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1.
Gamma‐ray spectrometry is an established method in geo‐sciences. This article gives an overview on fundamentals of gamma‐ray spectrometry that are relevant to soil science including basic technical aspects, and discusses influencing factors, inconsistencies, limitations, and open questions related to the method. Gamma‐ray spectrometry relies on counting gamma quanta during radionuclide decay of 40K, 238U, and 232Th, but secular equilibrium for the decay series of U and Th must be given as decays of their respective daughter radionuclides are used for determination. Secular equilibrium for U and Th decay series, however, is not always given leading to, e.g., anomalies in U concentration measurements. For soil science, gamma‐ray spectrometry is of specific value since it does not only detect a signal from the landscape surface, but integrates information over a certain volume. Besides, different spatial scales can be covered using either ground‐based or airborne sensing techniques. Together with other remote sensing methods, gamma signatures can provide completive information for understanding land forming processes and soil properties distributions. At first, signals depend on bedrock composition. The signals are in second order altered by weathering processes leading to more interpretation opportunities and challenges. Due to their physico‐chemical properties, radionuclides behave differently in soils and their properties can be distinguished via the resulting signatures. Hence, gamma signatures of soils are specific for local environments. Processes like soil erosion can superimpose gamma signals from in situ weathering. Soil mappings, available K and texture determination, or peat and soil erosion mapping are possible applications being discussed in this review.  相似文献   

2.
Information about the variability of different soil attributes within a field is essential for sustainable land management and precision agriculture. Mobile proximal gamma‐ray spectrometry can map soil characteristics of vast areas at different scales rapidly and cost‐effectively. This study aims at investigating reliability and capability of mobile‐gamma‐spectrometry (radiometrics) data to map typical soils of Middle Europe. In this paper, we investigate relationships between the radioelement concentrations (K, U, Th, and dose rate) and soil parameters (texture, CEC, pH, and organic‐C content) at four different field sites and soil textures. The data reliability is confirmed at the survey start. Mobile data have an excellent linear correlation (nearly 1:1) with the stationary readings (of identical devices, acquisition setups, and soil conditions) but moderate correlation with laboratory data (of different devices, setups, and sample conditions). Dried lab samples have systematically higher radioelement concentrations than the field soils (normally wet). Consequently, the mobile‐gamma‐spectrometric data is sufficiently accurate for soil mapping, and its calibration by laboratory data is less useful due to the varying environmental conditions. Single absolute radioelement concentrations show only moderate correlations with the different soil parameters, particularly clay content and CEC. This may be related to varying environmental conditions (soil moisture, soil structure, vegetation, land use, etc.) between the study sites. Investigations of the ratios of radioelement concentrations yield a clear improvement of their correlations to soil parameters, especially for sand and clay contents, CEC, and organic C. Additionally, multiple‐linear‐regression models were established using the element concentrations of potassium and thorium to predict silt content and pH. The results of the highly correlated models were confirmed by comparing with clay and silt content and pH value, respectively, to six additional independent field samples. Briefly, applications of gamma‐ray data for soil mapping offers the possibility of the development of quantitative relationships regarding soil parameters like sand and clay contents, CEC, and organic C. Classification of soil textures by gamma‐ray data seems to be promising, though a broader database of soils is needed for further research. We recommend gamma‐ray mapping as a complementary or even an alternative to common mapping techniques.  相似文献   

3.
Conventional soil sampling methods to obtain high‐resolution soil data are labour intensive and costly. Recently, gamma ray spectrometry has emerged as a promising technique to overcome these obstacles. The objective of our study was to investigate the prediction of soil clay contents using gamma‐ray spectrometry in three marine clay districts in the Netherlands: the southwestern marine district (SMD), the IJsselmeerpolder district (IJPD) and the northern marine district (NMD). The performance of linear regression models was investigated at field (<1 km2), regional (1–1000 km2) and district (>1000 km2) scales and for all the Dutch marine districts together. For this study, a database was available with 1371 gamma‐ray spectra measured on arable fields in marine clay districts during the period 2005–2008 and these were all linked to laboratory analyses of clay contents. At the field scale, linear regression models based on 40K, 232Th, or a combination of these revealed much smaller root mean squared error (RMSE) values (2–3%) compared with a model based on the field mean (8–10%). At the district scale, the regression models for the SMD and IJPD, which have comparable sediments, performed better than for the NMD. This indicates that the prediction of clay contents in late Holocene marine sediments may be made with gamma‐ray spectrometry provided that the origin of the parent material results in a unique fingerprint. Because of the heterogeneous parent material of all marine districts taken together, our study shows that no unique and precise fingerprint exists, and the RMSE of 6% between clay contents and gamma‐ray spectra is not much different from the RMSE of 7% when using the overall mean as a predictor.  相似文献   

4.
Sustainable agricultural systems are based on managing soils according to their capabilities and constraints. To facilitate the identification of constraints and appropriate management strategies for upland soils, a decision support framework ‘Soil Constraints and Management Package’ (SCAMP) has been developed. Basic soil data (both field and laboratory) are entered into an Access database and are processed to output reports that identify soil constraints to productivity and that tabulate appropriate management strategies. Where spatially referenced soil data are available, maps of constraints can be readily produced in a Geographic Information System. To demonstrate the ability of SCAMP to identify soil constraints at plot scale, it was applied to soil data sets from the two major soil types (Ferralsols and Acrisols) of Gia Lai Province, Vietnam. Phosphorus (P) fixation, aluminium toxicity and low cation exchange capacity (CEC) were identified as common constraints to productivity on Ferralsols, and low plant available water capacity, compaction and low K status as common constraints to productivity on Acrisols. Field experiments were undertaken on a Ferralsol and an Acrisol to assess management strategies for minimizing these constraints in the presence of adequate N, P and K. Maize (Zea mays) yields from the Ferralsol were increased by applying a plant amendment (Tithonia diversifolia) (selected to increase soil pH and decrease P fixation) and high activity clay (selected to increase CEC). Water‐soluble P fertiliser recovery was increased in this high P‐fixing soil by placing the fertiliser in a sub‐surface band. For the Acrisol, maize was grown in mounded rows and yields were maximized by applying a super‐absorbent material (selected to increase soil water holding capacity) or a high activity clay (selected to increase the low CEC of this soil). To demonstrate the usefulness of SCAMP on a catchment/regional scale, spatially referenced soil survey data of the Herbert River catchment, Queensland, Australia, were used to produce a map identifying areas of low pH, high acidification hazard and low CEC. These applications demonstrate the usefulness of SCAMP for linking soil data to management strategies for sustainable productivity at both plot and catchment scale.  相似文献   

5.
The conversion of tropical forests to agricultural land use is considered as a major cause for a decline in soil organic carbon (SOC) stocks. However, the extent and impact of different land uses on SOC stock development is highly uncertain, especially for tropical Africa due to a lack of reliable data. Interactions of SOC with the soil mineral phase can modify the susceptibility of SOC to become mineralized. Pedogenic Fe‐, Al‐oxides and clay potentially affect SOC stabilization in highly weathered soils typically found in the humid tropics. The aim of our study was to determine the impact of different land uses on SOC stock on such soils. For that purpose, 10 pedologically similar, deeply weathered acidic soils (Acrisols, Alisols) in the Eastern Usambara Mountains (Amani Nature Reserve, NE Tanzania) under contrasting land use were sampled to a depth of 100 cm. The calculated mean SOC stocks were 17.5 kg C m?2, 16.8 kg C m?2, 16.9 kg C m?2, and 20.0 kg C m?2 for the four forests, two tea plantations, three croplands, and one homegarden, respectively. A significant difference in mean SOC stock of 1.3 kg C m?2 was detected between forest and cropland land use for the 0–10 cm depth increment. No further significant impacts of land use on SOC stocks were observed. All soils have a clearly clay‐dominated texture. They are characterized by high content of pedogenic oxides with 29 to 47 g kg?1 measured for the topsoils and 36 to 65 g kg?1 for the subsoils. No positive significant relationship was found between SOC and clay content. Statistically significant positive relationships existed between oxalate‐extractable Fe, Al, and SOC content for cropland soils only. Compared to data published in literature the SOC stocks determined in our study were generally high independent of the established land use. It appears that efficient SOC stabilization mechanisms are counteracting the higher disturbance regime under agricultural land use in these highly weathered tropical soils.  相似文献   

6.
Depth‐dependent soil bulk density (BDS) is usually affected by soil‐specific factors like texture, structure, clay mineralogy, soil organic‐matter content, soil moisture content, and composition of soil solution and is also affected by external factors like overburden‐stress history or hydrological fluxes. Generally, the depth‐dependent BDS cannot be predicted or extrapolated precisely from a limited number of sampling depths. In the present paper, an easy method is proposed to estimate the state of soil mechanical stress by analyzing the packing characteristics of the profile using soil bulk‐density data. Results for homogeneous loess profiles exposed to the site‐specific climatic conditions show that the depth‐dependent relation of void ratio vs. weight of overburden soil can be described systematically so that deviations from the noncompacted reference state can be detected. We observed that precompaction increased from forest soils (reference) to agricultural soils with decreasing depth.  相似文献   

7.
Studies relating macro‐ and microscopic aspects of impacts of long‐term contaminative practices on soils are scarce. We performed such an approach by assessing the fate of metal pollutants in an area close to Paris, where sandy Luvisols were irrigated for 100 years with urban waste water. As a result, these soils display strong accumulation of organic matter, dissolved salts and metal pollutants in surface horizons, but also migration of metals to depth. We examined soil development and metal distribution patterns in two irrigated soils, in comparison with a non‐irrigated reference soil. Soil macromorphological characteristics were studied in the field. Soil micromorphology and micro‐scale metal distributions were both studied in situ in thin sections, the latter by synchrotron X‐ray mapping. Microscopic study focussed on characteristic parts of the Ap and Bt horizons, mainly involved in metal retention. For Ap horizons, both large and diffuse metal concentrations were revealed, mainly associated with organic matter and dissolved components added by irrigation water. For Bt horizons, zinc accumulation was detected on clay‐iron coatings. Our results suggest that with time, a double metal‐filtering capacity has developed in these sandy Luvisols: in the Ap horizon, an anthropogenic filter resulted from input of metal pollutants together with highly reactive organic matter, carbonates and phosphates, thus favouring metal immobilization and limiting migration to depth. In the Bt horizon, the evidence is of a second, natural filter. However, this filtering capacity is endangered by clay destruction due to ferrolysis, as revealed by micromorphology. Ferrolysis, here initiated by intensive irrigation practices, leads to a reduction of the natural filtering potential and an increasing risk of metal transfer towards the groundwater.  相似文献   

8.
In recent time, phytoliths (silicon deposition between plant cells) have been recognized as an important nutrient source for crops. The work presented here aims at highlighting the potential of phytolith‐occluded K pool in ferns. Dicranopteris linearis (D. linearis ) is a common fern in the humid subtropical and tropical regions. Burning of the fern D. linearis is, in slash‐and‐burn regions, a common practice to prepare the soil before planting. We characterised the phytolith‐rich ash derived from the fern D. linearis and phytolith‐associated potassium (K) (phytK), using X‐ray tomographic microscopy in combination with kinetic batch experiments. D. linearis contains up to 3.9 g K/kg d.wt, including K subcompartmented in phytoliths. X‐ray tomographic microscopy visualized an interembedding structure between organic matter and silica, particularly in leaves. Corelease of K and Si observed in the batch experiments confirmed that the dissolution of ash phytoliths is one of major factors controlling K release. Under heat treatment, a part of the K is made available, while the remainder entrapped into phytoliths (ca. 2.0–3.3%) is unavailable until the phytoliths are dissolved. By enhanced removal of organic phases, or forming more stable silica phases, heat treatment changes dissolution properties of the phytoliths, affecting K release for crops and soils. The maximum releases of soluble K and Si were observed for the phytoliths treated at 500–800 °C. For quantitative approaches for the K provision of plants from the soil phytK pool in soils, factors regulating phytolith dissolution rate have to be considered.  相似文献   

9.
Soil structure formation is essential to all soil ecosystem functions and services. This study aims to quantify changes in soil structure and microbial activity during and after field incubation and examine the effect of carbon, organic amendment and clay on aggregate characteristics. Five soils dominated by illites, one kaolinitic soil and one smectitic soil were sieved to 2 mm, and each soil was divided into two parts and one part amended with ground rape shoots (7.5 t ha?1) as an organic amendment. Samples were incubated in the field for 20 months with periodic sampling to measure water‐dispersible clay (WDC) and fluorescein diacetate activity (FDA). After incubation, WDC and FDA were measured on air‐dried 1–2‐mm aggregates. Tensile strength was measured on four aggregate classes (1–2, 1–4, 4–8 and 8–16 mm) and results used to assess soil friability and workability. Intact cores were also sampled to determine compressive strength. During incubation, the amount of WDC depended on soil carbon content while the trends correlated with moisture content. Organic amendment only yielded modest decreases (mean of 14% across all sampling times and soils) in WDC, but it was sufficient to stimulate the microbial community (65–100% increase in FDA). Incubation led to significant macroaggregate formation (>2 mm) for all soils. Friability and strength of newly‐formed aggregates were negatively correlated with clay content and carbon content, respectively. Soil workability was best for the kaolinite‐rich soil and poorest for the smectite‐rich soil; for illitic soils, workability increased with increasing organic carbon content. Organic amendment decreased the compression susceptibility of intact, incubated samples at smaller stress values (<200 kPa).  相似文献   

10.
Water dispersible clay (WDC) can influence soil erosion by water. Therefore, in highly erodible soils such as the ones in eastern Nigeria, there is a need to monitor the clay dispersion characteristics to direct and modify soil conservation strategies. Twenty‐five soil samples (0–20 cm in depth) varying in texture, chemical properties and mineralogy were collected from various locations in central eastern Nigeria. The objective was to determine the WDC of the soils and relate this to selected soil physical and chemical attributes. The soils were analysed for their total clay (TC), water‐dispersible clay (WDC), clay dispersion ratio (CDR), dispersion ratio (DR), dithionite extractable iron (Fed), soil organic matter (SOM), exchangeable cations, exhangeable sodium percentage (ESP) and sodium adsorption ratio (SAR). Total clay contents of the soil varied from 80–560 g kg−1. The USLE erodibility K ranges from 0·02 to 0·1 Mg h MJ−1 mm and WEPP K fall between 1·2 × 10−6–1·7 × 10−6 kg s m−4. The RUSLE erodibility K correlated significantly with CDR and DR (r = 0·44; 0·39). Also, a positive significant correlation (r = 0·71) existed between WEPP K and RUSLE K. Soils with high clay dispersion ratio (CDR) are highly erodibile and positively correlates (p < 0·51) with Fed, CEC and SOM. Also, DR positively correlates with Mg2+ and SOM and negatively correlate with ESP and SAR. Principal component analysis showed that SAR, Na+ and percent base saturation play significant role in the clay dispersion of these soils. The implication of this result is that these elements may pose potential problem to these soils if not properly managed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

11.
Alluvial soils with illite and vermiculite clay minerals are highly potassium (K)‐fixing. Such soils have been reported to require a huge amount of K fertilization for optimum plant growth. For halophytic plants such as sugar beet, sodium (Na) can be an alternative to K under such conditions. This study was conducted to investigate the possible substitution of K by Na fertilization with reference to K‐fixing soils. Three soils, i.e., Kleinlinden (subsoil), Giessen (alluvial), and Trebur (alluvial), differing in K‐fixing capacities, were selected, and sugar beet plants were grown in Ahr pots with 15 kg soil pot–1. Three treatments (no K and Na, K equal to K‐fixing capacity of soil, and Na equivalent to regular K fertilization) were applied. In a second experiment, containers (90 cm × 40 cm × 40 cm) were used with 170 kg Kleinlinden soil each, and one sugar beet plant per container was grown. In both experiments, plants were grown till beet maturity, and beets were analyzed for sucrose concentration and other quality parameters such as α‐amino nitrogen to calculate white‐sugar yield with the New Brunswick formula. The results showed that growth and quality of sugar beet were not affected by Na application, and ultimately there was no decrease in white‐sugar yield. Moreover, the soils with more K‐fixing capacity were more suitable for K substitution by Na. It is concluded that Na can substitute K in sugar beet nutrition to a high degree and soils with high K‐fixing capacity have more potential for this substitution.  相似文献   

12.
The analysis of the microfabric of soils developing from calcareous argillites (with sandstone interlayers) and their derivatives revealed the mechanisms of the transformation of the initial lithogenic features into pedogenic features. They include the release of primary carbonates and their segregation in secondary forms, the redistribution of iron oxides, and changes in the shape of the rock fragments and in the optical properties of the fine material in the lithomarge zone. The subsoil—the metamorphic BM horizon—is characterized by a high content of clay composed of chlorite-vermiculite and mica-smectite minerals along with kaolinite. The BM horizon is compact and has a massive microstructure with clay pseudomorphs over skeleton grains and with nonsegregational forms of iron oxide pedofeatures. The diagnostic properties of this horizon are clearly revealed in the soils on both hard rocks and loose colluvium deposits; in the latter case, they are supplemented with a stagnic marble-like pattern. The integrity of these features corresponds to the elementary pedogenic process of the metamorphism of the mineral mass in humid subtropics. In terms of micromorphology, this is a good example of pedoplasmation. The features testifying to the contribution of biota in the topsoils are few; dark compact nodules are common there. Zheltozems developed from hard rocks may be correlated with Cambisols in the WRB system; zheltozems developed from clayey colluvium display the features of clay illuviation; together with some physicochemical characteristics of these soils, they allow us to qualify such soils as Acrisols. There are also eluvial-gley variants of zheltozems with stagnic features.  相似文献   

13.
In the densely populated state of North Rhine‐Westphalia, soil erosion by water causes substantial on‐site degradation and off‐site damages. The implementation of soil‐conservation measures is improved, if soil erodibilities and erosion processes are known. In a state‐wide investigation, we aimed to representatively assess soil‐erosion processes and erodibilities of cultivated soils. For this purpose, we measured surface runoff and soil‐loss rates of 28 cultivated soils with field plots under artificial rain. In the field experiments, surface runoff and soil loss indicated high sealing susceptibilities and high erodibilities on soils of quite different textures including a clay silt, a loam silt, a loam sand, a sand loam, and two standard loams. Rill formation causing high soil‐loss rates was observed on a clay silt (soil BM) and on a loam silt (soil RB), the latter yielding an empirical K‐factor of 1.66 t ha–1 h N–1. K‐factors of other silty soils ranged from 0.04 to 0.48, whereas sandy soils and clayey soils had K‐factors ranging from 0.00 to 0.32, and 0.00 to 0.12, respectively. Comparatively high erodibilities of two silt clays were due to saturation overland flow. Erosion processes and erodibilities of soils with similar texture varied to a large extent, possibly caused in part by seasonal differences in the timing of erosion tests. Surface runoff was different in field experiments compared with laboratory experiments (companion paper) conducted with topsoil material taken from the field plots. In addition, higher concentrations of suspended sediment were recorded on average in the field than in the laboratory. These differences might reflect the influence of the subsoil and are due to higher transport capacities on longer plots in the field. Thus, laboratory experiments can complement but not replace costly field trials for K‐factor determination. Empirical K‐factors derived from field and laboratory experiments are in general lower than K‐factors of other soils in Germany or calculated K‐factors derived from pedotransfer functions, which might be attributed to a more maritime‐type climate in North Rhine‐Westphalia. Since the temporal variability of erodibility was not assessed, the reported K‐factors should be regarded as preliminary.  相似文献   

14.
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15.
Currently, potassium (K)‐ and phosphate (P)‐fertilizer recommendation in Germany is based on standardized soil‐testing procedures, the results of which are interpreted in terms of nutrient availability. Although site‐specific soil and plant properties (e.g., clay and carbon content, pH, crop species) influence the relation between soil nutrient content and fertilizer effectiveness, most of these factors are not accounted for quantitatively when assessing fertilizer demand. Recent re‐evaluations of field observations suggest that even for soil nutrient contents well within the range considered to indicate P or K deficiency, fertilizer applications often resulted in no yield increase. In this study, results from P‐ and K‐fertilization trials (in total about 9000 experimental harvests) conducted during the past decades in Germany and Austria were re‐analyzed using a nonparametric data‐mining procedure which consists of a successive segmentation of the data pool in order to elaborate a modified recommendation scheme. In addition to soil nutrient content, fertilizer‐application rates, nutrient‐use efficiency, and site properties such as pH, clay content, and soil organic matter, have a distinct influence on yield increase compared to an unfertilized control. For K, nutrient‐use efficiency had the largest influence, followed by soil‐test K content, whereas for P, the influence of soil‐test P content was largest, followed by pH and clay content. The results may be used in a novel approach to predict the probability of yield increase for a specified combination of crop species, fertilizer‐application rate, and site‐specific data.  相似文献   

16.
The traditional method of soil mapping involves classifying soil into pre‐existing classes using morphological observations and then air‐photograph interpretation to extrapolate the information. To accelerate the process, less costly ancillary data can be used to assist mapping. However, digital soil mapping (DSM) is still affected by the classifications used to identify soil types. One reason is because the morphological characteristics are not mutually exclusive, which causes misclassification. In this study, we used a DSM approach, where ancillary data were surrogate for morphological data, with soil types identified by numerical clustering of remotely and proximally sensed data collected across a farming district near Gunnedah, Australia. Remotely sensed data were obtained from an air‐borne gamma‐ray (γ‐ray) spectrometer survey, including potassium (K), thorium (Th), uranium (U) and total counts. Proximally sensed data were measured using EM38 (i.e. EM38h and EM38v). Using fuzzy k‐means and a linear mixed model with measured physical (e.g. clay) and chemical (e.g. CEC) properties from the topsoil (0–0.30 m) and subsoil (0.9–1.2 m), we found that k = 5 was also optimal given that mean‐squared prediction error (i.e. ) was minimised. The approach highlighted subtle differences in physical and chemical properties in productive areas. The DSM was unsuccessful in identifying small units; however, inclusion of elevation data might overcome this limitation. This research has implications for providing fast, accurate and meaningful DSM at a district scale, where traditional methods are too expensive.  相似文献   

17.
For the development of sustainable land‐management systems in the highlands of N Thailand, detailed knowledge about soil distribution and soil properties is a prerequisite. Yet to date, there are hardly any detailed soil maps available on a watershed scale. In this study, soil maps on watershed level were evaluated with regard to their suitability for agricultural land‐use planning. In addition to common scientific methods (as underlying the WRB classification), participatory methods were used to exploit local knowledge about soils and to document it in a “Local Soil Map”. Where the WRB classification identified eight soil units, the farmers distinguished only five on the basis of soil color and “hardness”. The “Local Soil Map” shows little resemblance with the detailed, patchy pattern of the WRB‐based soil map. On the contrary, the “Local Soil Map” is fairly similar to the petrographic map suggesting that soil color is directly related to parent material. The farmers' perception about soil fertility and soil suitability for cropping could be confirmed by analytical data. We conclude that integrating local soil knowledge, petrographic information, and knowledge of local cropping practices allows for a rapid compilation of information for land‐evaluation purposes at watershed level. It is the most efficient way to build a base for regional land‐use planning.  相似文献   

18.
We tested whether a ‘Lockerbraunerde’ from the heights of the Zittauer Gebirge in Eastern Saxony exhibited andic properties and classified it according to the rules of the World Reference Base for Soil Resources (WRB, 1998). To achieve this, we characterized a selected soil by means of routine soil analysis; selective dissolution procedures; X‐ray diffraction (XRD); X‐ray fluorescence (XRF), and Transmission Electron Microscopy (TEM). We used field criteria (Thixotropy; NaF‐field test) to obtain a map of the spatial distribution of soils with potential andic properties. We found that the soil fulfilled all requirements to be classified as an Andosol. The composition of the colloidal phases was exactly intermediate between sil‐andic and alu‐andic. At the same time, the soil had a spodic horizon [determined through the depth function of the Alo+½Feo criterion]. As there was no indication of vertical translocation of metal‐organic complexes, but sufficient evidence to suggest the downward movement of mobile Al/Si‐phases, we maintain to classify the soil as an Endoskeleti‐Umbric Andosol and propose the existence of a pedogenetic pathway intermediate between Podsolisation and Andosolization. We conclude that the spodic horizon in the WRB is not well defined because of the dominance of the Alo+½Feo criterion over morphological evidence. We further suggest the German soil taxonomy to be modified to better represent soils containing short range order minerals.  相似文献   

19.
Soil test indicators are needed to predict the contribution of soil organic N to crop N requirements. Labile organic matter (OM) fractions containing C and N are readily metabolized by soil microorganisms, which leads to N mineralization and contributes to the soil N supply to crops. The objective of this study was to identify labile OM fractions that could be indicators of the soil N supply by evaluating the relationship between the soil N supply, the C and N concentrations, and C/N ratios of water extractable OM, hot‐water extractable OM, particulate OM, microbial biomass, and salt extractable OM. Labile OM fractions were measured before planting spring wheat (Triticum aestivum L.) in fertilized soils and the soil N supply was determined from the wheat N uptake and soil mineral N concentration after 6 weeks. Prior to the study, fertilized sandy loam and silty clay soils received three annual applications of 90 kg available N (ha · y)?1 from mineral fertilizer, liquid dairy cattle manure, liquid swine manure or solid poultry litter, and there was a zero‐N control. Water extractable organic N was the only labile OM fraction to be affected by fertilization in both soil types (P < 0.01). Across both test soils, the soil N supply was significantly correlated with the particulate OM N (r = 0.87, P < 0.001), the particulate OM C (r = 0.83, P < 0.001), and hot‐water extractable organic N (r = 0.81, P < 0.001). We conclude that pre‐planting concentrations of particulate OM and hot‐water extractable organic N could be early season indicators of the soil N supply in fertilized soils of the Saint Lawrence River Lowlands in Quebec, Canada. The suitability of these pre‐planting indicators to predict the soil N supply under field conditions and in fertilized soils from other regions remains to be determined.  相似文献   

20.
Abstract

Comparative measurements of the clay fraction of soils were made with a beta‐ray gauge system, a density meter, and a hydrometer. Reliable clay fraction determinations could be made by a beta‐ray gauge, and a density meter in less than 25 minutes of sedimentation. The beta‐ray gauge measured clay fractions were not affected by surface tension which was the possible cause for variable results obtained with the gamma‐ray attenuation technique.  相似文献   

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