Determination of molybdenum in wet‐ashed digests of plant material using flameless atomic absorption

Abstract

A procedure using matrix‐compensated Mo standards to determine Mo in plant tissue by flameless atomic absorption is described. Concentration ranges of macroelements (N,P,K,Ca,Mg), microelements (Cu,B,Zn,Mn,Al,Fe), and HC1O₄. typical of those found in HNO₃‐HC1O₄ plant tissue digests were examined for their effect on the observed analytical value of Mo. The mean of 20 Mo determinations of NBS orchard leaves SRM 1571 was 0.28 ± 0.01 ppm Mo compared to the NBS certified value of 0.3 ± 0.1 ppm Mo. Recovery of Mo added to digests of orchard leaves and alfalfa tops ranged from 95 to 105%.     

Comparison of three techniques to determine al content in micro‐samples of plant material

Abstract

Comparisons are made of three methods of Al analysis in micro‐samples (≤ 100 mg) of plant material. Direct current plasma emission spectrometry (DCP), graphite furnace atomic absorption spectrometry (GFAAS), and pyrocatechol violet (PCV) all gave comparable results for the plant materials analyzed.

The importance of adequate sample dissolution of digested samples prior to analysis by PCV was strikingly apparent. Our results indicate that to insure complete formation of reactive Al species to complex with the dye that a combination of 12 N HCl and a 1 hr heat treatment at 70°C in a steam bath is necessary.

Residue decomposition of materials with HF acid resulted in more apparent Al only by DCP analysis. Contribution of the residue to the total Al content varied between 7 and 14%.     

Estimation of sulfate and amino acid sulfur in plant material by X‐ray spectrometry

Abstract

The SKα shift between the valences of sulfur has been used to determine by X‐ray spectrometry the two main forms of sulfur present in plant material, viz: oxidised S (S⁶⁺) and covalently bonded sulfur (S^c). S⁶⁺ and S^c were shown to correlate closely with sulfate, as determined by reduction with hydriodic acid, and cysteine+methionine S, respectively. The method is rapid and reliable provided the X‐ray spectrometer is stable and has high reproducibility in goniometer setting. The use of S⁶⁺ and S^c is recommended as an alternative to chemical methods for assessing the sulfur status of crops and the sulfur amino acid content of diets.     

Simple method for 14C‐labelling root material for use in root decomposition studies

Abstract

A method was devised in which plant roots can be easily and uniformly radiolabelled with ¹⁴C for use in soil decomposition studies. The roots were labelled from an exogenous sugar solution for a total period of 48 hours after which root decomposition studies could be performed. The method offers distinct advantages over the existing constant ¹⁴C‐CO₂ atmosphere labelling method.     

Spreading uniformity of granular bulk‐blended fertilizer

Abstract

This study was conducted to measure the field variability in nutrient rate of bulk blended granular fertilizer that was spread with a double‐spinner, ground driven spreader. The objective was to determine if such variation affected corn (Zea mays L.) yield and nutrient concentrations. Studies were conducted at two sites in Kentucky during 1987 to test the agronomic effects of varying granule size of urea (U) and diammonium phosphate (DAP) when they were blended with muriate of potash (KC1) to prepare a bulk‐blended mixed fertilizer. The control (uniform blend) blend components were all of the same granule size (2.0–3.36 mm). Two blends of identical analysis were prepared by using smaller (1.4–2.0 mm) granule sized U (fine urea) or DAP. Each of the three blend treatments was spread in swath widths of 12.19 m. Measurements were made every 2.44 m across the swath to measure rate of nutrient application, 10‐leaf stage growth of corn, ear leaf, nutrient concentration of com, harvest stand population, and grain yield. Despite measurable differences in applied nutrient rates due to the use of fine U and fine DAP as compared to the uniform treatment, there were no significant treatment effects on corn grain yields.     

Determination of boron in fresh and in dried plant material by plasma emission spectrometry after extraction with HF‐HCL

Abstract

The boron content of plant material was determined by ICP‐AES after a simple extraction with a mixture of HF and HC1. The method gave excellent agreement with the colorimetric determination by Azomethine H after dry‐ashing and with ICP‐AES after dry‐ashing. No significant interferences were found from 17 elements with ICP‐AES. A digestion procedure with only HNO₃, followed by ICP‐AES determination, gave low results at higher B levels. The HF‐HC1 extraction was applied to both fresh and dried material; the boron values thus obtained compared very well, which indicates that no loss of boron compounds occurs during drying.     

A phenol‐hypochlorite manual determination of ammonium‐nitrogen in Kjeldahl digests of plant tissue

Abstract

A phenol‐hypochlorite (Berthelot) procedure for determining NH₄‐N in acid digests of plant tissue is described. EDTA suppresses Cu interference and precipitation of hydroxides and phosphates. The oxidizing reagent includes an alkaline buffer to account for variations in acidity between digestion solutions, the main source of error in an unbuffered procedure. The reagent combinations and addition sequence employed allow for delays of up to at least 30 minutes between reagent additions without affecting the final colour intensity. The proposed procedure is as sensitive as similar methods used for determining NH₄‐N in natural waters and yields results which agree well with those obtained by steam distillation.     

Nitric acid digestion and multi‐element analysis of plant material by inductively coupled plasma spectrometry

Abstract

Inductively coupled plasma spectrometry (ICPS) was used for the simultaneous determination of P, K, S, Ca, Mg, Na, Al, Cu, Zn, Mn, Fe, Co, Mo and B in the nitric acid soluble portion of a variety of plant materials. Conditions for pre‐digestion, digestion and the requirement to grind cereal grain were investigated.

Digestion with nitric and perchloric acids caused loss of K (due to the low solubility of potassium perchlorate) and B (due to volatilization). The accuracy of Fe and Na determinations using nitric acid digestion was dependent upon the type of plant material.

The accuracy and precision of the proposed digestion and analytical procedure was confirmed by co‐operation in an interlaboratory quality assurance program using a variety of standard reference plant materials, and the analysis of National Bureau of Standards, Standard Reference Material 1571 (orchard leaves).     

Manganese‐iron interactions in the plant‐soil system

Dicotyledonous plants had significantly higher Mn and Fe intake rates on a near neutral soil, had a significantly higher Mn intake rate on a slightly calcareous soil, but had lower Mn and Fe intake rates on a calcareous soil, than monocotyledonous plants. This dependency on soil reaction suggests that dicots utilize primarily a chemical reduction mechanism, whereas monocots utilize some less pH‐dependent mechanism (possibly Mn(III)‐, Fe(III)‐organic complexation) to mobilize soil Mn and Fe. Soluble soil Mn and Fe fractions in the rhizosphere were consistently positively correlated with each other, as were Mn and Fe intake rates. These results suggest that for soil‐grown plants, Mn and Fe uptake was positively interrelated because both Mn and Fe were mobilized by similar root processes.     

Capability of Loss‐on‐Ignition as a Predictor of Total Organic Carbon in Non‐Calcareous Forest Soils

Abstract

Accurate analyses of large numbers of soil samples are needed in order to reduce the uncertainty of carbon inventories. Loss‐on‐ignition (LOI) is still considered the most convenient assessment method, but its accuracy and precision for predicting total organic carbon (TOC) is questioned. However, our estimation of measurement precision for different samples showed comparable relative standard deviations (RSDs) for LOI and TOC determinations. Highest precision was found in forest floor samples (RSD<1.2%) and lowest (RSD 5–10%) in sandy soil samples low in organic matter. Forest floor samples (n=66) and non‐calcareous mineral soil samples (n=654) were used to calibrate and validate predictive equations. Excellent linear relationships were found. For a wide range of soils the bivariate predictive equation TOC=?0.1046 Clay+0.5936 LOI (r²=0.98) was developed and validated. After correction for clay content, slopes averaged remarkably close to the traditional 0.58 conversion factor.     

Interrelationships of minerals in soil‐plant‐animal system at Kuti Ranch,Malawi

Abstract

An experiment was conducted in the central region of Malawi to study the relationship of minerals in soil‐plant‐animal systems to enable prediction of mineral status of beef cattle. Soil, forage and tissues (blood, bone and liver biopsy samples) were collected from cows at the same time in February, April, May, October and December for three consecutive years. Brahman x Malawi Zebu cows were supplemented with mono‐ and di‐calcium phosphate, salt and copper (plus cobalt and selenium) boluses.

Bone, liver and serum minerals (calcium, phosphorus, copper and zinc) correlated poorly to specific minerals in either forage or soil. A few minerals could explain more than 16% of their variation in animal tissues. Consequently, it was concluded that correlation coefficients among soil, plant and animal tissues are low or nonexistent. Therefore, until high, significant, reliable and reproducible correlation coefficients are established among soil, plant animal tissues, prediction of mineral status of animals by regression analysis from mineral content of soil or plants is likely to remain imperfect.     

Effects of autumn foliar application of 15n‐urea on nitrogen storage and reuse in apple 1

Effects of autumn foliar application of N‐urea on N storage and reuse in young apple seedling (Malus Pumila Mill.) were studied. Foliar application of urea^‐15 N (3.5%) during autumn enhanced the retranslocation of leaf N to other plant parts and increased stored N. Foliar N sprays increased the proteolytic activities of the leaves; therefore, such activities appear to be a major mechanism of retranslocation of leaf N. Foliar applied N enabled the plant to produce more growth during the following seasons. A considerable portion of the plant total N during second and third years was attributable to the foliarly applied N during the first year.     

Improved recovery of fluoride in plant material using a low temperature sealed chamber digestion technique in conjunction with a fluoride ion‐specific electrode

Abstract

Seven different sample preparation methods (five ashing and fusion methods, an acid digestion method, an oxygen flask combustion method) and the AOAC extraction method (975.04) were compared with a newly developed sealed chamber digestion method for the determination of fluoride (F) in vegetation. Subterranean clover tissue was the test material. Fluoride concentration in digests was measured using a F ion‐selective electrode. The sealed chamber digestion carried out with nitric acid in Teflon chambers at 120°C for 6 hours gave the highest F concentration in the plant material and the highest recovery of added F of all methods. Tests on several types of plant material confirmed the superiority of the closed chamber digestion. The superiority of the method is attributed to the complete solubilisation of F in the sample and elimination of losses of volatile F.     

Use of basic salts of iron and zinc as plant amend‐ments in soils

Abstract

In a greenhouse experiment, the effects of adding zinc (Zn) and iron (Fe) as either their basic salts or as commercial chelates were compared for the production of lettuce. The basic salts were found to be as effective as the chelates in providing Zn and Fe as well as being more environmentally safe.     

Stem‐infused nitrogen‐15 enrichment for evaluation of nitrogen use in maize

Abstract

Nitrogen use efficiency (NUE) of N fertilizer can be accurately estimated by tracing the fate of soil applied ¹⁵N‐labeling. However, 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 four levels of enriched ¹⁵N solution plus non‐infusion or infusion with water was conducted at Ottawa (45°22'N, 75°43'W), Canada to determine the effect of ¹⁵N atom % enrichment (a.e.) on physiological processes associated with NUE. At anthesis, 30 mL of 35.7 mmol N solution as ¹⁵NH₄ ¹⁵NO₃ at 5.0 (N05), 33.0 (N33), 66.0 (N66) and 99.2 (N99) ¹⁵N% a.e. was infused into the internode below the primary cob. The control plants were infused with distilled water. Photosynthesis was measured at 2, 4, 6, 24 h and 1 wk after infusion. Plants were sampled and separated into components at 4 d after anthesis (D4A) and at physiological maturity (PM). Dry weight, total N concentration, NH₄‐ and NO₃‐N, and ¹⁵N% a.e. of each component were determined. At D4A, the N33 and N66 treatments resulted in component ¹⁵N enrichment similar to that of N99 treatment. At PM, however, only N66 treatment produced results similar to that of N99. None of the infused ¹⁵N treatments interfered with ear‐leaf photosynthesis or component NH₄‐ and NO₃‐N concentrations. Infused ¹⁵N was easily moved out of the internode where it was infused, into most components, with the majority in the dominant sinks (cob, husk, and kernels). Nitrogen remobilization in both N66 and N99 treatments accounted for 62% of kernel N. These findings indicate that stem infusion is an appropriate approach to study N remobilization. Based on the concentrations investigated in this study, 66% or higher ¹⁵N% a.e. is required for accurate labeling when soil available N is high.     

Depletion of plant‐available silicon in soils: A possible cause of declining rice yields

Abstract

The phenomenon of yield decline in different rice ecosystems from many parts of the world has been reported to be associated with decreases in the effective nitrogen (N) supply from soil. However, many reports in the literature suggest that silicon (Si) is an agronomically essential element for sustainable rice production. Depletion of plant‐available Si in soils where rice is grown could be a possible limiting factor contributing to declining yields. In order to address this problem of yield decline or stagnation, it seems necessary to survey Si status of soils and rice grown in different ecosystems throughout the world and develop region‐specific integrated nutrient management systems that include the element Si.     

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.     

Evidence of depleted uranium‐induced hormesis and differential plant response in three grasses

General plant response to depleted uranium (DU) was tested using three widespread range‐grass species, Aristida purpurea Nutt. (purple threeawn), Buchloe dactyloides (Nutt.) Engelm. (buffalograss), and Schizachyrium scoparium (Michx.) Nash (little bluestem). Aboveground, belowground, and total biomass measures of these grasses were analyzed over the five different DU soil concentrations of 0, 50, 500, 5,000, and 25,000 mg kg^‐1. Differential plant response to DU was observed between the three grasses, wiith A. purpurea and B. dactyloides exhibiting a threshold‐type response in which no changes in biomass occurred until the highest treatment level of 25,000 mg kg^‐1 was reached. Schizachyrium scoparium, however, demonstrated a large degree of growth stimulation, or hormesis, at the 50 and 500 mg kg^‐1 DU concentrations. Several possible mechanisms of this hormetic response are offered.     

Evaluation of an anion‐exchange membrane for extracting plant available phosphorus in soils

Abstract

Anion‐exchange resins (AER) have been used to determine plant available phosphorus (P) since the fifties and their results have shown strong relationships with plant growth and P uptake irrespective of soil properties. However, this procedure is still not widely used by laboratories because of difficulties in handling resin beads under routine conditions. New kinds and different shapes of resins are being produced each with specific characteristics that must be evaluated before use in laboratory procedures. Thus the objective of this work was to evaluate an AER manufactured in membranes reinforced with a Modacrylic fabric. These anion‐exchange membrane (AEM) sheets are commercially available, making them suitable for soil testing. The membranes were cut in pieces (1.0×7.5 cm) identified as AEM‐strips. The AEM‐strips were soaked in 0.5M HCl for a few days and transferred, after being rinsed with deionized water (DI), to 0.5M NaHCO₃ to convert them to HCO₃ ^‐ form. The AEM‐strips and resin beads in nylon bags recovered 98.4 and 98.0% of the P content in an aqueous P solution, respectively. Three eluent solutions were evaluated with different shaking times. The 0.1M H₂SO₄ and 1.0M NaCl in 0.1M HCl were equally suitable for the molybdenum blue color development without any pH adjustment, while the pH of the 0.5M HCl was too low. The elution of P from the AEM‐strips was independent of time with a 15‐min shaking being adequate for removal of all P from the strips. A comparison of soil sample preparation demonstrated that it was not necessary to vigorously grind or sieve the soil to improve the repeatability of the results. The AEM‐strips were compared with other methods (Pi impregnated filter paper, Mehlich I and Bray 1) using 32 soils from Guatemala with widely varying physico‐chemical and mineralogical properties. Phosphorus extracted by the AEM and Pi procedures (similar principle) were highly correlated and gave similar results irrespective of soil type. The acid extraction (Mehlich I and Bray 1 methods) attacked soil components (apatites) resulting in higher and inconsistent amounts of P extracted which may not be available to plants; the correlation between these methods within soils of similar properties was good, but when all soils were considered together the relationship was not significant. This demonstrated that the acid extraction method for P is not suitable for soils containing apatites, while those based on a sink for P (AEM and Pi) can be applied irrespective of the type of soil.     

Comparison of phosphate‐phosphorus and total phosphorus in DTPA extracts for assessing plant‐available phosphorus in soilless potting media

Abstract

Hakea francisiana and H. laurina were grown in soilless media based on pine bark, to which had been added one of the following phosphorus (P) sources: crushed bone, rock phosphate, calcined rock phosphate, sewage sludge, or sludge compost. Available P was assessed through extraction with unbuffered 2 mM DTPA. Similar regression equations between shoot P content and P in 2 mM DTPA extracts of the media at potting were obtained for both total P in the extract (determined by inductively coupled plasma emission spectrometry) and PO₄‐P. The difference between them was small compared with the variation caused by different rates of dissolution of P the various sources during the growing period. Extractants give only an approximate guide to plant P uptake when the medium contains sources that slowly dissolve during the growing period. Nevertheless, the data indicate that, irrespective of P source, the maximum P concentration in a 2 mM DTPA extract (1:1.5 v/v) of the medium that is tolerated by P‐sensitive plants is 3–4 mg/L. This is similar to the concentration found previously for superphosphate as the source of P.