Influence of mineral and organic fertilizers on soil organic carbon pools

Abstract

The influence of farmyard manure (FYM) and equivalent mineral NPK application on organic matter content, hot water extractable carbon (HWC), microbial biomass C (C_mic), and grain yields in a long-term field experiment was assessed after 40 years in Hungary. The unfertilized plot, FYM fertilized plots and plots fertilized with equivalent NPK fertilizer contained 0.99%, 1.13% and 1.05% total organic carbon (TOC) respectively. Compared to the unfertilized plot, FYM application resulted in 8.2% higher TOC than equivalent NPK fertilization. The highest TOC was only 1.21%, much lower than expected for a soil containing 21.3% of clay. The quantity of HWC varied depending on the type of fertilization: Compared to control, FYM treatments lead to 29% more HWC than mineral fertilization (FYM: 328 mg kg^?1; NPK: 264 mg kg^?1). The impact of FYM and equivalent NPK fertilizer on C_mic was contrary. FYM and NPK resulted in 304 and 423 mg kg^?1 C_mic, respectively. The difference was 119 mg kg^?1; 42% as compared to the unfertilized plot. Despite the higher HWC content, FYM treatments lead to significantly less (35%) grain yields than equivalent NPK doses; C_mic content showed closer correlation to grain yields.     

Data integration model to assess soil organic carbon availability

Soil data acquisition and assessment are crucial phases in the evaluation of soil degradation scenarios. To overcome the lack of field data, flexible sampling approaches can be used to complement conventional soil sampling. For the assessment of soil quality, it is necessary to integrate different soil support data and to provide a coherent spatial characterization of soil properties. This study proposes a new model to combine soil data from two different supports: “point” data, which refers to the concentration measured in the topsoil layer, and “bulk” data, which refers to the concentration measured for the whole soil depth sampled. The method developed uses a geostatistical co-simulation algorithm based on the experimental bi-distribution between both types of soil supports to compute co-simulated values. This new approach was applied to assess Soil Organic Carbon (SOC) availability in the topsoil. The results were used to identify critical areas in the Left Margin of the Guadiana River; an area in the South of Portugal with a high susceptibility to desertification.     

Reproducibility of a soil organic carbon fractionation method to derive RothC carbon pools

Fractionation of soil is undertaken to isolate organic carbon with distinct functional properties, such as stability and turnover times. Soil organic carbon (SOC) fractionation helps us to understand better the response of SOC to changes in land use, management or climate. However, fractionation procedures are often poorly defined and there is little information available on their reproducibility in different laboratories. In a ring trial, we assessed the reproducibility of a SOC fractionation method introduced by Zimmermann et al. (2007). The isolated fractions were linked to the model pool sizes of the Rothamsted carbon model (RothC). We found significant differences between six laboratories for all five defined fractions in three different soils with coefficients of variation ranging from 14 to 138%. During ultrasonic dispersion, the output power (energy per unit time) was identified as an important factor controlling the distribution of SOC within these five fractions, while commonly only the output energy is standardized. The amount of water used to wet‐sieve dispersed soil slurry significantly influenced the amount of extracted dissolved organic carbon (DOC). We therefore suggest using a fixed amount of power for ultrasonic dispersion (20 W) and a minimum amount of water for wet sieving (2000 ml). RothC pool sizes were predicted from the measured fractions and compared with RothC equilibrium pool size distributions. This model initialization using measured SOC fractions, however, led to an over‐estimation of stable RothC SOC pools when compared with pool size distributions derived from RothC equilibrium runs under a bare fallow soil model simulation. To improve the isolation of particulate organic matter from stable mineral‐bound organic matter, we suggest that the density should be increased from 1.8 to 2.0 g cm^?3 in the density fractionation step. We formulated a modified fractionation procedure, which aims specifically to enhance reproducibility across laboratories and to improve the match of the isolated SOC fractions with RothC's SOC pools.     

关中平原地区果园和农田土壤有机碳组分及碳库特征

由于果树经济效益高,关中平原地区广泛推广农田转为果园。为明确关中平原地区农田转变为果园后土壤有机碳(SOC)组分含量及土壤碳库指数的差异,采用了野外调查和室内分析的方法,探究了关中平原地区农田生态系统中果园和农田的土壤碳组分及碳库管理指数的变化。结果表明,在0～20、20～60、60～100 cm土层中,果园土壤活性有机碳(LOC)含量较农田分别增加了33.91%、49.95%和35.37%;与农田相比,果园显著增加了20～60和60～100 cm土层LOC/SOC值,提高了深层土壤碳库活性,促进了土壤有机碳的利用;在0～100 cm土层的垂直梯度上果园和农田LOC含量均随土层深度增加而减少,土壤总有机碳含量无显著差异;果园的碳库指数(CPI)和碳库管理指数(CPMI)均大于农田,增幅分别达6.12%和72.72%。相关分析表明,土壤有机碳组分、碳库活度、碳库管理指数与土壤主要肥力因子如有效磷、速效钾相关性密切,可以作为该地区农田生态系统土壤肥力的主要监测因子。研究表明,关中平原土地利用方式从农田转变为果园,将有效活化深层土壤的固有碳库,促进有机碳的分解与利用,土壤性能向良性发展。     

Deforestation impacts soil organic carbon and nitrogen pools and carbon lability under Mediterranean climates

Journal of Soils and Sediments - Deforestation is one of the ecosystem disservices associated with accelerated loss of soil organic carbon (SOC) and nitrogen (TN). The objective of our study was to...     

长期施肥对红壤不同有机碳库及其周转速率的影响

通过土壤有机质物理分组和室内培养的方法,研究了长期定位施肥对红壤不同有机碳库及其周转速率的影响。结果表明:平衡施肥(NPK、2NPK)和施用有机肥(OM、NPKOM)显著提高玉米产量,降低产量年际变异系数,同时也显著提高了土壤有机碳(SOC)和活性有机碳(LOC)的含量。根据有机碳物理分组方法,将SOC分成五部分,其中,与矿物结合的有机碳占绝对优势,微团聚体中的粉黏粒(s+c_mM)和大团聚体中的粉黏粒(s+c_M)分别占SOC的31%～53%和28%～38%,其次为微团聚体间的细颗粒有机质(fPOM)和微团聚体中的细颗粒有机质(iPOM_mM),分别占8%～15%和7%～21%,粗颗粒有机质(cPOM)仅占5%～12%。施有机肥(OM、NPKOM)显著提高了颗粒有机碳组分,包括cPOM、fPOM和iPOM_mM组分碳的数量,但是对矿物结合态碳(s+c_M、s+c_mM)影响不明显。施无机肥对有机碳库组成(除s+c_mM外)影响不显著。在有机肥处理中(OM、NPKOM)土壤有机碳周转速率最快,相应的半衰期最短,是CK处理的0.47倍～0.70倍,是无机肥处理的0.11倍～0.95倍。原土有机碳周转时间与LOC/SOC呈显著正相关(r=0.66*)。研究表明平衡施肥和有机肥能提高土壤地力,同时还有利于土壤有机碳的积累。     

The impact of mulch type on soil organic carbon and nitrogen pools in a sloping site

Three mulch treatments were tested for their ability to control erosion on a sloping site. Additionally, the choice of mulch can also enhance revegetation success and improve soil organic matter input. This study aimed to investigate the effects of three mulching treatments, hydro-seeding, granite mulch and forest mulch, on soil C and N pools at different positions on highly erodible slope with approximately 30 % gradient. Soil moisture, total C (TC), total N (TN), hot water-extractable organic C (HWEOC), hot water-extractable total N (HWETN), microbial biomass C and N (MBC and MBN), inorganic N and potentially mineralisable N were measured. All variables were significantly higher in soils amended with forest mulch than those with hydro-seeding and granite mulch, for the same slope positions. Soil moisture was significantly higher in the lower slope position than middle and upper slope positions in hydro-seeding and granite mulch treatments, whereas no slope effect was observed on soil moisture under the forest mulch application. In the forest mulch treatment, the upper slope position had higher soil TC, TN, HWEOC, HWETN, MBC, MBN, NO₃ ^?-N and total inorganic N than the middle and lower slope positions. Five years following mulch application, forest mulch still exerted a significant influence on soil fertility compared to the other treatments and the influence on soil moisture suggests that this treatment would be the most effective in the control of water-driven soil erosion on this steep site.     

Comparison of chemical fractionation methods for isolating stable soil organic carbon pools

Stable soil organic matter (SOM) is important for long‐term sequestration of soil organic carbon (SOC), but the usefulness of different fractionation methods to isolate stable SOM is open to question. We assessed the suitability of five chemical fractionation methods (stepwise hydrolysis, treatment with H₂O₂, Na₂S₂O₈, NaOCl, and demineralization of the NaOCl‐resistant fraction (NaOCl + HF)) to isolate stable SOM from soil samples of a loamy sand and a silty loam under different land use regimes (grassland, forest and arable crops). The apparent C turnover time and mean age of SOC before and after fractionation was determined by ¹³C and ¹⁴C analysis. Particulate organic matter was removed by density fractionation before soils were exposed to chemical fractionation. All chemical treatments induced large SOC losses of 62–95% of the mineral‐associated SOC fraction. The amounts of H₂O₂‐ and Na₂S₂O₈‐resistant SOC were independent from land use, while those of NaOCl‐ (NaOCl + HF)‐ and hydrolysis‐resistant SOC were not. All chemical treatments caused a preferential removal of young, maize‐derived SOC, with Na₂S₂O₈ and H₂O₂ being most efficient. The mean ¹⁴C age of SOC was 1000–10000 years greater after chemical fractionation than that of the initial, mineral‐associated SOC and mean ¹⁴C ages increased in the order: NaOCl < NaOCl + HF ≤ stepwise hydrolysis ≪ H₂O₂≈ Na₂S₂O₈. None of the methods appeared generally suitable for the determination of the inert organic matter pool of the Rothamsted Carbon Model. Nonetheless, our results indicate that all methods are able to isolate an older, more stable SOC fraction, but treatments with H₂O₂ and Na₂S₂O₈ were the most efficient ones in isolating stable SOM.     

水稻-小麦轮作系统中土壤活性有机碳库对长期施用化肥，秸秆和粪便的敏感度

Labile soil organic carbon(SOC) pools, estimated through chemical fractionation techniques, are considered sensitive indicators of management-induced changes in quality and composition of soil organic matter. Although the impacts of organic manure and crop residue applications on C sequestration in rice-wheat system are fairly well documented, their influence on labile SOC pools is relatively less known. Impacts of organic manure, rice straw, and inorganic fertilizer nitrogen(N) applications on soil total organic carbon(TOC)and SOC pools including water-extractable organic C(WEOC), hot water-soluble organic C(HWOC), potassium permanganateoxidizable organic C(KMnO 4-C), microbial biomass C(MBC), mineralizable organic C(Cmin), and the oxidizable fractions of decreasing oxidizability(easily-oxidizable, oxidizable, and weakly-oxidizable) were investigated in an 11-year field experiment under rice-wheat system. The field experiment included treatments of different combinations of farmyard manure, rice straw, and fertilizer N application rates, with C inputs estimated to be in the range from 23 to 127 Mg ha-1. After 11 years of experiment, WEOC,HWOC, and KMnO 4-C were 0.32%–0.50%, 2.2%–3.3%, and 15.0%–20.6% of TOC, respectively. The easily-oxidizable, oxidizable,and weakly-oxidizable fractions were 43%–57%, 22%–27%, and 10%–19% of TOC, respectively. The applications of farmyard manure and rice straw improved WEOC, HWOC, KMnO 4-C, easily-oxidizable fraction, Cmin, and MBC, though the rates of change varied considerably from-14% to 145% and-11% to 83% of TOC, respectively. At the C input levels between 29 and 78 Mg C ha-1during the 11-year period, the greatest increase was observed in WEOC and the minimum in KMnO 4-C. Water-extractable organic C exhibited a relatively greater sensitivity to management than TOC, suggesting that it may be used as a sensitive indicator of management-induced changes in soil organic matter under rice-wheat system. All the other labile SOC pools exhibited almost the same sensitivity to management as TOC. Most of the SOC pools investigated were positively correlated to each other though their amounts differed considerably. Long-term applications of farmyard manure and rice straw resulted in build-up of not only the labile but also the recalcitrant pool of SOC, emphasizing the need for continued application of organic amendments for permanence of the accrued C under the experimental conditions.     

The relative impact of land use and soil properties on sizes and turnover rates of soil organic carbon pools in Subtropical China

The dynamics of soil organic carbon (SOC) pools determine potential carbon sequestration and soil nutrient improvement. This study investigated the characteristics of SOC pools in five types of cultivated topsoils (0–15 cm) in subtropical China using laboratory incubation experiments under aerobic conditions. The sizes and turnover rates of the active, slow and resistant C pools were simulated using a first‐order kinetic model. The relative influence of soil environmental properties on the dynamics of different SOC pools was evaluated by applying principal component analysis (PCA) and aggregated boosted trees (ABTs) analysis. The results show that there were significantly greater sizes of different SOC pools and lower turnover rates of slow C pool in two types of paddy soils than in upland soils. Land use exerted the most significant influence on the sizes of all SOC pools, followed by clay content and soil pH. The soil C/N ratio and pH were the major determinants for turnover rates of the active and slow C pools, followed by clay content which had more impact on the turnover rates of the active C pool than the slow C pool. It is concluded that soil type exerts a significant impact on the dynamics of SOC.     

Temporal dynamics of iron-rich, tropical soil organic carbon pools after land-use change from forest to sugarcane

Background, aim, and scope  

Land-use change can significantly influence carbon (C) storage and fluxes in terrestrial ecosystems. Soil–plant systems can act as sinks or sources of atmospheric CO₂ depending on formation and decomposition rates of soil organic matter. Therefore, changes in tropical soil C pools could have significant impacts on the global C cycle. This study aims to evaluate the impacts of long-term sugarcane cultivation on soil aggregation and organic matter, and to quantify temporal dynamics of soil organic matter in cultivated sugarcane plantation soils previously under a tropical natural secondary forest.     

Effect of long-term cropping systems on soil organic carbon pools and soil quality in western plain of hot arid India

Maintaining soil organic carbon (SOC) in arid ecosystem is important for soil productivity and restoration of deserted sandy soil in western plain of India. There is a need to understand how the cropping systems changes may alter SOC pools including total organic carbon (TOC), particulate organic C (POC), water soluble carbon (WSC), very labile C (VLC), labile C (LC), less labile C (LLC) and non-labile C (NLC) in arid climate. We selected seven major agricultural systems for this study viz., barren, fallow, barley–fallow, mustard–moth bean, chickpea–groundnut, wheat–green gram and wheat–pearl millet. Result revealed that conversion of sandy barren lands to agricultural systems significantly increased available nutrients and SOC pools. Among all studied cropping systems, the highest values of TOC (6.12 g kg^?1), POC (1.53 g kg^?1) and WSC (0.19 g kg^?1) were maintained in pearl millet–wheat system, while the lowest values of carbon pools observed in fallow and barren land. Strong relationships (P < 0.05) were exhibited between VLC and LC with available nutrients. The highest carbon management index (299) indicates that wheat–pearl millet system has greater soil quality for enhancing crop productivity, nutrient availability and carbon sequestration of arid soil.     

Conservation agriculture practice influences soil organic carbon pools in intensive rice-based systems of the Eastern Indo-Gangetic Plain

Studies of rice-based systems in the Indo-Gangetic Plain (IGP) have demonstrated the beneficial effects of Conservation Agriculture on soil organic carbon (SOC) status, along with increased soil health and crop productivity. However, it remains unclear as to the time for such treatments to have a positive effect. In this study of lentil-mung bean-rice and wheat-mung-rice rotations in Bangladesh positive effects of strip planting or bed planting, along with residue return, on SOC pools were apparent after 1.5 years, compared with intensive conventional tillage and limited residue return. Conventional tillage resulted in higher CO₂ emission compared with strip planting or bed planting as did high residue return. In the cereal-dominated rotation, the strip planting system sequestered carbon at a rate of 0.24–0.53 Mg C ha⁻¹ year⁻¹ (at 0–0.15 m depth) while conventional tillage was associated with a carbon loss of 0.52–0.82 Mg C ha⁻¹ year⁻¹. In the legume-dominated rotation, neither practice sequestered SOC. Under strip planting, a minimum annual crop residue input of 1.7 Mg C ha⁻¹ for the cereal-dominated system and 5.2 Mg C ha⁻¹ for the legume-dominated system was required to maintain SOC at equilibrium. We conclude that strip planting with high levels of crop residue return can be an effective and quick strategy in either slowing the loss of SOC or improving C sequestration in the intensive rice-based systems of the Eastern IGP.     

Nutrient management effects on organic carbon pools in a sandy loam soil under rice-wheat cropping

Agricultural management practices are known to influence soil organic C. While changes in total organic C (TOC) are relatively less discernible over short to medium-term, some extractable pools of TOC are considered early indicators of changes in TOC. Therefore, to devise nutrient management practices that can lead to C sequestration, it is important to study their effect on soil organic C pools that may respond rapidly to management. We studied the impact of balanced (NPK) and imbalanced (N, NP, NK and PK) application of fertilizer nutrients without and with farmyard manure (FYM) on total and labile pools of organic C viz. water soluble (WEOC), potassium permanganate oxidizable (KMnO₄-C), microbial biomass (MBC) and fractions of decreasing oxidizability after 5-cycles of rice-wheat cropping. Integrated use of NPK and FYM significantly increased TOC and extractable C pools in both surface (0–7.5 cm) and sub-surface (7.5–15 cm) soil. Majority of TOC (72%) was stabilized in less labile and recalcitrant fractions; the magnitude being higher under balanced (NPK+FYM) than imbalanced nutrient management (N+FYM). The results showed that balanced fertilizer application conjointly with FYM besides enlarging TOC pool favorably impacts soil organic matter composition under rice-wheat system.     

Comparing different multivariate calibration methods for the determination of soil organic carbon pools with visible to near infrared spectroscopy

A successful determination of spectrally active soil components with visible and near infrared reflectance spectroscopy (VIS-NIRS, 400-2500 nm) depends on the selection of an adequate multivariate calibration technique. In this study, the contents of thermolabile organic carbon (C_375 °C), the inert organic C fraction (C_inert) and the sum of both (total soil organic carbon, OC_tot) were estimated with three different methods: partial least squares regression (PLSR) as common standard tool, a combination of PLSR with a genetic algorithm (GA-PLSR) for spectral feature selection, and support vector machine regression (SVMR) with non-linear fitting capacities. The objective was to explore whether these methods show differences concerning their ability to predict soil organic carbon pools from VIS-NIR data. For this analysis, we used both measured spectra and also spectra successively blurred with uniformly distributed white noise. Soil sampling was performed in a floodplain (grassland plots) near Osnabrück (Germany) and comprised a total of 149 samples (109 calibration samples, 40 validation samples); spectral readings were taken in the laboratory with a fibre-optics ASD FieldSpec II Pro FR spectroradiometer.In the external validation, differences between the calibration methods were rather small, none of the applied techniques emerged to be the fittest with superior prediction accuracies. For C_375 °C and OC_tot, all approaches provided reliable estimates with r² (coefficient of determination) greater than 0.85 and RPD values (defined as ratio of standard deviation of measurements to standard error of prediction) greater than 2.5. For C_inert, accuracies dropped to r² < 0.50 and RPD < 1.5; after the removal of two extreme values (n = 38) results improved at best (GA-PLSR) to r² = 0.80 and RPD = 1.98. The noise experiment revealed different responses of the studied approaches. For PLSR and GA-PLSR, increasing spectral noise resulted in successively reduced r² and RPD values. By contrast, SVMR kept high coefficients of determination even at high levels of noise, but increasing noise caused severely biased estimates, so that regression models were less accurate than those of PLSR and GA-PLSR.     

不同比例尺农田土壤碳库模拟的最佳栅格单元分辨率

基于太湖地区1∶50 000、1∶1 000 000、1∶14 000 000三种比例尺土壤矢量图斑单元以及通过上述矢量图斑单元转换生成的不同分辨率的栅格单元,在1982年水稻土土壤有机碳库的基础上,利用DNDC(Denitrification-Decomposition)模型模拟了2000年水稻土表层(0~20 cm)土壤有机碳库,对比分析了不同分辨率栅格单元与3种比例尺矢量图斑单元的水稻土类型数量、面积、表层土壤有机碳储量以及有机碳密度的变化特征,并以矢量图斑单元获得的这4个指标结果为基准,用相对变异百分数(VIV)来判别基于三种比例尺DNDC模型模拟的最佳栅格单元分辨率。结果表明,在4个指标的│VIV│1%前提下,基于1∶50 000、1∶1 000 000、1∶14 000 000三种比例尺的最佳栅格模拟单元分辨率分别为0.2 km×0.2 km、2 km×2 km、17 km×17 km,既能保证模型模拟过程中的精度要求,又可以避免数据冗余,提高模拟效率。建立的土壤碳库模拟研究的比例尺与其最佳栅格单元分辨率对应转换关系,对区域土壤碳模拟研究具有重要参考价值。     

Effect of no-tillage with straw mulch and conventional tillage on soil organic carbon pools in Northern China

The dynamics of soil organic carbon (SOC) is imperative for maintaining soil quality. Our objective was to investigate the effects of tillage practices on SOC and its fractions at the depth (0–60 cm) of Chromic Cambisol profile in northern China. The experiment including no-tillage with straw mulch (NTSM) and conventional tillage (CT). Our results indicated that differences in SOC concentration and stock were primarily evident in the 0–10 cm layer. The particulate organic matter carbon (POM-C), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) levels in the top layers (0–10 cm) under the NTSM treatment were 28.5, 26.1 and 51.0% higher than CT. A positive correlation was observed between these labile C fractions and the SOC, and POM-C was the much more sensitive indicator of SOC quality than MBC and DOC. NTSM was unable to sustain the greater yields, and from 2006 to 2011, the mean maize yield for NTSM was significantly lower than that for CT (P < 0.05). NTSM resulted in higher SOC content and stocks in dryland farming systems but lower crop yields is a concern which needs to be addressed in order to make these systems acceptable to the farming community.     

Estimation of soil organic carbon losses and counter approaches from organic materials in black soils of northeastern China

Journal of Soils and Sediments - The northeast plain of China is one of three extensive regions with black soil rich in organic matter in the northern hemisphere. The replacement of natural...