玉米秸秆不同构件混合分解的非加和效应及其对土壤有机碳矿化的影响

[目的]研究玉米秸秆不同构件混合分解的非加和效应及其对黄绵土土壤有机碳矿化的影响,为秸秆还田背景下坡地土壤CO2排放提供理论支撑。[方法]采用室内模拟试验,试验设置无玉米秸秆土壤对照(CK)及4种玉米秸秆添加处理:茎+土壤(CKS)、叶+土壤(CKL)、鞘+土壤(CKLS)、混合玉米秸秆+土壤(CKM)。[结果]培养结束土壤有机碳矿化累积排放量实测值显著高于预测值,且促进作用主要是由培养初期快速分解阶段(1~28d)导致的。培养结束后混合玉米秸秆剩余质量预测值明显高于实测值,且元素含量发生明显改变,其中全氮含量预测值明显低于实测值,C/N预测值明显高于实测值。培养结束后CKS处理土壤微生物碳含量明显高于其他几种处理,其他几种处理差异不显著;添加玉米秸秆处理土壤微生物量氮明显降低,相应的土壤微生物量C/N增大,CKS,CKL和CKM处理与CK处理差异达到显著水平。土壤可溶性有机碳(DOC)含量CKLS和CKM处理明显高于其他3种处理,CKS与CKL处理与对照差异不显著。[结论]玉米秸秆不同构件按比例混合对玉米秸秆分解产生协同促进作用,混合分解过程促进氮累积。     

思茅松人工林土壤有机碳库特征

为探讨思茅松人工造林对土壤有机碳库的影响,以云南省普洱市思茅区8种定植模式及7个林龄的思茅松人工林为研究对象,对0～ 50 cm土层土壤有机碳质量分数及密度进行调查分析.结果表明：1）思茅松人工林土壤有机碳质量分数随土壤深度的增加而降低,8种定植模式13a思茅松人工林0～50 cm土壤有机碳质量分数皆大于思茅松天然林;不同林龄思茅松人工林土壤有机碳质量分数在4～10a处于降低阶段,12a以后开始升高.2）土壤可溶性碳质量分数随土壤深度的增加而减小,土壤微生物量碳主要集中于0 ～10 cm土层.3）8种定植模式思茅松人工林土壤有机碳密度在64.48 ～ 84.30 t/hm2之间,其中2m＆#215;4m定植模式最大,1m＆#215;1m模式最小;土壤可溶性碳密度数值范围为0.30 ～0.42 t/hm2,土壤微生物量碳密度为0.49 ～ 1.29 t/hm2;4～ 14 a思茅松人工林土壤有机碳密度和可溶性碳密度随林龄的增加呈现先降后升的特点,14a时土壤有机碳密度达92.14 t/hm2,可溶性碳密度达0.42 t/hm2;土壤微生物量碳密度10a时最大,达0.92 t/hm2.研究表明思茅松人工林具有较强的土壤碳积累能力.     

Storage and controlling factors of soil organic carbon in alpine wetlands and meadow across the Tibetan Plateau

Alpine wetlands and meadows across the Three Rivers Source Region (TRSR) store high soil organic carbon (SOC). However, information on factors affecting SOC storage is scanty. Herein, we investigated SOC storage and explored factors affecting SOC storage, including climate, soil properties and above- and belowground biomass, using 50 soil profiles across the TRSR on the Tibetan Plateau. The SOC storage was 491.9 ± 158.5 Tg C and 545.2 ± 160.8 Tg C in the TRSR alpine wetlands and meadow, respectively. The SOC stock was positively correlated with the mean annual precipitation. However, no significant correlation between SOC stock and mean annual temperature was observed, as opposed to the global trend. In addition, SOC stock was positively correlated with both the aboveground biomass (AGB) and belowground biomass (BGB). Soil pH indirectly affected SOC stock, while SOC stock positively correlated with Al and Fe oxyhydroxides. Compared with vegetation biomass and climatic factors, soil properties, including soil pH and Al and Fe oxyhydroxides (Al_o and Fe_o), affected not only SOC stock variation but also affected the impact of vegetation and climatic factors on SOC stock. Climate factors, AGB, BGB, soil pH, Al_o and Fe_o jointly accounted for 59% of SOC stock variation in alpine wetlands and 64% of SOC stock variation in alpine meadow. This study suggests that soil properties are the dominant factors affecting SOC variation in alpine wetlands and meadow on the Tibetan Plateau.     

不同植被恢复措施下剖面根系与SOC的分布特征

根系是影响水土流失和土壤有机碳（SOC）变化的重要因素。在水土流失区,研究不同植被恢复措施下,根系生物量和土壤有机碳的分布特征对了解区域土壤碳循环具有重要意义。在水土流失严重的黄土丘陵沟壑区的燕沟小流域,选择地形条件类似的梁峁坡,采集了10种不同植被治理恢复措施下的剖面（0—100 cm）根系和土壤样品,研究了根系生物量和SOC在剖面的分布特征。结果显示:不同治理措施下的SOC呈现出灌木 > 乔木 > 灌草 > 草本的趋势,而根系生物量呈现出乔木 > 灌木 > 灌草 > 草本的趋势;SOC和细根生物量都随土层深度的增加呈对数递减趋势,但同一土层SOC和细根生物量的分布不一致,且根系比SOC的分布浅。     

The soil organic carbon: Clay ratio in North Devon,UK: Implications for marketing soil carbon as an asset class

Building up stocks of agricultural soil organic carbon (SOC) can improve soil conditions as well as contribute to climate change mitigation. As a metric, the ratio of SOC to clay offers a better predictor of soil condition than SOC alone, potentially providing a benchmark for ecosystem service payments. We determined SOC:clay ratios for 50 fields in the North Devon UNESCO World Biosphere Reserve using 30 cm soil cores (divided into 0–10 cm and 10–30 cm depth samples), with soil bulk density, soil moisture and land-use history recorded for each field. All the arable soils exceeded the minimum desirable SOC:clay ratio threshold, and the ley grassland soils generally exceeded it but were inconsistent at 10–30 cm. Land use was the primary factor driving SOC:clay ratios at 0–10 cm, with permanent pasture fields having the highest ratios followed by ley grass and then arable fields. Approximately half of the fields sampled had potential for building up SOC stock at 10–30 cm. However, at this depth, the effect of land use is significantly reduced. Within-field variability in SOC and clay was low (coefficient of variation was ~10%) at both 0–10 cm and 10–30 cm, suggesting that SOC:clay ratios precisely characterized the fields. Due to the high SOC:clay ratios found, we conclude that there is limited opportunity to market additional carbon sequestration as an asset class in the North Devon Biosphere or similar areas. Instead, preserving existing SOC stocks would be a more suitable ecosystem service payment basis.     

黄土丘陵半干旱区人工柠条林土壤固碳特征及其影响因素

为了探讨黄土丘陵区不同生长年限的人工柠条林地土壤有机碳含量的变化特征及其影响因素,更好地阐明黄土丘陵区柠条林土壤的固碳机理,本文采用时空替代法,以撂荒2 a的坡耕地为对照,对黄土丘陵半干旱区不同林龄(10 a、17 a、26 a、34 a、40 a、50 a)人工柠条林地土壤有机碳(SOC)、全氮(STN)、全磷(STP)及柠条林的根系生物量和枯落物现存量进行了分析。结果表明:1)在0~60 cm的土层剖面上,0~20 cm土层SOC含量明显高于其他土层,并随土层深度的增加逐层递减,其中柠条林地0~20 cm土层SOC含量变化幅度为2.68~11.44 g·kg-1,而40~60 cm土层SOC含量仅在1.64~2.73 g·kg-1波动;与对照相比,随林龄增加柠条林地0~60 cm土层平均SOC含量先减小后增加最后趋于平稳:10 a和17 a柠条林SOC含量比对照显著降低了34.5%和26.9%,26 a柠条林的SOC含量显著升高,其值是对照的1.43倍,40 a和50 a柠条林SOC含量处于积累与消耗相对稳定的状态。2)对SOC含量与STN、STP含量及根系生物量和枯落物现存量进行相关性分析表明,SOC含量与STN含量、根系生物量及枯落物现存量之间存在极显著线性相关,但与STP含量相关性不明显,说明土壤中氮含量的增加能明显提高土壤的固碳能力,而根系生物量和枯落物现存量的多少能够决定土壤的固碳水平。     

Is glomalin an appropriate indicator of forest soil reactive nitrogen status?

In this paper we address total glomalin‐related soil protein (T‐GRSP) as a possible indicator of differences in forest soils related to reactive nitrogen and forest composition. We focused especially on the relationship between T‐GRSP (g kg⁻¹), soil organic carbon (SOC), and reactive nitrogen (N_r) availability among different categories of temperate forests and different horizons. Our study included 105 sampling sites divided into 5 categories, which vary in elevation and tree species composition (coniferous, deciduous, mixed). We detected significantly higher T‐GRSP and SOC in the F+H horizon under conifers. We assume that this observation might be attributed to suppression of decomposition of T‐GRSP and SOC by nature of coniferous litter. The lack of significant differences in T‐GRSP/SOC among the categories and the positive correlations between T‐GRSP and SOC in most of the categories confirmed the strong relationship of T‐GRSP with SOC. We found a significantly higher content of T‐GRSP in the F+H horizon for all studied forest categories. However, the contribution of T‐GRSP to SOC is significantly higher in the A horizon, which might be caused by stabilization of glomalin by mineral fraction, including clay minerals or by the belowground origin of glomalin. We found the increase of SOC with increasing N_r in the A horizon for most categories of forest. T‐GRSP follows this trend in the case of deciduous forests (decid), mixed forest (mixed), and mountain forests (mount). On the other hand, we detected a decrease of T‐GRSP with increasing N_r in the F+H horizon of coniferous forests (conif). Moreover the T‐GRSP/SOC decreases with the increase of N_r in the A horizon of conif, mixed and mount, which points to the higher sensitivity of forest with prevalence of coniferous trees. Our observations have confirmed an ecosystem‐specific relationship between T‐GRSP, SOC and N_r. We concluded that T‐GRSP in combination with T‐GRSP/SOC has the potential to reveal qualitative changes in soil organic matter (SOM) connected with increasing N_r.     

Dissolved and Soil Organic Carbon after Long‐Term Conventional and No‐Tillage Sorghum Cropping

Abstract

Distribution of dissolved (DOC) and soil organic carbon (SOC) with depth may indicate soil and crop‐management effects on subsurface soil C sequestration. The objectives of this study were to investigate impacts of conventional tillage (CT), no tillage (NT), and cropping sequence on the depth distribution of DOC, SOC, and total nitrogen (N) for a silty clay loam soil after 20 years of continuous sorghum cropping. Conventional tillage consisted of disking, chiseling, ridging, and residue incorporation into soil, while residues remained on the soil surface for NT. Soil was sampled from six depth intervals ranging from 0 to 105 cm. Tillage effects on DOC and total N were primarily observed at 0–5 cm, whereas cropping sequence effects were observed to 55 cm. Soil organic carbon (C) was higher under NT than CT at 0–5 cm but higher under CT for subsurface soils. Dissolved organic C, SOC, and total N were 37, 36, and 66%, respectively, greater under NT than CT at 0–5 cm, and 171, 659, and 837% greater at 0–5 than 80–105 cm. The DOC decreased with each depth increment and averaged 18% higher under a sorghum–wheat–soybean rotation than a continuous sorghum monoculture. Both SOC and total N were higher for sorghum–wheat–soybean than continuous sorghum from 0–55 cm. Conventional tillage increased SOC and DOC in subsurface soils for intensive crop rotations, indicating that assessment of C in subsurface soils may be important for determining effects of tillage practices and crop rotations on soil C sequestration.     

石羊河流域干旱荒漠区人工梭梭林对土壤碳库的影响

采用野外调查与室内分析相结合的方法,研究石羊河流域民勤干旱沙区种植人工梭梭林4,13,36年后的土壤有机碳(Soil organic carbon,SOC)、无机碳(Soil inorganic carbon,SIC)、全氮(Total nitrogen,TN)和总碳(soil total carbon,TC)含量及储量变化特征。结果表明:流动沙地种植梭梭后,0-50cm层灌丛下和行间SOC和TN含量总体随造林年限增加而增加,5-50cm层灌丛下SIC含量在13年梭梭林地最高。36,13年林地0-50cm层灌丛下SOC和TN储量均高于行间,而13年灌丛下SIC储量低于行间,4年灌丛下5-50cm层SOC、TN和SIC储量均低于行间。0-50cm层土壤有机碳、无机碳、全氮储量增幅分别为102.44%,24.66%,54.55%,36年林地SOC和TN储量随土层加深先降低后增加,但4,13年和流动沙地SOC、SIC和TN储量均随土层加深而增加。土壤有机碳占总碳比例随造林年限增加而增加。相关分析结果表明,土壤颗粒组成、造林年限、土层深度等与土壤有机碳和全氮储量显著相关(P0.01)。民勤干旱沙区造林提高了土壤碳库截存量,并且随林龄增长而增长。     

改变碳输入对南亚热带海岸沙地典型天然次生林土壤呼吸的影响

土壤呼吸是陆地生态系统碳循环的一个重要过程,开展环境因子和改变碳输入对土壤呼吸影响的研究具有重要意义.2015年3月-2016年2月,在南亚热带海岸沙地典型天然次生林中设置去除根系、去除凋落物、加倍凋落物和对照4种处理,采用LI-8100连续观测改变碳输入对土壤呼吸的影响.结果表明:改变碳输入没有显著影响l0cm土壤温度和湿度(P＞0.05);不同处理土壤呼吸速率存在明显的季节变化,表现为夏高冬低,最大值出现在5月或者6月,最小值出现在11月或12月;土壤呼吸速率的年均值为加倍凋落物＞对照＞去除根系＞去除凋落物,不同改变碳输入方式均降低了土壤呼吸的Q10值;矿质土壤呼吸、凋落物呼吸和根系呼吸对土壤总呼吸的贡献分别为41.24％、43.29％和15.45％;不同处理土壤呼吸速率分别与土壤温度和湿度呈显著的指数和线性正相关(P＜0.05),双因子模型能解释土壤呼吸变异的45％ ～ 69％;改变碳输入影响土壤可溶性有机碳和微生物生物量碳,不同处理土壤呼吸速率与可溶性有机碳和微生物生物量碳呈正相关.因此,改变碳输入引起土壤易变碳的变化进而影响土壤呼吸.     

Annual Burning Enhances Biomass Production and Nutrient Cycling in Degraded Imperata Grasslands

The invasive species Imperata cylindrica is a dominant grass covering a large part of degraded lands of India. Imperata is managed through traditional annual burning, a practice that is prevalent throughout tropical grasslands. A field experiment was conducted to quantify the effects of burning on aboveground and belowground biomass production and soil organic carbon (SOC), total nitrogen (TN), available phosphorus (Ave P), potassium (K⁺), calcium (Ca⁺), and magnesium (Mg⁺) concentrations in 0‐ to 15‐cm soil depth under Imperata grassland. The burnt site had 44% and 14% higher aboveground and belowground biomass over the un‐burnt control plots after 300 days of the fire event. The concentrations of SOC, TN, and Ave P increased soon after the fire but decreased regressively with time after the fire in both micro and macro soil aggregate size fractions. In contrast, concentrations of K⁺, Ca⁺, and Mg⁺ increased up to 30 days after the fire in both soil aggregate fractions. Burning did not significantly alter the stoichiometric ratios (C : N, C : P, and N : P) in macro aggregates. However, burning significantly reduced the C : N, C : P, and N : P ratios in micro aggregates during the first 0–30 days. Fire increased nutrient stocks (kg ha⁻¹) by 20–35% in the burnt site in comparison to an un‐burnt control site. It is concluded that the conventional practice of annual burning increases soil nutrients in surface soils and supports higher biomass production in Imperata‐covered degraded lands. Copyright © 2017 John Wiley & Sons, Ltd.     

Examining soil organic carbon in the mountainous peat swamps of the Zoigê Plateau in China's Qinghai-Tibet Plateau

Mountainous peatlands are one of the most important terrestrial ecosystems for carbon storage and play an important role in the global carbon cycle. An insight into the carbon cycle of peat swamps located in mountainous regions can be obtained by studying the distribution of soil organic carbon (SOC) and its relationships with environmental factors. This study focused on the development conditions of peat swamps in the Gahai wetlands, located on the Zoigê Plateau, China, with four different altitudinal gradients as experimental sample sites. The distribution of SOC and its relationship with environmental factors were analysed through vegetation surveys and a generalized additive model (GAM). The results show that with increasing altitude, soil temperature decreased while the soil pH and bulk density initially decreased then increased. On the contrary, the topographic wetness index (TWI), SOC content, above-ground biomass and litter count initially increased then decreased. The SOC content of the 0–30 cm soil layer was in the range 226–330 g·kg⁻¹ (coefficient of variation (CV) = 21.4%), and the 30–60 cm layer was 178–257 g·kg⁻¹ (CV = 17.5%) and was significantly correlated (p < .05) with above-ground biomass and litter count. Meanwhile, the SOC content in the 60–90 cm soil layer was in the range 132–167 g·kg⁻¹ (CV = 9.2%) with a significant correlation (p < .05) with soil temperature, pH, bulk density and topographic moisture index. The study showed that the SOC content exhibited more pronounced spatial patterns with increasing altitude, with the peak value in the shallow soil layer appearing in lower elevation areas compared with the deep soil layer. The level of variation changed from medium to low, reflecting the stable mechanism for maintaining SOC within the heterogeneous peat swamp environment.     

紫色土丘陵区坡面土壤有机碳含量及储量分布特征

为探明坡耕地土壤有机碳空间分布特征,对紫色土丘陵区坡耕地不同部位土壤有机碳及活性有机碳顺坡和深度分布进行分析。结果表明:坡耕地上坡土层深度仅为22.3cm,中坡和下坡土层深度约为上坡的2.09倍和3.30倍;与上坡比较,中坡和下坡土壤容重下降了0.2和0.04,土壤孔隙度增加了19.82%与3.83%。沿坡从上向下土壤有机碳及活性有机碳储量显著增加,下坡土壤有机碳及活性有机碳储量比上坡和中坡分别增加了674.74%,104.09%和958.51%,267.75%;不同部位土壤有机碳及活性有机碳含量随土层深度增加呈降低趋势,中坡和下坡土壤有机碳及活性有机碳含量的深度分布满足Y=alnX+b对数方程,上坡不符合该方程。坡耕地土壤有机碳与其活性有机碳含量呈极显著正相关。土壤沿坡耕地重新分配影响有机碳空间分布格局。     

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...     

滇中尖山河小流域不同土地利用类型土壤活性有机碳分布特征

土壤活性有机碳对土地利用方式最为敏感,定量分析不同土地利用方式对土壤活性有机碳分布特征的影响对流域的土壤碳循环研究具有重要意义。从滇中尖山河小流域坡耕地、荒草地、林地、园地4种不同土地利用类型角度,系统地分析了0—10,10—20,20—30 cm土层土壤有机碳（SOC）、微生物有机碳（MBC）、易氧化有机碳（EOC）及可溶性有机碳（DOC）的分布特征及其相关性。结果表明:不同土地利用类型下土壤SOC,MBC,EOC,DOC整体均表现为园地 > 林地 > 坡耕地 > 荒草地;4种土地利用类型MBC,EOC,DOC整体上随着土层深度的增加而逐渐降低,且主要分布在0—20 cm土层,在20—30 cm土层含量较低（低于30%）;4种土地利用类型下SOC和MBC,EOC,DOC呈极显著正相关关系,MBC,EOC,DOC两两之间也表现出极显著正相关。综上,退耕还林以及在荒草地种植人工林可作为提高土壤有机碳及活性有机碳含量的有效措施,并将在减少流域水土流失和面源污染、改善土壤质量、恢复土壤肥力等方面起到重要作用。     

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.     

Priming effect and its regulating factors for fast and slow soil organic carbon pools: A meta-analysis

The priming effect (PE) plays a critical role in the control of soil carbon (C) cycling and influences the alteration of soil organic C (SOC) decomposition by fresh C input.However,drivers of PE for the fast and slow SOC pools remain unclear because of the varying results from individual studies.Using meta-analysis in combination with boosted regression tree (BRT) analysis,we evaluated the relative contribution of multiple drivers of PE with substrate and their patterns across each driver gradient.The results showed that the variability of PE was larger for the fast SOC pool than for the slow SOC pool.Based on the BRT analysis,67%and 34%of the variation in PE were explained for the fast and slow SOC pools,respectively.There were seven determinants of PE for the fast SOC pool,with soil total nitrogen (N) content being the most important,followed by,in a descending order,substrate C:N ratio,soil moisture,soil clay content,soil pH,substrate addition rate,and SOC content.The directions of PE were negative when soil total N content and substrate C:N ratio were below 2 g kg~(-1)and 20,respectively,but the directions changed from negative to positive with increasing levels of this two factors.Soils with optimal water content (50%–70%of the water-holding capacity) or moderately low pH (5–6) were prone to producing a greater PE.For the slow SOC pool,soil p H and soil total N content substantially explained the variation in PE.The magnitude of PE was likely to decrease with increasing soil pH for the slow SOC pool.In addition,the magnitude of PE slightly fluctuated with soil N content for the slow SOC pool.Overall,this meta-analysis provided new insights into the distinctive PEs for different SOC pools and indicated knowledge gaps between PE and its regulating factors for the slow SOC pool.     

西藏色季拉山土壤微生物量碳和易氧化态碳沿海拔梯度的变化

为探讨不同海拔梯度对土壤活性有机碳库的影响,以西藏色季拉山(西坡)的高山灌丛(AS)、杜鹃林(RF)、急尖长苞冷杉林(AGSF1～6)和林芝云杉林(PLLF)为试验对象,研究林地土壤有机碳、微生物量碳和易氧化态碳的变化特征。结果表明:高海拔植被类型具有较高的土壤活性有机碳含量和分配比例。土壤有机碳含量与土壤pH值和容重呈显著负相关(p<0.05)。在土壤剖面垂直分布上,随着土壤深度增加,土壤总有机碳、微生物量碳和易氧化态碳含量均呈现随土层深度增加而逐渐减小的变化规律。土壤总有机碳、微生物量碳和易氧化态碳含量沿海拔梯度具有明显的变化规律,即随海拔的升高,土壤总有机碳、微生物量碳和易氧化态碳含量逐渐变大。土壤微生物量碳和总有机碳量有较好的正相关性,有机碳含量越高,土壤微生物量碳越大。     

追施不同量尿素下麦后复种油菜对耕层土壤有机碳及微生物量碳氮的影响

[目的]研究不同追施尿素量对麦后复种油菜生物产量和耕层土壤有机碳、土壤微生物量碳氮及碳库管理指数的影响,为麦后复种油菜尿素施用量提供依据。[方法]在古浪县进行小区试验,设置5个试验水平:追施尿素0,90,120,150,180kg/hm2。[结果]追肥可提高麦后复种油菜的生物产量;土壤有机碳、微生物量碳、微生物氮以及碳库管理指数均随追肥量的增加呈抛物线型变化的趋势;碳库指数和碳库管理指数的变化趋势同有机碳的变化趋势;有机碳、微生物量碳与碳库管理指数显著相关,有机碳与碳库管理指数极显著相关,微生物量碳与有机碳含量虽呈现正相关关系,但未达到显著相关性。[结论]综合油菜生物产量和土壤微生物量等指标,古浪县麦后复种油菜的施肥量以追施尿素120~150kg/hm2为宜。     

Simulating SOC changes in long-term experiments with RothC and CENTURY: model evaluation for a regional scale application

Abstract. Predictive, regional use of soil organic matter (SOM) models requires evaluation of the performance of models with datasets from long‐term experiments relevant to the scenarios of interest to the regional scale study, and relevant to the climate of the study region. Datasets from six long‐term experiments were used to evaluate the performance of RothC and CENTURY, two of the most widely used and tested SOM models. Three types of model run were completed for each site: (1) CENTURY model alone; (2) RothC model run to fit measured SOC values, by iteratively adjusting C inputs to soil; and (3) RothC model run using C inputs derived from CENTURY runs. In general, the performance of both models was good across all datasets. The runs using RothC (iteratively changing C inputs to fit measured SOC values) tended to have the best fit to model data, since this method involved direct fitting to observed data. Carbon inputs estimated by RothC were, in general, lower than those estimated by CENTURY, since SOC in CENTURY tends to turn over faster than SOC in RothC. The runs using RothC with CENTURY C inputs tended to have the poorest fit of all, since CENTURY predicted greater C inputs than were required by RothC to maintain the same SOC content. A plausible model fit to measured SOC data may be obtained with widely differing C input values, due to differences in predicted decomposition rates between models. It remains unclear which, if either, modelling approach most closely represents reality since both C inputs to soil and decomposition rates for bulk SOM are difficult to determine experimentally. Further progress in SOM modelling can only be the result of research leading to better process understanding, both of net C inputs to soil and of SOM decomposition rates. The use of default methods for estimating initial SOC pools in RothC and CENTURY may not always be appropriate and may require adjustment for specific sites. The simulations presented here also suggest details of SOC dynamics not shown by available measured data, especially trends between sampling intervals, and this emphasizes the importance of archived soil samples in long‐term experiments.