Charles A. Shand

A procedure for the simultaneous oxidation of total soluble nitrogen and phosphorus in extracts of fresh and fumigated soils and litters

Abstract An autoclave method based on the oxidation of dissolved organic matter with alkaline persulphate for the analysis of total soluble nitrogen (N) and phosphorus (P) in 0.01M calcium chloride (CaCl2), 0.5M potassium sulfate (K2SO4), or 0.2M sulfuric acid (H2SO4) extracts of fresh and fumigated soils is described. Autoclaving at 110°C for 30 min oxidized N at 50 mg N/dm3 from urea, glucosamine, and the sodium salt of ethylenediaminetetra‐acetic acid (EDTA) to nitrate (NO3). Recoveries decreased with increasing concentrations of total organic carbon (TOC), hence glucosamine and EDTA required an increased concentration of persulphate. Tests with added glucose showed that recovery of urea N was complete up to a carbon (C) concentration of 100 mg/dm3. For P, it was important that solutions of 0.01M CaCl2 were acidic after oxidation to avoid the precipitation of appatite. Recoveries of P from orthphosphate and inositol hexaphosphate dodeca sodium salt in water or in 0.2M H2SO4 were complete after oxidatio...

Phosphorus fractions in soil solution: Influence of soil acidity and fertiliser additions

The influence of soil acidity and phosphorus fertilization on phosphorus fractions and dissolved organic carbon (DOC) in soil solution was quantified experimentally in an iron humus podzol. Soil solution was isolated by centrifugation from top- and sub-soil samples. Total dissolved phosphorus (TDP), dissolved reactive phosphorus (DRP), dissolved organic phosphorus (DOP) and DOC increased as soil pH and P status increased. DOP was the fraction present at the highest concentration (0.080–0.464 mg P L−1) for the majority of samples. DOC and DOP concentrations which remained relatively constant down the soil profile were also highly correlated. Soluble organic P compounds may make a significant contribution to plant available soil P particularly for soils with low fertility levels. The relatively high DOP concentrations (ca 0.227 mg P L−1) found throughout the soil profile have important consequences with regards to P leaching and plant nutrition.

Distribution of radiocaesium in organic soils

Abstract Radiocaesium added to organic soils remains plant-available far longer than might be predicted from the behaviour of the element in mineral soils. To investigate this, the distributions of radiocaesium added to a low-ash peat and a peaty podzol were studied using sequential extraction with ammonium acetate, sodium pyrophosphate, sodium hydroxide, and ammonium acetate after peroxidation. Comparisons were made with the distribution reported for mineral soils. Changes in distribution between soil phases with time were measured on a sequence of samples treated with radiocaesium over a period of 4 years. Extractions were performed on soils pretreated with HF to remove mineral matter, on soil fractions enriched or depleted in mineral matter isolated physically by means of wet sieving, and on soil fractions obtained by density separation with chloroform and ‘Nemagon’. These experiments showed that, even in a highly organic peat, the mineral components were important for the eventual fixation of radiocaesium. Oxidizable organic matter corresponding to humin also strongly retained caesium.

Use of 31P-NMR to study the forms of phosphorus in peat soils

31P-NMR has been used to characterise the major forms of organic and inorganic phosphorus in soil derived alkali extracts and humic acids. Blanket peat, which had been under different fertilisation treatments for 10 years was compared with an agricultural mineral soil. In the mineral soil the phosphorus was shown to be in the form of inorganic orthophosphate and phosphate monoesters whereas the peat soil also contained phosphate diesters and other inorganic forms of phosphorus. Changes in various phosphorus pools in the peat soils were shown to correlate with differences in fertilisation regime and land management practice. Fertilisation with superphosphate increased phosphate monoester content in the peat, although vegetation type appeared to have greater impact on the phosphate monoester concentration. The degree of microbial activity, as indicated by the presence of polyphosphates and absence of phosphonates, correlated positively with vegetational improvement and fertilisation of the peat soils.

Recovering phosphorus from soil: a root solution?

Marc I. Stutter,*,† Charles A. Shand,† Timothy S. George,† Martin S. A. Blackwell,‡ Roland Bol,‡ Regina L. MacKay, Alan E. Richardson, Leo M. Condron, Benjamin L. Turner, and Philip M. Haygarth †The James Hutton Institute, Aberdeen, AB15 8QH, U.K. and Dundee, DD2 5DA, U.K. ‡Rothamstead Research North Wyke, Devon, EX20 2SB, U.K. College of Life Sciences, University of Dundee, Dundee, DD1 5EH, U.K. CSIRO Plant Industry, Black Mountain, Canberra, ACT 2601, Australia Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln 7647, Canterbury, New Zealand Smithsonian Tropical Research Institute, Republic of Panama Lancaster Environment Centre, Lancaster University, LA1 4YQ, U.K.

The determination of mercury in soils and related materials by cold-vapour atomic absorption spectrometry

Abstract A method for the determination of mercury in soils and related materials, by the cold-vapour, reduction-aeration absorption technique, is described. The mercury in the reduced sample solution is partitioned, by agitation, between the liquid phase and a fixed volume of air which is then blown through an absorption cell for measurement. Three preparative methods were developed, two of which use acid digestion and wet oxidation and the other direct oxidation in an oxygenflask combustion technique. Comparative analysis of natural samples by the three methods was used to validate the techniques developed, since no authenticated reference samples were available. For 1-g samples, the analytical range was 0.01–0.5 p.p.m.

Temporal changes in C, P and N concentrations in soil solution following application of synthetic sheep urine to a soil under grass

We have determined the temporal changes in the concentration of dissolved organic carbon (DOC) and P and N components in soil solution following application of synthetic sheep urine (500 kg N ha-1) to a brown forest soil in boxes sown with Agrostis capillaris. Three contrasting defoliation treatments (no cutting, single cut before urine application and regular cutting twice per week) plus a fallow soil were studied. The synthetic urine contained 15N labelled urea and was P-free. Intact soil cores were taken after 2, 7, 14, 21 and 56 d and centrifuged to obtain soil solution. The urea in the synthetic urine was rapidly hydrolysed in the soil, increasing soil solution pH, DOC and total dissolved phosphorus (TDP) concentrations. For the regularly defoliated sward, DOC and P reached maximum concentrations (4000 mg DOC L-1 and 59 mg TDP L-1) on day 7. From their peak values, pH and DOC and P concentrations generally decreased with time and at day 56 were near those of the control. Concentrations of NH4+ and NO3- in the no-urine treatments fluctuated and the greatest treatment differences were between the fallow soil and the soil sown with grass. Adding synthetic urine increased NH4+ concentrations during the first week, but NO3- concentrations decreased. This was consistent with the 15N labelling of the NO3- pool which required 3 weeks to reach that of 15NH4+. Dissolved organic nitrogen (DON) reached a maximum value at day 7 with a concentration of 409 mg N L-1. The DON in soil solution contained no detectable amounts of 15N label indicating that it was derived from sources in the soil. Differences in soil solution composition related to the effect of the other cutting treatments and the fallow treatment were small compared to the effect of synthetic urine addition.

Determination of dissolved organic phosphorus in soil solutions by an improved automated photo-oxidation procedure

An improved automated photo-oxidation procedure to determine dissolved organic phosphorus in soil solutions is described. Organically combined phosphorus is converted quantitatively to orthophosphate under UV radiation and an excess of dissolved oxygen. The orthophosphate is determined spectrophotometrically using the Murphy and Riley procedure, modified by increasing the concentration of ascorbic acid. Fluoride was added to the system to overcome potential interference when working with soil solution. The limit of detection was 0.64 mug/l. PO(4)(-3) -P and calibration was linear over the range studied (5-1000 mug/l. PO(4)(-3) -P).

Phytoavailability of Cd and Zn in soil estimated by stable isotope exchange and chemical extraction

The distribution of labile Cd and Zn in two contrasting soils was investigated using isotopic exchange techniques and chemical extraction procedures. A sewage sludge amended soil from Great Billings (Northampton, UK) and an unamended soil of the Countesswells Association obtained locally (Aberdeen, UK) were used. 114Cd and 67Zn isotopes were added to a water suspension of each soil and the labile metal pool (E-value) determined from the isotope dilution. Samples were obtained at 13 time points from 1h to 50 days. For the sewage sludge amended soil, 29 μg Cd g−1 (86% of total) and 806 μg Zn g−1 (65% of total) were labile and for the Countesswells soil the value was 8.6 μg Zn g−1 (13% of total); limits of detection prevented a Cd E-value from being measured in this soil. The size of the labile metal pool was also measured by growing plants for 90 days and determining the isotopic content of the plant tissue (L-value). Thlaspi caerulescensJ. & C. Presl (alpine penny cress), a hyperaccumulator of Zn and Cd, Taraxacum officinale Weber (dandelion) and Hordeum vulgare L. (spring barley) were used. L-values were similar across species and lower than the E-values. On average the L-values were 23±0.8 μg Cd g−1 and 725±14 μg Zn g−1 for the Great Billings soil and 0.29±0.16 μg Cd g−1 and 7.3±0.3 μg Zn g−1 for the Countesswells soil. The extractable metal content of the soils was also quantified by extraction using 0.1 M NaNO3, 0.01 M CaCl2, 0.5 M NaOH, 0.43 M CH3COOH and 0.05 M EDTA at pH 7.0. Between 1.3 and 68% of the total Cd and between 1 and 50% of the total Zn in the Great Billings soil was extracted by these chemicals. For the Countesswells soil, between 6 and 83% of the total Cd and between 0.1 and 7% of the total Zn was extracted. 0.05 M EDTA and 0.43 M CH3COOH yielded the greatest concentrations for both soils but these were less than the isotopic estimates. On the whole, E-values were numerically closer to the L-values than the chemical extraction values. The use of isotopic exchange provides an alternative estimate of the labile metal pool within soils compared to existing chemical extraction procedures. No evidence was obtained that T. caerulescens is able to access metal within the soil not freely available to the other plants species. This has implications for long term remediation strategies using hyperaccumulating plant species, which are unlikely to have any impact on non-labile Cd and Zn in contaminated soil.

Uptake and transport of phosphorus by Agrostis capillaris seedlings from rapidly hydrolysed organic sources extracted from32 P-labelled bacterial cultures

Cultures of the soil bacterium Serratia liquifaciens grimesii were grown with32 P labelled phosphate, to produce a uniformly32 P labelled source of microbial P. Extracts of the bacteria were prepared by sonication, dialysis and filtration to provide a clear sterile solution which was characterised in terms of dissolved organic and condensed P (DOP and DCP) and molecular weight range. The extract was used as a source of P to Agrostis capillaris L. seedlings in nutrient solution from which orthophosphate was omitted. In a time course experiment, root surface phosphatase activity increased as soon as extract was added to the root medium, DOP was rapidly hydrolysed and orthophosphate concentration increased rapidly. These processes were complete within about 8 h, after which phosphatase activity fell to its original level, and the plants absorbed molybdate reactive P from the nutrient solution so that it reached its original concentration over 48 h. DCP concentrations did not change significantly throughout the experiment. This work clearly demonstrated that DOP but not DCP, as a component of a bacterial extract produced by a relatively straightforward method, was quickly hydrolysed and the P made available for plant uptake.