No abstract available

[en] The goal was to develop an easy, fast, and economical procedure to produce plant digests that can be accurately analyzed by plasma emission spectrometry for foliar sulfur content. The closed vessel microwave procedure described requires less than 2 hours to produce 12 digested 0.5 gram samples from the point of weighing the samples to applying them to plasma emission spectrometry analysis. The procedure utilizes nitric acid and hydrogen peroxide as a predigestion. The predigested samples are then each microwaved for 2.25 minutes. With this procedure, sulfur levels are within an average of 1.27% of that reported for the NBS Citrus Standard, are within 102.25% to 99.44% of the values determined for wet ash digested materials and display recovery rates of 96 to 98% for known levels of sulfur in the range expected in plant foliage. (author)

[en] The isotopic signal provided by differential discrimination against atmospheric carbon dioxide (13CO2) by C3 and C4 plant photosynthetic pathways is being widely used to study the processes of carbon (C) fixation, soil organic matter formation, and mineralization in nature. These studies have been facilitated by the availability of automated C and nitrogen (N) combustion analyzers (ANCA) combined with continuous flow isotope ratio mass spectrometers (CFIRMS). Analysis of 13CO2 in these instruments requires consistent sample mass for best precision, a requirement that is easily satisfied for soil and tissue samples by adjusting sample weight. Consistent CO2 sample size is much more difficult to achieve using gas handling systems for samples of headspace gases when CO2 concentrations vary widely. Long storage of gaseous samples also is difficult. Extended respiration studies are most easily conducted by trapping CO2 in alkali and conversion to an insoluble carbonate. Thermal decomposition of the carbonate in an on-line ANCA allows consistent and optimal CO2 sample mass to be obtained. The use of precipitated carbonates also facilitates storage of samples and enables full automation of sample analysis using an ANCA interfaced to a CFIRMS. Calcium (Ca), strontium (Sr), and barium (Ba) carbonates were tested. Strontium carbonate (SrCO3) with the addition of vanadium pentoxide (V2O5) as a combustion catalyst was found most suitable

[en] Trace Distribution Coefficients (Kd values) for ¹³⁴Cs, ⁸⁵Sr, and ⁶⁰Co sorption were found to be a function of sediment type (soil type) and of the solution concentration of macroions including NA⁺, K⁺, and Ca⁺² over wide macroion concentration ranges. These Kd value functions are required as input sorption parameters to a mass transport model. Four methods were evaluated for measuring the Kd value macroion functional relationships for each sediment type. Precision, bias, and cost effectiveness were compared for choosing a preferred method. The prefered method, an empirical-statistical method (Box-Behnken method), was found to be as precise and unbiased as the other methods and the most cost effective. 12 references, 7 figures, 10 tables

[en] 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. (author)

No abstract available

[en] Nitrogen (N) use efficiency (NUE) of fertilizer N can be accurately estimated by tracing the fate of soil applied labelled fertilizer, but the quantity of N remobilization from non-kernel components into kernels in maize (Zea mays L.) plants is difficult to determine. A field experiment involving stem infusion with labelled 15N solution was conducted at Ottawa, Ontario (45 degrees 22'N, 75 degrees 43'W) for two years to determine whether stem infused 15N could be used to quantify N remobilization and the contribution of remobilized N to the grain. A current stay-green commercial hybrid was grown at three fertilizer N rates and infused with 30 mL 15N solution [35.7 mmol N as 15NH(4)15NO(3) at 99.2 15N% atom enrichment (a.e.)] into the internode below the primary cob at anthesis. The control plants were infused with distilled water. Sampling occurred at 3 d, 2 wk and 5 wk after anthesis and at physiological maturity

[en] Nitrogen (N) isotope ratio mass spectrometry (IRMS) by Dumas combustion and continuous flow mass spectrometry has become a wide-spread tool for the studies of N turnover. The speed and labor efficiency of 15N determinations from aqueous solutions such as soil solutions or soil extracts are often limited by sample preparation. Several procedures for the conversion of dissolved ammonium (NH4+) or nitrate NO3- to gaseous ammonia and its subsequent trapping in acidified traps have been elaborated in the last decades. They are based on the use of acidified filters kept either above the respective solution or in floating PTFE envelopes. In this paper, we present an improved diffusion method with a fixed PTFE trap. The diffusion containers are continuously kept in a vertical rotary shaker. Quantitative diffusion can thus be achieved in only three days. For solutions with NH4+ levels of only 1 mg N kg-1 and NO3- concentrations of 12 mg N kg-1, recovery rates of 98.8-102% were obtained. By addition of 15N labeled and non-labeled NH4+ and NO3- it was shown that no cross-contamination from NH4+ to NO3- or vice versa takes place even when one form is labeled to more than 1 at %15N while the other form has natural 15N content. The method requires no intermediate step of ammonia volatilization before NO3- conversion

[en] Isotopic nitrogen (N) research techniques may be required in watershed studies to determine the impact of landscape position on fertilizer efficiency and the soil supplying power. However, traditional approaches using 15N labeled fertilizer may not be suitable when farmer equipment is used. The delta 15N natural abundance isotopic approach has been used to evaluate N cycling in watersheds. The objectives of this study were to measure the precision of the delta 15N measurement by the Europa 20-20 ratio mass spectrometer (Europa Scientific Ltd, UK), and to compare the difference and delta 15N approaches for measuring fertilizer use by maize (Zea mays). A replicated field study containing two different N rates (0 and 15.7 g N m-2) were used for the study. Maize samples were collected at the 8th-leaf, silking, and plant maturity in 1992 and 1993. Samples were dried (80 degrees C), ground (1-mm), weighed (stover 12 mg and grain 3 mg), and analyzed for total N and delta 15N. Fertilizer utilization at the three growth stages was determined using the natural abundance delta 15N and nonisotopic difference (fertilizer-control) techniques. During the study, the Europa 20-20 ratio mass spectrometer (Europa Scientific Ltd, UK) analyzed over 100 samples a day and had consumable costs of less than $2.00 per sample. The standard deviations of the mean were less than 0.11 and 0.21 per thousand in 51 and 77% of the stover samples, respectively. In 1992, grain yields were not influenced by N fertilizer additions, while in 1993 grain yields were increased by N fertilizer. The difference method estimated that in 1992, 16% of the N fertilizer was utilized by the crop, while the natural abundance delta 15N approach estimated that 36% of the fertilizer N was used by the crop. Differences between calculated values by the two techniques resulted from the difference method calculating net fertilizer use, while the delta 15N approach calculated fertilizer contained in the plant

[en] The concentration of four pesticides (2,4-D, atrazine, phorate, and terbufos) in soil solution during sorption experiments was measured using UV spectrophotometry, Gas Liquid Chromatography (GLC), High Performance Liquid Chromatography (HPLC), and radiotracer technique. The presence of water soluble organic matter in soil solution interfered with the measurement of pesticide using the UV spectrophotometry. The use of GLC, HPLC, and radiotracer technique involving ¹⁴C gave a good estimate of the concentration of pesticide in soil solution. The pesticide remaining in soil can be quantitatively analyzed by extracting with a scintillation solution containing an organic solvent such as toluene or dioxane. Among the various centrifuge tubes glass tubes with Teflon caps sorbed negligible amount of pesticides and these tubes can be used for the sorption measurements