Mehlich‐1‐ and DTPA‐extractable lead in soils in relation to soil properties

Abstract

Mehlich‐1 and DTPA extractants are frequently used to predict metal availability in soils. Metal extractability by the acid or chelate extractant reflects the metal characteristics and metal‐soil interactions. In this study, samples of eight topsoils from the southeastern United States were incubated with added lead (Pb) at the rate of 40 mg#lbkg^‐1. After five months in the greenhouse, Mehlich‐1 and DTPA extractants were employed to extract Pb in both metal‐amended and natural soils. For the natural soils, Pb concentration in the DTPA extractant was always higher than that in the Mehlich‐1 extractant. This indicates that the DTPA chelate extractant is able to dissolve some Pb in soils which is not solubilized by protons. The negative correlation found between Mehlich‐1‐extractable Pb and soil clay content might result from two mechanisms: i) strong association between Pb and soil surfaces, or ii) readsorption of Pb during extraction. None of the correlations between DTPA‐extractable Pb and soil properties was significant, suggesting that the DTPA‐extractable Pb is not heavily dependent on soil properties. The DTPA extractant showed a high ability to solubilize Pb in the natural soils possibly due to a high affinity of Pb for soil organic matter.     

Use of loss‐on‐ignition to assess soil organic carbon in forest soils

Abstract

Forest floor and mineral soils were collected from 169 conifer and hardwood forested plots across Minnesota, Wisconsin, and Michigan. Regression equations were developed between LOI and organic C for 20% of the samples (n=337), and LOI was then used to predict organic C on all of the samples. Results indicated that LOI is a good estimator of organic C in these soils, but that separate equations were needed for different soil strata. Percent organic C in forest floors was greater in conifer stands compared to hardwood (means of 35.1 and 30.1%, respectively)     

A simple manual method for the determination of phosphate‐extractable (ion‐exchange membrane) sulphate in soils

Abstract

A simple manual method for measuring phosphate‐extractable sulphate in soils using basic laboratory equipment is described. Sulphate is extracted by a phosphated anion‐exchange membrane which, after elution, is measured turbidimetrically as barium sulphate. The results obtained by the proposed manual method compare well with a continuous flow analyser method using a range of Pacific Island soils.     

Pattern of iron distribution in the soil‐plant system and its possible relation to iron‐chlorosis

Abstract

The frequent concentration‐ranges of various nutrient elements in soils and in plants are compared. Iron is different from almost all other nutrient elements in the fact that its optimal concentration range in plants is much lower than its frequent concentration range in soils. It is suggested that this observation is related to a chemical‐physiological mechanism of control on the uptake of iron by plants which in turn may explain the situations in which iron deficiency conditions in plants arise.     

Comparison of behavior of natural and synthetic phosphate fertilizers in moderately water‐repellent sandy loam soil under winter rainfall

Abstract

This study compares the mobility of phosphate‐phosphorus (PO₄‐P) and total P derived from two commercial phosphate blends, namely a naturally reactive rock phosphate containing 12.5% P, and an synthetic phosphate containing 9% P, in small, undisturbed soil cores extracted from a paddock in a dairy farm approximately 35 km southeast of Warmambool in the Western Region of Victoria, Australia. Since both fertilizers contained major ions, the transport of sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) were also studied. The farm's soil, a water repellent, acid, dark brownish grey, sand loam is typical of many found in this rich beef and dairy region, and is used for pasture. Our results suggest that there was little difference in chemical dynamics, and by inference chemical bioavailability and ecological safety, between the two commercial phosphate materials.     

A new soil test method for the determination of plant‐available cadmium in soils

Abstract

A new soil test procedure using 1M NH₄Cl was developed for the extraction of plant‐available cadmium (Cd) from soils. Five grams of soil is weighed into a 50‐mL polyethylene vial to which 30 mL of 1M NH₄Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25°C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 μm nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH₄Cl‐extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10^‐7). In comparison with several commonly used extradants, such as ABDTPA, CaCl₂, NH₄OAc, and NH₄NO₃, the 1M NH₄Cl‐extracted Cd from soils was found to be a better index of Cd availability.     

Application of the Berthelot reaction to the determination of ammonium‐N in soil extracts and soil digests

Abstract

The phenol‐hypochlorite‐ammonium reaction of Berthelot can be utilized in manual procedures for the analysis of NH₄‐N in a variety of soils applications, including total N measurement in soils, particle size separates and soluble organic matter fractions, and in measuring NH₄‐N in soil extracts. A simple, convenient, and versatile procedure is described.     

Performance characteristics in the determination of soil‐water pH and soil‐SMP buffer pH using a flow‐through junction combination electrode

Abstract

A laboratory robot has been used to assess the performance of a commercially available flow‐through junction pH electrode. The electrode was tested for accuracy and precision in the determination of soil‐water pH (pH_w) and the Shoemaker, McLean, and Pratt buffer solution pH (pH_SMP). The significance of the pH_SMP determination lies in subsequent calculations of soil lime requirement (LR). Response times and hysteresis effects were compared under different operating conditions.     

Quantity‐intensity parameters of potassium in relation to uptake by guinea‐corn in representative soils of the ecological zones of Nigeria

Abstract

Quantity‐intensity (Q‐I) relation studies were often used to supplement information obtained from conventional soil tests for the estimation of potassium (K) needs of crops. With a view to ascertaining the reliability of the Q‐I relation parameters for comprehensive characterization of K dynamics in typical Nigerian soils, K values derived from Q‐I isotherms were related to neutral normal ammonium acetate (1 N NH₄OAc, pH 7.0) (exchangeable) K, other soil K forms [non‐exchangeable (K_ne), exchange (K_e), mineral K (K _m ), and solution K (K_s)] and the K uptake by Guinea‐corn (Sorghum bicolor, var. LS 187) subjected to weekly cuts in Neubauer cultivation vessels. Most of the soil K (about 98%) was in the form of soil minerals while less than 1% was plant available whereas about 1% was trapped within the interlattice layers of the clay minerals (as fixed K or K_ne). Mineral K (K_m) content was closely related to total K (K_t), but not to the other forms, K_ne, K_e, and K_s. A close relationship was noted between the two components of labile K (K_e and K_s). Except for % K saturation, the relationships between the K measurements with plant response were poor. The results of these investigations clearly demonstrate that the Q‐I relation could not adequately characterize the K dynamics of these tropical soils.     

A method for estimating organic‐bound iron and aluminum contents in soils

Abstract

Estimation of organic‐bound iron (Fe) and aluminum (Al) is an important diagnostic technique in pedology. The commonly used sodium pyro‐phosphate method yields somewhat ambiguous results and is inconvenient if an ultracentrifuge is not available in the laboratory. This study showed that 0.1M sodium nitrilotriacetate (NTA) could be used instead of pyrophosphate. The Fe and Al extracted by 0.1 M NTA were highly correlated to that by sodium pyrophosphate with R² = 0.993 for Fe and R² = 0.992 for Al, while the dissolution effects on standard mineral samples in NTA was kept at a minimum. NTA has the advantage of not requiring ultrafiltration, ultracentrifugation, or the addition of a flocculating agent as is the case for the pyrophosphate method.     

Vineyard soils under organic and conventional management—microbial biomass and activity indices and their relation to soil chemical properties

Eight vineyards in Pfaffenheim (P) and Turckheim (T) close to Colmar, France, forming four pairs of organic and conventional vineyards, were analyzed for microbial biomass and activity indices in relation to important soil chemical properties (carbon, nutrient elements, heavy metals) and also to differences between the bottom and top positions on the vineyard slope. The question was whether the vineyard management affects especially the soil microbiological indices. Three locations were on limestone (P-I, P-II, T-II), one on granite (T-I). The gravel content (>2 mm) ranged from 9 to 47%. The management systems had no significant main effect on the contents of organic C, total N, P, and S. The mean total contents of man-derived heavy metals decreased in the order Cu (164 μg g⁻¹ soil) > Zn (100 μg g⁻¹ soil) > Pb (32 μg g⁻¹ soil). The contents of microbial biomass C varied between 320 and 1,000 μg g⁻¹ soil. The significantly highest content was found at location P-II, the significantly lowest at the moderately acidic location T-I. The contents of microbial biomass N and adenosine triphosphate showed a similar trend. At location T-I, the fungal ergosterol-to-microbial biomass C ratio and the metabolic quotient qCO₂ were significantly highest, whereas the percentage of soil organic C present as microbial biomass C was lowest. Highest percentages of soil organic C present as microbial biomass C and lowest qCO₂ values were found in the organic in comparison with the conventional vineyards. None of the soil microbiological indices was significantly affected by the position on the slope, but all were significantly affected by the management system. This was mainly due to the highest index levels in the organic vineyard location P-II with the longest history in organic management.     

The effect of water and acid‐washing soil treatment on the measurement of pH,delta pH and zero point of charge in some variable charge soils

Abstract

This study was undertaken to determine the effect of previous water and acid‐washing soil treatment on soil pH, Delta pH and Zero Point of Charge of soil surface samples of three Hawaii soils, Molokai (Typic Torrox), Wahiawa (Tropeptic Eutrustox), and Hilo (Typic Hydrandept).

The acid‐washing treatment lowered the soil pH and shifted the Zero Point of Charge to lower pH values. The effect was greater in the Wahiawa and Molokai soils that are dominated by oxidic materials. Whereas the acid‐washing treatment did not change the magnitude of the negative charge in the Wahiawa and Molokai soils, it overestimated the magnitude of the positive charge in the Hilo soil. This phenomena probably was enhanced by the dominance of variable charge clay minerals in the Hilo soil. The results indicated that the acid‐washing treatment changed the nature of the charge characteristics of the soils, hence it should not be recommended in the characterization of the net charge in variable charge soils.     

Can an isotopic method allow for the determination of the phosphate‐fixing capacity of soils?

Abstract

This work was undertaken to determine the ability of an isotopic exchange kinetics method to measure the fixation of P by soils. The parameter, Pfix, the ratio of introduced carrier‐free ³²P over ³²P remaining in solution after one minute of exchange, was determined on a wide range (n = 127) of samples from surface horizons of temperate and tropical soils. Pfix was compared to two parameters derived from adsorption isotherms, the maximum quantity of adsorbed P (Pmax) and the quantity of P to be adsorbed to reach a concentration in solution of 0.2 mg P/L (Po.2). Results showed that Pfix was at least as good as Pmax and Po.2 to estimate the soil fixing capacity. Pfix was correlated to the clay and iron oxide (Fed) contents, and highly significant correlations with Fed were observed for Pfix than for Pmax or Po.2. The isotopic exchange kinetics method can be recommended to determine the soil phosphate fixing capacity. Moreover, because of its accuracy and the minimal disturbance of the soil‐solution equilibrium, the method could be used for routine analysis of soil P‐fertility status.     

A comparison between the walkley‐black and a dry combustion method for determining organic carbon in a humic brown soil,Papua New Guinea

Abstract

Regression equations for the relationship between Walkley‐Black carbon and carbon by dry combustion in a tropical humic brown clay soil were variable in four different vegetation regimes. In one case, statistically different correlation coefficients were obtained for grassland surface and the corresponding subsurface soils.

Calibration of the Walkley‐Black method against dry combustion carbon is recommended for each treatment in soil fertility studies as soil organic matter might have a different composition and hence carbon recovery value because of treatment.     

Effects of extraction period and soil.‐solution ratio on the amount of zinc extracted from soils by different extractants

Abstract

Investigations have examined the effects of extraction period and soil:solution ratio on the extraction of zinc from some New Zealand soils by EDTA, DTPA, HCl, Ca(NO₃)₂ and CH₃COONH₄. A high proportion of the zinc extracted by EDTA, DTPA, HCl, and Ca(NO₃)₂ was extracted rapidly, within the first 0.5 h, followed by small increases over the next 15 h. An exception occurred with a soil containing iron/manganese concretionary material. In this soil, with both EDTA and DTPA, there were significant increases in the amount of zinc extracted between 1 and 8 h. The amounts of zinc extracted by CH₃COONH₄ increased gradually with the time of extraction up to approximately 4 h.

Substantial increases in the amounts of zinc extracted with HCl, Ca(NO₃)₂ and CH₃COONH₄ were obtained by increasing the soil:solution ratio from 1:2.5 to 1:10. However, soil:solution ratio has little effect on the amounts of zinc extracted by EDTA or DTPA.     

Evaluation of efficient soil test methods for Zn and their critical vales in salt‐affects soils for rice

Abstract

Soil pot culture experiment was conducted on 22 soils of Balewal‐Phaguwala‐Narike (BPN) and 24 soils of Isri‐Langrian‐Narike (ILN) associations using rice (PR 106) as test crop at 0 and 7.5 ppm Zn levels. Chelating extractants 0.005M DTPA, 0.01M EDTA‐(NH₄)₂CO₃ and 0.05M EDTA, extracted more soil Zn than double‐acid and were significantly correlated with each other as well as with soil pH and clay in BPN and only with clay in ILN soil association. Soil CaCO₃ governed the double‐acid extractable Zn in these soils. Dry matter yield and Zn uptake by rice significantly increased with 7.5 ppm Zn application. The response was higher in ILN than BPN soil association, The DTPA method gave the highest correlation with Bray's yield and Zn uptake (r =0.72 and 0.55) followed by 0.05M EDTA (r ‐ 0.75 and 0.61) or EDTA‐(NH₄)₂CO₃ (r =0.70 and 0.61). The predictability of rice yield improved from 18–27 to 27–35, 32–43, 34–44 and 51–55 percent as a result of stepwise inclusion of pH, CaCO₃, organic carbon (OC) and clay respectively in the regression equation alongwith Zn extracted by chelating agents.

The critical levels of DTPA, EDTA‐(NH₄)₂CO₃ and EDTA extractable Zn significantly differed in the two associations and were 0.69, 0.82 and 1.24 ppm in BPN and O.BC, 1.09 and 1.42 ppm in ILN soil association. Soil properties further affected the critical levels. This for DTPA available Zn was 0.80 and 1.03 ppm in soil containing less and greater than 2% CaCO₃, 1.03 and 0.80 ppm in soils containing less and greater than 0.25% OC. These values for EDTA‐(NH₄)₂CO₃ available Zn were 1.09 and 0.91 ppm Zn in soils containing less and greater than 15% clay suggesting that critical levels of Zn for each category of soil properties should be considered while making recommendations of Zn fertilization of crops.,     

A routine method to study soil organic matter by particle‐size fractionation: Examples for tropical soils

Abstract

Particle size fractionation is becoming commonly used for studying soil organic matter (OM). However, isolation of clay and silt represents a long and thus tedious step in the fractionation procedure. We propose an approach identical to the one utilized in particle size analysis with an estimation of the recoveries from aliquots ("aliquot”; method) of the 0–2 and 0–20 μm fractions and no entire isolation ("decanting”; method) of clay and silt. In comparison with the “decanting”; method, the fraction and carbon (C) recoveries obtained by the “aliquot”; method were satisfactory, but those of nitrogen (N) being hardly interpretable because of an insufficient accuracy of the determination method. The recommended method saves time and laboratory space and could be used as a routine particle size fractionation of soil OM. Finally, this paper lists various methodological aspects of considerable significance but rarely reported in published studies.     

Variation of early growth and nutrient content of no‐till corn and soybean in relation to soil phosphorus and potassium supplies

Abstract

Knowledge of relationships between variation in early plant growth and soil nutrient supply is needed for effective site‐specific management of no‐till fields. This study assessed relationships between soil test phosphorus (STP) and potassium (STK) with early plant growth and P or K content of young corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants in eight no‐till fields. Composite soil (0–15 cm depth) and plant (V5‐V6 growth stages) samples were collected from 400‐m² areas at the center of 0.14‐ha cells of a 16‐cell square grid and from 2‐m² areas spaced 3 m along each of two 150‐m intersecting transects. Correlation, regression, multivariate factor analyses were used to study the relationships between the variables. Variability was higher for samples collected from the transects. Plant dry weight (DW), P uptake (PU), and K uptake (KU) usually were correlated with STP and STK but the correlations varied markedly among fields. Relationships between soil and plant variables could not always be explained by known nutrient sufficiency levels for grain production. Plant P concentration (PC) was not always correlated with STP and sometimes it increased linearly with STP, but other times increased curvilinearly until a maximum was reached. Plant K concentration (KC) usually was correlated with STK, however, and increased linearly with increasing STK even in fields with above‐optimum STK. The results suggest greater susceptibility of early growth to STP than to STK and greater plant capacity to accumulate K compared with P over a wide range of soil nutrient supplies. Variation in STK likely is a major direct cause of variation in KC over a wide range of conditions but variation in STP is not likely a major direct cause of variation in PC when high STP predominates.     

Potential of AFM–nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Purpose  

This exploratory study evaluates the potential of nanothermal analysis (nTA) coupled with atomic force microscopy (AFM) of soil samples for understanding physicochemical processes in soil and for linking the nanospatial and microspatial distribution of thermal characteristics with the macroscopic properties of soil samples.     

Amelioration of saline‐sodic soils with organic matter and their use for wheat growth

Abstract

Few reports highlight the effect of organic matter in improving the properties of saline soils. A laboratory study was conducted to determine the effect of adding farm yard manure (manure), Egyptian clover hay (clover hay), and wheat straw, at 1 and 3% of soil weight on water stability of soil aggregates (WSA), water‐holding capacity (WHC), pH, and electrical conductivity of soil extract (ECe) of a normal, saline, and saline sodic soil. After 90 and 180 days, WSA and WHC increased, while pH and ECe decreased. Soil properties improved most by adding 3% manure to all the soils. Wheat grown in these soils indicated significant differences for various growth and yield variables, especially the root growth, number and area of green leaves, and grain yield. Organic matter added to these soils increased WSA and WHC and decreased pH and Ece. The WHC had no correlation with pH, but was negatively correlated with Ece. Increased WSA caused the leaching of excess ions and reduced their toxicity, while enhanced WHC increased the availability of water to the roots and promoted growth. It is concluded that manure ameliorated salt affected soils and promoted wheat growth better than clover hay and wheat straw.