Tuber Cd Concentrations Research Articles

Cadmium in soils and potato tubers under grower management in two contrasting soil types of Hokkaido, Japan

ABSTRACT In Japan, little has been reported on cadmium (Cd) concentration in upland soils, and its relation to Cd concentration in crops and vegetables other than rice. Cd concentration in the surface soils and potato tubers of growers’ fields in two main potato production areas in Japan with contrasting soil types (Andisols and Inceptisols) was investigated. Soil and tuber samples were obtained from 90 growers’ fields with variable management histories. Total and Mehlich-3 soil Cd concentration were determined, and Cd concentration in the peeled potato tubers was also measured. A significant positive correlation was found between total Cd and phosphorous concentration in the soils reflecting the historical heavy application of phosphate fertilizer in both soil types. Although the total Cd concentration was much higher in Andisols, the Mehlich-3 Cd as well as tuber Cd concentration was lower in Andisols than in the Inceptisols, suggesting that Cd in Andisols may be specifically adsorbed by humic substances and amorphous clay minerals. The Cd concentration of the peeled potatoes in all samples was less than 100 μg kg−1 fresh weight below the threshold set by the Codex Alimentarius guidelines. The Cd concentration in the tubers tended to be higher when the soil phosphate retention index and base saturation were lower, and this tendency was stronger when both conditions are satisfied. Differences in soil properties and not the total soil Cd concentration were the dominant factor affecting potato tuber Cd accumulation. It is quite possible to reduce the amount of phosphate fertilizer appropriately to minimize the accumulation of Cd in both soil types as well as by increasing the soil base saturation to suppress the transfer of Cd from the soils to the potato tubers is especially important in the Inceptisols.

Roles of shoots and roots in cadmium uptake and distribution in tubers of potato (Solanum tuberosum L)

Potato cultivars vary in biomass production and Cd concentration. Differences in growth can lead to differences in tuber cadmium (Cd) concentration through growth dilution and/or limited uptake of Cd from the soil. The aims of this study were to investigate the relative importance of shoot (above ground plant parts) and root in dry weight (DW) accumulation, total Cd uptake and Cd distribution between organs and how this affects tuber Cd concentration. Three experiments were carried out, two with reciprocal grafting between high and low tuber Cd accumulating cultivars under two soil Cd conditions, and the other was involving the evaluation of F1 genotypes, from a cross between these high and low tuber Cd accumulating cultivars. These experiments were carried out under controlled greenhouse conditions. The results showed that the root system is important for total Cd uptake but less important for growth and Cd distribution between organs. On the other hand, the shoot system is important for regulating growth of shoot and roots, and for determining Cd distribution between organs. The data suggest that tuber Cd concentration was mainly regulated by shoot source and to a lesser extent by total uptake of Cd.

Genetic mapping of quantitative trait loci for tuber-cadmium and zinc concentration in potato reveals associations with maturity and both overlapping and independent components of genetic control.

Cd is a toxic metal, whilst Zn is an essential for plant and human health. Both can accumulate in potato tubers. We examine the genetic control of this process. The aim of this study was to map quantitative trait loci (QTLs) influencing tuber concentrations of cadmium (Cd) and zinc (Zn). We developed a segregating population comprising 188 F1 progeny derived from crossing two tetraploid cultivars exhibiting divergent tuber-Cd-accumulation phenotypes. These progeny were genotyped using the SolCap 8303 SNP array, and evaluated for Cd, Zn, and maturity-related traits. Linkage and QTL mapping were performed using TetraploidSNPMap software, which incorporates all allele dosage information. The final genetic map comprised 3755 SNP markers with average marker density of 2.94 per cM. Tuber-Cd and Zn concentrations were measured in the segregating population over 2years. QTL mapping identified four loci for tuber-Cd concentration on chromosomes 3, 5, 6, and 7, which explained genetic variance ranging from 5 to 33%, and five loci for tuber-Zn concentration on chromosome 1, 3, 5, and, 6 explaining from 5 to 38% of genetic variance. Among the QTL identified for tuber-Cd concentration, three loci coincided with tuber-Zn concentration. The largest effect QTL for both tuber-Cd and Zn concentration coincided with the maturity locus on chromosome 5 where earliness was associated with increased tuber concentration of both metals. Coincident minor-effect QTL for Cd and Zn sharing the same direction of effect was also found on chromosomes 3 and 6, and these were unrelated to maturity The results indicate partially overlapping genetic control of tuber-Cd and Zn concentration in the cross, involving both maturity-related and non-maturity-related mechanisms.

Cadmium uptake and partitioning in potato (Solanum tuberosum L.) cultivars with different tuber-Cd concentration.

Potatoes grown in soil with high Cd concentrations can accumulate high levels of Cd in the tubers. Although there is significant environmental variation involved in the trait of crop uptake of Cd, there are also distinctive cultivar differences. In order to understand this differential Cd accumulation mechanism, two potato cultivars were chosen that accumulate high and low levels of Cd in tubers. The patterns of Cd concentration, Cd content and dry weight accumulation of the two cultivars were examined at different stages of plant growth. The data suggest that differences in total Cd uptake and in Cd partitioning among organs are the mechanisms governing differential Cd-tuber accumulation in the two cultivars. The low tuber-Cd accumulator exhibited lower root-to-shoot and shoot-to-tuber translocation driven by higher root and shoot biomass that retained more Cd in roots and shoots, respectively, reducing its movement to the tubers. Higher remobilization and more efficient tuber loading was observed in the high tuber-Cd accumulator, indicating that remobilization of Cd from leaves to tubers was a major factor, not only in tuber-Cd loading, but also in the establishment of differential tuber-Cd levels. Regardless of cultivar differences, the concentration of Cd in the tuber was very low compared to that in other organs suggesting that, despite its high phloem mobility, Cd tends to be sequestered in the shoots.

Effects of Lime and Organic Amendments Derived from Varied Source Materials on Cadmium Uptake by Potato.

Repeated applications of Cd-rich phosphate fertilizers have resulted in elevated concentrations of this toxic element in some New Zealand soils. Exceedance of the food safety standard for Cd (0.1 mg kg fresh weight) has been reported for potato ( L.). Composts may efficiently sorb Cd in soil and therefore reduce its phytoavailability, leading to reduced uptake by plants. We aimed to determine the potential of various composts, shredded corn stover, and lime at two different rates to reduce the transfer of Cd from a soil (containing 1.45 mg kg Cd) to potato (var. 'Nadine'). In the control, the peeled tubers, skins, leaves, and stems had Cd concentrations of 0.04, 0.09, 0.26, and 0.53 mg kg dry weight, respectively. There was a 71% reduction in tuber Cd concentrations in potatoes grown in soil amended with 5% (w/w) shredded corn stover, although it significantly decreased potato biomass. Potatoes grown in soil amended with pig manure compost, mushroom compost, sawdust-animal waste compost, and municipal compost at rates of either 2.5 or 5% (w/w) reduced tuber Cd concentrations by 58 to 66%, 46 to 63%, 52 to 53%, and 29 to 49%, respectively. Lime (1.3%) application in soil reduced tuber Cd concentrations by 50%. Composts significantly increased tuber biomass. Further work is warranted to identify the key components of composts that result in reduced Cd uptake by plants.

INFLUENCE OF NITROGEN SUPPLY ON CADMIUM ACCUMULATION IN POTATO TUBERS

The effect of different levels and forms of nitrogen (N) fertilizer on cadmium (Cd) concentrations in potato (Solanum tuberosum L.) tubers, a large component of the northern European diet, was investigated with the aim of decreasing the Cd content. A high and a low Cd-accumulating cultivar were used in two field trials and a pot experiment. The N fertilizers tested were balanced N- phosphorus (P)- potassium (K) 11-5-18 + micronutrients, alkaline calcium nitrate and acidic ammonium sulfate at levels of 60, 160, and 240 kg N ha−1 at planting or (for the higher N doses) split between two or three occasions. The Cd concentration in tubers of both cultivars decreased when increasing the N fertilizer from 60 to 160 or 240 kg N ha−1, indicating that Cd uptake and translocation are not positively correlated to the growth rate of the potato plant. A strong positive linear correlation was found between the Cd concentration in leaves at 77 days after planting and the Cd concentration in tubers at harvest, irrespective of N treatment, although the Cd concentration was three-fold higher in the leaves. The genetic variation in leaf and tuber Cd accumulation was consistent, regardless of the form of N fertilizer used. Ammonium sulfate decreased soil pH and increased tuber Cd concentration in both cultivars compared with NPK fertilizer, possibly due to increased amounts of plant-available Cd arising from the pH decrease after ammonium sulfate application. The tuber Cd concentration in the low Cd-accumulating cultivar increased when fertilized with calcium nitrate, an effect attributed to Cd availability being influenced by the increased Ca2+ concentration.

Cadmium accumulation in potato tubers produced in Quebec

Cadmium (Cd) is a heavy metal present in soils that can accumulate at relatively high levels in potato (Solanum tuberosum L.) with no negative effect on growth. Our objectives were to investigate Cd concentration in potato tubers produced in Quebec and to relate some soil characteristics, especially pH, P, and Cd, to tuber Cd concentration. Potato tubers (n = 75) and soil samples (n = 64) were collected from 1999 to 2006 at five experimental sites. Tuber Cd concentration ranged from 0.04 to 0.20 mg kg–1 dry matter (DM), with a median value of 0.11 mg kg–1 DM, and never exceeded the proposed tolerance for potato of 0.05 mg kg–1 fresh weight or about 0.25 mg kg–1 DM. Tuber Cd concentration was weakly, although not significantly, related to soil available P content (r2 = 0.53, P = 0.064), indicating a possible influence of soil P on Cd uptake by potato. Tuber Cd concentration was not directly related to soil pH, or to DTPA- or Mehlich 3-extractable Cd in soils. The log-transformed tuber Cd concentration was significantly (r2adj = 0.87, P < 0.01) related to both soil pH and VCd13, a generated variable that accounts for interactions between soil Cd and clay content, soil organic matter, and soil concentrations of Fe, Al, Mn, P, K, S, Ca, Cu, Zn, and B. Single factors such as soil Cd, soil P, or pH could not solely explain Cd accumulation in tubers; interactions between selected soil properties and soil Cd should be considered.Key words: Cadmium, phosphorus, Solanum tuberosum L., accumulation

Elevated Cadmium Concentrations in Potato Tubers Due to Irrigation with River Water Contaminated by Mining in Potosí, Bolivia

Risk of cadmium (Cd) in the human food chain in Cd-contaminated areas is often limited by phytotoxicity from zinc (Zn) that is associated with the Cd contamination. A semiarid area, 60 km downstream of a tin mine in Bolivia, was surveyed where irrigation with Cd-contaminated river water (65-240 microg Cd L(-1)) has increased median soil Cd to 20 mg kg(-1) while median soil Zn was only about 260 mg kg(-1). Cadmium concentrations in potato tubers increased from background values (0.05 mg kg(-1) dry wt.) in soils irrigated with spring water to a median value of 1.2 mg kg(-1) dry wt. in the affected area. Median concentration of Cd in soil solutions was 27 microg L(-1) and exceeded the corresponding value of Zn almost twofold. Soil-extractable chloride ranged from 40 to 1600 mg Cl(-) kg(-1) and was positively correlated with soil total Cd. Increasing soil solution Cl(-) decreased the solid-liquid distribution coefficient of Cd in soil. Soil total Cd explained 64% of the variation of tuber Cd concentration while only 3% of the variation was explained by soil extractable Cl(-) (n = 49). The estimated dietary Cd intake from potato consumption by the local population is about 100 microg d(-1) which exceeds the WHO recommended total daily intake. It is concluded that the food chain risk of Cd in the irrigation water of the semiarid area is aggravated by the association with Cl(-) and, potentially, by the relatively large Cd/Zn ratio.

The uptake and partitioning of cadmium in two cultivars of potato (Solanum tuberosum L.)

The uptake and distribution of Cd in potatoes over the course of a growing season was investigated in two cultivars of potatoes that differed in tuber Cd concentration. Plants were grown in soil with supplemental Cd. The concentrations of Cd in different tissues varied greatly in the order roots>shoots>> tubers. After the initiation of tuber bulking, shoot growth ceased and the increase in total plant Cd was mostly due to accumulation in the tubers. The constancy of the Cd concentration in shoots suggested that import of Cd via the xylem must be matched by export in the phloem, which implied that Cd must have significant phloem mobility. It was found that the differences in tuber Cd between cultivars Wilwash and Kennebec were not due to differences in total uptake or growth, but to differences in Cd partitioning within the plant. This partitioning was specific to Cd and was not observed for a range of nutrient elements. Most of the differences in tuber Cd concentration between the cultivars could be accounted for by a 3-fold higher retention of Cd in the roots of cv. Wilwash. The involvement of root sequestration, and xylem and phloem pathways in the loading of Cd into tubers is considered.

Effect of current-season application of calcitic lime and phosphorus fertilization on soil pH, potato growth, yield, dry matter content, and cadmium concentration

Two glasshouse and three field experiments were conducted to investigate the effects of current-season application of calcitic lime and phosphorus (P) fertilizer on (i) soil pHw, (ii) growth of haulms (tops), (iii) tuber number, yield and dry matter content, and (iv) cadmium (Cd) concentrations in tubers of the potato (Solanum tuberosum L.) cultivars Russet Burbank, Crystal, and Pontiac grown in acid Entisols. Rates of calcitic lime ranged from 0 to 20 t ha−1, and rates of P, applied as single superphosphate, ranged from 0 to 100 kg ha−1. Liming increased surface (0–15 cm) soil pHw by up to 3.1 units while P fertilization increased it by only 0.3 of a unit. In the glasshouse experiments, total yields of leaves, stems and haulms were not significantly affected by the application of lime while plant height was increased. Phosphorus fertilization increased total leaf, stem and haulm yields and plant height. The number of tubers per plant and tuber yield were either unaffected (4 experiments) or decreased (1 experiment) by liming. Phosphorus fertilization significantly increased tuber yield and number in 3 experiments. The magnitude of the yield responses to applied P was greater in the glasshouse experiments than in the field experiments. Liming did not significantly affect tuber dry matter content which was however, increased by the application of P in the glasshouse experiments. There were no consistent interactions between lime and P in their effects on any of the growth or yield parameters measured. Application of lime, up to 10–15 t ha−1, significantly reduced tuber Cd concentrations in glasshouse experiments but not in field experiments. This discrepancy between field and glasshouse experiments indicates that the effects of liming on Cd availability in acid soils and on plant uptake need further investigation. Phosphorus fertilization significantly increased tuber Cd concentrations in 2 experiments. Based on our field experiments, further investigations are required to determine if banding superphosphate increases tuber Cd compared with broadcasting. It was found that for potato crops grown in acid Entisols, current-season application of calcitic lime was ineffective as an agronomic practice for growers to improve haulm growth and tuber yield response to applied P and to reduce Cd residues in tubers.

EFFECT OF NITROGEN SOURCE AND CALCITIC LIME ON SOIL pH AND POTATO YIELD, LEAF CHEMICAL COMPOSITION, AND TUBER CADMIUM CONCENTRATIONS

Three glasshouse experiments, using light textured soils, were conducted to investigate the effects of nitrogen (N) source and calcitic lime on i) soil pHw(soil pH in water), ii) tuber yield, iii) leaf chemical composition, and iv) cadmium (Cd) accumulation in tubers of the potato (Solanum tuberosum L.) cultivars Russet Burbank and Atlantic. The N sources applied were calcium nitrate, ammonium nitrate, urea, and ammonium sulfate. Rates of calcitic lime ranged from 0 to 20 t ha−1. Liming increased soil pHwvalues up to 2.8 units, and depending on sampling time, differences in soil pHwof up to 1.8 units occurred between the N sources. In 2 of the 3 experiments there was a significant interaction between lime and N source in their effects on tuber yield. When calcium nitrate was the N source, liming decreased tuber yields. In contrast, with ammonium sulfate yield increased. The effects of liming and N source on the chemical composition of the 5th leaf were not consistent between experiments. Liming significantly decreased potassium (K), sulfur (S), boron (B), and manganese (Mn) concentrations and increased calcium (Ca) and magnesium (Mg) concentrations. The application of ammonium sulfate consistently decreased Ca and Mg concentrations in the 5th leaf compared with calcium nitrate. Liming significantly decreased tuber Cd concentrations in all experiments. The use of calcium nitrate as the N source resulted in significantly higher Cd concentrations in tubers compared with ammonium sulfate when no calcitic lime was applied. It is possible that Ca added in this fertilizer enhanced Cd uptake through displacement of Cd from soil surfaces.

Prediction of cadmium concentrations in potato tubers (Solanum tuberosum L.) by pre-plant soil and irrigation water analyses

Potato tubers can accumulate high concentrations of cadmium (Cd) in edible portions, so that techniques to determine high risk Cd environments are required by growers. The use of combined soil and irrigation water analyses prior to crop planting was investigated as a means to predict risks of Cd accumulation in tubers. Soils and irrigation waters were analysed at 134 sites in the major potato production areas in Western Australia, South Australia, Tasmania, Victoria, and New South Wales. Irrigation waters were analysed for electrical conductivity (EC), major cations, and anions. Cadmium was extracted from soil using aqua regia (1 : 3 HNO3: HCl), EDTA (ethylenediamine-N,N,N′,N′-tetraacetate), DTPA (diethylene-triamine-pentaacetate), 0·01 M CaCl2, 0·01 M Ca(NO3)2, 0·1 M CaCl2, and 1·0 M NH4NO3. The preferred test procedure was validated in a subsequent sampling and analysis program at 39 sites. Irrigation water quality (EC or Cl concentration), measured prior to planting, explained the greatest variation in tuber Cd concentrations. Of the soil test procedures, only Cd extracted by 0·01 M CaCl2 significantly improved the predictive capacity of water EC. These 2 measures explained >55% of the variance in tuber Cd concentrations. The data set were transformed to generate a probability curve for exceeding Cd concentrations of either 0·05 or 0·1 mg/kg fresh weight, the latter being the current maximum permitted concentration (MPC) in Australia for potato tubers. The probability of producing potato tubers exceeding 0·05 and 0·1 mg/kg fresh weight was >50% once irrigation water EC increased above 1·4 and 3·0 dS/m, respectively. Using the relationships developed, growers should be able to quantify Cd risks by a simple test of irrigation water EC prior to planting and, if further precision is needed, also determine CaCl2-extractable Cd in soil.

Cadmium in Australian Potato Tubers and Soils

AbstractCadmium (Cd) has been identified as a potential contaminant in foods posing health risks to humans and, in Australia, potatoes (Solanum tuberosum L.) have been identified as contributing a large proportion of the average dietary Cd intake. To assess the concentrations of Cd in Australian potatoes and soil factors likely to lead to high Cd concentrations, commercial crops and soils were sampled at 352 sites throughout potato production areas in Australia. Across all states, fresh weight (FW) tuber Cd concentrations ranged from 0.004 to 0.232 mg kg−1 with an overall mean value of 0.041 and a median of 0.033 mg kg−1 (FW). Approximately 92 samples out of 359 (25.6%) exceeded the current maximum permitted concentration (MPC) of 0.05 mg kg−1 (FW) and 18 (5.0%) exceeded 0.1 mg kg−1 (FW). Concentrations of Cd (EDTA‐extractable) in topsoils ranged from 0.01 to 0.59 mg kg−1 with mean and median values of 0.14 and 0.10 mg kg−1, respectively. There was no relationship between Cd concentrations in soil and tubers. Stepwise forward multiple regression analysis of the data indicated that Cl and Zn concentrations in the topsoil, soil pH, and potato cultivar accounted for 57% of the variation in tuber Cd concentrations, with Cl being the dominant factor. Comparison of soil‐plant transfer coefficients (TCs) for Cd with limited international data sets suggests that TCs for Australian soils used for potato production are relatively high.

Speciation of cadmium in soil solutions of saline/sodic soils and relationship with cadmium concentrations in potato tubers (Solanum tuberosum L.)

Fifty commercial potato crops and associated soils were sampled. Soil solutions were extracted from rewetted soils by centrifugation, and solution composition was related to Cd concentrations in tubers. Soils were also extracted with 0·01 M Ca(NO3)2 and 0·01 M CaCl2 solutions, and Cd2+ activities in the extracts were calculated by difference using the stability constants for formation of CdCl2-nn species. The soils had saline solutions (>4 dS/m), and Cl- and SO2-4 in solution markedly affected the speciation of Cd in soil solution, with chloro-complexes, in particular, dominating. While low soil pH was associated with high (>25 nM) concentrations of Cd in soil solution, chloro-complexation also led to high concentrations of Cd in solution, even at neutral to alkaline soil pH values. Tuber Cd concentrations were not related to activities of Cd2+ in soil solution or to activities in dilute salt extracts of soil. Tuber Cd concentrations were related to the degree of chloro-complexation of Cd in solution. The relationship of tuber Cd concentrations to chloro-complexation in soil solution suggests that Cd species other than the free Cd2+ ion are involved in the transport through soil and uptake of Cd by plants.

Increased Soil Salinity Causes Elevated Cadmium Concentrations in Field-Grown Potato Tubers.

Elevated Cd concentrations have been observed in potato (Solatium tuberosum L.) tubers from commercial crops in certain regions of southern Australia. Reasons for enhanced Cd uptake by tubers were investigated by a survey of commercial crops and associated soils. Eighty-nine sites were selected and paired tuber and soil samples taken. Concentration of Cd in tubers was compared to potato variety, tuber elemental composition, and chemical-physical characteristics of topsoil (0-150) and subsoil (150-300 mm). Tuber Cd concentrations were positively related to soil electrical conductivity (EC) and extractable Cl (R2 = 0.62, P < 0.001) in the topsoil, with extractable Cl accounting for more variation than EC. Tuber Cd concentrations were not strongly related (R2 = 0.23, P < 0.05) to potato variety alone. However, inclusion of variety and EDTA-extractable Zn with water-extractable Cl in a multivariate model resulted in a small but significant improvement in the variance accounted for by the model (R2 =0.73, P < 0.001). Tuber Cd was unrelated to tuber concentrations of P or S, but was positively related to concentrations of major cations in the tuber, particularly Na. Soil pH, total C, EDTA-extractable Cd, or particle-size distribution were not correlated to tuber Cd concentrations, either singly or after inclusion in a multivariate model with soil Cl concentrations. As Cl is known to mobilize soil Cd and increase its phytoavailability, elevated Cd concentrations in potato tubers in southern Australia appear to be largely a result of the use of saline irrigation waters.

Effect of cultivar on uptake of cadmium by potato tubers

Cadmium (Cd) accumulation in tubers by commercial potato cultivars was assessed at 12 sites around Australia having differing soil and environmental conditions. At all but two sites there were significant differences in tuber Cd concentrations between cultivars. Some major commercial cultivars had tuber Cd concentrations only half that of others. Advanced breeding lines showed further potential to reduce Cd accumulation. Mean tuber Cd concentrations of the 14 most common cultivars, averaged across all sites, ranged from 30 to 50 8g kg-1 fresh weight (FW), below the maximum permitted concentration (MPC) of 50 8g kg-1 of Cd (FW). However, at some sites certain cultivars exceeded the MPC. A modified joint regression analysis of the data indicated that no cultivars have consistently low or consistently high tuber Cd concentrations across a range of environments. While differences between cultivars were significant, the range in Cd concentrations found between sites was generally greater than the range in Cd concentrations between cultivars at any one site. Thus soil and other site factors (e.g. irrigation water quality, climate, etc.) play a dominant role in controlling Cd accumulation by current commercial cultivars and there is a need to breed new cultivars resistant to Cd accumulation under a wide range of environments.

Field studies of cadmium in potatoes (Solanum tuberosum L.). Response of cvv. Russet Burbank and Kennebec to two double superphosphates of different cadmium concentration

Separate field experiments were conducted with Russet Burbank and Kennebec potatoes on a basaltic krasnozem where tuber cadmium (Cd) responses were examined over three rates of banded phosphorus (P), supplied as double superphosphate (DSP) containing either 15 or 90 mg Cd kg-1. In both cultivars, tuber Cd concentrations increased with rate of DSP. This response was due more to the amount of P supplied in the DSP than the amount of Cd supplied in the DSP and may be a result of banded P encouraging root proliferation in the fertilizer band. Even with DSP at 15 mg Cd kg-1, Cd additions at rates of DSP needed for high yields were 6-20 times higher than corresponding rates of Cd removal in tubers. Examination of data from all studies of Cd in Russet Burbank on Tasmanian krasnozems showed a significant relationship between petiole and tuber Cd concentrations, but the estimation of a petiole concentration associated with the critical tuber Cd concentration in Australia was subject to unacceptable uncertainty due to variation between sites.

Field studies of cadmium in potatoes (Solanum tuberosum L.) I. Effects of lime and phosphorus on cv. Russet Burbank

Field experiments were conducted at three sites on basaltic krasnozems to examine cadmium (Cd) responses of Russet Burbank potatoes to different rates of broadcast lime and banded phosphorus (P). Double superphosphate (DSP, containing 15 and 90 mg Cd kg-1) and triple superphosphate (TSP, 12 mg Cd kg-1)) were the sources of P. In a fourth experiment, lime was banded with the basal fertilizer. Despite producing a range of topsoil pH (1:5 H20) of 5.2 to 7.1, broadcast lime had no effect on tuber Cd concentrations. Lime had no effect when banded with the basal fertilizer, and the practice did not adversely affect yields. With broadcast lime, Cd availability from the fertilizer band may have been unaffected. However, there were also no lime x P interactions at any site, suggesting that lime also had no effect on the availability of Cd in the soil. It is possible that Tasmanian krasnozems, with their high organic matter and iron oxide content, restrict the availability of Cd in the soil such that pH change exerts little net influence on Cd availability. Increasing amounts of Cd applied in P fertilizer increased tuber Cd concentrations significantly, but the increases were less per unit of P than those found previously when TSP with 151 mg Cd kg-1) was used.

Response of potatoes (Solanum tuberosum cv. Russet Burbank) to band-placed and broadcast high cadmium phosphorus fertiliser on heavily cropped krasnozems in north-western Tasmania

Four field experiments were conducted to examine the yield response and cadmium (Cd) concentration of potatoes (Solanum tuberosum L. cv. Russet Burbank) grown with banded or broadcast phosphorus (P) fertiliser at rates up to 240 kg P/ha. The Cd content of the triple superphosphate (TSP) was 151 mg/kg. All 4 sites were on intensively cropped, high P-fixing krasnozem soils in north-western Tasmania, with concentrations of Colwell-extractable P ranging from 112 to 210 mg/kg. All sites showed economic yield responses to banded P, but broadcast P was much less effective except at the site where the response to banded P was least. Yield responses came mostly through increased tuber number, but at 1 site the tubers were also bigger. There was no effect of P on tuber size distribution or specific gravity. Increasing rates of banded TSP increased tuber Cd concentrations by 50-300% at the 3 sites where they were measured; broadcast TSP had little effect. Tubers from the site with pH 6.0 had much higher Cd concentrations than those from the sites with pH 6.5 and 6.6. Petiole Cd concentrations were about 5 times greater than tuber concentrations.