Priming effects in different soil types induced by fructose, alanine, oxalic acid and catechol additions

It is well established that certain substrate additions to soils may accelerate or retard the mineralisation of soil organic matter. But up to now, research on these so called ‘priming effects’ was almost exclusively conducted with arable soils and with plant residues or glucose as additives. In this study, the effects of the uniformly ¹⁴C-labelled substrates fructose, alanine, oxalic acid and catechol on the mineralisation of soil organic carbon (SOC) from different horizons of two forest soils (Haplic Podzol and Dystric Cambisol) and one arable soil (Haplic Phaeozem) under maize and rye cultivation were investigated in incubation experiments for 26 days. Apart from the controls, all samples received substrate additions of 13.3 μg substrate-C mg⁻¹ C_org. During the incubation, CO₂-evolution was measured hourly and the amount of ¹⁴CO₂ was determined at various time intervals. In almost all soils, priming effects were induced by one or several of the added substrates. The strongest positive priming effects were induced by fructose and alanine and occurred in the Bs horizon of the Haplic Podzol, where SOC mineralisation was nearly doubled. In the other soil samples, these substrates enhanced SOC mineralisation by +10 to +63%. Catechol additions generally reduced SOC mineralisation by −12 to −43% except in the EA horizon of the Haplic Podzol where SOC-borne CO₂-evolution increased by +46%. Oxalic acid also induced negative as well as positive priming effects ranging from −24 to +82%. The data indicate that priming effects are ubiquitously occurring in surface and subsoil horizons of forest soils as well as in arable soils. Although a broad variety of soils was used within this study, relationships between soil properties and priming effects could not be ascertained. Therefore, a prediction on occurrence and magnitude of priming effects based on relatively easily measurable chemical and physical soil properties was not possible. Nevertheless, the data suggest that positive priming effects are most pronounced in forest soils that contain SOC of low biodegradability, where the added substrates may act as an important energy source for microbial metabolism.     

耕地土壤有机碳组分的季节变化

Carbon fractions in soils apparently vary not only in space, but also over time. A lack of knowledge on the seasonal variability of labile carbon fractions under arable land hampers the reliability and comparability of soil organic carbon(SOC) surveys from different studies. Therefore, we studied the seasonal variability of two SOC fractions, particulate organic matter(POM) and dissolved organic carbon(DOC), under maize cropping: POM was determined as the SOC content in particle-size fractions, and DOC was measured as the water-extractable SOC(WESOC) of air-dried soil. Ammonium, nitrate, and water-extractable nitrogen were measured as potential regulating factors of WESOC formation because carbon and nitrogen cycles in soils are strongly connected. There was a significant annual variation of WESOC(coefficient of variation(CV) = 30%). Temporal variations of SOC in particle-size fractions were smaller than those of WESOC. The stocks of SOC in particle-size fractions decreased with decreasing particle sizes, exhibiting a CV of 20%for the coarse sand-size fraction(250–2 000 μm), of 9% for the fine sand-size fraction(50–250 μm), and of 5% for the silt-size fraction(20–50 μm). The WESOC and SOC in particle-size fractions both peaked in March and reached the minimum in May/June and August, respectively. These results indicate the importance of the time of soil sampling during the course of a year, especially when investigating WESOC.     

Priming effects of sugars,amino acids,organic acids and catechol on the mineralization of lignin and peat

The ¹⁴C‐labeled substrates glucose, fructose, alanine, glycine, oxalic acid, acetic acid, and catechol were incubated at 20 °C in a model system that consisted of sand mixed with lignin or peat (3 % C_org). Each substrate was added at either 80 or 400 μg C (g sand)^—1. During 26 days of incubation with an inoculum extracted from forest soil, the amount of CO₂ evolved was measured hourly. The amount of ¹⁴CO₂ was determined after 4, 6, 12, 19, and 26 days. After 26 days of incubation, each substrate showed priming effects, but not in all examined treatments. Most substrates stimulated the degradation of the model substances (positive priming effects). Negative priming effects only were found in the lignin system with oxalic acid and catechol addition at both concentrations. The strongest positive priming occurred in the peat system with the oxalic acid addition of 80 μg C g^—1 where 1.8 % of the peat were mineralized after 26 days, compared to 0.7 % in the control. The addition of 400 μg alanine‐C g^—1 caused the strongest increase in lignin mineralization, amounting to 3.9 % compared to 2.8 % in the control. During the incubation the extent of priming changed with time. Most substrates caused the strongest effects during the first 4 to 10 days of incubation. The extent of priming depended on substrate type, substrate concentration, and organic model substance. Possibly this is due to the activation of different microorganisms.     

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.     

添加牛粪对长期不同施肥潮土有机碳矿化的影响及激发效应

为了探讨长期不同施肥潮土有机碳矿化对添加牛粪的响应特征及添加牛粪对长期不同施肥潮土有机碳矿化的激发效应,以始建于1986年的长期定位试验为平台,通过室内恒温培养的方法研究添加等氮量牛粪后长期不同施肥(不施肥,CK;常量有机肥,SMA;常量化肥,SMF;常量有机无机配施,1/2(SMA+SMF))潮土有机碳矿化、土壤有机碳及活性碳库组分(微生物量碳、可溶性有机碳、颗粒有机碳和易氧化有机碳)含量的变化特征。结果表明:无论添加牛粪与否,长期不同施肥潮土有机碳矿化过程均符合一级动力学方程,而牛粪的添加显著增加了长期不施肥、长期单施化肥和长期有机无机配施土壤的有机碳矿化速率常数,增长幅度分别为21.74%、35.00%和45.00%;添加牛粪提高了长期不同施肥潮土有机碳、微生物量碳、颗粒有机碳和易氧化有机碳含量,却显著降低了可溶性有机碳含量;牛粪对长期不施肥、长期施用常量有机肥、常量化肥和常量有机无机配施潮土有机碳矿化的正激发效应分别达到了48.56%、3.60%、48.43%和3.92%,且对长期不施肥及长期施用常量化肥潮土的激发效应显著高于对长期施用常量有机肥及长期有机无机配施土壤;冗余分析显示添加牛粪对长期不同施肥土壤有机碳矿化的激发效应与土壤活性组分碳氮比呈正相关,与土壤养分含量呈负相关。该研究不仅为合理施用有机肥和实现农田生态系统的可持续发展提供理论依据,还有利于实现农业资源再利用及其效益最大化。     

Molecular composition and structure of organic matter in density fractions of soils amended with corn straw for five years

Corn straw is an important source of carbon (C),and when applied to soil,it alters the accumulation and distribution of organic C.However,the mechanistic pathways by which newly added C is stored and stabilized in soil remain a subject of interest and debate among scholars.In this study,we investigated the chemistry of organic matter in different density fractions of Haplic Cambisol (sandy clay loam) in a field experiment with corn straw at8 900 kg ha^-1year^-1under no tillag...     

The quality of exogenous organic matter: short-term effects on soil physical properties and soil organic matter fractions

We examined the short-term effect of five organic amendments and compared them to plots fertilized with inorganic fertilizer and unfertilized plots on aggregate stability and hydraulic conductivity, and on the OC and ON distribution in physically separated SOM fractions. After less than 1 year, the addition of organic amendments significantly increased ( P  <   0.01) the aggregate stability and hydraulic conductivity. The stability index ranged between 0.97 and 1.76 and the hydraulic conductivity between 1.23 and 2.80 × 10⁻³ m/s for the plots receiving organic amendments, compared with 0.34–0.43, and 0.42–0.64 × 10⁻³ m/s, respectively, for the unamended plots. There were significant differences between the organic amendments (P <  0.01), although these results were not unequivocal for both soil physical parameters. The total OC and ON content were significantly increased ( P  <   0.05) by only two applications of organic fertilizers: between 1.10 and 1.51% OC for the amended plots versus 0.98–1.08% for the unamended and between 0.092 and 0.131% ON versus 0.092–0.098% respectively. The amount of OC and ON in the free particulate organic matter fraction was also significantly increased ( P  <   0.05), but there were no significant differences ( P  <   0.05) in the OC and ON content in the POM occluded in micro-aggregates and in the silt + clay-sized organic matter fraction. The results showed that even in less than 1 year pronounced effects on soil physical properties and on the distribution of OC and ON in the SOM fractions occurred.     

连续五年生物垃圾堆肥施用后地中海蔬菜种植系统中土壤有机碳的变化

Biowaste compost can influence soil organic matter accumulation directly or indirectly. A 5-year experiment was conducted to assess the influence of biowaste compost on the process of soil aggregation and soil organic carbon(SOC) accumulation in a Mediterranean vegetable cropping system. The study involved four treatments: biowaste compost(COM), mineral NPK fertilizers(MIN), biowaste compost with half-dose N fertilizer(COMN), and unfertilized control(CK). The SOC stocks were increased in COM, COMN, and MIN by 20.2, 14.9, and 2.4 Mg ha~(-1)over CK, respectively. The SOC concentration was significantly related to mean weight diameter of aggregates(MWD)(P 0.05, R~2= 0.798 4) when CK was excluded from regression analysis. Compared to CK, COM and COMN increased the SOC amount in macroaggregates( 250 μm) by 2.7 and 0.6 g kg~(-1)soil, respectively, while MIN showed a loss of 0.4g kg~(-1)soil. The SOC amount in free microaggregates(53–250 μm) increased by 0.9, 1.6, and 1.0 g kg~(-1)soil for COM, COMN, and MIN, respectively, while those in the free silt plus clay aggregates( 53 μm) did not vary significantly. However, when separating SOC in particle-size fractions, we found that more stable organic carbon associated with mineral fraction 53 μm(MOM-C) increased significantly by 3.4, 2.2, and 0.7 g kg~(-1)soil for COM, COMN, and MIN, respectively, over CK, while SOC amount in fine particulate organic matter(POM) fraction(53–250 μm) increased only by 0.3 g kg~(-1)soil for both COM and COMN, with no difference in coarse POM 250 μm. Therefore, we consider that biowaste compost could be effective in improving soil structure and long-term C sequestration as more stable MOM-C.     

莎草诱导土壤有机碳的激发效应

为了探索添加莎草后土壤有机碳的激发效应发生机制,采用室内控制试验,向培育土壤内添加莎草碎片、增施氮磷元素,测定土壤有机碳(SOC)含量、微生物量、土壤δ_(13)C值,计算土壤中"新碳"(源于莎草的)和"旧碳"(土壤原有的)的含量。结果表明,75 d后,对照组SOC降低了11 mg·kg~(-1),氮磷营养组SOC降低了10 mg·kg~(-1),莎草组SOC含量先升高而后下降(最终降低了44 mg·kg~(-1)),莎草+氮磷营养组SOC含量先升高而后下降(最终增加了75 mg·kg~(-1))。土壤δ_(13)C值的变化说明土壤添加莎草后,"旧碳"分解速率加快,诱导了激发效应的发生。添加莎草组中,77.8%的莎草被微生物呼吸作用消耗掉,22.2%转化成"新碳"固定到土壤中。除去激发效应消耗的土壤碳(144 mg·kg~(-1)),土壤总有机碳含量降低了30 mg·kg~(-1);莎草+氮磷处理中,64.0%的莎草被呼吸作用消耗掉,36.0%被固定于土壤中,除去激发效应消耗的94 mg·kg~(-1),总土壤有机碳增加了68 mg·kg~(-1)。莎草处理中,土壤激发效应损失的碳量占莎草分解碳量的37.0%,植物+氮磷处理仅占29.3%,土壤激发效应损失的"旧碳"量远低于莎草呼吸作用损失的碳量。本研究结果为进一步探究土壤添加莎草后激发效应机理提供了参考依据。     

Effects of fallow or planting wheat (Triticum aestivum L.) and fertilizing P or fertilizing P and N practices on soil carbon and nitrogen in a low-organic-matter soil

Soil carbon (C) and nitrogen (N) are important for maintaining soil fertility, and they are considerably affected by soil use and management. In the present study, we conducted an 8-year ?eld experiment on loessial dryland soil (Eum-Orthic Anthrosol, Food and Agriculture Organization of the United Nations (FAO)) in the southern Loess Plateau, China. We tested four soil management regimes—i.e., winter wheat (Triticum aestivum L.) cultivation with phosphorus (P) fertilization (WP), winter wheat cultivation with N and P fertilization (WNP), natural fallow (NF) and bare fallow (BF)—to evaluate their effects on soil C and N fractions. After 8 years, compared with the WNP treatment, the total soil organic nitrogen (SON) in the WP treatment decreased by 14.6% and 36.8%, and microbial biomass nitrogen (MBN) by 35.6% and 61.1%, at 0–20 and 20–40 cm soil depths, respectively. The soil heavy fraction nitrogen (HFN) and light fraction nitrogen (LFN) in the WP treatment also decreased by 36.6% and 39.4%, respectively. Furthermore, BF treatment decreased total soil organic carbon (SOC), heavy fraction carbon (HFC), LFN and MBN at both soil depths with average reductions of 43.4%. The NF treatment decreased light fraction carbon (LFC) by 17.0% at 0–20 cm soil depth, as well as MBN by 24.8% and 71.2%, and inorganic C by 29.1% and 23.8%, at 0–20 and 20–40 cm soil depths, respectively. There was no significant difference of microbial biomass C concentration among the WP, NF and BF treatments. These results confirmed that a lack of N fertilization decreased SON, BF reduced both SOC and SON, and NF decreased soil inorganic C. Therefore, the managements of a recommended rate of N fertilizer application and shortened time of bare fallow are critical for maintaining or increasing SON fraction sequestration, and natural fallow management is not a useful method for maintaining soil fertility in dryland in the Loess Plateau in China.

Abbreviations: HFC: heavy fraction carbon; HFN: heavy fraction nitrogen; LFC: light fraction carbon; LFN: light fraction nitrogen; MBC: microbial biomass carbon; MBN: microbial biomass nitrogen; SOC: soil organic carbon; SON: soil organic nitrogen     

不同有机物料对苏打盐化土有机碳和活性碳组分的影响

【目的】在大同盆地苏打盐化土上,研究不同有机物料对春玉米产量、土壤有机碳及活性碳组分的影响,明确土壤有机碳及活性碳组分与主要盐碱指标的相关关系,为苏打盐化土改良及有机物料资源化利用提供理论支撑。【方法】2016-2017年在山西省北部怀仁县开展田间定位试验,设对照(CK)、风化煤、生物炭、牛粪和秸秆5个处理,各处理有机物料施用量按照每年9000 kg/hm^2等有机碳投入量折算,收获时对春玉米进行测产。2017年春玉米收获后,采集土壤样品测定土壤有机碳总量(SOC)和水溶性有机碳(WSOC)、易氧化有机碳(EOC)、轻组有机碳(LFOC)含量,分析土壤活性碳组分占有机碳的比例、土壤有机碳及活性碳组分与盐碱指标之间的关系。【结果】与CK相比,生物炭和秸秆处理春玉米产量无明显差异,而风化煤和牛粪处理春玉米产量则分别显著提高30.2%和30.3%。添加有机物料促进了0-20 cm土层SOC累积,其中以风化煤和牛粪处理效果最佳,较CK分别提高47.6%和36.1%。在有机碳组分方面,风化煤和牛粪处理提高WSOC、EOC含量的效果显著高于生物炭、秸秆处理;风化煤、牛粪和秸秆处理的LFOC含量显著高于生物炭处理。四类有机物料处理的WSOC占总有机碳的比例差异不显著,牛粪处理的占比显著高于CK。EOC占总有机碳的比例以牛粪处理最高,风化煤次之,且二者均显著高于CK处理;LFOC占总有机碳的比例则表现为秸秆、牛粪>风化煤、生物炭> CK。此外,添加有机物料能有效降低0-20 cm土层土壤pH、电导率(EC)和碱化度(ESP),其中以风化煤和牛粪处理降幅最大。相关分析表明,土壤SOC与pH、EC和ESP呈显著负相关。【结论】通过有机物料改良效果比较,发现牛粪和风化煤处理能促进苏打盐化土有机碳累积,提高可溶性、易氧化态及轻组有机碳组分在总有机碳中的占比,降低土壤pH、EC和ESP,明显提高春玉米产量。因此,风化煤和牛粪是山西北部苏打盐化土良好的改良剂。     

Changes of soil organic carbon and its fractions in relation to soil physical properties in a long-term fertilized paddy

Soil organic carbon (SOC) has an important role in improving soil quality and sustainable production. A long-term fertilization study was conducted to investigate changes in SOC and its relation to soil physical properties in a rice paddy soil. The paddy soils analyzed were subjected to different fertilization practices: continuous application of inorganic fertilizers (NPK, N–P–K = 120–34.9–66.7 kg ha⁻¹ yr⁻¹ during 1967–1972 and 150–43.7–83.3 kg ha⁻¹ yr⁻¹ from 1973 to 2007), straw based compost (Compost, 10 Mg ha⁻¹ yr⁻¹), a combination of NPK + Compost, and no fertilization (control). Soil physical properties were investigated at rice harvesting stage in the 41st year for analyzing the relationship with SOC fraction. Continuous compost application increased the total SOC concentration in plough layers and improved soil physical properties. In contrast, inorganic or no fertilization markedly decreased SOC concentration resulting to a deterioration of soil physical health. Most of the SOC was the organo-mineral fraction (<0.053 mm size), accounting for over 70% of total SOC. Macro-aggregate SOC fraction (2–0.25 mm size), which is used as an indicator of soil quality rather than total SOC, covered 8–17% of total SOC. These two SOC fractions accumulated with the same tendency as the total SOC changes. Comparatively, micro-aggregate SOC (0.25–0.053 mm size), which has high correlation with physical properties, significantly decreased with time, irrespective of the inorganic fertilizers or compost application, but the mechanism of decrease is not clear. Conclusively, compost increased total SOC content and effective SOC fraction, thereby improving soil physical properties and sustaining production.     

In-situ warming does not change soil priming effect induced by glucose addition in a temperate forest

Priming effect (PE) on soil organic carbon (SOC) decomposition caused by the addition of organic carbon (C) is an important ecological process in regulating soil C cycle. Additionally, most priming studies are confined to laboratory trials, while the assessment of soil PE under field conditions with variable weather conditions is scarce. This study assessed the direct effects of glucose addition and in-situ warming on the extent of PE under field conditions in a temperate forest. We evaluated soil PE using ¹³C-glucose labelling, a simple and novel technique, based on the Keeling plot method. Glucose addition significantly enhanced native SOC decomposition and induced strong PE. However, the effect of in-situ warming on the extent of PE was not significant. This study confirms the importance of PE in regulating SOC turnover under field conditions.     

Carbon and nitrogen mineralization after maize harvest between and within maize rows: a microcosm study using 13C natural abundance

The sequestration of carbon in soil is not completely understood, and quantitative information about the rates of soil organic carbon (SOC) turnover could improve understanding. We analyzed the effects of the uneven distribution of crop residues after harvest of silage maize on C and N losses (CO₂‐C, dissolved organic carbon (DOC) and nitrogen (DON), and NO₃^–) from a Haplic Phaeozem and on the occurrence of priming effects induced by the decomposition of accumulated maize residues. Soil columns were taken from a continuous maize (since 1961) field after harvest i) between maize stalk rows (M_bare), ii) within the maize rows including a standing maize stalk (M_stalk), and iii) from a continuous rye (since 1878) field after tillage (rye stalk and roots were mixed into the Ap horizon). The soil columns were incubated for 230 days at 8 °C with an irrigation rate of 2 mm 10^–2 M CaCl₂ per day. Natural ¹³C abundance was used to distinguish between maize‐derived C (in SOC and maize residues) and older C originating from former C₃ vegetation. The uneven distribution of maize residues resulted in a considerably increased heterotrophic activity within the maize rows as compared with soil between seed rows. Cumulative CO₂ production was 53.1 g CO₂‐C m^–2 for M_stalk and 23.3 g CO₂‐C m^–2 for M_bare. The contribution of maize‐derived C to the total CO₂ emission was 83 % (M_stalk) and 67 % (M_bare). Calculated as difference between CO₂‐C release from M_stalk and M_bare, 19 % of the maize residues (roots and stalk) in M_stalk were mineralized during the incubation period. There was no or only a marginal effect of the accumulation of maize residues in M_stalk on leaching of DOC, DON, and NO₃^–. Total DOC and DON leaching amounted to 2.5 g C m^–2 and 0.16 g N m^–2 for M_stalk and to 2.1 g C m^–2 and 0.12 g N m^–2 for M_bare. The contribution of maize‐derived C to DOC leaching was about 25 % for M_stalk and M_bare. Nitrate leaching amounted to 3.9 g NO₃^–‐N m^–2 for M_stalk and to 3.5 g NO₃^–‐N m^–2 for M_bare. There was no priming effect induced by the decomposition of fresh maize residues with respect to CO₂ or DOC production from indigenous soil organic carbon derived from C₃ vegetation.     

长期施肥对栗褐土有机碳含量及其组分的影响

【目的】作为土壤质量的重要指标,土壤有机碳及其组分在耕地生产力和作物产量方面发挥着重要作用。本文以25年长期定位施肥试验为依托,分析了不同施肥处理对栗褐土有机碳含量及其组分的影响,为调控农田土壤肥力及栗褐土有机碳库的管理提供科学依据。【方法】田间试验开始于1988年,设置8个施肥处理为不施肥(CK);单施氮肥(N);氮磷肥合施(NP);单施低量有机肥(M1);低量有机肥与氮肥合施(M1N);低量有机肥与氮磷肥合施(M1NP);高量有机肥与氮肥合施(M2N);高量有机肥与氮磷肥合施(M2NP)。于第25年玉米播种前,采集以上处理的耕层(0—20 cm)土壤样品。借助有机碳物理分组方法和化学分析方法,测定了土壤总有机碳和有机碳各组分的含量。【结果】长期施用不同肥料不同程度地提高了栗褐土总有机碳、游离态颗粒有机碳以及闭蓄态颗粒有机碳含量,其中有机肥与化肥配施尤其是高量有机肥与化肥配施的作用更加明显。与不施肥相比,高量有机肥与无机肥配施(M2N、M2NP)总有机碳含量增加了121.1%、166.8%,游离态颗粒有机碳增加了239.2%、359.2%,闭蓄态颗粒有机碳增加了288.4%、289.9%。单施氮肥(N)及有机肥与氮磷肥配施(M1NP、M2NP)可显著提高矿物结合态有机碳含量,增幅分别为27.8%、34.8%、33.3%。不施肥条件下,栗褐土有机碳中颗粒有机碳与矿物结合态有机碳所占的比例相当,长期施肥提高了颗粒有机碳特别是闭蓄态颗粒有机碳的比例,降低矿物结合态有机碳所占的比例,闭蓄态颗粒有机碳成为栗褐土有机碳的主要贮存库。相关分析表明,长期施肥条件下栗褐土游离态、闭蓄态颗粒有机碳含量之间及其与总有机碳含量之间均呈极显著正相关,矿物结合态有机碳含量与总有机碳及其他组分的有机碳之间均无明显相关。【结论】化肥、有机肥以及有机肥与化肥配施能够提高栗褐土游离态颗粒有机碳、闭蓄态颗粒有机碳以及总有机碳含量。高量有机肥与化肥配施更有助于栗褐土游离态、闭蓄态颗粒有机碳的积累,有利于土壤养分有效性的提高和有机碳品质的改善。氮肥单施、有机肥与氮磷肥配施则是提高矿物结合态有机碳含量的有效措施。     

Effects of different quality plant residues on soil carbon accumulation and aggregate formation in a tropical sandy soil in Northeast Thailand as revealed by a 10‐year field experiment

Particulate organic matter (POM) plays important role in soil organic carbon (SOC) retention and soil aggregation. This paper assesses how quality (chemical composition) of four different‐quality organic residues applied annually to a tropical sandy loam soil for 10 years has affected POM pools and the development of soil aggregates. Water‐stable aggregate size distribution (>2, 0·25–2, 0·106–0·25 mm) was determined through wet sieving. Density fractionation was employed to determine POM (light—LF, and heavy—HF fractions, 0·05–1 mm). Tamarind leaf litter showed the highest SOC (<1 mm) accumulation, while rice straw showed the lowest. LF‐C contents had positive correlations with high contents of C and recalcitrant constituents, (i.e. lignin and polyphenols) of the residues. Dipterocarp, a resistant residue, showed the highest LF‐C, followed by the intermediate residues, tamarind, and groundnut, whereas HF was higher in groundnut and tamarind than dipterocarp residues. Rice straw had the lowest LF‐ and HF‐C contents. Tamarind had the highest quantity (51 per cent) of small macroaggregates (0·25–2 mm), while dipterocarp had the most (2·1 per cent) large macroaggregates (>2 mm). Rice straw had the lowest quantities of both macroaggregates. Similar to small‐sized HF (0·05–0·25 mm), small macroaggregates had positive correlation with N and negative correlation with C/N ratios, while large macroaggregates had positive correlations with C and recalcitrant constituents of the residues. Tamarind, with intermediate contents of N and recalcitrant compounds, appears to best promote small macroaggregate formation. Carbon stabilized in small macroaggregates accounted for the tamarind treatment showing the largest SOC accumulation. Copyright © 2010 John Wiley & Sons, Ltd.     

不同秸秆还田模式对土壤有机碳及其活性组分的影响

为了探讨不同秸秆还田模式对土壤有机碳(total organic carbon,TOC)及活性碳组分的影响,设置了秸秆不还田(CK)、秸秆直接还田(CS)、秸秆转化为食用菌基质,出蘑后菌渣还田(CMS)和秸秆过腹还田(CGS)4种还田模式。通过田间小区试验,研究了不同秸秆还田模式下,土壤有机碳及活性组分的变化规律。结果表明不同秸秆还田模式均提高了土壤有机碳含量,但不同还田模式下土壤有机碳含量差异不显著(P0.05),和CK相比,CS、CMS和CGS处理下,土壤有机碳质量分数分别增加9.0%、23.9%和26.7%。不同秸秆还田模式也提高了土壤活性碳组分含量。在不同秸秆还田模式下,土壤溶解性有机碳(dissolved organic carbon,DOC)含量表现为CSCMSCGSCK,且不同处理间差异显著(P0.01)。和CK相比,CS、CMS和CGS处理下,土壤DOC质量分数分别增加64.6%、29.4%和8.9%。土壤微生物量碳(microbial biomass carbon,MBC)含量表现为CMSCGSCSCK,且差异显著(P0.05)。和CK相比,CS、CMS和CGS处理下,土壤MBC质量分数分别增加28.9%、84.7%和59.3%。土壤易氧化态碳(easily oxidizable carbon,EOC)含量表现为CMSCSCGSCK,且差异显著(P0.01)。和CK相比,CS、CMS和CGS处理下,土壤EOC质量分数分别增加24.1%、55.7%、和9.3%。不同秸秆还田模式显著影响土壤活性碳组分在总有机碳中占的比例,改变土壤有机碳质量。在不同秸秆还田模式下,DOC/TOC表现为CSCMSCKCGS、MBC/TOC表现为CMSCGSCSCK、EOC/TOC表现为CMSCSCKCGS,且不同处理间均差异显著(P0.01)。从提高土壤质量角度,推荐秸秆-菌渣还田模式,在该模式下,土壤MBC/TOC和EOC/TOC均最大,土壤碳素有效性高、易于被微生物利用,有利于作物生长。从提高土壤固碳角度,推荐秸秆过腹还田模式,在该模式下,土壤DOC/TOC最小,且土壤有机碳含量最高,有利于碳的固定和保存。该研究结果可为秸秆合理高效利用、改善农业土壤碳库质量提供参考。     

美国路易斯安那州土壤碳估算的尺度效应——美国STATSGO和SSURGO两大最新土壤数据库的比较研究

Estimation of soil organic carbon (SOC) pools and fluxes bears large uncertainties because SOC stocks vary greatly over geographical space and through time.Although development of the U.S.Soil Survey Geographic Database (SSURGO),currently the most detailed level with a map scale ranging from 1:12 000 to 1:63 360,has involved substantial government funds and coordinated network efforts,very few studies have utilized it for soil carbon assessment at the large landscape scale.The objectives of this study were to 1) compare estimates in soil organic matter among SSURGO,the State Soil Geographic Database (STATSGO),and referenced field measurements at the soil map unit;2) examine the influence of missing data on SOC estimation by SSURGO and STATSGO;3) quantify spatial differences in SOC estimation between SSURGO and STATSGO,specifically for the state of Louisiana;and 4) assess scale effects on soil organic carbon density (SOCD) estimates from a soil map unit to a watershed and a river basin scale.SOC was estimated using soil attributes of SSURGO and STATSGO including soil organic matter (SOM) content,soil layer depth,and bulk density.Paired t-test,correlation,and regression analyses were performed to investigate various relations of SOC and SOM among the datasets.There were positive relations of SOC estimates between SSURGO and STATSGO at the soil map unit (R2=0.56,n=86,t=1.65,P=0.102;depth:30 cm).However,the SOC estimated by STATSGO were 9%,33% and 36% lower for the upper 30-cm,the upper 1-m,and the maximal depth (up to 2.75 m) soils,respectively,than those from SSURGO.The difference tended to increase as the spatial scale changes from the soil map unit to the watershed and river basin scales.Compared with the referenced field measurements,the estimates in SOM by SSURGO showed a closer match than those of STATSGO,indicating that the former was more accurate than the latter in SOC estimation,both in spatial and temporal resolutions.Further applications of SSURGO in SOC estimation for the entire United States could improve the accuracy of soil carbon accounting in regional and national carbon balances.     

Short-term effects of tillage practices on soil aggregate fractions in a Chinese Mollisol

Abstract

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (D_m) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in D_m of soil aggregate size distribution among tillage treatments, which suggested that D_m could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.     

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

Soil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P < 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths >10 cm. All parameters were positively correlated (P < 0.01); linear regressions exhibited similar patterns (P < 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.