Near infrared spectroscopy techniques for soil contamination assessment in the Nile Delta

Heavy metals concentration is considered one of the factors directly affecting soil and crop quality and, thus, human health. The objective of the current work was to critically examine the suitability of Vis- NIR (350–2500 nm) measurements for calibration procedures and methods to predict contaminated soil. 25 different sites were selected adjacent to drain Bahr El-Baqar east of Nile Delta. Spectroradiometer ASD was used to measure the spectral reflectance profile of each soil site. The concentrations of three heavy metals (Cr, Mn and Cu) were determined in the studied samples. Stepwise multiple linear regression (SMLR) was used to construct calibration models subjected to the independent validation. The obtained regression models were of good quality (R² = 0.82, 0.75, and 0.65 for Cr, Mn, and Cu, respectively). Thus, Visible and Nearinfrared (Vis-NIR) reflection spectroscopy is cost- and time-effective procedure that can be used as an alternative to the traditional methods of determination of heavy metals in soils.     

Near infrared reflectance spectroscopy (NIRS) could be used for characterization of soil nematode community

Studying soil nematofauna provides useful information on soil status and functioning but requires high taxonomic expertise. Near infrared reflectance (NIR) spectroscopy (NIRS) has been reported to allow fast and inexpensive determination of numerous soil attributes. Thus the present study aimed at assessing the potential of NIRS for determining the abundance and diversity of soil nematodes in a set of 103 clayey topsoil samples collected in 2005 and 2006 from agricultural soils in the highlands of Madagascar.The morphological characterization of soil nematofauna involved extraction through elutriation then counting under binoculars and identification at family or genus level using microscopy, on ca. 150-g fresh soil samples. Taxa were assigned to five trophic groups, namely bacterial feeders, fungal feeders, obligate plant feeders, facultative plant feeders, and omnivores and predators (together). In addition, four ecological indexes were calculated: the Enrichment index, Structure index, Maturity index, and Plant parasitic index.Oven-dried (40 °C) < 2-mm sieved 5-g soil subsamples were scanned in the NIR range (1100-2500 nm), then spectra were fitted to nematofauna data using partial least square regression. Depending on the sample set considered (year 2005, year 2006, or both years), NIRS prediction of total nematode abundance was accurate (ratio of standard deviation to standard error of cross validation, i.e. RPD ≥ 2) or acceptable (RPD ≥ 1.6). Predictions were accurate, acceptable, or quasi-acceptable (RPD ≥ 1.4) for several of the six most abundant taxa, and to a larger extent, for most trophic groups (except facultative plant feeders); but they could not be made for taxa present in a small number of samples or at low abundance. By contrast, NIRS prediction of relative abundances (in proportion of total abundance) was poor in general, as was also the prediction of ecological indexes (except for the 2006 set). On the whole, these results were less accurate than NIRS predictions of soil attributes often reported in the literature. However, though not very accurate, NIRS predictions were worthwhile considering the labor-intensity of the morphological characterization. Most of all, NIRS analyses were carried out on subsamples that were probably too small (5 g) to allow representative sampling of nematofauna. Using larger samples for NIRS (e.g. 100 g) would likely result in more accurate predictions, and is therefore recommended. Scanning un-dried samples could also help improve prediction accuracy, as morphological characterization was carried out on samples not dried after sampling.Examining wavelengths that contributed most to NIRS predictions, and chemical groups they have been assigned to, suggested that NIRS predictions regarding nematofauna depended on constituents of both nematodes and preys’ food. Predictions were thus based on both nematofauna and soil organic properties reflected by nematofauna.     

Determination of bulk density of soil clod by saturation

A method for the bulk density determination on soil clod is described. Clods are oven-dried, weighed and equilibrated over water saturated sand columns. Total volume of the clod is computed from the volume of its components - solid, and air. Air volume is calculated from the increase in weight of the dry clod on saturation.     

土壤容重对土壤物理性状和小麦生长的影响

以黑土和白浆土为试材 ,进行筒栽试验 .结果表明 ,适宜小麦生长的容重范围分别为 1 .1 5～1 .3 0 g/cm3和 0 .9～ 1 .0 5g/cm3.     

Building and testing conceptual and empirical models for predicting soil bulk density

The development of pedotransfer functions offers a potential means of alleviating cost and labour burdens associated with bulk‐density determinations. As a means of incorporating a priori knowledge into the model‐building process, we propose a conceptual model for predicting soil bulk density from other more regularly measured properties. The model considers soil bulk density to be a function of soil mineral packing structures (ρ_m) and soil structure (Δρ). Bulk‐density maxima were found for soils with approximately 80% sand. Bulk densities were also observed to increase with depth, suggesting the influence of over‐burden pressure. Residuals from the ρ_m model, hereby known as Δρ, correlated with organic carbon. All models were trained using Australian soil data, with limits set at bulk densities between 0.7 and 1.8 g cm^?3 and containing organic carbon levels below 12%. Performance of the conceptual model (r² = 0.49) was found to be comparable with a multiple linear regression model (r² = 0.49) and outperformed models developed using an artificial neural network (r² = 0.47) and a regression tree (r² = 0.43). Further development of the conceptual model should allow the inclusion of soil morphological data to improve bulk‐density predictions.     

Comparison of clod and core methods for determination of soil bulk density

Abstract

An interagency forest monitoring program has been initiated on a systematic network of forested plots often accessible only by foot traffic along a compass line. Extensive site classification and physiochemistry data are being collected for vegetation and soil indicators of forest health. In order to select a suitable technique for obtaining an estimate of mineral soil bulk density, conventional clod and core methods were compared across a wide range of forest soils within the Coastal Plain of southeastern Virginia. Replicate soil clods and cores were collected from two to four horizons within each of six pedons representing different soil series. Following analysis, the sample data were used to evaluate main and interaction effects due to differences in the method, series, horizon, and texture effects. Differences between the clod and core data were highly significant on average (P < 0.001) as were all of the main effects. Both methods exhibited high precision (average CV < 5%) within the individual horizons sampled. The two data sets were highly correlated (r = 0.98), and the regression equation used to predict clod bulk density with data from the core method is: Clod BD = (1.011 x Core BD) + 0.068; standard errors of ±0.042 and ±0.048 for the slope and intercept, respectively. From an operational standpoint, the core method appears to have many advantages over the clod method for sampling in remote locations.     

Soil condition classification using infrared spectroscopy: A proposition for assessment of soil condition along a tropical forest-cropland chronosequence

Soil fertility depletion in smallholder agricultural systems in sub-Saharan Africa presents a formidable challenge both for food production and environmental sustainability. A critical constraint to managing soils in sub-Saharan Africa is poor targeting of soil management interventions. This is partly due to lack of diagnostic tools for screening soil condition that would lead to a robust and repeatable spatially explicit case definition of poor soil condition. The objectives of this study were to: (i) evaluate the ability of near infrared spectroscopy to detect changes in soil properties across a forest-cropland chronosequence; and (ii) develop a heuristic scheme for the application of infrared spectroscopy as a tool for case definition and diagnostic screening of soil condition for agricultural and environmental management. Soil reflectance was measured for 582 topsoil samples collected from forest-cropland chronosequence age classes namely; forest, recently converted, RC (17 years) and historically converted, HC (ca.70 years). 130 randomly selected samples were used to calibrate soil properties to soil reflectance using partial least-squares regression (PLSR). 64 randomly selected samples were withheld for validation. A proportional odds logistic model was applied to chronosequence age classes and 10 principal components of spectral reflectance to determine three soil condition classes namely; “good”, “average” and “poor” for 194 samples. Discriminant analysis was applied to classify the remaining 388 “unknown” samples into soil condition classes using the 194 samples as a training set. Validation r² values were: total C, 0.91; total N, 0.90; effective cation exchange capacity (ECEC), 0.90; exchangeable Ca, 0.85; clay content, 0.77; silt content, 0.77 exchangeable Mg, 0.76; soil pH, 0.72; and K, 0.64. A spectral based definition of “good”, “average” and “poor” soil condition classes provided a basis for an explicitly quantitative case definition of poor or degraded soils. Estimates of probabilities of membership of a sample in a spectral soil condition class presents an approach for probabilistic risk-based assessments of soil condition over large spatial scales. The study concludes that reflectance spectroscopy is rapid and offers the possibility for major efficiency and cost saving, permitting spectral case definition to define poor or degraded soils, leading to better targeting of management interventions.     

Shear strength of surface soil as affected by soil bulk density and soil water content

This paper proposes a new method to measure the soil strength parameters at soil surface in order to explain the processes of soil erosion and sealing formation. To simulate the interlocks between aggregates or particles within top 2 mm of the soil, a piece of sandpaper (30 particles cm⁻²) was stuck on the bottom face of a plastic box of diameter of 6.8 cm with stiffening glue and used as shear media. The soil strength for the soils from sandy loam to clayey loam was measured with penetrometer and the new shear device at soil surface at different bulk density and soil water content. The normal stresses of 2, 5, 8, 10 and 20 hPa were applied for the new shear device. The results indicated that significant effect of bulk density on soil strength was detected in most cases though the difference in bulk density was small, ranging from 0.01 to 0.09 g cm⁻³. It was also indicated that the measurement with the new shear device at soil surface was reproducible. The changes in soil shear strength parameters due to changes in bulk density and soil moisture were explainable with the Mohr–Coulomb’s failure equation and the principles of the effective stress for the unsaturated soils. The implications of the method were later discussed.     

The calibration of a high resolution gamma-ray transmission system for measuring soil bulk density and an assessment of its field performance

The calibration of a high resolution gamma-ray density probe and a simple experiment comparing the probe with an earlier, lower resolution version are described. An assessment is made of the performance of the probe in three experiments investigating compaction by tractor wheels, two of which were in the field and the third in an indoor soil tank. A linear calibration relationship was obtained, although the addition of a quadratic term improved the fit of the curve slightly. The probe was found to be much more accurate than the earlier version within 100 mm of the soil surface where treatment effects were largest and most numerous in the field experiments, and thin layers of high density could be detected. Over the 15 month period of the experiments, the stability of the system was found to be satisfactory.     

Critical soil bulk density and strength for pea seedling root growth as related to other soil factors

Bulk density and soil strength are two major soil physical factors affecting root growth of pea seedlings. This study was conducted to determine the influence of soil texture, organic carbon content and water content on critical bulk density and strength. Soil from the plough layer (PL) and beneath the sub-soil (SUB) was used. By soil packing and adjusting the water content between 30% and 100% of field water capacity (FWC) a wide range of bulk density (1.3–1.7 Mg m⁻³) and strength (0.24–6.66 MPa) were obtained. Pea (Pisum sativum L.) was grown in the packed cores of 100 cm³ for 72 h at 20°C. Regression models were developed to explain root growth in terms of bulk density, soil strength, silt and clay (<60 μm) content, organic carbon, and water content. The regression curve of root growth as a function of soil strength showed that 40% of maximum root length can be regarded as an indicator of very poor root growth. By substituting this value into the root growth equations we calculated a critical bulk density and strength in terms of fraction<60 μm, organic carbon percentage and water content. The values of critical bulk density in both layers and of critical soil strength in the sub-soil increased with a decreasing content of fraction<60 μm. Irrespective of fraction<60 μm content, the critical bulk density and strength decreased as soil water content decreased. Critical soil strength was more sensitive than critical bulk density to changes in fraction<60 μm content and water content. This study provides data and a method for predicting critical bulk density and soil strength in relation to other soil properties for pea seedling root growth.     

Near infrared spectroscopy for determination of various physical,chemical and biochemical properties in Mediterranean soils

The potential of near infrared (NIR) reflectance spectroscopy to predict various physical, chemical and biochemical properties in Mediterranean soils from SE Spain was evaluated. Soil samples (n = 393) were obtained by sampling 13 locations during three years (2003–2005 period). These samples had a wide range of soil characteristics due to variations in land use, vegetation cover and specific climatic conditions. Biochemical properties also included microbial biomarkers based on phospholipid fatty acids (PLFA). Partial least squares (PLS) regression with cross validation was used to establish relationships between the NIR spectra and the reference data from physical, chemical and biochemical analyses. Based on the values of coefficient of determination (r²) and the ratio of standard deviation of validation set to root mean square error of cross validation (RPD), predicted results were evaluated as excellent (r² > 0.90 and RPD > 3) for soil organic carbon, Kjeldahl nitrogen, soil moisture, cation exchange capacity, microbial biomass carbon, basal soil respiration, acid phosphatase activity, β-glucosidase activity and PLFA biomarkers for total bacteria, Gram-positive bacteria, actinomycetes, vesicular-arbuscular mycorrhizal fungi and total PLFA biomass. Good predictions (0.81 < r² < 0.90 and 2.5 < RPD < 3) were obtained for exchangeable calcium and magnesium, water soluble carbon, water holding capacity and urease activity. Resultant models for protozoa and fungi were not accurate enough to satisfactorily estimate these variables, only permitting approximate predictions (0.66 < r² < 0.80 and 2.0 < RPD < 2.5). Electrical conductivity, pH, exchangeable phosphorus and sodium, metabolic quotient and Gram-negative bacteria were poorly predicted (r² < 0.66 and RPD < 2). Thus, the results obtained in this study reflect that NIR reflectance spectroscopy could be used as a rapid, inexpensive and non-destructive technique to predict some physical, chemical and biochemical soil properties for Mediterranean soils, including variables related to the composition of the soil microbial community composition.     

Near infrared spectroscopy for cost effective screening of foliar oil characteristics in a Melaleuca cajuputi breeding population

The identification of Melaleuca cajuputi leaf samples (trees) that demonstrate enhanced oil characteristics using near infrared (NIR) spectroscopy is described. Leaf samples from an unthinned M. cajuputi seedling seed orchard in Indonesia were collected and air-dried, and their 1,8-cineole content and oil concentrations were determined. NIR spectra of the leaves were obtained, and calibrations for 1,8-cineole content and oil concentration were developed using spectra that had been selected using spectral features; that is, no knowledge of 1,8-cineole content or oil concentration was used to select the calibration samples. The calibrations were used to predict the 1,8-cineole content and oil concentration of the remaining samples. It was demonstrated that NIR spectroscopy could be used to identify leaf samples that had high 1,8-cineole contents and oil concentrations. The technique has the potential to greatly reduce the time involved in ranking large numbers of samples for these attributes, as is a requirement in tree breeding programs to enhance oil production.     

Near infrared reflectance spectroscopy: A tool to characterize the composition of different types of exogenous organic matter and their behaviour in soil

In addition to total organic carbon and nitrogen, potential organic carbon mineralization under controlled laboratory conditions and indicators such as the indicator of remaining organic carbon in soil (I_ROC), based on Van Soest biochemical fractionation and short-term carbon mineralization in soil, are used to predict the evolution of exogenous organic matter (EOM) after its application to soils. The purpose of this study was to develop near infrared reflectance spectroscopy (NIRS) calibration models that could predict these characteristics in a large dataset including 300 EOMs representative of the broad range of such materials applied to cultivated soils (plant materials, animal manures, composts, sludges, etc.). The NIRS predictions of total organic matter and total organic carbon were satisfactory (R²_P = 0.80 and 0.85, ratio of performance to deviation, RPD_P = 2.2 and 2.6, respectively), and prediction of the Van Soest soluble, cellulose and holocellulose fractions were acceptable (R²_P = 0.82, 0.73 and 0.70, RPD_P = 2.3, 1.9 and 1.8, respectively) with coefficients of variation close to those of the reference methods. The NIRS prediction of carbon mineralization during incubation was satisfactory and indeed better regarding the short-term results of mineralization (R²_P = 0.78 and 0.78, and RPD_P = 2.1 and 2.0 for 3 and 7 days of incubation, respectively). The I_ROC indicator was predicted with fairly good accuracy (R²_P = 0.79, RPD_P = 2.2). Variables related to the long-term C mineralization of EOM in soil were not predicted accurately, except for I_ROC which was based on analytical and well-identified characteristics, probably because of the increasing interactions and complexity of the factors governing EOM mineralization in soil as a function of incubation time. This study demonstrated the possibility of developing NIRS predictive models for EOM characteristics in heterogeneous datasets of EOMs. However, specific NIRS predictive models still remain necessary for sludges, organo-mineral fertilizers and liquid manures.     

Soil bulk density corrections for providing a better relationship with root growth in gravelly soil

Abstract

Bulk density of a Tifton (Plinthitic Paleudult; fine loamy, siliceous, thermic) soil containing 5.8 to 11.0% of the sample weight as pebbles was 0.06–0.12 g/cc lower when corrections were made for presence of pebbles or concretions. A method for determining the bulk density of the soil matrix between pebbles or concretions is outlined. After adjustment, the bulk density at which root penetration was inhibited in this soil closely approximated that for soils which do not contain concretions. The proposed procedure reflects more nearly how bulk density changes where plant roots are growing than previously published procedures do.     

Influence of soil moisture stress and soil bulk density on the imbibition of corn seeds in a sandy soil

The imbibition of corn seeds (Zea mays L.) was examined in a sandy soil compacted to simulate the effect that might be expected from pressure wheels behind a planting machine.Water uptake was found to be exponential and to be the only factor contributing to the increase in volume of the seed during imbibition. Changes in bulk density of the soil over the range from 0.90 to 1.31 Mg cm^?3 produced no significant effects on water uptake.It was therefore concluded that the degree of contact between seed coat and soil particles is not an important factor in influencing the rate of imbibition of corn seeds under the specific conditions which were examined.Water flux into the seeds was calculated to be several orders of magnitude lower than bulk soil water flux at all soil water potentials tested. Estimates of seed coat permeability suggest that, for corn, this factor is the major restriction on entry of water into the seed during imbibition.At a field level, the widespread use of pressure wheels behind corn planters as a means of increasing seed/soil contact appears not to be necessary in sandy soils.     

Variation in soil bulk density and hydraulic conductivity within a quasi-circular vegetation patch and bare soil area

Journal of Soils and Sediments - Soil bulk density and hydraulic conductivity are two of many key factors for vegetation establishment and the other way around. Variations in them may cause patchy...     

Effects of traffic on soil aeration, bulk density and growth of spring barley

This paper reports the results of field experiments on several different soils to quantify the effects of different numbers of passes of vehicular traffic on soil aeration status (measured in terms of oxygen diffusion rate, ODR and redox potential, Eh), soil bulk density and development of spring barley. In a further series of field experiments, the effects of single and dual wheels were compared and the effectiveness of a soil loosener operating behind the wheels was evaluated. Additionally, some microplot experiments are reported in which a range of known values of soil bulk density were produced and the effects on soil aeration and development of spring barley were evaluated. It is shown that repeated wheeling, even by a tractor of only about 2 tonnes weight, can produce soil conditions in which aeration can be limiting for crop growth. The use of dual wheels resulted in lower values of soil bulk density and associated greater soil aeration. The loosener alleviated the compaction produced by wheels and also improved soil aeration. For a sandy loam soil, greatest root growth and crop yield occurred at a bulk density of 1.43 Mg m⁻³. Soil aeration as a component of soil physical quality is discussed.     

A personal computer program for calculation of soil bulk density coefficient of linear extensibility,and linear shrinkage

Abstract

A computer program was developed to calculate bulk density(BD), coefficient of linear extenslbility(COLE), linear extensibility(LE), and linear shrinkage(LS) in the presence or absence of coarse fragments (>2mm). When coarse fragments are present in a soil clod, COLE and linear extensibility calculations become more complex, requiring additional equations and correction factors. The calculation of linear shrinkage is not sensitive to coarse fragments, thus requiring a single equation. This BASIC computer language program is accommodating to various parameter imputs and correction factors for fast calculation of BD, COLE, LE and LS in soil clods with and without coarse fragments.