Microwave oven‐drying of soil samples for chemical testing in Brazil

Abstract

In this experiment, we investigated the effect of microwave oven‐drying on soil samples for chemical tests. Samples were irradiated until they achieved a constant weight and for one‐half the time required. Two other treatments were applied, air‐drying at room temperature and forced air oven‐drying at 60°C. Samples were analyzed for water pH, 0.01M CaCl2 pH, organic carbon (C), Mehlich 1 and resin available phosphorus (P), exchangeable potassium (K) and calcium (Ca) plus magnesium (Mg), and potential acidity [1N calcium acetate (pH 7.0) extractable hydrogen (H) plus aluminum (Al)]. The results showed that microwave‐drying can induce erroneous interpretations of the “fertility status”; of the soil, thereby affecting fertilizer recommendations and lime requirement determinations.     

Effects of drying on the ion exchange capacity and cation adsorption properties of some New Zealand soils

Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.     

Impact of drying method on broiler litter analyses

Abstract

Drying broiler litter prior to chemical analyses may alter its chemical composition and result in excessive or inadequate nutrient applications to crops if such analyses are used for recommendation purposes. A study was conducted to determine the effect of drying method and temperature on broiler litter N, P, K, Cu, Fe, and Zn contents. Treatments consisted of no drying (ND), air drying (AD), oven drying at 40°C (OD40), oven drying at 60°C (OD60), microwave drying at 40°C (MW40), microwave drying at 60°C (MW60), and freeze drying at ‐40°C (FD). All drying treatments lost N when compared to ND, and greatest losses were observed with the FD, OD60 and AD treatments; losses were 15, 12 and 12% of the ND total N, respectively. Changes in broiler litter P, K, Cu, Fe and Zn due to drying were small and were inconsequential with respect to agronomic and environmental considerations. It appeared that maintaining broiler litter in a moist, refrigerated state before chemical analyses was more desirable than drying. However, our results show that from a practical standpoint, the MW40 treatment may be a desirable alternative.     

Effect of Drying on Phosphorus Distribution in Poultry Manure

Abstract

Laboratory drying may alter manure phosphorus (P) distribution. The effects of freeze, air (22°C), and oven (65°C) drying on sequentially fractioned poultry manure P were examined. Higher drying temperatures resulted in lower percentage of dry matter. Increased H₂O‐ and decreased sodium bicarbonate (NaHCO₃)‐extractable P with drying provided evidence that drying increases poultry manure P solubility. Labile fractions were predominantly inorganic P (P_i), whereas sodium hydroxide (NaOH) and hydrochloric acid (HCl) fractions had significant amounts of organic P (P_o). Drying altered H₂O‐ and NaHCO₃‐extractable P_i but had no consistent effect on P_o in these fractions. This work suggests that variations due to drying should be taken into consideration when evaluating manures for P availability or when comparing data in which different drying methods have been utilized.     

Effects of moist storage and different drying temperatures on the extractability of iron,copper, manganese,and zinc in soil samples

Abstract

The objective of this study was to investigate the effect of different pretreatments on the extraction of cationic micronutrients [iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn)] from four different soils. Samples were either stored in the field‐moist state for seven days before drying or dried immediately. Three drying treatments were used: air‐dried (72 hours), oven‐dried at 40°C (48 hours), or oven‐dried at 105°C (24 hours). Micronutrients were then extracted with 0.1N HC1 or diethenetriamine‐pentacetic acid (DTPA). Storage, drying temperature, extractant, and soil type all influenced micronutrient extractability. In general, a higher temperature increased the level of micronutrient extracted. However, the reverse effect was also observed. The effect of storage was variable and probably depended on the sample moisture content. We conclude that the results from routine analysis and experimentally determined indices can only be compared if soil samples are subjected to the same pretreatments. Hence, rigorous standardization of the sample preparations is imperative for accurate determination of plant‐available micronutrients.     

A comparative study between an electrostatic and conventional methods of drying soil samples

Abstract

Drying of soil samples exposed to high fluxes of air ions of both polarity, produced by corona electrodes, were studied by a beta‐ray gauge. The conventional methods of air‐drying and oven‐drying of soil samples were compared with the new technique. Fluxes of 0.94 x 10¹² positive and 1.83 x 10¹² negative air ions cm^‐2 s^‐1 reduced drying time of samples by at least three times over the air‐drying controls. Although oven‐drying at a high temperature was the fastest drying method, air ions maintained steady‐state soil temperature during the drying process at 4.5° and 7.3°C below that of the control and ambient temperatures, respectively. There was no significant change in pH, electrical conductivity, and organic matter content values of the dried soil samples of Dalhousie clay, Macdonald sandy loam and St. Sophie sand. Electric wind produced by the ionic drag is proposed to be the principal driving force for the enhancement of evaporation rates from the soil samples. Electroconvection and electrostriction that arise due to the interactions of an external electric field with soil dielectrics may also have contributed to the drying enhancement.     

Effects of drying and wetting on extractable aluminum in strongly acid soils and in aluminum-saturated clays

A number of field-moist strongly acid soils, NaObr-treated soils, and Al-saturated clays were subjected to drying and wetting treatments in the laboratory. Oven drying of samples resulted in decreases in extractable Al and increases in extractable H from field-moist soils containing more than 12 mequiv./100 g exchange acidity and from Al-saturated clays, and wetting the samples resulted in the reverse. However, when field-moist soil samples containing less than 7 mequiv./100 g exchange acidity were oven dried, both the extractable Al and extractable H tended to increase. Removing organic matter with NaOBr from a soil sample low in exchange acidity resulted in a change from an increase to a decrease in extractable Al upon oven drying. In all cases, the extractable Al and extractable H contents fluctuated cyclically with repeated drying and wetting. The cause for the observed changes was attributed to Al hydrolysis, with additional influence from soil acidity buffering, Al interlayer formation, and inorganic and organic matter dissolution.     

Evaluation of methods for soil inorganic nitrogen analysis

Abstract

This study determined the effects of soil preservation methods on inorganic nitrogen (N) analysis and evaluated methods of soil inorganic N analysis. Soils were preserved by oven‐drying at 55'C, air‐drying at 27°C, and freezing at ‐ 7°C. Inorganic N results were compared with initial N levels prior to imposing preservation treatments. Soil preservation effects on ammonium‐nitrogen (NH₄ ⁺‐N) were not consistent across soil types. Soil nitrate‐nitrogen (NO₃ ^‐‐N) levels after air‐drying and freezing compared most favorably with initial levels indicating that both are acceptable methods of soil inorganic‐N preservation. Levels of NH₄ ⁺‐N averaged across soils were 3.9 mg/kg for steam distillation, 4.2 mg/kg for sodium salicylate‐hypochlorite, and 3.7 mg/kg for indophenol blue. When compared with steam distillation averaged across soils, NO₃ ^‐‐N for cadmium‐copper (Cd‐Cu) reduction was 4 mg/kg greater, followed by nitrate electrode at 3 mg/kg, and salicylic acid at 2 mg/kg. Recovery of added N ranged from 83.3 to 94.8% for the NH4+‐N methods and from 74.8 to 112.4% for the NO₃ ^‐‐N methods with the nitrate electrode averaging 98.3%.     

Development of a Germination Process for Producing High β‐Glucan,Whole Grain Food Ingredients from Oat

Germination can be used to improve the texture and flavor of cereals. However, germination generally causes breakdown of β‐glucans, which is undesirable with respect to the functional properties of β‐glucan. Our aim was to assess possibilities of germinating oat without substantial loss of high molecular weight β‐glucan. Two cultivars, hulled Veli and hull‐less (naked) Lisbeth were germinated at 5, 15, and 25°C and dried by lyophilization or oven drying. Elevated germination temperatures led to an increase in Fusarium, aerobic heterotrophic bacteria, Pseudomonas spp., lactic acid bacteria, enterobacteria, and aerobic spore‐forming bacteria. Therefore, the germination temperature should be kept low to avoid excessive growth of microbes. Of the samples germinated at 15°C, only one contained low amounts of the Fusarium toxin deoxynivalenol (52 μg/kg). Germination led to the breakdown of β‐glucans, but the decrease in the molecular weight of β‐glucan was initially very slow. A short germination schedule (72 hr, 15°C) terminated with oven drying was developed to produce germinated oat with retained β‐glucan content. Compared with the native oat, 55–60% of the β‐glucan could be retained.     

Analysis of sugarbeet petioles for phosphorus

Abstract

The influence of method of drying on concentrations of total P, extractable phosphate and two N fractions in petioles from recently matured sugarbeet leaves was studied. Method of drying had no or small effects on total P, total N and nitrate‐N. However, method of drying had a marked effect on the value of extractable phosphate. Concentrations of phosphate‐P extractable with water and 2% acetic acid were least with freeze‐dried material and increased as temperature of oven drying was varied from 70 to 100°C. Extractable phosphate‐P in tissue dried by a particular method was lower when acetic acid was the extractant. Quantity of extract‐able phosphate‐P in oven‐dried material was not influenced by substitution of ascorbic acid for stannous chloride and elimination of the H₂O₂ oxidation step in the analytical procedure. Leaf position greatly affected concentrations of total P and acetic‐acid soluble phosphate‐P. Both parameters at a given sampling date decreased with increasing age of leaf.     

Influence of pre‐storage drying conditions and duration of storage on the effectiveness of root inoculum of Glomus aggregation

A greenhouse experiment was undertaken to evaluate the influence of pre‐storage drying treatments and duration of storage on the effectiveness of root inoculum of Glomus aggregatum. Conditions under which roots were dried prior to storage had little or no effect on the level of arbuscular mycorrhizal (AM) effectiveness measured in terms of pinnule phosphorus (P) content of Leucaena leucocephala leaves after the first 14 days of storage. As duration of storage was further prolonged the time required by root inocula for initiating AM effectiveness and attaining peak levels of effectiveness was progressively prolonged relative to that required by the crude inoculum. However, the two sources of inoculum had similar peak AM effectiveness in many instances. Roots dried in the greenhouse or in the oven at 40°C were significantly inferior to that dried at 60°C. Root inocula stimulated growth of the indicator plant to the same extent as the crude inoculum after 14 days of storage. However, the effectiveness of root inocula in stimulating growth declined with further increase in duration of storage. Among root inocula tested, that dried at 60°C prior to storage was relatively more effective than that dried in the greenhouse or in the oven at 40°C. The overall inferiority of root inocula to that of the crude inoculum appears to be related to loss of viability of root inocula with increase in duration of storage.     

Cooking Characteristics and Quality of Noodles from Food Sorghum

Three white food sorghums, ATx631*RTx436, ATxARG*RTx436, and SC283‐14, were decorticated, milled into flour and processed into 100% sorghum noodles. Flour, water, and salt (1%) were preheated using a hotplate or a microwave oven. The mixtures were put through a forming extruder to produce noodles. Extruded noodles were dried by three methods: air‐dry method (23°C, 48 hr); one‐stage (60°C, 30% rh, 3 hr), or two‐stage (60°C, 100% rh for 2 hr followed by 60°C, 30% rh for 2 hr). Noodles were evaluated dry and after cooking. Sorghum flours with smaller particle sizes yielded better noodles. The microwave preheating method yielded better noodles than the hot‐plate method. Stronger and firmer noodles, dry or cooked, were prepared using two‐stage drying compared with the other drying methods. Fine flour that was preheated using a microwave oven and dried using the two‐stage method gave the best noodles with moderate (10%) dry matter loss. Optimized processing conditions yielded sorghum noodles with good qualities when properly cooked.     

Heat Treatments of Milled Rice and Properties of the Flours

The effects of autoclave and oven treatments on the gelatinization of rice flour and on the rheological characteristics of its pastes were studied by differential scanning calorimetry (DSC), rapid viscoanalysis (RVA), and rotational viscometry. Flours from autoclave‐treated rice (ATR) and oven‐treated rice (OTR) were prepared, respectively, by heating at 120°C for 60 min and 160°C for 60 min followed by drying (ATR sample), and grinding at 2.2–12.9% moisture content. The rice flour dispersions were adjusted between pH 6.3 and 2.8 using 0.2M citrate buffer. The retort processing of rice flour in water pastes were done at 120°C for 20 min either once or twice. The gelatinization peak temperature (PT and T_o) and the peak temperature corresponding to the amylose‐lipid complexes (T_p3) of ATR increased at pH 6.3 and 2.8 compared with OTR and UTR flour. This indicates that the internal structures of the starch granules in ATR became more stable to heat and acid, even though the damaged starch content of ATR was 23% compared with 16 and 7%, respectively, for untreated rice flour (UTR) and OTR. The OTR flour pastes showed a gel‐like behavior at pH 4.5 after retort processing in water at 120°C for 20 min; however, the ATR mixture behaved more like a liquid paste. Decreases in the reducing sugar content of OTR and ATR pastes suggested that enzymes in the heat‐treated rice were denatured, which retarded the hydrolysis of glucose chains and the rupture of starch granules during pasting.     

Residual Soil Nitrate: A Comparison between Air-Dried and Field-Moist Soil Samples

In the framework of the European nitrate directive (91/676/EEG), losses of nitrate (NO₃)– nitrogen (N) to both surface and groundwater are limited to 50 mg/l. Because the residual NO₃-N in the soil profile after harvest is considered the main determinant of nitrate leaching during wintertime, the Flemish government imposed a limit value of 90 kg NO₃-N ha^?1 up to a soil depth of 90 cm between 1 October and 15 November. This study compared two different soil sample preparation methodologies. When samples were analyzed immediately upon arrival, no differences in NO₃-N concentration were observed. However, although field-moist samples are maintained at 4 °C, nitrification is not completely stopped, as indicated by the increased NO₃-N concentration in field-moist samples 10 days after storage at 4 °C . In contrast, nitrification in air-dried samples is stopped during the oven drying when 40 °C is reached. Moreover, the reproducibility was significantly greater in air-dried samples as compared to field-moist samples.     

Cation treatment and drying‐temperature effects on nonylphenol and phenanthrene sorption to a sandy soil

The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na⁺, Ca²⁺, or Al³⁺ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na⁺ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca²⁺ and Al³⁺ decreased it. The ¹H‐NMR relaxometry analyses showed that Al³⁺ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca²⁺ or Na⁺. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.     

Analysis of Kjeldahl digests by the salicylate method: Optimizing pH and buffering improves both sensitivity and precision

Abstract

Digest acidity can interfere strongly with ammonium analysis using salicylate‐indophenol colorimetry, but many methods over‐neutralize acids so that buffering capacity and sensitivity are reduced. To optimize analysis of acidic digests, we replaced the phosphate buffer with salicylate. Base was added stoichiometrically to neutralize acids and dissociate one‐half the salicylate to reach the phenolic pKa (approx. 13). Sample flow was 20% of total flow and a 60°C water bath was used. This gave optimal sensitivity and minimized interferences due to acidity fluctuations. The limit of detection was 1 μM in digest solution.     

Effect of moisture and temperature regimes on available phosphorus in wetland rice soils

Abstract

A laboratory experiment was conducted to evaluate the effects of water and temperature regimes on availability of soil phosphorus (P). Four soil samples with variable levels of available P collected from a long‐term P frequency trial were incubated under two moisture regimes, continuous waterlogging (CWL) and alternate wetting and drying (AWD) at 20°C and 30°C temperature for 90 days. The samples were extracted with 0.5M NaHCO₃ for available P determination after incubation. Increase in temperature increased available P content and this increase was more prominent in CWL conditions. Available P in all the soils tested was higher under CWL than AWD conditions, however, the increase in available P due to CWL environment was more pronounced in soils with higher available P.     

Kinetics of ammonia volatilization of anhydrous ammonia applied to a vertisol as influenced by Farm Yard manure,sorbed cations and cation exchange capacity

Abstract

In laboratory experiments, effects of added Farm Yard Manure (FYM), sorbed cations and cation exchange capacity (CEC) on NH₃ volatilization of anhydrous ammonia applied to a Vertisol were studied at 0.3 bar soil Moisture Tension and 25 ± 1°C. On addition of FYM or with increase in CEC the volatilization of retained ammonia was reduced while the effect of the sorbed cations was in the order : K‐Soil > Na‐Soil > Ca‐Soil > Mg‐Soil. The results suggest that the volatilization of retained NH₃ followed First order reaction kinetics, with a rapid rate of volatilization in the initial 8 to 10 h followed by a retarded rate up to 144 h.     

Adenosine triphosphate (ATP) and microbial biomass in soil: Effects of storage at different temperatures and at different moisture levels

Abstract

On air‐drying, the ATP contents of two moist soils fell to about one quarter of their original values. When a freshly‐sampled soil (field temperature 5.5°C) was stored moist (43% water holding capacity) for 7 days at 25°C the ATP content increased from 4.54 to 7.84 μg ATP g^‐1 soil. Storage at 10°C caused a smaller increase; to 5.39 μg g^‐1 soil. Microbial biomass C also increased on storage but the relative increase was less than that of ATP. Thus the biomass C/ATP ratio fell from 234 in the freshly sampled soil to 168 in the soil stored moist for 7 days at 25°C. The ATP content declined to less than half its starting value if storage was under waterlogged conditions.

The ATP method for determining microbial biomass in soil depends on the use of a constant factor (5.85 mg ATP g^‐1 biomass C) for converting ATP content to biomass C. This factor came from work on soils that had been stored moist at 25°C for several days before biomass C and ATP measurements were made: it is only applicable to soils that have been stored in this way.     

Mercury intrusion porosimetry of some New Zealand soils in relation to clay mineralogy and texture

Pore size distributions in the 10/10⁴ nm e.c.d. range in aggregates from three New Zealand soils with largely monomineralic clay fractions, were determined by mercury porosimetry after oven drying and also after critical point drying following methanol and then CO² exchange from a range of water contents. A soil containing halloysite showed considerable porosity in the fine pores (10–30 nm) regardless of the method of drying. A smectitic soil showed virtually no porosity in the 10²–10⁴ nm range when oven dry. A soil containing allophane was dominated by large pores (> 10³ nm). The change from a fine (clayey) to a coarser (clay loam) texture within the profile of one soil was reflected in an increase in large pores.