Organic matter quality and management effects on enrichment of soil organic matter fractions in contrasting soils in Zimbabwe

Spatial variability of soil total nitrogen (N), available N (KCl extractable NH₄⁺ and NO₃⁻), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province, southwestern China in June and August 2000. In a study area of 90 × 105 m², three soil samples were collected from each 5 × 5 m² plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification were measured by in situ core incubation and the rates were estimated based on the difference of NH₄⁺ and NO₃⁻ contents between the two sampling dates. Total N, NH₄⁺, and NO₃⁻ were all spatially structured with different semivariogram ranges (from high to low: NH₄⁺, NO₃⁻, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH₄⁺ was the dominant soil inorganic N form in the system. Both NH₄⁺ and NO₃⁻ affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification as indicated by greatly increased soil NO₃⁻ content. High spatial auto-correlations (>0.7) were found between available N and NH4⁺, available N and NO₃⁻ on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation between NH₄⁺ and NO₃⁻ were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values, particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold for detection in this study.     

Carbon and nitrogen dynamics along the decay continuum: Plant litter to soil organic matter

Decay processes in an ecosystem can be thought of as a continuum beginning with the input of plant litter and leading to the formation of soil organic matter. As an example of this continuum, we review a 77-month study of the decay of red pine (Pinus resinosa Ait.) needle litter. We tracked the changes in C chemistry and the N pool in red pine (Pinus resinosa Ait.) needle litter during the 77-month period using standard chemical techniques and stable isotope, analyses of C and N.Mass loss is best described by a two-phase model: an initial phase of constant mass loss and a phase of very slow loss dominated by degradation of lignocellulose (acid soluble sugars plus acid insoluble C compounds). As the decaying litter enters the second phase, the ratio of lignin to lignin and cellulose (the lignocellulose index, LCI) approaches 0.7. Thereafter, the LCI increases only slightly throughout the decay continuum indicating that acid insoluble materials (lignin) dominate decay in the latter part of the continuum.Nitrogen dynamics are also best described by a two-phase model: a phase of N net immobilization followed by a phase of N net mineralization. Small changes in C and N isotopic composition were observed during litter decay. Larger changes were observed with depth in the soil profile.An understanding of factors that control lignin degradation is key to predicting the patterns of mass loss and N dynamics late in decay. The hypothesis that labile C is needed for lignin degradation must be evaluated and the sources of this C must be identified. Also, the hypothesis that the availability of inorganic N slows lignin decay must be evaluated in soil systems.     

Chemical and biological indicators of soil quality in organic and conventional farming systems in Central Italy

In the past decade, there has been increased scientific interest in the so-called organic farming, especially in comparison with conventional agriculture. Many recent studies compare these two fundamentally different systems for soil properties, in different regions of the world. In this study, two adjacent fields in Central Italy, one managed according to organic, and the other according to conventional farming methods, were studied to determine the effects of these two agricultural systems on soil quality indicators at the farm level. Chemical and microbiological properties were chosen as indicators of soil quality and were measured at soil depth intervals of 5–20 and 20–35 cm, after 7 years of organic certified and conventional management methods. The field under organic management showed significantly better soil nutritional and microbiological conditions; with increased level of total nitrogen, nitrate and available phosphorus, and an increased microbial biomass content, and enzymatic activities (acid phosphatase, protease and dehydrogenase). No consistent increase in total organic carbon was observed. Results of the study suggest that, over the period of 7 year, organic management method strongly affects soil quality indicators. Large differences between the two soils were found in terms of microbiological properties, which are sensitive soil indicators of changes occurred under the different farming systems.     

Temperature sensitivity and substrate quality in soil organic matter decomposition: results of an incubation study with three substrates

Kinetic theory suggests that the temperature sensitivity of decomposition of soil organic matter should increase with increasing recalcitrance. This ‘temperature–quality hypothesis’ was tested in a laboratory experiment. Microcosms with wheat straw, spruce needle litter and mor humus were initially placed at 5, 15 and 25 °C until the same cumulative amount of CO₂ had been respired. Thereafter, microcosms from each single temperature were moved to a final set of incubation temperatures of 5, 15 and 25 °C. Straw decomposed faster than needle litter at 25 and 15 °C, but slower than needle litter at 5 °C, and showed a higher temperature sensitivity (expressed as Q₁₀) than needle litter at low temperatures. When moved to the same temperature, needle litter initially incubated at 5 and 15 °C had significantly higher respiration rates in the final incubation than litters initially placed at 25 °C. Mor humus placed at equal temperatures during the initial and final incubations had higher cumulative respiration during the final incubation than humus experiencing a shift in temperature, both up‐ and downwards. These results indicate that other factors than substrate quality are needed to fully explain the temperature dependence. In agreement with the hypothesis, Q₁₀ was always higher for the temperature step between 5 and 15 °C than between 15 and 25 °C. Also in agreement with the temperature–quality hypothesis, Q₁₀ significantly increased with increasing degree of decomposition in five out of the six constant temperature treatments with needle litter and mor humus. Q₁₀s for substrates moved between temperatures tended to be higher than for substrates remaining at the initial temperature and an upward shift in temperature increased Q₁₀ more than a downward shift. This study largely supports the temperature–quality hypothesis. However, other factors like acclimation and synthesis of recalcitrant compounds can modify the temperature response.     

Estimation of soil organic matter by geostatistical methods: Use of auxiliary information in agricultural and environmental assessment

Mapping soil properties such as soil organic matter (SOM), or soil organic carbon (SOC) content represent a problem often arising in agronomic and environmental surveys, since point data must be spatialized with the best interpolation. Deterministic methods (Inverse Distance Weighting, Splines, ecc.) do not account for the error, thus probabilistic methods as geostatistics (e.g. Ordinary Kriging, OK) have been successfully applied for many years. Maps derived from this kind of stochastic interpolation, based only on a recognized autocorrelation among measured points, could not be suitable in representing the reality, since they usually show a smoothed pattern. Hybrid interpolation methods, such as Regression Kriging (RK), combine an interpolation based only on point data and an interpolation based on a regression of the target variable with other continuous variables, spatially related, well known on the whole area.In the Teramo province, central Italy, a set of 250 soil samples, collected from the surface horizon of agricultural soils is available. From these samples the estimation of soil texture, SOC, SOM related to texture and C/N both by OK and RK was performed. The following predictors were used for RK: (i) indexes derived from Landsat TM imagery, (ii) morphometric parameters derived from DEM, (iii) soil subsystems map 1:250,000. The maps obtained by both OK and RK in this survey show substantial agreement, without significant improvement in map accuracy using auxiliary information.     

Stable isotope ratios of soil carbonate and soil organic matter as indicators of forest invasion of prairie near Ames,Iowa

Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C₃ plants which have been introduced by agricultural practices. The ¹³C values of soil organic matter from the prairie and forest endmembers indicate C₄ and C₃ dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average ¹³C of-2.0, indicating that the carbonate formed under a C₄ vegetation. These results indicate that the ecosystem was a C₄-dominated prairie and therefore suggest a recent arrival of forests and other C₃ plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest.     

Characterization of soil organic matter from a sandy soil in relation to management practice using FT-IR spectroscopy

Previous results from differently fertilized long-term field experiments on a sandy soil suggested that the chemical composition of soil organic matter (SOM) is affected by fertilization. The objective of this paper is to confirm this finding for a site with higher soil-clay contents. Four combinations of different fertilizer treatments at long-term field experiment located at a sandy loam were selected: liquid manure (LM), liquid manure+N (LM+N), straw+N (S+N) and mineral nitrogen only (N). Soil organic matter was extracted using sodium pyrophosphate solution at pH of 10 and hot water. The extracts were analyzed using Fourier-Transform infrared spectroscopy. The results indicate that the composition of SOM from the hot water extracts did not show significant differences while the sodium pyrophosphate extracted SOM is affected by the type of fertilization. Soil samples fertilized with LM+N and S+N show the highest intensity of the carboxyl band. This can be explained by the fact that the combination of S+N fertilization with green manure leads to an enrichment of carboxyl groups in SOM. Differences between the band intensities of the treatments for the SOM samples are, however, not as distinct as for the sandy soil samples. This is possibly a result of the higher clay content and lower age of the long-term experiment at the sandy loam site. The intensity of the carboxyl band of the SOM is correlated with the cation exchange capacity of the soil samples. The composition of SOM may, in addition to the SOM content, be used for studying quantitative effects of different management practices or even land use changes on soil properties. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Vesicular-arbuscular mycorrhizal effectiveness in an acid soil amended with fresh organic matter

A greenhouse investigation was undertaken to determine the influence of fresh organic matter on the formation and functioning of vesicular-arbuscular mycorrhizal symbiosis in Leucaena leucocephala grown in an acid aluminum-rich ultisol. In soil not amended with fresh organic matter or lime, plants failed to grow. Mycorrhizal infection level, mycorrhizal effectiveness measured in terms of pinnule P content of L. leucocephala leaves and dry matter yield of the legume increased with increase in fresh organic matter. Although VAM colonization level and dry matter yield of L. leucocephala were significantly higher if the test soil was limed (7.2 cmole OH^–) than if amended with fresh organic matter, the latter was as effective as lime in off-setting the detrimental effect of aluminum on mycorrhizal effectiveness. The lower mycorrhizal colonization level and the lower dry matter yield noted in the soil treated with fresh organic matter appears to be related to the inadequacy of Ca in the soil amended with fresh organic matter. These observations are supported by the low calcium status of soil and plant tissues in the absence of lime. It is concluded that while fresh organic matter, in appropriate amounts, could protect sensitive plants and VAM symbiosis against Al toxicity in acid soils, maximum mycorrhizal inoculation effects are not likely to be attained unless the soils are also amended with Ca.Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No 3740.     

Primary oxidation of organic matter in the soil

Summary The course of respiration rate during glucose decomposition in a soil sample was studied. The whole process of oxidation (mineralization) is divided into two principal parts: the primary oxidation which occurs while the substrate is still present and the secondary oxidation after the disappearance of the substrate. The primary oxidation brought about by two different components: the oxidative component represents the sum of enzyme activity present originally in the soil sample, and the assimilative component is built up during the process by synthesis of microbial enzymes. The size of the oxidative component is correlated with the biological potency of soil. Sometimes, an intermediary stage can be observed at the beginning of the secondary oxidation. A method is given for enumeration of the proportions of the two components involved in primary oxidation. The biochemical and pedological meaning of these data is discussed.     

Integrated management systems and N fertilization: effect on soil organic matter in rice-rapeseed rotation

Aims

Understanding the effects of long-term crop management on soil organic matter (SOM) is necessary to improve the soil quality and sustainability of agroecosystems.

Method

The present 7-year long-term field experiment was conducted to evaluate the effect of integrated management systems and N fertilization on SOM fractions and carbon management index (CMI). Two integrated soil-crop system management (ISSM-1 and ISSM-2, combined with improved cultivation pattern, water management and no-tillage) were compared with a traditional farming system at three nitrogen (N) fertilization rates (0, 150 and 225 kg N ha^?1).

Results

Management systems had greater effects on SOM and its fractions than did N fertilization. Compared with traditional farming practice, the integrated management systems increased soil organic carbon (SOC) by 13 % and total nitrogen (TN) by 10 % (averaged over N levels) after 7 years. Integrated management systems were more effective in increasing labile SOM fractions and CMI as compared to traditional farming practice. SOC, TN and dissolved organic matter in nitrogen increased with N fertilization rates. Nonetheless, N addition decreased other labile fractions: particulate organic matter, dissolved organic matter in carbon, microbial biomass nitrogen and potassium permanganate-oxidizable carbon.

Conclusions

We conclude that integrated management systems increased total SOM, labile fractions and CMI, effectively improved soil quality in rice-rapeseed rotations. Appropriate N fertilization (N150) resulted in higher SOC and TN. Though N application increased dissolved organic matter in nitrogen, it was prone to decrease most of the other labile SOM fractions, especially under higher N rate (N250), implying the decline of SOM quality.     

Retention of soil organic matter by occlusion within soil minerals

Reviews in Environmental Science and Bio/Technology - The stabilization of soil organic matter is crucial for global carbon cycling processes as soil stores large amounts of organic carbon. The...     

Phosphorus control of soil organic matter accumulation and cycling

The present level of understanding of P controls on organic matter accumulation and cycling in a pedological context owes much to soil sequence studies, and the hypotheses that emerged from them to explain the variation of P compounds with soil type and development. It is now widely accepted that nutrient transformations in soil are closely linked through a more dynamic biological cycle in which microorganisms have a central role. Concepts developed to account for the effects of P on N cycling, and for interpreting inter-relationships of C, N, P and S in both a pedological and biological context have yet to be tested adequately across different ecosystems. These concepts are discussed, in relation to some recent supporting evidence.     

The role of organic matter in soil manganese equilibrium

Summary Tests were conducted to determine the role of additions of fresh organic matter (ground cotton seed hulls) to an alluvial loam soil of pH 8 on manganese equilibrium. It was shown that organic matter has a reducing potential which, when added to the soil, resulted in a rapid and marked increase in exchangeable manganese. The reduction is enhanced by higher temperatures (21.1vs 37.7°C) and additions of water (field capacityvs air dry) and incubation periods up to 3 days. It is suggested that the shift in the soil manganese equilibrium, induced by such factors as waterlogging or anaerobic conditions, will be more pronounced when soils contain high levels of organic matter.Patterns of the standard deviations of sample exchangeable manganese data within treatments showed that the variance is highest in moist soil, lower concentrations of added organic matter, and at longer durations of incubation. Re-oxidation of manganese occurred at lower levels of added organic matter (2 and 4%) and extended incubation time (5 to 9 days).The investigation reported in this paper (67-10-36) is in connection with a project of the Kentucky Agricultural Experiment Station and is published by permission of the Director.     

Links between plant community composition,soil organic matter quality and microbial communities in contrasting tundra habitats

Plant communities, soil organic matter and microbial communities are predicted to be interlinked and to exhibit concordant patterns along major environmental gradients. We investigated the relationships between plant functional type composition, soil organic matter quality and decomposer community composition, and how these are related to major environmental variation in non-acid and acid soils derived from calcareous versus siliceous bedrocks, respectively. We analysed vegetation, organic matter and microbial community compositions from five non-acidic and five acidic heath sites in alpine tundra in northern Europe. Sequential organic matter fractionation was used to characterize organic matter quality and phospholipid fatty acid analysis to detect major variation in decomposer communities. Non-acidic and acidic heaths differed substantially in vegetation composition, and these disparities were associated with congruent shifts in soil organic matter and microbial communities. A high proportion of forbs in the vegetation was positively associated with low C:N and high soluble N:phenolics ratios in soil organic matter, and a high proportion of bacteria in the microbial community. On the contrary, dwarf shrub-rich vegetation was associated with high C:N and low soluble N:phenolics ratios, and a high proportion of fungi in the microbial community. Our study demonstrates a strong link between the plant community composition, soil organic matter quality, and microbial community composition, and that differences in one compartment are paralleled by changes in others. Variation in the forb-shrub gradient of vegetation may largely dictate variations in the chemical quality of organic matter and decomposer communities in tundra ecosystems. Soil pH, through its direct and indirect effects on plant and microbial communities, seems to function as an ultimate environmental driver that gives rise to and amplifies the interactions between above- and belowground systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

土地利用方式对土壤有机质的影响

通过对地带性常绿阔叶林、杉木人工林、农田、竹林等不同土地利用方式下土壤有机质总量、活性有机质及其组分的研究,发现土地利用方式对土壤有机质和活性有机质各组分的影响差异显著,其中阔叶林含量最高,杉木人工林低于阔叶林,竹林和农田最低。这些差别主要是由于凋落物的数量、质量以及各种管理措施不同所致。     

Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska

The influence of discontinuous permafrost on ground‐fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four‐way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground‐fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5 cm depth was about 0.5°C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems.     

Growth and symbiotic effectiveness of an arbuscular mycorrhizal fungus in organic matter in competition with soil bacteria

Shallow coastal waters, where phototrophic purple sulfur bacteria (PSB) regularly form massive blooms, are subjected to massive diurnal and event-driven changes of physicochemical conditions including temperature and salinity. To analyze the ability of PSB to cope with these environmental factors and to compete in complex communities we have studied changes of the environmental community of PSB of a Baltic Sea lagoon under experimental enrichment conditions with controlled variation of temperature and NaCl concentration. For the first time, changes within a community of PSB were specifically analyzed using the photosynthetic reaction center genes pufL and M by RFLP and cloning experiments. The most abundant PSB phylotypes in the habitat were found along the NaCl gradient from freshwater conditions up to 7.5% NaCl. They were accompanied by smaller numbers of purple nonsulfur bacteria and aerobic anoxygenic phototrophic bacteria. Major components of the PSB community of the brackish lagoon were affiliated to PSB genera and species known as marine, halophilic or salt-tolerant, including species of M arichromatium, H alochromatium, T hiorhodococcus, A llochromatium, T hiocapsa, T hiorhodovibrio, and T hiohalocapsa. A dramatic shift occurred at elevated temperatures of 41 and 44°C when M arichromatium gracile became most prominent which was not detected at lower temperatures.