutrient management practices (NMPs). Three classes of indigenous NMPs were identified: crop placement, mulching, and the use of inputs. Crop placement comprised intentional cultivation of certain crops in ash patches or near to tree trunks and stumps. Mulching was done with weeds and crop residues, on the soil surface next to crops or in planting holes. Crop placement was found in 88.8% of fields and mulching in 57.4%, while inputs were used in only 1.7%. Nutrient management seemed to be restricted to an optimal allocation of crops to nutrient sources in the field.Relationships were weak between the frequency of crop placement or mulching and indices of land or labor availability. Fallow length seems to be negatively correlated to crop placement at rotten trunks or stumps or in ash patches and positively to placement near recently felled trees. Crop placement and mulching of crop residues were used less often in simplified crop associations than in traditional intercrops. Nutrient inputs were mainly given to monocrops. Application of purchased inputs concentrated on commercial crops.Most respondents knew the advantages and risks of currently practiced methods, but often lacked information on the use of locally available internal inputs (refuse, kitchen ash, manure). Application of internal inputs was considered too labor demanding. The use of purchased inputs was limited by high prices. Soil fertility was in most cases not regarded as a problem.     

农田土壤碳循环过程及其量化方法

已有研究表明除了作物碳（根际沉积碳和秸秆碳）对农田土壤有机碳（SOC）的输入外，土壤碳还来源于土壤自养微生物固定SOC的贡献以及土壤无机碳（SIC）的固定（无机化学途径和微生物的生物矿化途径）.农田SOC的高低主要受到外源作物碳输入和原有SOC分解的平衡作用.作物碳输入在短期内通常促进SOC的分解，呈现正（根际）激发效应.通过整合分析主要作物的根际激发效应和秸秆还田的激发效应的研究，发现作物根系生长和秸秆还田引起的（根际）激发效应大小平均值分别为75%和67%.尽管秸秆还田通过激发效应引起SOC分解的额外释放，但是土壤残留秸秆碳通常大于激发效应导致SOC的额外损失，因此秸秆还田可能增加SOC的储量.在农田系统中，秸秆碳和根际沉积碳往往共存，这导致土壤碳输入和输出至少有3个碳源（根际沉积碳、秸秆碳和土壤碳），由于多碳源体系的区分方法存在挑战，目前这两种作物碳（根际沉积碳和秸秆碳）对SOC分解的激发效应影响是不清晰的.最后，提出了新量化方法，可以多源区分根际CO₂排放以及SOC中作物碳输入的碳源，以及区分碱性土壤中无机化学和微生物途径对SIC的贡献.研究有助于提高对农田土壤SOC和SIC输入和输出途径的理解，以及农田土壤碳平衡评估的精确度.     

长期施肥下浙江稻田不同颗粒组分有机碳的稳定特征

依托浙江水网地区稻田长期定位施肥试验(1996~2013年),利用固态13C核磁共振波谱技术,研究长期不同施肥措施下土壤各颗粒组分有机碳含量及其化学结构特征.结果表明,与不施肥对照(CK)相比,秸秆与化肥配施(NPKRS)、栏肥与化肥配施(NPKOM)、单施化肥(NPK)和单施栏肥(OM)处理均显著(P0.05)增加了砂粒(2~0.02 mm)、粉粒(0.02~0.002mm)和黏粒(0.002 mm)组分中有机碳含量;而单施秸秆(RS)处理仅显著增加砂粒组分有机碳含量.此外,与单施化肥处理相比,有机肥和化肥配施促进了新增有机碳在粉粒和黏粒组分的分配,更有利于新增有机碳的稳定.应用13C-NMR波谱技术进行结构表征,结果表明粉粒和黏粒组分有机碳的化学结构存在明显差异,粉粒组分烷氧碳、芳香碳的相对含量高于黏粒,而烷基碳、羰基碳的相对含量低于黏粒.长期有机肥与化肥配施下粉粒和黏粒烷基碳相对含量较单施有机肥处理分别降低9.1%~11.9%和13.7%~19.9%,烷氧碳的相对含量则分别增加2.9%~6.3%和13.4%~22.1%,表明有机肥与化肥配施处理降低了粉粒和黏粒组分有机碳的分解程度.长期单施化肥处理下粉粒和黏粒组分有机质的芳化度和疏水性低于单施有机肥处理和不施肥处理,有机质的矿化稳定性较低.长期有机肥与化肥配施,尤其是NPKOM处理,通过增加化学抗性化合物和碳水化合物的积累,并且减缓活性组分的分解提高粉粒和黏粒组分有机碳含量,是促进稻田土壤有机碳可持续积累的有效措施.     

秸秆还田模式对农田土壤碳库特性及产量的影响

为探明南方稻麦两熟制农田秸秆还田模式对土壤总有机碳、活性有机碳、碳库管理指数和稻麦产量的影响,论文通过8 a的水稻-小麦轮作田间定位试验,设置了4个秸秆还田模式处理：秸秆不还田（CK）、秸秆稻麦季均还田（RW）、仅麦秸稻季还田（W）、仅稻秸麦季还田（R）。结果表明,与CK处理相比,秸秆还田显著提高了0~20 cm土壤的总有机碳、活性有机碳、稳定态有机碳（P<0.05）;不同秸秆还田模式处理之间的土壤总有机碳、稳定态有机碳差异均不显著（P>0.05）,RW处理的活性有机碳、碳库活度指数、碳库管理指数与R处理无显著差异性（P>0.05）,显著大于W处理（P<0.05）;RW与R处理的水稻产量均值无显著差异性（P>0.05）,显著大于W处理;活性有机碳、碳库管理指数与水稻产量均值呈极显著相关（P<0.01）,与小麦产量均值关系不密切（P>0.05）;上述结果表明,与稻麦两季还田模式相比,南方稻麦两熟制农田实施仅稻秆麦季还田模式,并不影响作物稳产性与土壤地力的提升。     

长期施肥对黄土高原梯田土壤养分特征和微生物资源限制的影响

长期不同施肥处理会改变土壤的理化性质和微生物生物量,但长期不同施肥对黄土高原梯田土壤微生物胞外酶活性变化和养分特征的影响尚不清楚.本研究以中国科学院安塞水土保持综合试验站长期养分定位试验样地为基础,分析了不施肥(CK)、有机肥与氮肥混施(MN)、有机肥与磷肥混施(MP)、有机肥、氮肥与磷肥混施(MNP)、单施有机肥(M...     

Managing crop residues, fertilizers and leaf litters to improve soil C, nutrient balances, and the grain yield of rice and wheat cropping systems in Thailand and Australia

This paper reports on the influence that residue and fertilizer management have on nutrient balances, soil organic matter (SOM) dynamics, and crop yields of a flooded rice system in northeast Thailand (1992–1997) and a wheat–forage legume rotation in eastern Australia (1992–1998). Both soils had been subject to at least 18 years of cultivation and had lost up to 90% of the original labile (C_L) and 85% of the total carbon (C_T).For the rainfed rice cropping systems of northeast Thailand, a system is described in which small applications of leaf litter from locally grown trees are applied annually to rice paddy soils prior to transplanting. Annual applications of 1500 kg ha⁻¹ of leaf litter from different locally grown shrubs for five seasons resulted in increases in rice grain yield in 1997 of between 20 and 26% above the no-leaf litter control. Nutrient balances, determined by the difference between the inputs (fertilizer and added leaf litters) and outputs (grain and straw), indicated net positive balances of up to 457 kg N ha⁻¹, and 60 kg P ha⁻¹, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits of up to −13 kg S ha⁻¹ and −52 kg P ha⁻¹, where no leaf litter was applied and rice straw was removed following harvest. Soil carbon (C) concentrations increased significantly only where higher fertilizer rate and rice stubble retention were combined.The poor management of fertilizers and crop residues, and excessive cultivation has also resulted in large soil fertility losses in the grain growing areas of Eastern Australia. After five wheat and two legume/fallow crops, negative N balances of up to −303 kg ha⁻¹ were calculated for the treatments where wheat stubble was not retained and bare fallow leys were used. The balance of nutrients such as K, which are contained in larger proportions in stubble, were found to be up to −362 kg ha⁻¹ on the straw-removed treatments and up to +29 kg ha⁻¹ on the straw-retained treatments. Forage legume leys resulted in short term increases in C_L and the carbon management index (CMI).Sustainable farming systems require that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system. Increases in soil C levels require sustained periods of balanced fertilization and residue retention.     

秸秆连续还田配施化肥对稻-油轮作土壤碳库及作物产量的影响

依据田间连续7 a秸秆还田定位试验,探讨秸秆还田配施化肥对巢湖地区农田土壤剖面（0~20、20~50和50~80 cm）的土壤总有机碳（TOC）、可溶性有机碳（DOC）、颗粒有机碳（POC）、活性有机碳（LOC）、碳库管理指数（CPMI）和作物产量的影响.试验设置无秸秆还田+无施肥（CK）、常规施肥（F）、秸秆还田+常规施肥（SF1）和秸秆还田+80%常规施肥（SF2）这4个处理,分析不同土层土壤总有机碳和组分含量、CPMI和油菜-水稻产量的变化规律.结果表明,以CK为参考,常规施肥和秸秆还田配施化肥均提高了垂直剖面土壤总有机碳和组分的含量,且不同土层土壤总有机碳和组分的含量随土层深度增加而逐渐降低.在0~20 cm土层,与F处理相比,SF1和SF2处理显著提高TOC、DOC、POC和LOC的含量,增幅分别为：14.23%~28.97%、7.86%~27.01%、16.46%~24.24%和5.89%~6.64%（P<0.05）;在20~50 cm土层,SF1较F处理的TOC和LOC的含量显著增加9.43%和8.34%（P<0.05）,SF2较F处理的DOC和POC的含量显著增加17.51%和65.83%（P<0.05）;在50~80 cm土层,各处理间土壤总有机碳和组分的含量均无显著差异.秸秆还田配施化肥对土壤碳库管理指数影响显著,SF1较F处理显著提高0~50 cm土层的CPMI,而F处理的CPMI在50~80 cm土层最大,但各处理间均无显著差异.秸秆还田配施化肥对作物产量具有显著提升作用,且SF1处理的产量最高,SF1较F处理的水稻、油菜和周年产量分别显著增加6.19%、7.67%和6.54%（P<0.05）.总的来说,稻-油轮作模式下秸秆还田配施化肥对提高巢湖地区土壤碳库、土壤肥力和作物产量具有重要意义.     

Agricultural management affects earthworm and termite diversity across humid to semi-arid tropical zones

Earthworm and termite diversity were studied in 12 long-term agricultural field trials across the sub-humid to semi-arid tropical zones of Eastern and Western Africa. In each trial, treatments with high and low soil organic C were chosen to represent contrasts in long-term soil management effects, including tillage intensity, organic matter and nutrient management and crop rotations. For each trial, a fallow representing a relatively undisturbed reference was also sampled. Earthworm taxonomic richness decreased in the direction fallow > high-C soil > low-C soil and earthworm abundance was higher in fallow than under continuous crop production. Termite abundance was not significantly different between fallow and high and low-C treatments and termite taxonomic richness was higher in fallow soil than in the two cropping systems. We concluded that fewer species of earthworms and termites were favored under agricultural management that led to lower soil C. Results indicated that the soil disturbance induced by continuous crop production was more detrimental to earthworms than to termites, when compared to the fallow.     

Are soils of Iowa USA currently a carbon sink or source? Simulated changes in SOC stock from 1972 to 2007

Upscaling the spatial and temporal changes in carbon (C) stocks and fluxes from sites to regions is a critical and challenging step toward improving our understanding of the dynamics of C sources and sinks over large areas. This study simulated soil organic C (SOC) dynamics within 0–100 cm depth of soils across the state of Iowa in the USA from 1972 to 2007 using the General Ensemble biogeochemical Modeling System (GEMS). The model outputs with variation coefficient were analyzed and assembled from simulation unit to the state scale based upon major land use types at annual step. Results from this study indicate that soils (within a depth of 0–100 cm) in Iowa had been a SOC source at a rate of 190 ± 380 kg C ha^?1 yr^?1. This was likely caused by the installation of a massive drainage system which led to the release of SOC from deep soil layers previously protected under poor drainage conditions. The annual crop rotation was another major force driving SOC variation and resulted in spatial variability of annual budgets in all croplands. Annual rate of change of SOC stocks in all land types depended significantly on the baseline SOC levels; soils with higher SOC levels tended to be C sources, and those with lower levels tended to be C sinks. Management practices (e.g., conservation tillage and residue management practices) slowed down the C emissions from Iowa soils, but could not reverse the general trend of net SOC loss in view of the entire state due mainly to a high level of baseline SOC stocks.     

耕作深度调控秸秆还田对农田土壤呼吸的影响

秸秆还田和耕作深度处理是影响农田土壤呼吸最重要的农业管理措施之一,但二者交互作用影响农田土壤呼吸的机制尚不清楚.基于此,针对中国的旱地农田生态系统,利用已发表的116篇研究论文,借助Meta分析技术,探究秸秆还田和耕作深度处理及其二者交互作用对农田土壤呼吸的影响及其调控因素,为农田生态系统实现“碳中和”提供重要的数据支撑和理论依据.结果表明,免耕导致土壤呼吸减少了8.3%,而浅耕和深耕处理对土壤呼吸的影响不显著,但对土壤呼吸的增加量仍呈现出深耕>浅耕>免耕的趋势.虽然,浅耕和深耕对土壤呼吸和土壤有机碳（SOC）的影响均相对较小,但是免耕导致土壤呼吸减少了8.3%的同时却又导致SOC增加了7.05%,因此实施免耕措施对农田土壤固碳减排具有重要意义.此外,耕作深度会显著调控秸秆还田对土壤呼吸的影响,且土壤呼吸的增加量呈现出深耕秸秆还田>浅耕秸秆还田>免耕秸秆还田的趋势,整体平均增加了14.51%.秸秆还田后不同深度耕作处理下土壤呼吸的增加量与土壤容重、农作物产量、土壤有机碳、以及土壤温度和水分的改变量密切相关,且对土壤呼吸增加量的贡献呈现出土壤容重>农作物产量>土壤有机碳>土壤水分>土壤温度的趋势.虽然SOC在深耕秸秆还田、浅耕秸秆还田和免耕秸秆还田处理下分别增加了29.32%、10.12%和23.94%,但是土壤呼吸在深耕秸秆还田和浅耕秸秆还田处理分别增加了29.32%和18.92%,而在免耕秸秆还田处理下仅增加1.2%.所以,免耕秸秆还田也有利于农田土壤固碳减排.因此,在中国的旱地农田生态系统中,耕作深度会调控秸秆还田对土壤呼吸的影响程度,而这种调控主要与土壤理化性质有关,尤其与土壤容重关系最为紧密,且免耕和免耕秸秆还田均是有利于农田土壤固碳减排的重要农业管理措施.     

Organic carbon stratification and size distribution of three typical paddy soils from Taihu Lake region, China

Developing realistic soil carbon (C) sequestration strategies for China’s sustainable agriculture relies on accurate estimates of the amount, retention and turnover rates of C stored in paddy soils. Available C estimates to date are predominantly for the tilled and flood-irrigated surface topsoil (ca. 30 cm). Such estimates cannot be used to extrapolate to soil depths of 100 cm since soil organic carbon (SOC) generally shows a sharp decrease with depth. In this research, composite soil samples were collected at several depths to 100 cm from three representative paddy soils in the Taihu Lake region, China. Soil organic carbon distribution in the profiles and in aggregate-size fractions was determined. Results showed that while SOC decreased exponentially with depth to 100 cm, a substantial proportion of the total SOC (30%–40%) is stored below the 30 cm depth. In the carbon-enriched paddy topsoils, SOC was found to accumulate preferentially in the 2–0.25 and 0.25–0.02 mm aggregate size fractions. σ13C analysis of the coarse micro-aggregate fraction showed that the high degree of C stratification in the paddy topsoil was in agreement with the occurrence of lighter @1313C in the upper 30 cm depth. These results suggest that SOC stratification within profiles varies with di erent pedogenetical types of paddy soils with regards to clay and iron oxyhydrates distributions. Sand-sized fractions of aggregates in paddy soil systems may play a very important role in carbon sequestration and turnover, dissimilar to other studied agricultural systems.