Evaluation of an assay of the free beta-subunit of choriogonadotropin and its potential value in screening for Down's syndrome

In this study I investigated the analytical and clinical performance of the measurement of the free beta-subunit of choriogonadotropin (hCG) in normal pregnancies and in pregnancies affected by Down's syndrome. Free beta-hCG in maternal serum has been shown to be increased in Down's syndrome-affected pregnancies and is proportionally increased in more cases than is total hCG. This study confirms previous findings of low concentrations of unconjugated estriol and alpha-fetoprotein in maternal serum in Down's syndrome-affected pregnancies. Using a multivariate risk analysis of maternal age and concentrations of alpha-fetoprotein, unconjugated estriol, and hCG in maternal serum, I determined that, at a risk cutoff value of 1 in 300, 52% of Down's cases could be detected with total hCG in the calculation, compared with 66% with the free beta-hCG concentration. The false-positive rate was 5.9% in both cases. Therefore, free beta-hCG can be used effectively in a screening program for Down's syndrome; however, further studies are required to ascertain whether the measurement of free beta-hCG has any advantages over the use of total hCG for detecting Down's syndrome.

Effect of xylazine in heifers under thermoneutral or heat stress conditions

A study was performed to assess the effect of xylazine HCl (0.1 mg/kg of body weight, IV) in heifers maintained at thermoneutrality (18 C, 42% humidity) or under heat stress (33 C, 63% humidity) conditions. Xylazine caused 50 and 70% decreases in serum insulin concentrations in the thermoneutral and heat-stressed heifers, respectively. Xylazine-induced hypoinsulinemia was associated with hyperglycemia. In the thermoneutral group, serum glucose concentrations increased from a basal concentration of 75 mg/dl to 150 mg/dl after 15 minutes. In the heat stress group, the serum glucose concentration increased from 65 mg/dl to 105 mg/dl. Hyperglycemia peaked at 2 hours and remained high for 6 hours after xylazine administration. Heat-stressed heifers took a longer time (107 minutes) to stand than did heifers under thermoneutral conditions (41 minutes). The time to regain sensation to pain was significantly prolonged in heat-stressed heifers. Xylazine had no effect on body temperature and respiration rate in heifers under the thermoneutral condition, whereas it markedly induced hyperthermia and suppressed respiration rate in the heat-stressed heifers. Furthermore, the pulse rate was slightly decreased in thermoneutral heifers and was markedly decreased in the heat-stressed heifers.

Assessment of the phosphorus status of oilseed rape by plant analysis

Phosphorus (P) concentrations in young plants of rapeseed (Brassica napus cv. Wesway) were related to seed and oil yields to develop a tissue test for the diagnosis of P deficiency. Critical P concentrations were defined as those concentrations required to sustain 90% of maximum yield. In 2 field experiments in successive seasons on a P-deficient soil, rates of triple superphosphate from 2.5 to 120 kg/ha were banded with the seed. The lowest P concentration in young shoots (17-19 weeks from sowing) associated with a P supply that was adequate for plant growth was approximately 0.31%. The youngest fully-expanded leaf was a reliable plant part to sample, its P concentration being about 0.05% lower than the concentration of the whole shoot. Critical P concentrations in young plants for sustaining 90% of maximum seed and oil yields were higher, namely 0.33 and 0.28% for whole shoots and youngest fully-expanded leaves respectively. The critical P concentration in seeds was about 0.35%.

Antenatal diagnosis of neural tube defects using a coated bead immunoassay for acetylcholinesterase in amniotic fluid

The development and validation of a coated bead immunoassay for amniotic fluid acetylcholinesterase is outlined. The assay has good precision (between assay CV of 6.8% within the normal range), and is linear up to 250 arbitrary units/L. The clinical validity of this assay has been assessed using a panel of amniotic fluid samples from normal and abnormal pregnancies. At an assay cut off level of 200 arbitrary units/L, all cases of neural tube defect-affected pregnancies were identified and the number of false positives was very small. False positives resulted from severe blood staining of the amniotic fluid. Since the monoclonal antibody used recognises red cell membrane acetylcholinesterase and the stored amniotic fluids had been frozen and thawed a number of times, the extent of this problem needs to be further assessed using freshly collected samples. The performance of this assay was found to be superior to the differential inhibitor colorimetric method and close to that of the electrophoretic procedure. The quantitative nature of the assay and the independence from operator technique makes it a useful adjunct to the measurement of amniotic fluid AFP in the prenatal diagnosis of neural tube defects.

Neurone specific enolase in amniotic fluid: a potential marker of anencephaly

Normal values for neurone specific enolase in amniotic fluid have been found to follow a non gaussian distribution with a 1-99 centile range of 1.10-4.32 micrograms/L. Neurone specific enolase levels have been shown to be raised in the amniotic fluid of pregnancies complicated by anencephaly, although not those complicated by open spina bifida. Neurone specific enolase measured by radioimmunoassay is capable of totally discriminating between normal pregnancies and those complicated by anencephaly. The study demonstrates the possible value of investigating other neuronal proteins which may find value as adjuncts to amniotic fluid Alpha fetoprotein levels in the prenatal diagnosis of Neural Tube Defects.

Screening for Down's syndrome using serum alpha fetoprotein: a retrospective study indicating caution

A report was made on the outcome of a four year retrospective study in 27 064 pregnancies, of the clinical efficiency, sensitivity, and specificity of a screening programme for Down's syndrome based on reported strategies related to the measurement of maternal serum alpha fetoprotein. This study identified 27 pregnancies affected by Down's syndrome with a median multiple of the median maternal serum alpha fetoprotein concentration of 0.82. This figure is considerably higher than that obtained from previous reports on this subject. With an age related multiple of the median maternal serum alpha fetoprotein strategy, 30.8% of Down's affected pregnancies were identified as well as 11.6% of unaffected pregnancies. Perhaps a United Kingdom collaborative study should begin to investigate the reasons for such wide population variance in the reports for the median multiple of the median for Down's affected pregnancies. Until such studies are carried out, screening for Down's syndrome based on low maternal serum alpha fetoprotein concentration is premature.

Development of a light-scattering immunoassay for thyroxine-binding prealbumin in plasma or serum

This paper describes the development of an assay for the measurement of thyroxine binding prealbumin in plasma or serum, based on the technique of fixed-time kinetic immunoturbidimetry with the Cobas Bio centrifugal analyser. The assay has good precision (coefficient of variation < 5%) and a detection limit of 15 mg l . The assay is rapid, economical, and the results compare well with those obtained by an established procedure. The technique has wide applicability to instruments which can make kinetic measurements and could prove useful in the clinical monitoring of patients receiving nutritional support and in the identification of nutritionally-at-risk groups prior to surgery. The assay further emphasises the sensitivity and usefulness of kinetic immunoturbidimetry for the measurement of low concentrations of proteins.

A preliminary testing of plant analysis procedures for the assessment of the sulfur status of oilseed rape

The effects of sulfur and nitrogen supply on the distribution of sulfur in oilseed rape (Brassica napus cv. Oro) grown in a sulfur-deficient soil in a glasshouse were examined to provide basic information for the development of a diagnostic test for sulfur status. Even though the traditional diagnostic indices (total sulfur and sulfate concentration) were directly related to sulfur supply and exhibited wide ranges in values between deficient and non-deficient tissue, they suffered a number of drawbacks in the case of oilseed rape. The shape of the yield/composition relationship precludes the use of either total nitrogen to total sulfur ratio or the proportion of the total sulfur present as sulfate in very young plants as indices for predicting the adequacy of sulfur supply up to first seed set. However, either index looked promising at 59 days from sowing, especially if specific plant parts were selected for analysis. For diagnosis of the current sulfur status the proportion of the total sulfur present as sulfate gave a good indication at each sampling date, and the critical value for the shoots was relatively stable with respect to age and nitrogen supply. Total nitrogen to total sulfur ratio was satisfactory as a diagnostic index for the 59-day-old plants only. Whilst the relationships established between the indices on one hand, and plant part, age and nitrogen supply on the other, should also apply in the field environment, the magnitude of the critical ratios requires confirmation for practical application.

The measurement of amniotic fluid alpha 2 macroglobulin by fixed time kinetic immunoturbidimetry

We have developed an assay for alpha 2 macroglobulin in amniotic fluid, based on the technique of Fixed Time Kinetic Immunoturbidimetry. The assay is precise (CV 5% between assays) and has a detection limit of 0.4 mg/l. We have determined the reference range for alpha 2 macroglobulin from 100 amniotic fluid samples from none Neural Tube Defect pregnancies. The data indicates no significant variation of alpha 2 macroglobulin with gestational age and that the results in none Neural Tube Defect pregnancies showed a narrow reference range with a mean of 1.67 mg/l and -/+ 2 SD range of 0.23--3.11 mg/l (99 percentile = 3.65 mg/l). Results in 25 Neural Tube Defect pregnancies are presented.

Improved discrimination in the detection of neural tube defects: five biochemical tests compared

Five biochemical tests, which have been proposed as possible adjuncts to the measurement of amniotic fluid alphafetoprotein for the identification of neural tube defects, have been measured in 49 normal and 46 neural tube defect affected pregnancies. One test, the alphafetoprotein component non-reactive with concanavalin A, was ineffective in differentiating normal and abnormal. The remaining four procedures, the activity of acetyl and total cholinesterase, the concentration of alpha 2 macroglobulin and the electrophoretic identification of acetyl cholinesterase effectively separated the normal and abnormal populations. The relative merits of these four latter tests in the evaluation of false positive and false negative amniotic fluid alphafetoprotein results, as well as in liquor samples with high alphafetoprotein levels associated with abnormalities not of neural origin, are discussed.

Immunonephelometric and immunoturbidimetric assays for proteins

Immunonephelometric and immunoturbidimetric techniques for the measurement of proteins have developed and expanded rapidly in recent years and are fast replacing the time-honoured gel precipitation techniques. The reasons for this are primarily an increased awareness of the value of specific protein measurements with the impetus of improved chemical reagents and advances in instrument technology. This review discusses the background to such free fluid phase immunochemical measurement systems and the developments which have occurred in this field. The following topics are reviewed. (1) The theoretical background of light scattering theory as applied to the measurement of antibody-antigen complexes. (2) The nature and kinetics of the antibody-antigen reaction in fluid media and the effect of enhancing polymers. (3) The sample and antibody requirements for nephelometric and turbidimetric assay. (4) Instrumental systems for nephelometry. (5) Instrumental systems for turbidimetry. (6) Methods of establishing, assessing and monitoring nephelometric assays for specific proteins in the laboratory.

Effect of sulfur application on selenium content of subterranean clover plants grown at different levels of selenium supply

To assess the feasibility of adding selenium to pastures likely to be associated with White Muscle Disease and related disorders in stock, plants of subterranean clover (Trifolium subterraneum L.) were raised in pots and supplied with rates of selenium (as selenate) and sulfur (as sulfate) in factorial combinations. On the soil used, increasing rates of selenium progressively depressed growth of clover and increased its selenium concentration; sulfur stimulated growth up to an addition of about 16 yg S/g and depressed the selenium concentration only when selenium was added. More sulfur was required to depress the selenium concentration to a threshold level, which was characteristic of a particular selenium application rate, at high initial selenium levels than at low. Clover growth was reduced when the sulfur to selenium ratio in the tops was less than 50: 1. Application rates greater than 0.025 �g Se/g soil (= 40 g/ha) produced young clover plants with excessive levels of selenium for consumption by stock. The safe rate for application to a mixed pasture is likely to be considerably less than that value. Field experiments confirmed that appreciable diminution of the selenium concentration in pasture as a result of sulfur addition occurred only when selenium was in plentiful supply. Grasses were much more affected than clovers. It is concluded that the negative interaction demonstrated between selenium and sulfur is of no practical significance when each is added at rates appropriate to the treatment of low sulfur-low selenium pastures.

Kinetic immunoturbidimetry of human choriomammotropin in serum

The sensitivity of kinetic immunoturbidimetry as a method for the measurement of specific proteins has been shown previously to be equivalent to 1 mg of analyte per liter. We confirm this in the method for human choriomammotropin described here. A relatively large sample volume is required, which results in other components of serum influencing the immunoprecipitin reaction. The technique is shown to be precise, and results compare well with those by a commonly available radioimmunoassay. The method performs well, as judged from results obtained for assayed quality control materials and in an external quality assurance program. The method is rapid (instrument assay time 120 s per sample), automated, and economical for routine use.

Kinetic immunoturbidimetry of human choriomammotropin in serum

The sensitivity of kinetic immunoturbidimetry as a method for the measurement of specific proteins has been shown previously to be equivalent to 1 mg of analyte per liter. We confirm this in the method for human choriomammotropin described here. A relatively large sample volume is required, which results in other components of serum influencing the immunoprecipitin reaction. The technique is shown to be precise, and results compare well with those by a commonly available radioimmunoassay. The method performs well, as judged from results obtained for assayed quality control materials and in an external quality assurance program. The method is rapid (instrument assay time 120 s per sample), automated, and economical for routine use.

Critical phosphorus levels in sunflower plants

To provide a basis for a tissue test for the diagnosis of P deficiency in sunflower crops, the influence of plant part and age on the critical P percentage (P concentration in tissues required to sustain 90% of maximum yield) was examined. In a glasshouse experiment, the known mobility of phosphate within the plant was reflected in the occurrence of the highest P concentration in the youngest leaves. Laminae contained more P than petioles on a dry-weight basis. Stem internodes contained less P than the adjoining petiole near the base ofthe plant but more near the apex. Three field experiments indicated that the lamina of the youngest fully-expanded leaf was a suitable plant part for diagnosis. Critical P concentrations for this tissue decreased from about 0.35% at the fourth week from sowing to 0.20% at the tenth week.

Sulfur and nitrogen fertilizer effects on wheat. I. Concentrations of sulfur and nitrogen and the nitrogen to sulfur ratio in grain, in relation to the yield response

Grain samples from a factorial (5 sulfur x 3 nitrogen treatments) field experiment with Olympic wheat, which showed yield responses to both factors, were analysed for total sulfur and nitrogen. Sulfur application increased the grain sulfur concentration more with high than with low nitrogen treatment, but had only small effects on the nitrogen concentration in grain. Nitrogen application increased the grain sulfur concentration at high but not low sulfur and increased grain nitrogen concentration at all sulfur treatment levels. The critical grain sulfur value for yield was 0.12% in treatments adequately supplied with nitrogen, but plots with low nitrogen (sulfur-unresponsive) also had grain sulfur values below 0.12 %. Grain from sulfur-responsive plants could be distinguished from grain from unresponsive plants because the former had less than 0.12% sulfur and nitrogen/sulfur ratios wider than 17/1. Results from a glasshouse experiment with three cultivars were consistent with this. The findings suggest that seed analysis may be a useful method for diagnosis of the sulfur status of cereal crops.

Kinetic immunoturbidimetric measurement of thyroxine binding globulin

We describe the extension of kinetic immunoturbidimetry to measurement of low-concentration proteins in serum, specifically thyroxine binding globulin. Method performance is superior to that of currently available direct assays for this protein by radioimmunoassay or the Laurell "rocket" techniques. The assay is rapid (1-min measurement period), economical, and results compare well with those by established techniques. The technique has wide applicability to instruments with kinetic measuring ability and could provide a useful support to other non-isotopic thyroid-function tests. The assay further emphasizes the sensitivity and usefulness of kinetic immunoturbidimetry for measuring low concentrations of proteins.

Kinetic immunoturbidimetric measurement of thyroxine binding globulin

We describe the extension of kinetic immunoturbidimetry to measurement of low-concentration proteins in serum, specifically thyroxine binding globulin. Method performance is superior to that of currently available direct assays for this protein by radioimmunoassay or the Laurell "rocket" techniques. The assay is rapid (1-min measurement period), economical, and results compare well with those by established techniques. The technique has wide applicability to instruments with kinetic measuring ability and could provide a useful support to other non-isotopic thyroid-function tests. The assay further emphasizes the sensitivity and usefulness of kinetic immunoturbidimetry for measuring low concentrations of proteins.

The variable influence of an alpha component in pregnancy plasma on four different assay systems for the measurement of pregnancy-specific beta1 glycoprotein

Four methods (radioimmunoassay, electroimmunoassay, laser nephelometry and kinetic immunoturbidimetry) have been evaluated for the measurement of proteins with pregnancy-specific beta1 glycoprotein immunoreactivity. The influence of two maternal plasma proteins with different electrophoretic mobilities (alpha2 and beta1) but with similar antigenic determinants has been assessed in each assay system. The radioimmunoassay method, which utilises a homogeneous preparation of pregnancy-specific beta1 glycoprotein for the preparation of iodinated tracer, and the kinetic immunoturbidimetric assay which measures antigen-antibody complex formation over the first minute of the reaction, were both considerably more specific for the beta1 component of pregnancy specific beta1 glycoprotein immunoreactivity than the laser nephelometric or electroimmunoassay methods.

Voluntary heart-rate changes mediated by muscle tension and respiration

20 undergraduates completed heart-rate mediation treatments (isometric exercise, relaxation, hyperventilation, and hypoventilation) with and without feedback. Heart rate increased during tension, decreased with relaxation, and changed even more with feedback. During hyperventilation the heart rates were lower than during hypoventilation, and this difference was even greater during trials with feedback. This paradoxical finding was attributed to the shallowness of the breathing. Additional data from an experiment on voluntary heart-rate control (n = 31) without feedback and one with biofeedback of heart rate (n = 18) showed that subjects were following heart-rate increase and decrease instructions with altered respiration rates. These observations are interpreted as indicating that biofeedback changes in heart rate are mediated by skeletal muscle tension, respiration, and other mediating mechanisms.

Kinetic immunoturbidimetry: the measurement of pregnancy specific beta 1 glycoprotein

The extension of kinetic immunoturbidimetry to the measurement of low concentration proteins has been described using the protein pregnancy-specific beta 1 glycoprotein. The technique has a precision superior to that of all other methods currently available. The assay is rapid, cheap and compares well with other published methods. The assay further emphasises the usefulness of the technique of kinetic immunoturbidimetry.

Kinetic immunoturbidimetry: the estimation of albumin

The applicability of commercially available antisera for use in kinetic immunoturbidimetry has been studied using the protein albumin as a simple model. The sensitivity of the kinetic immunoturbidimetric approach has been found to be comparable to published data for nephelometric systems, being able to detect concentrations of protein as low as 1 mg/l. The technique has shown to be as precise as most dye binding techniques for the measurement of albumin, producing a within batch C.V. of 1.0% and a between batch C.V. of 1.5%. The technique was found to be comparable to another immunological technique (RID). The fast assay time (30--60 sec), cost and good precision makes this the method of choice for routine albumin measurement. The extreme sensitivity of the technique of kinetic immunoturbidimetry makes the technique applicable to the estimation of a wide range of proteins in blood, urine and CSF.

A rapid kinetic assay for glucose using glucose dehydrogenase

An automated kinetic assay for the determination of glucose in blood is described. The method employs the enzyme glucose dehydrogenase in the presence of mutarotase, with nicotinamide adenine dinucleotide as hydrogen acceptor. The analytical parameters of the method are determined and the flexibility of the method in relation to sample volume and sensitivity is discussed. Finally, the method is compared with automated glucose oxidase and hexokinase procedures.

The diagnosis of sulphur deficiency in wheat

In a glasshouse experiment with wheat (Triticum aestivum L.), changes in the concentrations of total sulphur, sulphate sulphur, amide nitrogen, and total nitrogen/total sulphur ratio with age, plant part, and nitrogen and sulphur supply, were studied. This was done so that more reliable methods can be devised for the assessment of the sulphur status of this species.Each of the indices studied was strongly related to the current and subsequent sulphur status of the wheat plant. Amide nitrogen provided the greatest relative change in values between sulphur-deficient and sulphur-adequate plants, and on that basis was the most sensitive index. However, each of these indices had shortcomings which could preclude its general acceptance as a useful indicator of sulphur status. The most promising index of sulphur status was shown to be the proportion of total sulphur held as sulphate. This criterion was unaffected by nitrogen supply or plant age. The data suggest that wheat plants containing more than one-tenth of their sulphur as sulphate are adequately supplied with sulphur.

Problems associated with measuring sweat chloride concentration with an ion-specific electrode

The measurement of sweat chloride concentration was investigated by using the Orion 417 skin chloride electrode. The effects of variation in pilocarpine concentration, iontophoresis period, and sweat collection period were also investigated. The results show that the sweat chloride concentration is directly related to the amount of sweat produced. When the amount of sweat collected falls below a certain level, there is an apparent increase in sweat chloride concentration. A procedure is recommended for the measurement of sweat chloride concentration which offers good precision (coefficient of variation 9.8%) and the minimum of inconvenience to the patient.

Influence of reagent quality and reaction conditions on the determination of serum albumin by the bromcresol green dye-binding method

In an age of reference methodologies and sophisticated quality control techniques it is surprising that so little attention is paid to the quality of the reagents that are used. This paper reports on an investigation of the bromcresol green dye-binding procedure for the estimation of serum albumin in which particular attention has been paid to changes in the reagent components that contribute to the performance of the method. It has been shown that detailed attention to the quality control of the reagents can improve the precision and interlaboratory comparison in the estimation of serum albumin.

Flow cell modification of a filter fluorimeter producing improved throughput and precision

A modification of a Corning-EEL 244 filter fluorimeter to take a Hellma fluoronephelometric flow cell is described, and the characteristics of a standard flow cell and the Hellma flow cell are compared by the use of a continuous flow fluorimetric calcein-calcium method. The study shows that by this modification a considerable improvement in precision, carryover, and throughput is possible. The kinetically better Hellma flow cell enables speeds in excess of 70 per hour to be achieved with carryover and precision better than that obtained at 40 per hour with the standard flow cell. Curve regeneration of signals using the Hellma flow cell can also be carried out, enabling a further increase in analytical rate to be obtained.

Diagnostic indices for sulphur status of subterranean clover

The variations in total sulphur, sulphate sulphur, and total nitrogen/total sulphur ratio, (N/S)t, in subterranean clover (Trifolium subterraneum L.) with age of plant, nutrient status, and plant part were studied in a glasshouse experiment on a sulphur-deficient soil. The concentrations of total sulphur and sulphate sulphur in the plant increased with increasing sulphur supply and decreased with plant age or with supplemental nitrogen. Overall, the laminae contained a higher concentration of total sulphur than the petioles; when the optimal concentration for growth was present, the concentration in the laminae was approximately twice that in the petioles. In sulphur-deficient plants there was little difference between the sulphate concentrations in laminae and petioles. In young sulphur-sufficient plants, higher concentrations were found in the petioles than in the laminae but this was reversed for the older plants. With increasing sulphur supply there were bigger relative increases in sulphate than in total sulphur and the magnitude of both these fractions changed more in petioles than in laminae. In general, the (N/S)t ratio increased with age of plant or supplemental nitrogen, and decreased with increasing sulphur supply. The changes with age were smaller in the laminae than in the petioles. Petioles had a higher ratio than laminae in sulphur-deficient clover, and a lower ratio where sulphur was adequate. Critical concentrations of total and sulphate sulphur in the tissue were lowered by extra nitrogen, fell markedly as the plant aged, but were not much affected by the maturity of the plant part. The (N/S)t ratio changes less with all factors than the other two indices, and thus promises fewer problems in interpretation.

A study of factors influencing continuous flow kinetics: the use of serum calcium estimation as a model

Previous studies of continuous flow kinetics have described an "AutoAnalyzer" peak in terms of two time constants, lag constant "a" and exponential constant "b". Further investigations described here define some of the factors which affect these constants and hence peak shape and analytical performance. This communication outlines the application of this information to the development of an automated method for the determination of serum calcium, having a carry-over of less than 1% and an analytical rate greater than 100/hour. The instaneous colour reaction, simple hydraulics, removal of the dialysis step, and the use of an integral debubbling flow cell have enabled small kinetic constants to be achieved. Over a period of three months' routine use between-batch co-efficient of variation (C.V.) was 1.4%.

An assessment of the nutrient status of soils in northern East Gippsland

Likely nutrient disorders were identified in an omission-type pot trial with white clover. The soils, taken from four virgin sites, were developed on the four main parent materials in the area, viz., tuff, basalt, shale, and granite. All were deficient in phosphorus and sulphur; three were deficient in molybdenum (the exception was the granitic soil), but only the granitic soil was deficient in copper. No other nutrients were deficient or in toxic amounts for clover growth, but oats responded to nitrogen on all four soils. The variability between soils sharing similar parent materials was studied in four easily defined suites by interpreting the analysis of 12 samples from each suite. Soils derived from acid volcanic rocks were consistently moderately acid, deficient in P, S, and Mo but variable in K and Cu status. Soils derived from basalt were typically less acid than those of the previous suite, had a wide range in P, K and Mo status, contained adequate Cu, but were consistently deficient in S. Soils derived from sedimentary rocks were typically moderately acid, consrstently deficient in P, S and Mo, but were variable in K and Cu status. The granitic soils ranged from moderately acid to neutral in reaction, had a wide range in P status and K status, were consistently deficient in S and often in Mo or Cu. The phosphorus sorption capacity was consistently low in the granitic soils but very variable in the other suites. Estimates of the amount of phosphorus required as a corrective dressing in the field suggest consistently low requirements by the granitic soils (10-30 kg P ha-1) whereas requirements ranged up to 120 kg P ha-1 in the other suites.

Factors in the molybdenum and phosphorus status of soils on the Dorrigo Plateau of NSW

Samples of 50 virgin surface soils were collected from the Dorrigo Plateau of New South Wales within the 90-220 cm rainfall zone. The parent rocks were granites, sediments, basalt, and trachyte. The soils were used in a pot trial in which clover plants were grown with and without added molybdenum or phosphate. Laboratory measurements were made of the soils' ability to adsorb molybdate and phosphate and of extractable molybdate and phosphate. Regression equations, which included terms both for adsorption, and for extractable molybdate or phosphate, gave a good description of the yield of clover plants grown on the soils without added molybdate or phosphate, respectively. The ability of the soils to adsorb molybdate and phosphate increased with annual rainfall. The apparent influence of rainfall on adsorption was greater for soils derived from basalt or trachyte than for soils derived from granite or sedimentary rocks. Oxalate-extractable molybdate was lower in soils derived from sedimentary rocks than from basaltic or trachytic rocks. Soils derived from granite varied widely, two having very high contents. Fluoride-extractable phosphate was very low in soils derived from trachyte, granite, and sedimentary rocks, reflecting the phosphorus levels in the parent rocks. Fluoride-extractable phosphate was also low on the krasnozems despite large variations in the phosphate content of the parent rock. On the other basaltic soils the extractable phosphate was directly related to the phosphate content of the parent rock.

Assessment of the phosphorus and sulphur status of subterranean clover pastures. 2. Soil tests

Values obtained by a number of established soil test procedures for phosphorus and sulphur were correlated with yield responses to addition of the relevant nutrient, by subterranean clover-based pastures at 21 sites in south-eastern New South Wales. Colwell's bicarbonate-soluble P and Bray's P, phosphorus values showed sufficiently close associations with response to added phosphorus to be useful for predictive purposes ; Bray's P, values generally gave smaller coefficients. In general, the pasture on soils testing less than 25 p.p.m. bicarbonate-extractable P in the surface three inches responded appreciably to applied phosphorus (relative yields were <85 per cent). The corresponding value for the Bray P, procedure was 10 p.p.m. P. Soil samples from 0-1, 0-3, and 3-6 inch depths gave similar correlations with response. The time of soil sampling did not affect the relationships but winter pasture production was not as closely related to soil test values as was spring production. By contrast, soil tests for sulphur were not reliable but some discrimination between soils could be made with a 500 p.p.m. phosphate extraction. Values from soil samples collected in the winter were less closely related to response than were values from samples collected in the autumn.

Assessment of the phosphorus and sulphur status of subterranean clover pastures. 3. Plant tests

Field experiments were carried out in south-eastern New South Wales to establish the relationships between three plant tests for phosphorus and for sulphur, and the yield responses of subterranean clover pastures to applied phosphorus and sulphur. Subterranean clover plants (CV. Mt. Barker), sampled early in the growing season of 1963 and on five occasions at approximately monthly intervals in 1964, were analysed for total and soluble phosphorus and for total and reducible sulphur. The third plant test involved a comparison of the leaf area responses measured seven days after transfer to appropriate nutrient solutions of clover plants sampled in the field plots at the beginning of each growing season. Correlation coefficients (R) varying from 0.546 to 0.908 were obtained for the curvilinear regression of relative yields on total phosphorus contents of the clover, but only under conditions of an adequate sulphur supply. The correlation coefficients for soluble phosphorus were generally lower and differed greatly between samplings. The correlation coefficients for the curvilinear regressions of yield responses on the total or reducible sulphur content of clover, under conditions of ample phosphorus supply, were never less than 0.606 at the end of the season, and for some of the earlier samplings were as high as 0.947. The correlation coefficients (r) between leaf area responses and yield responses to phosphorus were 0.576 and 0.716, and those for sulphur 0.710 and 0.692 in 1963 and 1964 respectively. In contrast to those based on leaf analysis, the relationships between leaf area responses and yield response for each one of the elements were not affected by the level of supply of the other element.

The residual value of a sulphatic fertilizer applied to a basaltic soil

Yield responses d a native pasture on a basaltic soil near Willow Tree, New South Wales, were measured in the second, fourth, and seventh years after the application of several rates of calcium sulphate in the first year. The value of the residues declined sharply at first and then more slowly. Fifty per cent of the potential response by the legumes (the responsive component of the pasture) was achieved by an application of 7lb of sulphur an acre in the first year ; residues from an application of 20 lb of sulphur an acre were required in the second year, and from 48 lb S of sulphur an acre in the fourth year, to obtain the equivalent responses. By the seventh year, effects were too small to allow the derivation of a comparable figure.

A comparison of several procedures for estimating the sulphur status on soils

The sulphur status of a number of soils was determined by several laboratory procedures. The chemical procedure which extracted amounts of sulphur showing the most satisfactory correlation with the sulphur-supplying ability of the soils (as measured by plant growth) was an extraction of the soil with a potassium dihydrogen phosphate solution containing 500 p.p.m. phosphorus. The superiority of this procedure over the other extraction procedures tested (cold-water extraction, hot-water extraction, acetate extraction, and Williams and Steinbergs's heat-soluble method) probably lies in its ability to displace adsorbed sulphate. The sulphate which was extractable by the phosphate solution was found to have decreased after cropping, by an amount which was closely related to, but not of the same order as, the sulphur taken up by the plants. The difference (uptake minus decrement), which represents the net mineralized sulphur, was small relative to the amounts of extractable sulphate initially present. Microbiological assay using Aspergillus niger was an equally reliable method for assessing sulphur status and had the advantage of simplicity. Except in two brigalow soils, the sulphur obtained by Aspergillus was very similar to that extracted by phosphate, which suggests that Aspergillus is able to obtain adsorbed sulphate.

Soil sulphate changes in the presence and absence of growing plants

To determine whether sulphate addition to sulphur-deficient soils affects mineralization of organic sulphur, an experiment was conducted in undrained pots with five soils of differing properties. Initial and final extractable soil sulphate (water-soluble and adsorbed), and sulphur taken up by Phalaris tuberosa L., were measured. Where plants were grown, mobilization of the organic sulphur occurred at the nil, 4 p.p.m., 12 p.p.m., and 36 p.p.m. levels of sulphate sulphur addition in four out of the five soils. In the fifth soil, a lateritic krasnozem, only at the nil and 4 p.p.m. levels was there any net release of sulphate. All five soils immobilized added sulphate at the 108 p.p.m. level. In the absence of plants, with one exception, no net mineralization of organic sulphur occurred following additions of sulphate. In the pots without added sulphate there was slight mineralization (less than under plants) in all soils but the lateritic krasnozem. The modifying effect of growing plants is obviously of great significance in the cycling of sulphur in soil. The relative intensity of immobilization and mineralization was affected by the presence of growing plants. This effect was probably due to the activities of rhizosphere microorganisms.

Growth and chemical composition of white clover as affected by sulphur supply

Plants of white clover (Trifolium repens L. var. Ladino) were grown in sand culture with four levels of sulphur supply. Growth increased with increasing sulphur supply, all plants except those at the highest sulphur level showing deficiency symptoms. As the severity of the deficiency increased, the root system formed a proportionately larger part of the plant, and the stems and petioles smaller proportions; the proportion of the whole plant formed by the laminae was reduced to only a slight extent. Nitrogen and sulphur fractions were examined in the laminae, nitrogen at each of three harvests and sulphur at the second harvest. The percentages of protein nitrogen and of total nitrogen increased as sulphur supply increased, protein nitrogen forming a greater proportion of the total nitrogen at the higher sulphur levels. In contrast, protein sulphur formed the bulk of the total sulphur in deficient plants, but as sulphur supply approached an adequate level for growth, there was a marked increase in non-protein organic sulphur and a smaller increase in sulphate sulphur. In this respect, white clover appears to differ from legumes other than Trifolium spp. and from non-legumes, all of which accumulate sulphur mainly as sulphate.