Use of ammonium bicarbonate DTPA soil test to evaluate elemental availability and toxicity

Abstract

The literature published on the use of the Soltanpour and Schwab Ammonium Bicarbonate‐DTPA (AB‐DTPA) soil test shows that it can be used to determine availability and toxicity indices for many elements. It has been shown to be an effective test for measuring the availability indices of P, K, Zn, Fe, Mn, Mo, Pb, Ni, Cd and Se. Theoretically, it can also be used to determine the availability indices for S, Cu and As. The AB‐DTPA test can predict toxicity of B as well as the standard hot water rest, although within the non‐toxic range of B, it is not as effective as the hot water test. The hot water test alone predicts B availability well, but the AB‐DTPA B test result requires inclusion of soil water pH, organic matter and clay contents in a regression equation for predicting B availability. This test is not suitable for determination of exchangeable plus soluble Ca and Mg (high levels), as these precipitate as carbonates during extraction. The AB‐DTPA test procedure with analysis by an inductively‐coupled plasma spectrometer for simultaneous determination of elements, makes soil and overburden testing very efficient.     

Freezing as a means of preserving samples in soil respiration studies

Summary Freezing was investigated as a means of preserving samples in soil respiration studies. Concentrations of CO₂ in the headspaces of incubation bottles before and after freezing, and respiration rates derived from fresh or frozen samples were not significantly different over periods of up to 30 days. Freezing permits many samples to be assayed for respiratory activity at one time, increases the accuracy of the incubation period and defers the need to analyse headspace concentrations of CO₂ until it is convenient.     

Mineralisation and humification of plant matter in soil samples as a tool in the testing of soil quality

Since life is inevitably dependent on the assimilation and dissimilation of carbon, and since most of the organic carbon is bound in soil humic matter, the mineralisation and humification of plant carbon in soil should be monitored, so as to evaluate soil quality and avoid ecological risks. For this reason we suggested an incubation test of thirty days in duration with soil samples amended or not with lucerne meal as a source of plant carbon. During the incubation period, CO₂ release is to be measured repeatedly, and thereafter contents of humic acids (HA) and fulvic acids (FA) should be estimated and compared with those determined in the original soil samples. Our results obtained with samples from non-fertilized or long-term (?>?40 years) fertilized plots of two field trials indicate that fertilization by NPK?+ farm yard manure resulted in (i) a slight enhancement of C mineralisation, i.e., CO₂ release from soil, and (ii) a significant increases of HA and FA contents. Soil samples from a reclaimed mine spoil, and either fertilised or not with sewage sludge did not show distinct differences in the same parameters. The practicability of the incubation test as a tool in the monitoring of soil quality should be further proved using samples from differently affected soils.     

Uniformity of soil test results as influenced by volume weight

Abstract

Samples of four soils having a wide range of volume weights (0.65, 1.02, 1.25, 1.62 g/cm³) were either weighed or measured by volume and extracted with: (a) the Bray P₁ extractant, (b) the Mehlich double acid extractant for P, K, Ca, Mg, Mn, Zn and (c) neutral N NH₄OAc for K, Ca, Mg all at a soil/extracting solution ratio of 1:10. The soil test results were recorded on a volume basis in mg/dm³ and on a weight basis in mg/kg.

The test values for all macronutrients obtained with all extractants decreased, relative to a constant volume, with increasing VW of soil when analyzed and expressed on a weight basis. Results based on the use of a volume sample (scooped) but calculated on an assumed weight of soil changed the values in direct ratio of 1/assumed VW. The use of an assumed VW has no justification, since uniform soil test results can be obtained when expressed on a volume basis by either using a scooped sample of known volume or a weighed sample followed by multiplication with the VW of each soil.     

Micromorphological analysis to characterize structure modifications of soil samples submitted to wetting and drying cycles

The physical characteristics of the soil surface are of extreme importance in relation to energy and matter transfer processes between the atmosphere and the soil. Soil internal structure changes can be due to natural or artificial causes and one important natural process is the alternation of wetting and drying (W–D) processes, which induce swelling and shrinking of soil particles, causing modifications in pore size and shape. To study the consequence of these W–D events on possible modifications in pore size distribution, pore number, and pore shape of soil samples collected in metal rings pore image analysis was used. Samples were taken from profiles of three soils of different characteristics, named as Geric Ferralsol (GF), Eutric Nitosol (EN), and Rhodic Ferralsol (RF). Confined volumetric samples (50 cm³) were submitted to none (T₀), three (T₁), and nine (T₂) subsequent W–D cycles. Image cross sections of resin impregnated soil permitted the micrometric and macrometric characterization of changes in soil structure induced by sequences of W–D cycles. Duncan's statistical test indicated that there were significant differences (α = 0.05) among treatments for all soil samples. General conclusions indicate that total pore area increased for all soils after repeated W–D processes, specifically 19.0 to 28.9% for GF, 5.9 to 11.7% for EN, and 13.0 to 17.2% for RF. Main changes of pore diameter occurred in pores larger than 500 μm, and minor changes were observed in the total number of these pores. It is demonstrated that soil samples undergo important changes in their structures after repeated W–D cycles. The information presented here is very important for the evaluation of soil water retention curves and other soil hydric properties, because soil samples used in these procedures are collected in rings and frequently submitted to several W–D cycles.     

Fluctuations in soil test values for potassium as influenced by time of sampling

Abstract

Soil samples were taken at frequent intervals in 1975 and 1976 from a factorial set of lime ‐K treatments initiated in December 1970 to determine the effect time of sampling has on K soil test values. Previous work at this site had shown wide fluctuations in K soil test values due to sample time thus necessitating a more detailed study than was previously made. Such information is necessary if accurate K fertilizer recommendations are to be made. Samples from 28 unfertilized plots showed that months of sampling significantly affected K soil test values. Soil test values for K were highest in late May and declined as the growing season progressed, remaining low until the relatively higher exchangeable K was re‐established the following spring.

Disregard for this phenomenon could result in inaccurate recommendations for K fertilizer.     

From the micro-scale to the habitat: Assessment of soil bacterial community structure as shown by soil structure directed sampling

Natural structural units of a luvisol under maize crop were studied to assess if soil structure directed sampling could improve the understanding of arrangements of bacteria in spatially constraint location. Three habitats were defined: (i) soil around fine lateral roots (rhizo-aggregates), (ii) soil close to basal roots (core clods) and (iii) unplanted soil between rows (bare soil clods). These habitats were also investigated with maize plants resulting from Azospirillum lipoferum CRT1 inoculated seeds as a model of enhanced fine root system. Rhizo-aggregates were clearly separated from each other (disconnected habitat) in contrast to micro-samples (fragments) from clods, which belong to cohesive macro-structures. Genetic fingerprints on metagenomic extracts were used to characterize the structure of bacterial communities on 95 micro-samples from the three habitats. For eubacteria, automated RISA (Ribosomal Intergenic Spacer Analysis) of ITS (Internal Transcribed Spacer) profiles were performed. PCR-RFLP on nifH gene were used to describe the N-fixer guilds. Exploratory multivariate analyses (PCA and MDS) revealed bacterial community patterns in the sampled habitats. On the basis of ITS profiles, rhizo-aggregates harboured closely related communities, distant from those of the unplanted soil, and each sampled rhizo-aggregate could therefore be considered as a sub-unit of the whole macro-habitat, comprising all the fine roots. The observed low dissimilarity of disconnected rhizo-aggregates is likely to result from the direct influence of maize root tips on the recruitment of rhizosphere bacteria. Molecular fingerprints of nifH from basal root clods (core) were more similar to bare soil than to rhizo-aggregates, indicating similar ecological conditions without, or with, at least, poor maize exudating root influence. Although our study was performed on a limited number of situations, the distribution of bacteria was revealed to be patterned by soil structure units, which is a first step to improve the modelling of microbial ecology in soils.     

Sonic dispersion of soil DTPA solution suspension as an extraction procedure for DTPA micronutrient test

Abstract

To examine sonic dispersion as an extraction procedure for DTPA micronutrient test, soil DTPA solution suspensions were sonicated to extract Fe, Zn, Mn, and Cu. The elements extracted after 15 or 60 seconds sonication were compared with those extracted after 1/2 or 2 hours shaking.

The mean differences between Fe, Zn, Mn, or Cu extracted after 15 seconds sonication and those extracted after 1/2 hour shaking were not significant. However, the extractions obtained after 2 hours shaking were significantly higher than those obtained after 15 or 60 seconds sonication.

The elements extracted after 15 or 60 seconds sonication correlated significantly with those extracted after 1/2 or 2 hours shaking. Therefore, 15 or 60 seconds sonication can replace 2 hours shaking in the extraction procedure for DTPA micronutrient test. However, 15 seconds sonication is more convenient than 60 seconds and does not require cooling of soil solution suspension during sonication. Therefore 15 seconds sonication ‐ a replacement for 2 hours shaking to extract Fe, Zn, Mn, and Cu ‐ is recommended.     

Microplate-scale fluorometric soil enzyme assays as tools to assess soil quality in a long-term agricultural field experiment

We investigated the potential of microplate-scale fluorometric soil enzyme assays to differentiate plots under contrasting long-term organic and mineral N fertilization regimens to determine the relevance of this analytical approach to soil quality related studies.Enzymes involved in the breakdown of cellulose and hemicellulose showed maximum activities in plots amended with manure. Conversely, the enzymes involved in the hydrolysis of starch and phosphate esters peaked under mineral N fertilization. Linear regression analysis indicated close associations between enzyme activities and other fundamental soil properties related to soil quality, and principal component analysis separated the soil samples according to their responses to organic and mineral N fertilization. We conclude that microplate-scale fluorimetry is a fast throughput tool for the measurement of multiple soil enzyme activities as soil quality indicators.     

不同植被覆盖类型黑土水分动态变化特征

采用中子水分仪定位监测方法,研究黑土区平水年大豆地、草地和裸地3种覆盖类型土壤水分变化特征.结果表明:土壤水分空间垂直动态变化随深度增加而降低,基于变异系数(CV)将土壤水分垂直变化分为4层,即水分速变层、活跃层、次活跃层和相对稳定层.不同覆盖类型下,土壤水循环深度依次为大豆地>草地>裸地,土壤水循环强度依次为草地>大豆地>裸地;3种覆盖类型的土壤剖面含水量在作物生长季节内呈增长型变化特征,裸地0～20 cm土层各时段土壤含水量均高于草地和大豆地;30 cm土层以下土壤水分含量依次为草地>裸地>大豆地.该区土壤储水量主要受降雨调控,3种植被覆盖类型下,土壤水分的总蒸散量依次为草地>大豆地>裸地.     

Thermal destruction of soil water repellency and associated changes to soil organic matter as observed by FTIR spectroscopy

The heat generated during wildfires often leads to increases in soil water repellency. Above a critical heating threshold, however, its destruction occurs. Although the temperature thresholds for repellency destruction are relatively well established, little is known about the specific changes in the soil organic matter that are responsible for repellency destruction. Here we report on the analysis of initially water repellent surface soil samples (Dystric Cambisol, 0–5 cm depth) by transmission Fourier Transform Infrared (FTIR) spectroscopy analysis before and after destruction of its water repellency by heating to 225 °C in order to investigate heating-induced changes in soil organic matter (SOM) composition. Although assignment of absorption bands is made difficult by overlapping of some bands, it was possible to distinguish bands relevant for hydrophobicity of SOM in the soil before heat treatment. The most significant decrease in absorbance following water repellency destruction took place in the frequency area corresponding to stretching vibrations of aliphatic structures within SOM. The results suggest that besides a general decrease of SOM content during heating, the loss of soil water repellence is primarily caused by the selective degradation of aliphatic structures.     

Evaluating the efficiency of sampling methods in assessing soil macrofauna communities in arable systems

The soil fauna is often a neglected group in many large-scale studies of farmland biodiversity due to difficulties in extracting organisms efficiently from the soil. This study assesses the relative efficiency of the simple and cheap sampling method of handsorting against Berlese–Tullgren funnel and Winkler apparatus extraction. Soil cores were taken from grassy arable field margins and wheat fields in Cambridgeshire, UK, and the efficiencies of the three methods in assessing the abundances and species densities of soil macroinvertebrates were compared. Handsorting in most cases was as efficient at extracting the majority of the soil macrofauna as the Berlese–Tullgren funnel and Winkler bag methods, although it underestimated the species densities of the woodlice and adult beetles. There were no obvious biases among the three methods for the particular vegetation types sampled and no significant differences in the size distributions of the earthworms and beetles. Proportionally fewer damaged earthworms were recorded in larger (25 × 25 cm) soil cores when compared with smaller ones (15 × 15 cm). Handsorting has many benefits, including targeted extraction, minimum disturbance to the habitat and shorter sampling periods and may be the most appropriate method for studies of farmland biodiversity when a high number of soil cores need to be sampled.     

Microbiological parameters as indicators of soil quality under various soil management and crop rotation systems in southern Brazil

The objective of this work was to identify soil parameters potentially useful to monitor soil quality under different soil management and crop rotation systems. Microbiological and chemical parameters were evaluated in a field experiment in the State of Paraná, southern Brazil, in response to soil management [no-tillage (NT) and conventional tillage (CT)] and crop rotation [including grain (soybean, S; maize, M; wheat, W) and legume (lupin, L.) and non-legume (oat, O) covers] systems. Three crop rotation systems were evaluated: (1) (O/M/O/S/W/S/L/M/O/S), (2) (O/S/L/M/O/S/W/S/L/M), and (3) (O/S/W/S/L/M/O/M/W/M), and soil parameters were monitored after the fifth year. Before ploughing, CO₂-emission rates were similar in NT and CT soils, but plough increased it by an average of 57%. Carbon dioxide emission was 13% higher with lupin residues than with wheat straw; decomposition rates were rapid with both soil management systems. Amounts of microbial biomass carbon and nitrogen (MB-C and MB-N, respectively) were 80 and 104% higher in NT than in CT, respectively; however, in general these parameters were not affected by crop rotation. Efficiency of the microbial community was significantly higher in NT: metabolic quotient (qCO₂) was 55% lower than in CT. Soluble C and N levels were 37 and 24% greater in NT than in CT, respectively, with no effects of crop rotation. Furthermore, ratios of soluble C and N contents to MB-C and MB-N were consistently lower in NT, indicating higher immobilization of C and N per unit of MB. The decrease in qCO₂ and the increase in MB-C under NT allowed enhancements in soil C stocks, such that in the 0–40 cm profile, a gain of 2500 kg of C ha⁻¹ was observed in relation to CT. Carbon stocks also varied with crop rotation, with net changes at 0–40 cm of 726, 1167 and −394 kg C ha⁻¹ year, in rotations 1, 2 and 3, respectively. Similar results were obtained for the N stocks, with 410 kg N ha⁻¹ gained in NT, while crop rotations 1, 2 and 3 accumulated 71, 137 and 37 kg of N ha⁻¹ year⁻¹, respectively. On average, microbial biomass corresponded to 2.4 and 1.7% of the total soil C, and 5.2 and 3.2% of the N in NT and CT systems, respectively. Soil management was the main factor affecting soil C and N levels, but enhancement also resulted from the ratios of legumes and non-legumes in the rotations. The results emphasize the importance of microorganisms as reservoirs of C and N in tropical soils. Furthermore, the parameters associated with microbiological activity were more responsive to soil management and crop rotation effects than were total stocks of C and N, demonstrating their usefulness as indicators of soil quality in the tropics.     

沿海区土壤线虫对海水入侵土壤盐渍化的响应

在2013年对大连市大魏家镇海水入侵污染区域进行了土壤理化性质和线虫群落调查,在此基础上,应用线虫多样性指数和功能类群指数研究海水入侵土壤盐渍化以及不同土地利用方式对土壤线虫群落结构的影响。研究期间共鉴定出土壤线虫30科48个属。其中食细菌类群的比例最高,共17属,占总数42.81%;其次为杂食/捕食类群,共9个属,占总数25.26%。优势属为Plectus。结果显示:海水入侵已造成该地区土壤盐渍化;土壤盐分与线虫生态指数SR、f/b、NCR、PPI、MI、PPI/MI、PP%、FF%、BF%和OP%存在显著的相关关系;土地利用方式、土壤盐分对线虫群落的生态指数影响显著,是影响该地区土壤线虫群落结构的主要因素。通过开展土壤线虫对海水入侵土壤盐渍化响应的研究,为促进沿海受海水污染区土壤生态系统的健康发展提供科学依据。     

长白山苔原生态系统土壤酶活性及微生物生物量对增温的响应

采用开顶箱(open-top chamber,OTC)增温方法 (+1.1~1.9℃),研究了长白山苔原生态系统土壤酶活性、土壤微生物生物量、土壤微生物群落结构及土壤微生物呼吸对温度升高的响应。结果表明,连续三个生长季(6-9月)增温,没有明显地改变土壤蔗糖酶(58.1和45.9 mg g-124 h-1)和纤维素酶(0.34和0.26 mg g-172 h-1)的活性,但土壤脲酶活性升高80.1%(0.82和0.46 mg g-124 h-1),过氧化氢酶活性也升高10.1%(1.18和1.07 ml KMnO4g-1h-1)。增温与对照条件下土壤微生物生物量碳含量(0.85和0.75 mg g-1)、氮(0.07和0.06 mg g-1)、磷(0.013和0.011 mg g-1)和土壤微生物呼吸(6.1和6.3μmol m-2s-1)无明显差异。相关分析表明,土壤微生物生物量月际间明显的变化与土壤含水量及土壤有机质的相对变化有关。增温改变了土壤微生物的群落结构。增温并未引起与碳循环相关的酶活性、土壤微生物生物量和土壤微生物呼吸发生明显变化,可能是短期增温及增温幅度不足以使土壤微生物活性产生明显的改变。     

Pu同位素在土壤侵蚀示踪中的应用

137Cs示踪技术目前在土壤侵蚀研究中应用最为广泛,但是随着环境中137Cs的衰变,寻找可以替代的放射性核素具有十分重要的意义。人造放射性核素Pu同位素与137Cs来源相同,但半衰期更长,且更容易被土壤中的细颗粒物质吸附。特别是随着测量技术的发展,电感耦合等离子体质谱技术(ICP-MS)以及加速器质谱技术(AMS)等的应用,使得Pu同位素的测量较137Cs更高效、灵敏。因而Pu同位素成为可以替代137Cs进行土壤侵蚀示踪的理想元素。本文从Pu的来源及分布、Pu在土壤中的吸附和固定、Pu同位素的测量方法三个方面分析Pu同位素示踪土壤侵蚀的基础,并对Pu同位素示踪土壤侵蚀的基本原理和应用现状加以简述,探讨了今后Pu同位素在土壤侵蚀示踪应用中的主要研究方向。     

Phosphorus fractions and sorption processes in soil samples taken in a forest-savanna sequence of the Gran Sabana in southern Venezuela

P fractions and sorption processes were studied in samples taken from the organic surface layer and in the underlying mineral soil of a forest-savanna sequence consisting of: (1) tall primary forest (TPF), (2) tall secondary forest (MSF), (3) low secondary forest (LSF), and (4) open savanna (S) in la Gran Sabana, South Venezuela. The organic surface layer in the TPF and MSF showed the highest P concentrations in all analysed P fractions. P in this organic layer was mainly associated with inorganic forms, suggesting that this layer is an important source of bio-available P. The organic surface layer was not present in LSF and S probably because of the occurrence of recurrent surface fires. The conversion of forest to savanna influenced the distribution of the different forms of P in the soil. While non-occluded (resin-+NaOH-P extractable) and organic (NaHCO₃-+NaOH-+HCl-Po) P declined from the forest to savanna, occluded (concentrated HCl-extractable+residual P) forms increased. The correlation between sorption maxima and soil organic C was not significant; however, organically bound forms of Al were the main component that explained the adsorption capacity of these soils. The above findings suggest that the organic surface layer and the soil organic matter are important for maintaining P fertility in the undisturbed and little disturbed forests. However, when the system is heavily perturbed by fire the organic surface layer, the main P source, disappears and the patterns of P cycling change.     

Effects of pretreatment of soil samples on N mineralization in incubation experiments

Summary We studied the effects of pretreating soil samples (field-fresh, drying at 40° and 105°C, freezing/thawing) on N mineralization in an incubation experiment and on the dynamics of the organic N fraction extracted by K₂SO₄ solution. The soil samples were collected from plots in a long-term field experiment with the application of mineral fertilizer and farmyard manure. Compared with the field-fresh soil samples, freezing/thawing resulted in higher NO ₃ ^– -N contents while the NH ₄ ⁺ -N and the organic N content were increased by drying at 105°C. During the incubation period N mineralization was highest after the samples were dried at 105°C and a little lower in those dried at 40°C. After freezing/thawing the order of magnitude of N mineralization remained the same. The difference in organic N between the beginning and the end of the incubation experiment and the mineral N content at the end of the experiment were correlated significantly. Despite this correlation, however, the change in the organic N content underestimated the N mineralization rates.     

Responses of soil microarthropods to changes in soil water availability in tallgrass prairie

 Changes in precipitation and soil water availability predicted to accompany global climate change would impact grasslands, where many ecosystem processes are influenced by water availability. Soil biota, including microarthropods, also are affected by soil water content, although little is known about how climate change might affect their abundance and distribution. The goal of this study was to examine soil microarthropod responses to altered soil water availability in tallgrass prairie ecosystems. Two separate experiments were done. The first utilized control and irrigated plots along a topographic gradient to examine the effects of soil water content on microarthropod densities. Microarthropods, mainly Acari, were significantly less abundant in irrigated plots and were generally less abundant at the wetter lowland sites. The second study utilized reciprocal core transplants across an east-west regional precipitation gradient. Large, intact cores were transplanted between a more mesic tallgrass site (Konza Prairie) and a more arid mixed-grass site (Hays) to determine the effects of different soil water regimes on microarthropod abundance and vertical distribution. Data from non-transplanted cores indicated greater total microarthropod densities at the drier Hays site, relative to the wetter Konza Prairie site. Data from the transplanted cores indicated significant effects of location on Acari densities in cores originating from Hays, with higher densities in cores remaining at Hays, relative to those transplanted to Konza. Acari densities in cores originating from Konza were not affected by location; however, oribatid mite densities generally were greater in cores remaining at Konza Prairie. These results confirm the importance of soil water content in affecting microarthropod densities and distributions in grasslands, and suggest complex, non-linear responses to changes in water availability. Received: 14 April 1998     

黑土土壤水分反射光谱特征定量分析与预测

选择单一土类黑土作为研究对象, 并准确调配其不同含水量,实验室测定土壤高光谱反射率,利用光谱分析与统计方法,定量描述了不同含水量黑土反射光谱特征,并建立了黑土含水量反射光谱预测模型,结果表明,随土壤含水量的增加,达到一定阈值（300 g kg-1）,反射率存在过饱和现象,但其倒数对数微分可以有效去除饱和问题;土壤反射率倒数对数微分对土壤含水量的响应表现出三个变化阶段,导致1 870 nm波段的倒数对数微分也表现为非线性变化,需要利用分段函数进行土壤含水量的光谱精确速测。