Organic Matter Dynamics in Soils Regenerating from Degraded Abandoned Rubber Plantation in Orogun Area of the Rainforest Zone of Southern Nigeria

Optimal soil-sampling design for rubber tree management based on fuzzy clustering

Various research issues related to soil organic matter in permafrost soils are still poorly investigated. At the same time, numerous investigations have shown the importance of permafrost soils, as they serve as a huge reservoir of organic matter. This work is aimed at the investigation of permafrost-affected soils in the southern part of the Yamal region, namely at the assessment of composition (fractional, elemental and molecular) of soil organic matter in topsoils formed under different biogeoclimatogenic conditions in tundra and forest tundra. Special attention was given to assessment of potential vulnerability of soil organic matter in the context of Arctic warming. Results showed the predominance of fulvic acids in the humus of the studied soils, which indicates mineralization risks in the humic substances system of Arctic soils under conditions of further warming. The 13C-NMR analysis of humic acids revealed that all the studied soils are characterized by higher portions of aliphatic groups of carbon and decreased portions of aromatic groups and revealed early stages of the humification process in studied soils. These results contribute to scarcely distributed research of soil organic matter in permafrost soils of the Arctic. Moreover, our research provided new data on the vulnerability of soil organic matter and its possible mineralization risks under pronounced climate change in the Arctic using the modern instrumental technique.

Chapter 1 Soil Organic Matter: Its Importance in Sustainable Agriculture and Carbon Dioxide Fluxes

In the central-eastern Tibetan Plateau (TP) there is abundant organic matter in topsoils, which plays a crucial role in determining soil hydraulic properties that need to be properly described in land surface models. Limited soil parameterizations consider the impacts of soil organic matter (SOM), but they still show poor performance in the TP. A dedicated field campaign is therefore conducted by taking undisturbed soil samples in the central TP to obtain in-situ soil hydraulic parameters and to advance SOM parameterizations. The observed findings are twofold. 1) The SOM pore-size distribution parameter, derived from measured soil water retention curves, has been demonstrated to be much underestimated in previous studies. 2) SOM saturated hydraulic conductivity is overestimated. Accordingly, a new soil hydraulic parameterization is established by modifying a commonly used one based on observations, which is then evaluated by incorporating it into Noah-MP. Compared with the original ones, the new parameterization significantly improves surface soil liquid water simulations at stations with high surface SOM content, especially in the warm season. A further application with the revised Noah-MP indicates that SOM can enhance sensible heat flux but decrease evaporation and subsurface soil temperature in the warm season, and tends to have a much weak effect in the cold season. This study provides insights into the role of SOM in modulating soil state and surface energy budget. Note that, however, there are many other factors at play and the new parameterization is not necessarily applicable beyond the TP.

Purpose Paddy chronosequence provides a unique way to investigate soil development. This study investigated dynamic profiles of aggregate and soil organic matter in topsoils of two 2,000-year paddy chronosequences.

Soils of mountain regions are estimated to contain large amounts of organic matter (OM), equivalent to stocks found in high-latitude boreal and tundra soils. Mountain environments are also experiencing profound changes in land management under the influence of socio-economic pressures as well as the need to adapt to climate change, which is occurring at a faster rate than in lowland areas. These anthropogenic impacts are expected to strongly affect soil OM storage. Most studies of land-use change have however focused on topsoil OM; whether similar trends will hold true for subsoil OM remains unknown. Using Rock-Eval pyrolysis as a proxy for soil OM dynamics, we showed that the hierarchy of controls on OM properties and transformations varied greatly with increasing soil depth. In the topsoil, OM properties were related to the nature of plant inputs, their degree of in-mixing with the mineral matrix and the occurrence of seasonal water saturation. In the subsoil however, the foremost predictors of OM properties were geochemical parameters. This shift in the nature of determinants of OM dynamics indicates that shallow and deep soil OM pools should respond differently to external forcings. Podzolic profiles showed the strongest decoupling of topsoil and subsoil OM properties. We focused on this soil type to specifically investigate the effects of land use on subsoil OM. We selected field sites from the Coastal Range of British Columbia, Canada and the Pennine Alps, Switzerland representing undisturbed and managed forest, shrubland and pasture. Samples were analyzed for organic C content, OM quality and reactive mineralogy. Results showed that herbaceous cover was associated with an increase in topsoil but not subsoil OM. In the subsoil, variations in OM content and properties were associated with changes in reactive Al and Fe mineral phases. Overall, our data indicate that organo-mineral and organo-metal interactions are of prime importance to OM accumulation in the subsoil, and that understanding the response of deep soil C stocks to land use change will require consideration of the geochemical and mineralogical environment. Our results further suggest that so-called reactive mineral phases may themselves be impacted by land use, in turn affecting deep soil C stabilization and destabilization processes.

Decomposing crop residues contribute to soil organic matter (SOM) accrual; however, the factors driving the fate of carbon (C) and nitrogen (N) in soil fractions are still largely unknown, especially the influence of soil mineralogy and autochthonous organic matter concentration. The objectives of this work were (1) to evaluate the retention of C and N from crop residue in the form of occluded and mineral-associated SOM in topsoil (0–20 cm) and subsoil (30–70 cm) previously incubated for 51 days with 13C-15N-labelled corn residues, and (2) to explore if specific minerals preferentially control the retention of residue-derived C and N in topsoil and subsoil. We used topsoil and subsoil having similar texture and mineralogy as proxies for soils being rich (i.e., topsoil) and poor (i.e., subsoil) in autochthonous organic matter. We performed a sequential density fractionation procedure and measured residue-derived C and N in occluded and mineral-associated SOM fractions, and used X-ray diffraction analysis of soil density fractions to investigate their mineralogy. In accordance with our hypothesis, the retention of C and N from crop residue through organo-mineral interactions was greater in subsoil than topsoil. The same minerals were involved in the retention of residue-derived organic matter in topsoil and subsoil, but the residue-derived organic matter was associated with a denser fraction in the subsoil (i.e., 2.5–2.6 g cm−3) than in the topsoil (i.e., 2.3–2.5 g cm−3). In soils and soil horizons with high clay content and reactive minerals, we find that a low SOM concentration leads to the rapid stabilization of C and N from newly added crop residues.

<p>Due to the continued ice retreat with global warming, areas of deglaciated forefields will strongly increase in the future, leading to the emergence of new terrestrial ecosystems in many regions of the world. The soil chronosequences resulting from glacier retreat have long been a key tool for studies focusing on the mechanisms of soil formation and soil organic matter storage.</p><p>This study aimed at identifying general patterns in soil organic matter (SOM) build-up during the initial stage of soil formation and ecosystem development (0–500 years) in different glacier forefields around the world. For this purpose, we measured total soil organic matter concentration (C and N), its stable isotopic composition (<sup>13</sup>C, <sup>15</sup>N) and its distribution in carbon pools of different biogeochemical stability over time in ten soil chronosequences on glacier forefields (four Andeans, one Canadian Rockies, one Greenland, two Alps, one Caucasus, one Himalaya). The distribution of SOM in carbon pools was estimated with Rock-Eval® thermal analysis. We then tested the effect of time and climatic variables (temperature, precipitation) on the build-up of soil organic matter (total concentration, isotopic signature and distribution in carbon pools).</p><p>We found a positive correlation between the rate of SOM accumulation and the average temperature of the warmest quarter (three-month period). We also noted significant traces of atmospheric deposition of anthropogenic origin in some forefield glaciers, particularly in the northern hemisphere. The build-up of soil carbon pools showed consistent trends across the soil chronosequences of the ten glacier forefields. During the first decades of soil formation, the very low SOM quantities were dominated by a very stable carbon with a small but significant labile carbon pool. This may highlight the presence of organic matter derived from ancient carbon on the different forefield glaciers, decomposed by an active living trophic network of soil microorganisms. The overall stability of SOM then slowly decreased with time, reflecting the soil carbon input from plants.</p><p>We conclude that while the rate of SOM accumulation is driven by climate (air temperature of the growing season), the build-up of soil carbon pools shows a consistent temporal trajectory on the different glacier forefields around the world.</p>

在黄土高原、胶东半岛和北京郊区果园选择11个采样区, 按照5~10年、10~15年和15年以上3个园龄段, 利用GPS定位系统, 共采集0~20 cm表层土壤样品99份, 并在取样果园附近选择普通农田作为对照采集土壤样品33份, 测定了果园与普通农田土壤的有机质含量, 并从果园土壤有机质数量特征、果园与农田差异特征以及有机质随园龄段变化特征3个方面进行统计分析。研究结果表明: 胶东半岛栖霞和北京郊区果园土壤有机质含量较高, 黄土高原宝塔较低。与农田相比, 60%多的果园土壤有机质未发生显著变化, 明显提高的果园不到30%, 明显降低的果园不到10%; 土壤有机质发生变化的果园, 平均提高0.62%, 平均降低0.20%; 随园龄增加, 两个样点果园土壤有机质明显提高, 其他果园变化不显著。在优质高产果园区, 果园土壤有机质提高归因于施用有机肥、果园种草、青草或秸秆还田。总体上看, 典型区域果园土壤有机质高低值差异较大, 土壤有机质含量普遍不高, 果业持续发展能力较低。

National digital soil map of organic matter in topsoil and its associated uncertainty in 1980's China

Soil properties of Quercus variabilis forest on Youngha valley at Mt. Worak National Park were studied as a part of Korea National Long-Term Ecological Research. Soil sampling was carried out along the 50 cm soil depth with 10cm intervals at every quarter from May 2005 through July 2006. Fresh soil was used for <TEX>$NH_4{^+}-N,\;NO_3{^-}-N$</TEX>, and soil water content determination. Remaining soils were air dried in the shade, and then used for determination of soil pH, T-N, T-P and exchangeable cation. Average soil organic matter in top soil was <TEX>$8.5{\pm}1.2%$</TEX> and decreased with soil depth. Bulk density of top soil was <TEX>$0.82{\pm}0.07g/cm^3 $</TEX>and increased with soil depth. Soil organic matter and bulk density showed a negative linear correlation (<TEX>$R^2=0.8464$</TEX>). Soil pH in top soil and subsoil was similar. T-N, <TEX>$NH_4{^+}-N,\;NO_3{^-}-N$</TEX> and T-P in top soil were <TEX>$1.9{\pm}0.5mg/g,\;7.3{\pm}1.0mg/kg,\;2.0{\pm}0.4mg/kg\;and\;0.2{\pm}0.05mg/g$</TEX>, respectively. <TEX>$K^+,\;Ca^{2+}\;and\;Mg^{2+}$</TEX> in top soil were <TEX>$84.6{\pm}24.4,\;408.8{\pm}137.8\;and\;93.4{\pm}23.0mg/kg$</TEX>, respectively. They decreased with soil depth. Amounts of organic matter, T-N, <TEX>$NH_4{^+}-N,\;NO_3{^-}-N$</TEX>, T-P, <TEX>$K^+,\;Ca^{2+}\;and\;Mg^{2+}$</TEX> in 50 cm soil depth were 250.9, 3.45, 0.025, 0.003, 0.639, 0.181, 0.845 and 0.302 ton <TEX>$ha^{-1}\;50cm-depth^{-1}$</TEX>, respectively.

The study dealt with the assessment of impact of deforestation on soil through a comparative analysis of soil physicochemical properties of natural forest and deforested areas. Soil samples from three depths (top, middle and bottom) under natural forest and nearby deforested areas were collected to investigate soil properties. Forest soils show no significant change in particle size distribution. Bulk density of forested soils shows the significant differences in top and middle layers. Soil pH in top and middle soil, organic matter in top soil and available phosphorus in middle soil of the forest site are found to be significantly higher than that of the deforested soils. Forest soils also have significantly higher level of exchangeable Ca2+, K+ in top and middle soil and Mg2+ at all depth than those of deforested site. Exchangeable Na+ and cation exchange capacity (CEC) are observed unchanged in both sites. The results suggest that change in soil properties was more obvious in surface and sub surface portions of both areas. The study shows that deterioration of physicochemical properties occurred due to deforestation.

Assessment of spatial uncertainty for delineating optimal soil sampling sites in rubber tree management using sequential indicator simulation

Potential effects of land-use/land-cover (LULC) transformation from lowland rainforest into oil-palm plantations on silicon (Si) pools in tropical soils remain poorly understood, although appropriate levels of plant-available Si in soils may contribute to maintain high crop yields and increase the vitality and drought resistance of oil palms. Therefore, the aim of our study was to identify possible effects of such LULC change on soil Si pools. For this purpose, we compared soil Si pools under lowland rainforest and ca. 20 year-old oil-palm plantations in Jambi Province, Indonesia. The investigated soils were Acrisols and Stagnosols, in which we quantified six different soil Si pools following a sequential extraction procedure to evaluate, whether 20 years of oil-palm cultivation has led to a depletion of these soil Si pools. The considered pools included mobile Si, adsorbed Si, Si bound in soil organic matter (SOM), Si included in pedogenic oxides and hydroxides, and Si in amorphous silica of biogenic and pedogenic origin. Finally, we also determined total Si. All oil-palm plantations established on sloping terrain and Acrisols only showed decreased Si stocks of mobile Si, adsorbed Si and SOM-bound Si; those established in floodplains and Stagnosols had decreased stocks of SOM-bound Si and biogenic-amorphous silica. Lower Si stocks were mostly attributed to a missing “stable” phytolith pool in the subsoil and less organic matter in topsoils under oil-palm plantations. When comparing well-drained and riparian areas, flooding seemed to increase phytolith dissolution. We conclude that 20 years of oil-palm cultivation has not yet led to a significant depletion of soil Si pools. As topsoils comprise the highest concentrations of SOM-bound Si and Si in amorphous silica of biogenic origin but are susceptible to erosion and surface runoff under managed oil-palm plantations, it would be advisable to instate specific management practices that maintain organic-rich and well-aired topsoils on oil-palm plantations.

Soil organic matter (SOM) is of global importance as it represents a greater carbon pool than atmosphere or terrestrial vegetation and it strongly regulates primary productivity. SOM is thus integral to global climate change mitigation and food security. Recent advances reveal a pivotal role of soil microbes in both SOM formation and decomposition, placing them at the nexus of global biogeochemical cycles. However, the soil microbial traits that best promote SOM formation and persistence, and the environmental conditions that best promote such traits, remain poorly characterised – particularly in the tropics. In this thesis, I evaluated the interplay between microbial function and composition, vegetation, and SOM dynamics in tropical soils. My experimentation spanned laboratory and field study scales in two continents: (i) soil carbon cycling was examined following manipulations of soil microbial composition and function under controlled laboratory conditions in microcosms, (ii) the responses of soil microbes and SOM were compared in decadalold high diversity rainforest restoration plantings and reference soils under pasture and old-growth rainforest in tropical northeast Australia, and (iii) tropical tree monoculture and mixed species plantings in the Philippines were assessed for restoration of soil microbial traits and SOM. Several insights were gained that advance knowledge on SOM dynamics in the tropical context. Soil microbial substrate use efficiency, an indicator of SOM formation potential, changed significantly with microbial composition, increasing with greater fungal dominance. Stable SOM under Australian rainforest restoration plantings was unchanged circa two decades after plantation establishment, with no sign of recovery towards reference old- growth rainforest levels, which coincided with similarly stagnant microbial recovery. Soil microbial composition explained most of the variation in SOM across land uses in the Philippines, where SOM was also slow to recover, and microbial composition in turn correlated strongly with aboveground plant composition. The results thus indicate that (i) microbial composition can have a direct influence on efficiency of formation of SOM precursor material (microbial residues), and (ii) slow microbial recovery with reforestation coincides with slow SOM recovery. In combination with previous research suggesting that microbial traits are major determinants of SOM formation and persistence, the results prompt me to speculate that reliable restoration of stable SOM through tropical reforestation may often be constrained by limited restoration of the soil microbial community. This in turn may require more comprehensive restoration of aboveground plant community composition, or, potentially, upon active manipulation of soil microbial communities to circumvent long lag times that may prevent effective restoration of soil function. Future developments in forest restoration and climate mitigation efforts may require a shift towards integrating the soil microbial community. A deliberate and nuanced examination of soil microbial communities is needed to clarify their role in soil recovery, with a focus on designing and testing more effective interventions to overcome barriers to the recovery of degraded land.