C. W. Gray

Atmospheric accessions of heavy metals to some New Zealand pastoral soils

Total heavy metal deposition was monitored at seven rural sites across New Zealand to determine the rate of atmospheric deposition of heavy metals to soils and to evaluate any regional and temporal variations in metal deposition. Heavy metal deposition was collected monthly in Warren Spring Laboratory type inverted frisbees. The rate of heavy metal deposition followed the order Zn>>Cu>Cr>Pb>Ni>>Cd. There were no obvious trends with regards to either seasonal or spatial deposition for any of the heavy metals measured. With the exception of Zn, heavy metal deposition in New Zealand was generally lower than rates measured in other countries. This reflects the general lack of high temperature industrial processes from urban-based industrial processes that are an important source of heavy metal aerosols in other industrialised regions worldwide. The inverted frisbee technique used provides a reliable indication of the magnitude of deposition of heavy metals from the atmosphere at a reasonable cost and with manageable logistical effort for a national survey.

The effect of long-term phosphatic fertiliser applications on the amounts and forms of cadmium in soils under pasture in New Zealand

This paper presents the results of an investigation into the rate of Cd accumulation and changes in forms of Cd in a soil that has been subjected to long-term superphosphate fertiliser application. Results indicate that there had been a significant accumulation of Cd in the soil during the past 44 years. On the high fertiliser treatment (376 kg superphosphate ha-1 yr-1), Cd was estimated to have accumulated at a rate of 7.8 g ha-1 yr-1. During the course of the trial, there was an increase in the proportion of Cd associated with exchangeable and soil organic matter fractions on the fertilised plots, which was related to a corresponding increase in soil organic carbon levels. Results also indicate that although there was a large proportion of added Cd associated with the organic fraction, the concentration of applied Cd occurring in the residual fraction was also substantial (i.e >25% of added Cd). In addition, an investigation into the effects of residence time of Cd in the soil indicated that there was a redistribution of Cd into less soluble forms with time (i.e. residual Cd), along with a decrease in total soil Cd concentrations. There was also evidence of movement of Cd down the soil profile in this irrigated soil. The implications of these results for Cd phytoavailability are discussed.

Effect of soil pH on cadmium phytoavailability in some New Zealand soils

Abstract The effect of soil pH on plant cadmium (Cd) concentrations was investigated in a glasshouse study, in conjunction with an evaluation of eight soil extractants as predictors of Cd concentrations in different plant species. Results showed that in general, increasing soil pH from 5.5 to 7.0 significantly decreased Cd concentrations in clover, lettuce, carrot, and ryegrass, and to a lesser extent in wheat, although the magnitude of the reduction varied between plant species and soil types. Soil extractants which were sensitive to soil pH e.g., 0.05M Ca(NO3)2, IMNH4CI, and O.O5MCaCl2 or extract moderate amounts of Cd e.g., IA/NH4OAC and 0.04M EDTA were found to be the most effective in predicting plant Cd concentrations. Cd solubility as predicted using a semi‐empirical equation which contained terms for pH, organic matter, and total Cd concentration was also found to be successful in estimating plant Cd concentrations for a number of plant species. It appears that pH may be a powerful tool in the man...

Cadmium concentrations in some New Zealand wheat grain

Abstract The variation in wheat (Triticum aestivum L.) grain cadmium (Cd) concentrations between different cultivars was investigated along with a preliminary ranking of soil properties in terms of their importance in controlling wheat grain Cd concentrations. Results indicate that there is considerable variation in Cd concentrations in New Zealand wheat grain samples. The mean Cd concentration for wheat in this study is 54 μg kg1 fresh weight (FW). Ten percent of the grain samples examined in this study are non‐compliant with the maximum permissible concentration (MPC) for Cd in wheat grain. However almost 50% of non‐compliant samples were found at a single site, and at a number of sites no samples exceeded MPC. There was a 4‐fold range in the abilities of different wheat cultivars to accumulate Cd in grain. There was also seasonal variation in Cd uptake for wheat cultivars grown at the same site. Extractable soil Cd using a weak salt reagent yielded the highest correlation with grain Cd concentrations in spring wheat across all soils, whereas no significant relationships were found for winter wheat. There were no significant simple correlations between major soil properties and wheat grain Cd concentrations for either winter or spring wheat. For winter wheat, a multiple regression model with terms for total zinc (Zn) and CaCl2‐extractable Cd yielded the highest correlation with winter wheat Cd concentrations (r2 = 0.59 P < 0.05). Low Cd accumulating wheat cultivars can be selected for use at sites where the Cd concentration in grain exceeds the MPC. Future work is required to determine which soil properties are important in controlling wheat grain Cd concentrations.

Fractionation of soil cadmium from some new zealand soils

Abstract The concentrations and forms of soil cadmium (Cd) in 12 different New Zealand topsoils were investigated using a sequential fractionation procedure. Total soil Cd concentrations were low and ranged between 0.03 μg g‐1 to 1.34 μg g‐1 and were highly correlated with total soil phosphorus (r2=0.85, P<0.01). Results indicated that there was a wide range in the concentrations of Cd associated with individual soil fractions and large variations between soils. On average for all soils, the smallest proportion of Cd was in exchangeable forms, i.e., 3%, with 12% in the crystalline oxide fraction, 13% in the amorphous oxide fraction and the greatest proportion of Cd associated with the organic 34% and residual 38% fractions. There was evidence to show that a soil extractant which is commonly used to predict plant uptake of Cd from soils, i.e., 0.04 M ethylene diamine terra acetic acid (EDTA), extracts Cd from both exchangeable and organic forms of soil Cd.

Effect of nitrogen fertiliser applications on cadmium concentrations in durum wheat (Triticum turgidum) grain

Abstract The effect of different rates of nitrogen (N) fertiliser application on cadmium (Cd) concentrations in the grain of two durum wheat (Triticum turgidum L.) cultivars was investigated at three different field trial sites in Canterbury, New Zealand. The mean Cd concentration in this study was 66 μg kg−1 fresh weight (FW), which is 30% below the maximum level (ML). Uptake of Cd was higher in ‘CRDW17’ compared with ‘Waitohi’ at all three sites. Also increasing amounts of calcium ammonium nitrate (CAN) fertiliser increased the Cd concentration in durum wheat grain at all three sites. Wheat grain Cd concentrations were not found to be related to any measured soil properties. Grain Cd concentrations were in most instances positively correlated with total biological yield (TBY). This response may be the result of the combined effects of fertiliser salts on ionic composition of the soil solution, and increased root interception and enhanced mass flow of Cd related to increased TBYs. The evidence suggests that it is TBY rather than grain yield that is more important with regards to Cd uptake in durum wheat.

The effect of ryegrass variety on trace metal uptake

Abstract Trace metal deficiencies in soils can have adverse effects on plant production and animal health. Conversely, trace metals at elevated concentrations in soils can be phytotoxic. The exploitation of intraspecies variation in plant trace metal accumulation may be one way to manage both trace metal deficiency and phytotoxicity that can occur in some soils. An investigation was undertaken to determine the variation in Co, Cd, Ni, Cu, Zn, Mn, and Fe uptake in different ryegrass varieties. Eleven different ryegrass varieties were grown in a glasshouse experiment on two soils that contained elevated or background metal concentrations. We found that there was up to a 2.5‐fold range in trace metal concentrations between ryegrass varieties grown on the contaminated soil, with the short rotation/annual ryegrass varieties, i.e., ‘Flanker’, ‘Tabu’, and ‘Archie’, generally accumulating significantly smaller amounts of Cd, Zn, Ni, Mn, and Co than the other varieties tested. Metal uptake in the uncontaminated soil indicated much smaller differences between varieties. Dilution effects could in part explain the differences in metal concentrations between varieties for the contaminated soil, however there were no relationships between yields and trace metal concentrations for uncontaminated soil. It appears that there may be potential for selecting ryegrass varieties for the management of trace metal uptake in pasture soils, however further evaluation of results in field trials is required.

Effects of air drying or sample storage on soil-solution properties of biosolids-amended soil

Accurate measurements of heavy metal soil-solution concentrations in soils are important for studies of metal bioavailability. The effect of air-drying or storage of field-moist soil samples at 4°C for up to 64 d on copper (Cu), nickel (Ni), and zinc (Zn), macronutrient cation and anions, and soluble organic carbon (SOC) concentrations in soil-solutions was determined using soils sampled from experimental field plots amended 3 y previously with Cu-, Ni-, or Zn-spiked biosolids. The soil at the field site was a Templeton fine sandy loam (Udic Ustochrept), and each of the three metals was applied at 4 different rates (12 plots in total). All data were subjected to analysis of variance, and comparisons between post-sampling treatments for major nutrient cations and anions and SOC were based on mean values from all 12 field plots. The Cu, Ni, and Zn treatments were not replicated in the field, and post-sampling treatment comparisons for soil-solution Cu, Ni and Zn were based on the means of triplicate determinations of single samples. The concentrations of cations (Ca2+, Mg2+, K+, Na+) and anions ( Cl−, ) in soil-solution were increased (by between 38 and 259%) by air-drying and, apart from also increased with storage time. In contrast, Cu, Ni, Zn, and SOC concentrations were decreased by air-drying (up to a 70% decrease in the case of Zn). Copper and Ni solution concentrations also decreased with increased storage time, as did the SOC concentration, while there was no change in Zn concentration. The results suggest that to obtain soil-solution that reflects in situ conditions, extraction should be carried out on field-moist samples as soon as possible after sampling.