Below‐ground and above‐ground production of vegetational organic matter along a climosequence in alpine grasslands

The distribution of vegetational organic matter above‐ and below‐ground and its productivity was analyzed in an alpine area along a climosequence ranging from subalpine to alpine climates. Emphasis is placed on the quantification of carbon (C) and nitrogen (N) fixed in the above‐ground and below‐ground vegetation and its annual input. Annual C‐input ranged from 17.9 to 60.2 g m^—2 year^—1 and the N‐input from 0.74 to 2.48 g m^—2 year^—1. Above‐ground phytomass and the annual production rate of organic matter showed a distinct correlation with the altitude and, thus, the climate. However, the measurement of the above‐ground phytomass is bound to methodological problems: the commonly used harvesting method seems to underestimate the real situation. The harvesting method yielded in its average 100 to 300 g m^—2 phytomass which was 35—83% of the values obtained by the soil core method. Thus, the calculation of turnover times of above‐ground vegetation greatly depends on the method used. Calculated turnover times based on the harvesting method did not correlate with the climate while a clear tendency of lower turnover times with increasing altitude could be observed using the soil core method. The amount of below‐ground phytomass was in the range of 1880 to 2469 g m^—2 and the corresponding annual C‐input (fixation in the roots) between 91.1 and 162 g m^—2 year^—1 and the N‐input between 2.68 and 4.99 g m^—2 year^—1. The below‐ground phytomass and its production rate in high alpine zones are of greater importance and exceed the above‐ground ones. With increasing altitude, furthermore, the importance of the below‐ground phytomass increases with respect to the biomass and to the C‐ and N‐input. For high alpine areas, the phytomass is concentrated in the uppermost soil horizons. About 88.7 to 94.5% of the below‐ground phytomass was found in the soil compartment 0‐20 cm. The below‐ground production rate of phytomass in alpine grassland is fundamental in order to calculate any C or N budgets and potential inputs to SOM: its neglection would introduce most significant errors in modeling any C or N cycles.     

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.     

不同封育年限草地土壤有机质组分及其碳库管理指数

土壤有机质对草地封育的生态效应具有重要指示作用,本文结合野外调查和室内分析,研究了半干旱区不同封育年限草地土壤有机质组分及其碳库管理指数变化,以分析土壤有机质对草地封育的响应特征,从而为该区土壤质量的改善和植被建设的生态效应评价提供依据。研究结果表明,土壤有机质及不同活性有机质含量均随土层加深而降低,且在各土层基本表现出封育18年、封育23年封育13年未封育封育3年的趋势。除封育3年土壤的3种活性有机质碳库管理指数在090cm土壤剖面均低于100外,封育13年草地060cm土层、封育18和23年草地090cm土层的3种活性有机质碳库管理指数均高于100,表明随年限的延长,封育对土壤有机质的改善深度也在加深。土壤3种活性有机质与有机质及多数土壤性质呈极显著正相关,能更为灵敏和直观地表征土壤管理的长期效应和土壤质量变化。     

Seasonal development of above‐ and below‐ground organs of Trifolium pratense in grass–legume mixture on different soils

Grass–legume mixtures are suitable for crop rotations in organic farming. However, seasonal development of below‐ground organs of Trifolium pratense in mixtures and on different soils was neglected. We asked (1) how the diameter of the root neck, the maximum order of branching as well as (2) the nodule traits are affected by locality and time, and (3) how above‐ground plant traits of red clover vary in space and time. Red clover was investigated in grass–legume mixtures in the first year of vegetation. Five sites in S Germany were sampled at the day of cut at the end of May, the beginning of July, and at the end of August, respectively. Under similar climatic conditions root traits (diameter of the root neck, order of root branching, size of nodules, and proportion of senescent nodules) differed with soil conditions and time within the season. Root diameter increased during the season. Higher sand content fostered root branching and branched roots developed more nodules. Thinner roots had more active nodules (pink). Root diameter and non‐active senescent (green) or moribund (brown) nodules increased at the end of season. Nodule activity differed more according to season than to soil conditions. The number of nodules per plant (12.5–19.5) decreased from May to August. Cylindrical nodules were found on 85–100% of the plants and branched nodules only on 0–25%. The height of plants was lowest in May and increased in July. The mean number of stems per plant (3.3–6.3) was highest in August. Understanding red clover traits and N₂ fixation is interesting scientifically as well as agronomical. Organic and conventional farmers can both benefit of our findings.     

Assessing the impact of interfering organic matter on soil metaproteomic workflow

Soil organic matter (SOM) is biologically, chemically, and physically complex. As a major store of nutrients within the soil, it plays an important role in nutrient provision to plants. An enhanced understanding of SOM utilisation processes could underpin better fertiliser management for plant growth, with reduced environmental losses. Metaproteomics can allow the characterisation of protein profiles and could help gain insights into SOM microbial decomposition mechanisms. Here, we applied three different extraction methods to two soil types to recover SOM with different characteristics. Specifically, water-extractable organic matter, mineral-associated organic matter and protein-bound organic matter were targeted with the aim to investigate the metaproteome enriched in those extractions. As a proof-of-concept, replicated extracts from one soil were further analysed for peptide identification using liquid chromatography followed by tandem mass spectrometry. We employed a framework for mining mass spectra for both peptide assignment and fragmentation pattern characterisation. Different extracts were found to exhibit contrasting total protein and humic substance content for the two soils investigated. Overall, water extracts displayed the lowest humic substance content (in both soils) and the highest number of peptide identifications (in the soil investigated) with the most frequent peptide hits associated with diverse substrate/ligand binding proteins of Proteobacteria and derived taxa. Our framework also highlighted a strong peptidic signal in unassigned and unmatched spectra, information that is currently not captured by the pipelines employed in this study. Taken together, this work points to specific areas for optimisation in chromatography and mass spectrometry to adequately characterise SOM-associated metaproteomes.     

Spatio‐temporal change of soil organic matter content of Jiangsu Province,China, based on digital soil maps

Estimation of spatio‐temporal change of soil is needed for various purposes. Commonly used methods for the estimation have some shortcomings. To estimate spatio‐temporal change of soil organic matter (SOM) in Jiangsu province, China, this study explored benefits of digital soil maps (DSM) by handling mapping uncertainty using stochastic simulation. First, SOM maps on different dates, the 1980s and 2006–2007, were constructed using robust geostatistical methods. Then, sequential Gaussian simulation (SGS) was used to generate 500 realizations of SOM in the area for the two dates. Finally, E‐type (i.e. conditional mean) temporal change of SOM and its associated uncertainty, probability and confidence interval were computed. Results showed that SOM increased in 70% of Jiangsu province and decreased in the remaining 30% during the past decades. As a whole, SOM increased by 0.22% on average. Spatial variance of SOM diminished, but the major spatial pattern was retained. The maps of probability and confidence intervals for SOM change gave more detailed information and credibility about this change. Comparatively, variance of spatio‐temporal change of SOM derived using SGS was much smaller than sum of separate kriging variances for the two dates, because of lower mapping variances derived using SGS. This suggests an advantage of the method based on digital soil maps with uncertainty dealt with using SGS for deriving spatio‐temporal change in soil.     

Land‐use change in subalpine grassland soils: Effect on particulate organic carbon fractions and aggregation

Abandonment of mountain grassland often changes vegetation composition and litter quantity and quality, but related effects on labile soil organic matter (SOM) are largely unknown. The aim of this study was to investigate the impacts of grassland management and abandonment on soil carbon distribution in light (< 1.6 g cm^–3) particulate organic matter (POM) and aggregation along a gradient of management intensity including hay meadows, pastures, and abandoned grasslands. The reduction of management intensity is an interregional phenomenon throughout the European Alps. We therefore selected sites from two typical climate regions, namely at Stubai Valley, Austria (MAT: 3°C, MAP: 1097 mm) and Matsch Valley, Italy (MAT: 6.6°C, MAP: 527 mm), to evaluate effects of land‐use change in relation to climate. Free water‐floatable and free POM (wPOM, fPOM), and an occluded POM fraction (oPOM), were isolated from three water‐stable aggregate size classes (2–6.3 mm, 0.25–2 mm, < 0.25 mm) using density fractionation. Aggregate mean weight diameter slightly decreased with decreasing management intensity. In contrast to absolute POM‐C, fPOM‐C increased in aggregates at both sites with abandonment. Because the oPOM‐C was less affected by abandonment, the ratio of oPOM‐C : fPOM‐C shifted from > 1 to < 1 from meadow to abandoned grassland in aggregates at both sites and thus independent of climate. This suggests that in differently managed mountain grasslands free and occluded POM are functionally different SOM fractions. In bulk soil, the oPOM‐C : fPOM‐C ratio is better suited as an indicator for the response of SOM to management reduction in subalpine grasslands than the total soil C, absolute or relative POM‐C content.     

县域土壤有机质动态变化及其影响因素分析

本文以河北省曲周县为例, 采用 1980 年和 1999 年两次全县的土壤肥力监测以及农户调查数据和统计数据, 系统分析了过去 20 年中土壤有机质的动态及其与之相关的农作管理方式的变化。 结果显示, 在过去的近 20 年 间, 曲周县土壤表层的有机质含量呈现增长的趋势, 导致这种变化的农作管理方式有化肥施用量的大幅度提升、秸 秆还田量的增加、盐碱地的开垦利用、灌溉面积和复种指数的提高以及主要种植模式和种植作物的土壤有机质处 于正平衡状态。 然而当前的生产管理方式尽管有利于土壤有机质积累, 但是也带来了一系列的生态环境问题。 实 施保护性耕作、降低化肥用量、提高秸秆还田量和有机肥的用量成为今后农业生产管理方式调整的主要方向。     

Optimized conditions for determination of total soil organic matter in diverse samples by mass loss on ignition

Reliable measurement of soil organic matter (SOM) contents is crucial to assessment of soil health, productive longevity and the effects of climate change. In this study, the loss‐on‐ignition (LOI) method has been used to determine the SOM of dried soil samples with a wide range of clay, sand and silt contents from the Agricultural Laboratory Proficiency (ALP) program. Regressions of ALP participant data against LOI measurements at 350–650°C indicate that the extent of SOM oxidation depends more on the ignition temperature and time than on the sample compositions. Thus, LOI data from ignition at 350–550°C for 12 h relative to ignition at 650°C for 12 h converge at 650°C and the average coefficient of variance decreases to ≈ 4% at 650°C. Also examined are regressions of soil organic C from direct dry combustion as standards with LOI measured at 360°C for 2 h, LOI measured at 650°C for 12 h and with the Walkley‐Black procedure used in the ALP program.     

长期不同施肥条件下黑土的有机质含量变化特征

以吉林公主岭黑土有机肥化肥配施30年长期定位试验结果为材料,分析了长期不同施肥下黑土有机质的变化特征。结果表明,长期不施肥或单施化肥(M0区)土壤有机质含量呈下降趋势,30年下降幅度为2.1%～7.9%;施用常量有机肥(M2区)和高量有机肥(M4区)的土壤有机质含量呈增加趋势,30年M2区和M4区有机质累积增加幅度分别为42.2%～50.0%和81.5%～94.7%。M2区和M4区有机质增加幅度因施用有机肥中有机质含量的变化可分为两个阶段,1980～1992年增加幅度分别平均为2.4%和9.3%,12年后随着有机肥中有机质含量增加,后18年M2区和M4区有机质累积增加幅度分别平均为41.4%和71.5%。施用相同化肥条件下配施不同水平有机肥,各处理间土壤有机质含量差异达到显著水平;而在施用相同有机肥条件下配施不同化肥时,各处理间有机质含量差异不显著。由此可以得出,有机肥的数量和有机质含量是影响土壤有机质含量变化的主要因素,因此,选择合适的有机肥数量和有机质含量是提升土壤有机质的主要措施,在东北黑土上施用优质高量有机肥可迅速提高土壤有机质含量。     

Long‐term effects of tillage,nutrient application and crop rotation on soil organic matter quality assessed by NMR spectroscopy

Crop and land management practices affect both the quality and quantity of soil organic matter (SOM) and hence are driving forces for soil organic carbon (SOC) sequestration. The objective of this study was to assess the long‐term effects of tillage, fertilizer application and crop rotation on SOC in an agricultural area of southern Norway, where a soil fertility and crop rotation experiment was initiated in 1953 and a second experiment on tillage practices was initiated in 1983. The first experiment comprised 6‐yr crop rotations with cereals only and 2‐yr cereal and 4‐yr grass rotations with recommended (base) and more than the recommended (above base) fertilizer application rates; the second experiment dealt with autumn‐ploughed (conventional‐till) plots and direct‐drilled plots (no‐till). Soil samples at 0–10 and 10–30 cm depths were collected in autumn 2009 and analysed for their C and N contents. The quality of SOM in the top layer was determined by ¹³C solid‐state NMR spectroscopy. The SOC stock did not differ significantly because of rotation or fertilizer application types, even after 56 yr. However, the no‐till system showed a significantly higher SOC stock than the conventional‐till system at the 0–10 cm depth after the 26 yr of experiment, but it was not significantly different at the 10–30 cm depth. In terms of quality, SOM was found to differ by tillage type, rate of fertilizer application and crop rotation. The no‐till system showed an abundance of O‐alkyl C, while conventional‐till system indicated an apparently indirect enrichment in alkyl C, suggesting a more advanced stage of SOM decomposition. The long‐term quantitative and qualitative effects on SOM suggest that adopting a no‐tillage system and including grass in crop rotation and farmyard manure in fertilizer application may contribute to preserve soil fertility and mitigate climate change.     

Assessment of cropping‐system impact on soil organic matter levels in short‐term field experiments

It has been suggested that short‐term field experiments are not suitable for the quantitative assessment of cropping‐systems impact on soil organic matter (SOM) levels in arable soils, as expectable temporal changes are very small compared to a large spatial variation of SOM background levels. However, applying an optimized sampling design based on repeated sampling in small plots, we were able to detect soil total carbon (STC) and nitrogen (STN) changes in the magnitude of ≈ 1% (STC) and ≈ 2% (STN) of background levels with only four replications, respectively. Gradually enlarging the sample size up to n = 24 did not considerably improve change detectability with STC, but with STN (n = 15 allowing for the dection of ≈ 1% change of background levels). The common calculation of minimum detectable differences (MDD) based on a state analysis of SOM levels instead of repeated measurements considerably underestimated change detectability.     

耕作对土壤有机物和土壤团聚体稳定性的影响

Agricultural sustainability relates directly to maintaining or enhancing soil quality. Soil quality studies in Canada during the 1980‘s showed that loss of soil organic matter (SOM) and soil aggregate stability was standard features of non-sustainable land management in agroecosystems. In this study total soil organic carbon (SOC), particulate organic matter (POM), POM-C as a percentage of total SOC, and aggregate stability were determined for three cultivated fields and three adjacent grassland fields to assess the impact of conventional agricultural management on soil quality. POM was investigated using solid-state ^13C nuclear magnetic resonance (NMR) to determine any qualitative differences that may be attributed to cultivation. Results show a highly significant loss in total SOC, POM and aggregate stability in the cultivated fields as compared to the grassland fields and a significant loss of POM-C as a percentage of total SOC.Integrated results of the NMR spectra of the POM show a loss in carbohydrate-C and an increase in aromatic-C in the cultivated fields, which translates to a loss of biological lability in the organic matter. Conventional cultivation decreased the quantity and quality of SOM and caused a loss in aggregate stability resulting in an overall decline in soil quality.     

Soil organic carbon and nitrogen fractions and water‐stable aggregation as affected by cropping and grassland reclamation in an arid sub‐alpine soil

This paper investigates effects of cropping abandonment and perennial grass growing on soil organic C and N pools and aggregate stability, by comparing soils under native grassland, crop cultivation, perennial grass growing and cropping abandonment, in degraded cropland at a sub‐alpine site in north‐western China. The pools of total and particulate organic C (115 and 37 Mg ha⁻¹) in the 0–30 cm soil layer of native grassland were reduced by 31 and 54% after 30 years of crop cultivation. After 4 years of conversion from cropland to perennial grass growing total and particulate organic C pools were increased by 29 and 56%, whereas 4 year cropping abandonment increased particulate organic C by 36%. Rapid increases in total and particulate N were also found in perennial grass growing and cropping abandonment soils. The native grassland soil and soils of cropping abandonment and perennial grass growing had higher carbohydrate C concentrations in the 0–10 cm layer than the cropped soil. The rapid recovery of particulate organic fraction and carbohydrates in the re‐vegetated soils were probably due to higher plant biomass inputs and lower organic matter decomposition compared with those in the cropped soil. Aggregate stability of the 0–30 cm soil layer was significantly decreased by crop cultivation but showed a good recovery after 4 year re‐vegetations. This study suggests that reduction of soil organic matter and aggregate stability under crop cultivation may be remedied by cropping abandonment or perennial grass growing. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Labile and stable pools of organic matter in soil amended with sewage sludge biochar

One of the main advantages of using biochar for agricultural purposes is its ability to store carbon (C) in soil for a long-term. Studies of labile and stable fractions of soil organic matter (SOM) may be a good indicator of the dynamics of biochar in soils. This study evaluated the effects of applying sewage sludge biochar (SSB) in combination with mineral fertilizer on fractions of SOM. To conduct this evaluation, 15 Mg ha^?1 of SSB combined or not with mineral fertilizer (NPK) was applied to the soil in two cropping seasons. Apart from total organic C (TOC), the labile and stable fractions of SOM were also determined. The combined use of SSB and NPK resulted in higher TOC, a 22% to 40% increase compared to the control and to the NPK treatments, respectively. The SSB produced at a lower temperature increased the labile fractions of SOM, especially the microbial biomass C, showing its capacity to supply nutrients in the short-term. The stable pools of SOM are increased after adding SSB produced at a higher temperature. It was concluded that pyrolysis temperature is a key-factor that determines the potential of SSB to accumulate C in labile and stable fractions of SOM.     

Driving forces of soil organic matter change in Jiangsu Province of China

Soil organic matter (SOM) is a key property determining soil functions and a major form of carbon stored in soil. Understanding the spatial and temporal variability of SOM and the driving forces responsible for spatial and temporal changes is important to assess regional soil quality and carbon sequestration potential and, particularly, to establish better practices for land use and management. We evaluated the spatio‐temporal change in SOM content from 1979–1982 to 2006 and its driving forces in Jiangsu Province, East China, using geostatistics. The results showed that mean SOM content increased from 16.60 ± 8.50 to 18.31 ± 8.32 g/kg over a 26‐yr period. The maps of SOM generated by ordinary kriging represented the increasing trend from north to south across the province in the two periods. The level of SOM in 1979–1982 affected the pattern of change: the SOM increasing in areas initially with a small content while decreasing in areas having a large content. The map of SOM change showed that the rate of increase decreased from north to south within the province. Increased fertilizer application promoted crop production with more residual biomass being retained in the soil, which resulted in increased SOM content. Land use changes to paddy, upland or forest improved SOM content, whereas abandoning land reduced SOM content.     

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.