Soil Organic Matter In Topsoil Research Articles

Elemental stoichiometry and Rock-Eval® thermal stability of organic matter in French topsoils

Abstract. The quality and quantity of soil organic matter (SOM) are key elements that impact soil health and climate regulation by soils. The Rock-Eval® thermal analysis technique is becoming more commonly used, as it represents a powerful method for SOM characterization by providing insights into bulk SOM chemistry and thermal stability. In this study, we applied this technique on a large soil sample set from the first campaign (2000–2009) of the French Soil Quality Monitoring Network (RMQS – Réseau de mesures de la qualité des sols). Based on our analyses of ca. 2000 composite surface (0–30 cm) samples collected across mainland France, we observed a significant impact of land cover on both the SOM thermal stability and elemental stoichiometry. Cropland soils had a lower mean hydrogen index value (a proxy for the SOM H/C ratio) and a higher thermal stability than grasslands and forests. Regarding the oxygen index (a proxy for the SOM O/C ratio), we observed significant differences among the values for croplands, grasslands, and forests. Positive correlations of the temperature parameters with the clay content and pH highlight the protective effect of clay on organic matter as well as the impact of pH on microorganisms' mineralization activity. Surprisingly, we found weak effects of climatic parameters on the thermal stability and stoichiometry of SOM. Our data suggest that topsoil SOM is on average more oxidized and biogeochemically stable in croplands. More generally, the high number and even distribution of data across the whole French territory allow one to build a national interpretative reference for these indicators in surface soils.

The Quantified and Major Influencing Factors on Spatial Distribution of Soil Organic Matter in Provincial-Scale Farmland—A Case Study of Shandong Province in Eastern China

Soil organic matter (SOM) is an important component of soil and plays an important role in improving the soil’s physical and chemical properties. Ascertaining the spatial distribution of soil organic matter and its main controlling factors in the context of provincial scale farming is of important guiding significance for soil carbon sequestration, emission reduction and sustainable utilization. Using 257 soil profiles from the second soil survey in Shandong Province, GIS, we applied geostatistical methods to study the spatial distribution characteristics of SOM in topsoil. In addition, correlation and regression analyses were used to explore the main controlling factors over the spatial variation of SOM. The results showed that the mean amount of SOM in Shandong province ranged from 1.20–74.90 g·kg−1, with a coefficient of variation of 73.52%, which is a medium level of variation. The distribution of SOM in the study area was patchy, with higher levels of organic matter in the central, eastern, and northern parts, and lower levels of organic matter in the south-west. The comprehensive explanatory ability of all factors reached 52.30%. Soil type and parent material were the main controlling factors for the spatial variability of SOM in the Shandong Province, followed by soil texture and land use type, with topography and climatic factors having relatively little influence.

Soil organic matter and nitrogen in varying management types of coffee-pine agroforestry systems and their effect on coffee bean yield

Abstract. Sudharta KA, Hakim AL, Fadhilah MA, Fadzil MN, Prayogo C, Kusuma Z, Suprayogo D. 2022. Soil organic matter and nitrogen in varying management types of coffee-pine agroforestry systems and their effect on coffee bean yield. Biodiversitas 23: 5884-5891. Coffee cultivation in agroforestry systems is mostly planted without soil fertility management. While there are several management interventions to improve soil quality in agricultural practices, it is not clear whether particular treatments, such as adding organic fertilizers and nitrogen fertilizers could increase coffee production in agroforestry settings. This study aimed to analyze soil organic matter and nitrogen in varying management types and its effect on coffee bean yield in a coffee-pine agroforestry setting in East Java, Indonesia. We evaluated four types of coffee management (treatments) namely: (i) no management, (ii) pruning coffee plant branches, (iii) a combination of pruning and addition of fertilizers with a planting distance of pine trees of 3 x 2 m, and (iv) pruning under pine trees with a planting distance of 6 x 2 m. The soil organic matter, total and available soil nitrogen were measured at 0-0.2 m and 0.2-0.4 m soil depths. We measured coffee bean yield to 100 coffee plants per plot. The coffee bean yield in the no-management treatment reached 376 kg ha-1, while the yield under the other three treatments increased up to 3.9 times compared with no-management. This increasing coffee bean yield did not correlate with soil organic matter in topsoil, with a correlation between coffee bean yield and total ant available soil nitrogen being positive and negative, respectively. We concluded that the limitation of N in the coffee-pine agroforestry system would require management intervention in the form of adding nitrogen fertilizers to increase coffee bean yield.

Faster carbon turnover in topsoil with straw addition is less beneficial to carbon sequestration than subsoil and mixed soil

AbstractIn arable soils, the topsoil and subsoil are commonly mixed in the operation of deep tillage. It is not yet clear whether the influence of crop straw on soil organic matter (SOM) mineralization of the mixed soil (from the topsoil and subsoil) is different from that of solely the topsoil or subsoil. We conducted a 120‐d incubation experiment with the addition of 13C‐labeled maize (Zea mays L.) straw to study SOM mineralization and straw decomposition in the topsoil (0–15 cm), subsoil (15–30 cm), and their mixture (0–30 cm). Straw addition promoted SOM mineralization and thus induced a positive priming effect. The mineralization of SOM in topsoil with straw addition was 122% higher than in subsoil, and 45% higher than in mixed soil. After the 120‐d incubation, 12–16% of straw C was mineralized as CO2, contributing approximately 50–70% to the total CO2 production. Furthermore, straw C was also incorporated into SOM fractions, with 34, 7, and 59% in the light fraction, particulate organic C (coarse and fine), and mineral‐associated organic C (MAOC) in topsoil, respectively. The SOM mineralization and priming were greater in the topsoil with higher dissolved organic C and NO3–N throughout the incubation. Despite more straw C retained in MAOC in topsoil, the significant decrease in total MAOC with straw addition indicated that SOM turnover induced by fresh C application was probably faster in topsoil than the subsoil and mixed soil. Our findings indicated that both subsoil and mixed soil tended to sequester C with straw addition, whereas topsoil C turnover was faster than subsoil in the presence of straw addition.

Soil Organic Matter in Soils of Suburban Landscapes of Yamal Region: Humification Degree and Mineralizing Risks

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.

English

Farmers can play an important role in climate change mitigation through sustainable soil management practices. Semi-structured interviews were conducted in the Atwima Nwabiagya municipality of Ashanti region, Ghana, to explore farmers' knowledge and perceptions of their soils, soil fertility, applied management practices, and climate change on soil organic carbon. The interviews included topics related to farmers’ access to training and its impact in adopting and changes in management strategies. Summary for interviews was prepared based on notes and recordings and analyzed with the Qualitative Content Analysis (QCAmap) software using emergent codes. Results show that farmers had a lot of knowledge on soil organic matter (SOM) and how it affects climate and the relationship between SOM and soil fertility. They also acknowledged that their management practices affect quantities of SOM in topsoil and subsoil and soil fertility. The adoption of current and new management practices including, the use of organic and inorganic fertilizers, manure, mulching, and shade management, is a reflection of their newly acquired knowledge and understanding of fertility sustaining processes. The study highlights the relationship between farmers' training and changes in their adopted practices and how management practices affect SOC influencing climate change and soil fertility. Key words: soil organic carbon, cocoa farmers, perception, soil management, soil fertility and climate change.

Amendment of straw biochar increased molecular diversity and enhanced preservation of plant derived organic matter in extracted fractions of a rice paddy

While biochar enhanced carbon sequestration and stability of soil organic matter (SOM), changes in organic molecular composition in biochar-amended soils had been poorly addressed. In this study, molecular composition changes of a paddy topsoil 2 years following amendments at 10 t ha−1 OC equivalent with untreated (CS), manured (CM) and charred (CB) maize straw were compared to no amendment (CK). Topsoil SOM was sequentially extracted with ultrapure water (UWE), solvent (TSE), base hydrolysis (BHY) and CuO oxidation (CUO) and molecular compounds in these extracted fractions were detected quantitatively by GC/MS. Compared to CK, SOC content was increased respectively by 12% under CS and CM, and by 36% under CB. Fraction abundance both of UWE and CUO was increased but that of TSE unchanged under CS and CM, while that of BHY unchanged under CS but increased by > 60% under CM and CB, respectively. Under CB relative to CS and CM, abundance of TSE and BHY fractions was greatly increased but that of UWE and CUO unchanged. Specifically, abundances of water-soluble monosaccharides, low molecular weight organic acids and lignin-derived phenols, especially cinnamyl-based monomers, were all enhanced under CS, but abundances of n-alkanols, fatty acids in free lipids and di-acids and hydroxyl fatty acids in bound lipids were decreased under both CS and CM. In contrast, CB amendment increased abundances of n-alkanols, alkanes and sterols in free lipids while enhanced molecular and functional group diversity of UWE and TSE fractions. Overall, short-term crop residue amendment altered the abundance and molecular diversity of OM mainly associated with short-lived UWE and labile TSE fractions and biochar enhanced preservation of plant derived molecules mainly in lipids. Thus, returning crop residue as biochar could be a sustainable approach to enhance not only SOM pool but molecular diversity also in agricultural soils.

Dynamics of Organic Matter of Soil Profiles with Different Vegetation Conditions from the Chinese Loess Plateau: δ13C and δ15N Approaches

To understand the biogeochemical processes associated with soil organic matter (SOM) decomposition, we analyzed the SOM contents, the δ13C and δ15N values of the dominant species foliage, litter and SOM from soil samples for five soil profiles with different vegetation conditions in the Loess Plateau, Northwestern China. Results showed that the amounts of soil organic carbon (SOC) and total nitrogen (TN) mainly concentrated on the surface soil and differentiated according to the vegetation conditions in the following order: broad-leaved forest > coniferous woodland > shrub forest > grassland > wasteland. SOC and TN contents decreased with depth and varied in the ranges of 1.1–31.2 g/kg and 0.3–3.7 g/kg, respectively. Compared with the other regions, the 13C and 15N were enriched and the δ13C and δ15N values of topsoil SOM respectively increased in the ranges of 0.5%o–3.2%o and 0.7%o–4.6%o during litter degradation to SOM on the surface soil, which was controlled by SOM turnover rates. This result indicates that the effect of isotopic fractionation was obvious during the transformation of SOM from plant debris to SOM in topsoil, which resulted in great increments of SOM δ13C and δ15N. Litter inputs lowered the surface soil δ13C and δ15N values while decomposition increased δ13C and δ15N values in deeper soil. Foliage and litter inputs averaged 1.0% and 1.3% δ15N and -28.3% and -27.0% δ13C, respectively. The five soil profiles with different vegetation conditions had similar characteristics in variations of SOM δ13C and δ15N and increased with depth, respectively. However, the patterns of δ13C in our sites were less pronounced than the patterns of δ15N primarily because the discrimination against 13C during organic matter decomposition is weaker than the discrimination against 15N. Except for the shrub profiles, significant correlations were found between the two stable isotopes, 15N and 13C. Combined with information on SOM contents, the variations of the isotopic values of SOM showed a mixing process of litter inputs between different soil profiles. Two controls of soil isotopic compositions were established: new litter inputs and overall isotopic fractionation during decomposition. In conclusion, the overall isotopic fractionation during decomposition left residual soil N and C enriched in 15N and 13C, explaining the high δ15N and δ13C values observed in deeper soil.

Organo-Mineral Interactions Are More Important for Organic Matter Retention in Subsoil Than Topsoil

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.

Tree mycorrhizal type predicts within‐site variability in the storage and distribution of soil organic matter

Forest soils store large amounts of carbon (C) and nitrogen (N), yet how predicted shifts in forest composition will impact long-term C and N persistence remains poorly understood. A recent hypothesis predicts that soils under trees associated with arbuscular mycorrhizas (AM) store less C than soils dominated by trees associated with ectomycorrhizas (ECM), due to slower decomposition in ECM-dominated forests. However, an incipient hypothesis predicts that systems with rapid decomposition-e.g. most AM-dominated forests-enhance soil organic matter (SOM) stabilization by accelerating the production of microbial residues. To address these contrasting predictions, we quantified soil C and N to 1m depth across gradients of ECM-dominance in three temperate forests. By focusing on sites where AM- and ECM-plants co-occur, our analysis controls for climatic factors that covary with mycorrhizal dominance across broad scales. We found that while ECM stands contain more SOM in topsoil, AM stands contain more SOM when subsoil to 1m depth is included. Biomarkers and soil fractionations reveal that these patterns are driven by an accumulation of microbial residues in AM-dominated soils. Collectively, our results support emerging theory on SOM formation, demonstrate the importance of subsurface soils in mediating plant effects on soil C and N, and indicate that shifts in the mycorrhizal composition of temperate forests may alter the stabilization of SOM.

Soil quality of semi-arid conservation reserve program lands in Eastern New Mexico

ABSTRACTA study was conducted to evaluate selected soil quality indicators in lands that have been in Conservation Reserve Program (CRP), which is a federal program in the United States offering annual rental payments and cost-share assistance to farmers who establish long-term vegetation covers on their erosion prone lands. The study site has semi-arid climate, and soils with grass vegetation covers for 15 years were compared with adjacent cultivated croplands that have never been in the CRP. Field measurements were performed and surface soil samples (0–0.15 m) were collected from multiple sites having either coarse textured or fine textured soils. Soil measurements assessed included bulk density (BD), penetration resistance (PR), wet aggregate stability (WAS), dry aggregate size distribution (DASD), soil organic matter (SOM), permanganate oxidizable carbon, nitrate nitrogen, extractable potassium and phosphorus, electrical conductivity, pH, sodium adsorption ratio, and soil micronutrients (copper, iron, manganese, and zinc). Results showed a significant effect of CRP management compared to the cropped fields for BD, WAS, and PR only, with the CRP fields being less compacted and having higher WAS than the cropped lands. CRP land did not significantly differ from cropped lands in SOM and for many other measurements. The effect of soil texture was significant for DASD, SOM, copper, and manganese, with the fine textured soils having more favorable measurements than the coarse textured soils. CRP management did not produce significant increase in topsoil SOM compared to cropped lands of the study area.

Aggregate dynamics and associated soil organic matter in topsoils of two 2,000-year paddy soil chronosequences

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.

Cutin and suberin biomarkers as tracers for the turnover of shoot and root derived organic matter along a chronosequence of Ecuadorian pasture soils

Forest‐to‐pasture conversion has been reported to increase soil organic matter (SOM) in mineral topsoils in the tropical mountain rainforest region of south Ecuador, with subsequent decreases following pasture abandonment. Until now the mechanisms behind these changes have not been fully understood. To elucidate their varied preservation patterns, we analysed root‐ and shoot‐derived organic matter and assessed their contribution to the formation of SOM in topsoils (0–5 cm) on a chronosequence of pastures (Setaria sphacelata (Schumach.); C4) established after slash and burn of the natural forest (diverse C3 plant species) and an abandoned pasture site invaded by bracken fern (Pteridium arachnoideum (Kaulf.) Maxon.; C3). Cutin and suberin biomarkers of the two plant species (grass and bracken) and of forest litter were identified after saponification and their contribution to SOM was studied by compound‐specific stable carbon isotope analyses. Our results showed specific root and shoot biomarkers for the two plant species and for forest litter, which often did not correspond to the classification of root‐versus shoot‐specific monomers reported in the literature. This illustrates the importance of direct biomarker determination rather than using results from studies with different plants. Shoot‐ as well as root‐derived OM of forest and grass origin contributed to the stable SOM pool with decadal turnover times. Forest‐derived monomers contributed more to the stable SOM pool compared with grass‐derived monomers. ω‐hydroxy carboxylic acids and α,ω‐alkanedioic acids of forest origin may have been stabilized in these tropical soils by bonding to soil minerals. Rapid degradation of grass‐derived lipids from the same compound classes suggests a saturation of the mineral binding capacity. In pasture soils, the accumulation of SOM was mainly driven by large inputs of root OM. The accumulated SOM during pasture use is, however, lost rapidly after abandonment.

Organic matter of subsoil horizons under broadleaved forest: Highly processed or labile and plant-derived?

Between 30 and 63% of the soil organic matter (SOM) is stored below 30 cm, making subsoil-SOM an important source and sink in the global carbon cycle. Nevertheless, detailed information on the composition of subsoil-SOM remains scarce. This study aims to evaluate the chemical composition of SOM in topsoil and subsoil horizons in broadleaved forests on acid loamy soils. Six sites were chosen in Northern Belgium under beech, oak and hybrid poplar, on Gleysols, Umbrisols, Cambisols and Albeluvisols on loamy Quaternary deposits. Analytical pyrolysis–gas chromatography/mass spectrometry (pyrolysis–GC/MS) was performed on the dialyzed alkaline extract, which represents between 41 and 90% of the total organic carbon for the selected sites. All extracts show a significant shift in chemical composition between the topsoil and the subsoil. While topsoil-SOM mainly differs according to input and nutrient status, subsoil-SOM shows high relative amounts of alkanes and alkenes or polysaccharides for coarse and fine textured soils respectively. Lignins, lignin-derived phenols or aromatics were not major contributors to subsoil-SOM, regardless of soil type. Furthermore, results show that very labile plant-derived molecules are present in the subsoil, i.e. long-chain aliphatics and (cellulose-derived) anhydrosugars. The organic matter signature of the subsoil samples was evaluated for typical indications of fresh material, decay, podzolisation and anaerobic processes, and indicates root input and stabilization of certain labile plant-derived compounds against microbial decay to be important in the subsoil.

Effects of land‐use change on chemical composition of soil organic matter in tropical lowland Bolivia

AbstractLand‐use change affects not only the amount of soil organic matter (SOM) but also its composition. We performed cross‐polarization magic angle spinning (CPMAS) 13C and 15N nuclear magnetic resonance (NMR) spectroscopy to investigate the chemical composition of bulk SOM in topsoils (0–15 cm) under different land use, namely native forest (NF), 27‐year cropland with wheat/soybean rotation (CL) and 27‐year rangelands with guineagrass (RG) and with bahiagrass (RB), in south‐east Bolivia. The findings of this study showed only a subtle alteration of composition of bulk SOM despite the large changes in carbon (C) content. Nevertheless, NF and RB showed a slightly lower abundance of aromatic C but a higher proportion of alkyl C compared to CL and RG where the loss of organic matter was substantial. This suggests that relatively stable components dominated by aromatic structures had relatively enriched during SOM decomposition under agricultural practices. A slight disparity of SOM composition observed between RG and RB (less O‐alkyl C but more aromatic C in RG than RB) suggests that grass species influenced SOM quality even under the same land use, namely the rangeland. On the other hand, organic N composition was less affected by land use or management practice than C forms.

Evaluation of switchgrass and sainfoin intercropping under 2:1 row-replacement in semiarid region, northwest China

Field experiments were carried out under natural conditions to compare the aboveground biomass, root growth and distribution, and topsoil nutrition contents of switchgrass ( Panicum virgatum ) and sainfoin (Onobrychis viciaefolia ) grown in sole cropping and 2:1 row-replacement intercropping in semiarid loess region on Loess Plateau of northwest China. The sole and intercropping was compared based on the aboveground biomass, water use efficiency (WUE), soil organic matter (SOM) and total nitrogen (TN), and root biomass and distribution. The aboveground biomass production was measured every year at the end of growth seasons in 2001 - 2005. Root biomass and vertical distribution were studied only in 2005. Topsoil SOM and TN contents were measured discontinuously during the study period. Results showed that intercropping reduced the aboveground biomass production of sainfoin significantly compared with its pure stand. The WUE of sole switchgrass was significantly the highest in each year among the three stands, while the intercropped stand was significantly higher than sole sainfoin on five-year averaged. The aggressivity of sainfoin to swichgrass decreased along with the growth years. Before 2005, the land equivalent ratio (LER) was bigger than 1.0 and actual yield loss (AYL) was positive. Under intercropping, root biomass input and root: shoot ratio in switchgrass reduced, while sainfoin inputs more photosynthate to root growth. Switchgrass had high root biomass and wide distribution vertically and horizontally indicates a higher belowground competitive ability in the mixture. It indicated a flexible distribution strategy of switchgrass tending to increase soil exploitation and space sequestration efficiency in soil layers. SOM and TN increased significantly for the three stands at the end of the fourth growth year, especially for the mixture. Switchgrass and sainfoin intercropped under 2:1 row-replacement can be a short-term rotation tillage choice with respect to soil management in the area. Key words:

Spatial and temporal distribution of carbon isotopes in soil organic matter at the Dinghushan Biosphere Reserve, South China

The spatial and temporal distribution of carbon isotopes (13C, 14C) in soil organic matter (SOM) were studied based on SOM content, SOM Δ14C and SOM δ13C of thinly layered soil samples for six soil profiles with different elevations at the Dinghushan Biosphere Reserve (DHSBR), South China. The results indicate that variations of SOM δ13C with depth of the soil profiles at different elevations are controlled by soil development, and correlate well with SOM composition in terms of SOM compartments with different turnover rates, and SOM turnover processes at the DHSBR. The effect of carbon isotope fractionation was obvious during transformation of organic matter (OM) from plant debris to SOM in topsoil and SOM turnover processes after the topsoil was buried, which resulted in great increments of OM δ13C, respectively. Increments of SOM δ13C of topsoil from δ13C of plant debris were controlled by SOM turnover rates. Both topsoil SOM δ13C and plant debris δ13C increase with elevation, indicating regular changes in vegetation species and composition with elevation, which is consistent with the vertical distribution of vegetation at the DHSBR. The six soil profiles at different elevations had similar characteristics in variations of SOM δ13C with depth, alterations of SOM contents with depth and that SOM 14C apparent ages increasing with depth, respectively. These are presumably attributed to the regular distribution of different SOM compartments with depth because of their regular turnover during soil development. Depth with the maximal SOM δ13C value is different in mechanism and magnitude with penetrating depth of 14C produced by nuclear explosion into atmosphere from 1952 to 1962, and both indicate controls of topography and vegetation on the distribution of SOM carbon isotopes with depth. Elevation exerts indirect controls on the spatial and temporal distribution of SOM carbon isotopes of the studied mountainous soil profiles at the DHSBR. This study shows that mountainous soil profiles at different elevations and with distinctive aboveground vegetation are presumably ideal sites for studies on soil carbon dynamics in different climatic-vegetation zones.

Impact of oasis establishment on underground environment in salinized sandy lands

The salinized sandy lands are the important reclaimable reserve wastelands in the south area of the Xinjiang Uygur Autonomous Region of China. But it is necessary that the ecological environment of the area is not destroyed by action of oasis development. The main factor to hinder oasis development is land salinization. Rational oasis establishment rebuilds wastelands with lower productivity and utilization efficiency for the growth of agriculture, forestry, and stock raising. The results of surveying sub-soil environment of Aimugaike×Awati oasis in Hotian County of the Xinjiang Uygur Autonomous Region show that the underground water and soil environment are not deteriorated under the rational management and administration, which could be coordinated for obtaining economic and environmental benefit. During the oasis establishment period from 1997 to 1999, the plowland area has reached 166.7 hm 2 , and the seed cotton yield per unit area has reached 2250 kg·hm -2 , the area of timber forest and active sand break forest has reached 20 hm 2 , the area of fruit trees is 71.5 hm 2 ; and the soil moisture has decreased from 22.07% to 18.12%. In the first year of oasis establishment, the soil type has changed salt soil into light salt soil, in the second year the soil has been out of salt harm; and the content of soil organic matter in topsoil has increased obviously.

Cropping of Miscanthus in Central Europe: biomass production and influence on nutrients and soil organic matter

The objective of the present study was to investigate the impact of biomass development of Miscanthus×giganteus (Greef et Deu.) on the concentration of plant nutrients and the accumulation in soil as well as quality of soil organic matter (SOM). Field trials with 4–9 year-old Miscanthus stands were investigated and sampled at four experimental sites in Germany in the years 1994–1999. From 1994 to 1996 the above-ground standing biomass at the end of the vegetation periods ranged from 14.8 to 33.5 t ha −1 dry matter (DM). The below-ground growing biomass (rhizomes, roots) reached 15 to 25 t DM ha −1 (before sprouting in spring). Mean pre-harvest losses (harvesting date: February/March of the following year) of 4.5 t DM ha −1 originated from senescent leaves and shoot-tips fallen to the ground during winter. This amount corresponds to about 26% of the whole above-ground biomass (harvested biomass+pre-harvest losses+harvested residues). Direct harvested residues (stubble mass) varied between 0.7 and 3.1 t DM ha −1. Therefore 23–51% of the biomass grown could not be harvested. The mean harvested biomass was 11.7 t DM ha −1. The largest concentrations of N, P, K and Mg in plant materials were observed in the pre-harvest losses, whereas the harvested biomass had the lowest concentrations. The concentration of nutrients in the harvested biomass was 61% (N), 64% (P), 55% (K) and 50% (Mg) of the concentration in the biomass at the end of the vegetation period. These differences are explained by nutrient losses due to fallen leaves and shoot-tips and nutrient translocation into below-ground plant parts. The higher concentrations of plant available K in soil indicate that Miscanthus cropping enhances the cycling of nutrients in the plant–soil system. As a result of the high input of leaves, rhizomes and roots, the sandy soils were characterized by increased concentration of organic carbon (C org; mean:+2.0 g kg −1 and total nitrogen (N t; mean:+0.2 g kg −1). The storage of SOM in topsoils was increased by 11.7 t ha −1. Moreover, the Miscanthus residues affected the quality of SOM. In a plot with Miscanthus, increased proportions of alkanes, alkenes, sterols and free fatty acids were observed by pyrolysis-field ionization mass spectrometry.