A. H. C. Roberts

Cadmium status of soils, plants, and grazing animals in New Zealand.

Abstract The accumulation of cadmium (Cd), a biotoxic heavy metal, in the food chain is undesirable. A national survey of soils and plants and random testing of kidneys from grazing animals slaughtered for export was conducted to assess Cd accumulation in New Zealand (NZ) pastoral agriculture. Average total Cd content of pastoral soils (0–7.5 cm) was 0.44 (Xg Cd/g compared to 0.20 |xg Cd/g for “native” (non‐agricultural) soils. Total soil Cd was highly correlated to total soil P. An increase in total soil P is a reflection of fertiliser history thus phosphatic fertiliser use is implicated in Cd accumulation in pastoral soils. The elevated pastoral soil Cd levels were not clearly reflected in grass or legume species but were displayed in weed species viz, 0.28 ug Cd/g c.f. 0.14 μg Cd/g for pastoral and native sites respectively. Over the period 1988–91, 22–28% of sheep and 14–20% of cattle kidneys sampled exceeded the NZ maximum residue level of 1 μg Cd/g. Kidney Cd content was highly age‐related. Cadmium ...

Farm dairy effluent: A review of published data on chemical and physical characteristics in New Zealand

Abstract Increased concern about environmental degradation and a move towards sustainable farming systems has lead to closer attention being paid to farm dairy effluents (FDE). Treatment of FDE in New Zealand is mainly through land application, or through oxidation ponds. Since the introduction of the Resource Management Act, 1991, regional councils require dairy farmers to be more accountable for the management of effluent from their dairy farms. Regulations have been imposed to limit the application of nitrogen (N) to land from FDE, and these limits range from 150 to 200 kg N ha‐1 yr‐1. Farmers, consultants, and regional councils require information on the chemical composition, particularly N content, of effluents, so that land effluent application systems can be designed and managed within the guidelines or regulations imposed. Data gathered from previous investigations on effluents in New Zealand found an average solids content of 0.9% dry matter. Between 1977 and 1997 the mean N content of FDE doubled from approximately 200 to 400 mg N I‐1. The trend for higher N concentrations is likely to continue as dairy herd numbers increase. The most likely reason for the increase in N is that volume of washwater used per cow has proportionately decreased as herd size has increased, thus, FDE has become more concentrated with levels above 400 mg N I‐1 increasingly common. Average values of phosphorus (P) and potassium (K) in FDE were 70 and 370 mg I‐1, respectively. Slurries obtained from anaerobic ponds, which require periodic de‐sludging about every 5 years, had average nutrient concentrations of 1650, 290, and 510 mg 1‐1 for N, P, and K, respectively, representing an accumulation of minerals over the 5 years.

Fluoride accumulation in pasture forages and soils following long-term applications of phosphorus fertilisers

Ingestion of soils with high fluoride (F) concentration may cause chronic fluorosis in grazing animals. Analysis of New Zealand pasture soils with long-term phosphorus (P) fertilisation histories showed that total surface soil (0-75 mm depth) F concentration increased up to 217-454 mg kg-1 with P fertiliser application. One-third to two-thirds of F applied in fertilisers resides in the top 75 mm soil depth. Pasture forage accumulation of F was low, and therefore, F intake by grazing animals through pasture consumption is expected to be much lower than F intake by soil ingestion. Ten annual applications of single superphosphate (30 and 60 kg P ha-1 year-1) to a Pallic Soil (Aeric Fragiaqualf) significantly increased total F and labile F (0.01 M CaCl2 extract) concentrations to 200 and 120 mm depths, respectively, of the 300 mm depth investigated. The mobility of F in the soil profile was similar to two other elements, P and cadmium derived from the fertiliser.

Defining the relationships between pasture production and soil P and the development of a dynamic P model for New Zealand pastures : a review of recent developments

Abstract A database was constructed comprising records from 2255 pasture phosphorus (P), potassium (K) and sulphur (S) field trials, of which 1799 included one or several rates of P. Subsets of this data were selected based on predetermined criteria to define the relationships between relative pasture production and available soil P (0–75 mm, Olsen P in μg P cm–3 soil)—the P production functions—for the major soil groups in New Zealand. These relationships, and their 95% confidence intervals, were defined using Bayesian statistics. For those soil groups for which there was sufficient data, the production functions were well defined and gave reasonably precise estimates of the relative pasture yield for a given Olsen P. For example, for the volcanic soils, the relative pasture production is most likely (P < 0.05) to be in the range 88–94% at Olsen P 25 and 98–100% at Olsen P 50. The shape of the production functions was similar for all soil groups—the relative pasture production increased with increasing Olsen P up to an asymptote—except the pumice soils and the podzols, which showed irregularities. The production function for the podzols was also flatter. There was good agreement between the empirically derived production functions and those generated from a dynamic P model. The Olsen P level required to achieve 97% maximum production was estimated for all soil groups. These ranged from 10 to 45 depending on soil group. The critical Olsen P levels were related to the soil anion storage capacity (ASC, a laboratory measure of P buffer capacity) and to soil volume weight (g cm–3 of sieved and dried soil), although not strongly. The field measured P buffer capacity (?PF)—the amount of soluble fertiliser P (kg P ha–1) required above maintenance to increase the Olsen P (0–75 mm) level by 1 unit—was estimated for selected trials. There was reasonable agreement between these estimates and those derived from the P model (?PM), and these results indicated that ?P decreases with increasing Olsen P. The results imply that factors other than those related to soil chemical properties affect the relationship between soil P and pasture production. The factors which determine the relationship between pasture production and soil P are defined and discussed. These were assigned to two categories: those factors which affect the ability of the soil to supply P for plant uptake and those that affect the ability of the plant to acquire soil P. It is concluded that further progress towards improving our ability to predict pasture responses to fertiliser P will depend on quantifying the latter effects. Based on these results and the development of a dynamic P model, an econometric P model was developed for New Zealand pastures which enables consultants to quantify the likely agronomic, financial and investment effects of any given fertiliser strategy on a given farm or block within a farm. This was not previously possible but is essential for the sustainable use of P fertilisers in pastoral farming.

Concentrations of arsenic, cadmium, copper, lead, and zinc in New Zealand pastoral topsoils and herbage

Abstract A national survey of agricultural topsoils and pastures was undertaken in the early 1990s to establish benchmark heavy metal concentrations. In total, 398 sites were sampled covering the major soil groups throughout the North and South Islands of New Zealand. Both pastoral farmed (312) and non‐farmed (86) sites were sampled. Composite soil samples were taken from two depths, as well as pasture samples from the same area, and analysed for arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) concentrations. There was significant (P < 0.05) enrichment of Cd at the 0–7.5 cm depth in five of the eight soil groups on farmed sites (0.44 mg kg–1), over background non‐farmed soils (0.20 mg kg–1). Total soil Cd was highly correlated (P < 0.001) to total soil phosphate (P) suggesting Cd enrichment in pastoral soils was related to fertiliser P applications. There was no enrichment of As, Cu, Pb, or Zn at the 0–7.5 cm depth on farmed soils compared with non‐farmed soils. Results showed that soil concentrations of these elements were either typical of worldwide averages, or at the lower end of these ranges. There was, however, a significant (P < 0.05) increase in Cu concentrations in the 0–2.5 cm depth on most farmed soils (14.3 mg kg–1), compared with non‐farmed soils (11.4 mg kg‐1). The main difference in heavy metal concentrations between non‐farm and pastoral pasture species was in the weed component. In general, the Cu, Zn, Pb, and As concentrations were essentially pedogenic in origin.

Relationship between pasture dry matter yield and soil Olsen P from a series of long‐term field trials

Abstract Forty‐six data‐sets from a series of 17 long‐term field trials measuring the effects of rates and forms of phosphate (P) fertiliser on pasture production and soil fertility in New Zealand were used to characterise the relationship between pasture dry matter (DM) yield in any year (expressed as relative yield, RY) and soil Olsen P test at the end of the annual DM measurement period. Average coefficients of variation in the measurement of these parameters were 7% and 17% for DM yield and Olsen P, respectively. The results failed to demonstrate that the RY at any site in any year could be reliably assessed from a common relationship between RY and the Olsen P test. However, the mean relationship did take the general “diminishing returns” form as expressed by the Mitscherlich equation, and as Olsen P levels increased the probability of low RY decreased. There was no evidence that RY increased with increase in Olsen P test values above 20, with the exception of the one yellow‐brown pumice soil in the ...

A model to predict kidney and liver cadmium concentrations in grazing animals

Abstract Cadmium (Cd) accumulation in the kidneys and liver of older grazing animals is a major concern in New Zealand and Australian agriculture. Use of phosphate fertilisers containing high Cd concentration is the main cause of this accumulation. A simple mathematical model running in a user‐friendly computer package was developed to predict annual accumulation of Cd in kidneys and liver of animals grazing pastures of known herbage Cd concentration and phosphate fertiliser history. Results from the model showed that kidney and liver Cd concentration of sheep were most sensitive to fertiliser Cd concentration, moderately sensitive to pasture ingestion rate, and least sensitive to soil ingestion rate. The model was validated using kidney Cd data from a farmlet‐scale sheep‐grazing trial. Kidney Cd concentrations predicted by the model were strongly correlated with measured mean kidney Cd concentrations. The relationship between the measured and predicted Cd concentrations is not statistically different fro...

Pasture production and soil phosphorus fractions resulting from six previous annual applications of triple superphosphate or Sechura phosphate rock

Abstract The effects of six annual applications of either Sechura phosphate rock (SPR) or triple superphosphate (TSP) on pasture production and soil phosphorus (P) fractions were compared at eight New Zealand sites. At most sites, pasture production resulting from residual fertiliser P was significantly (P < 0.05) greater for SPR than it was for corresponding rates of TSP. Molybdenum (Mo) present in the SPR may have contributed to this effect at four of the sites where Mo deficiency was suspected. Sequential extraction (alkali followed by acid) was used to determine chemical forms of residual fertiliser P in soil samples from all sites. Fertiliser P which had reacted with the soil or been adsorbed on soil surfaces was alkali-soluble whereas undissolved apatite residues were acid-soluble. SPR-treated soil had significantly (P < 0.05) higher amounts of acid-soluble P than TSP-treated soil, lower amounts of alkali-soluble P (except at two sites), and higher amounts of total P (except at three sites). The gre...

Patterns of, and a model for, dry matter yield response in grass/clover pastures to annual applications of triple superphosphate fertiliser

Abstract Pasture herbage dry matter (DM) responses to annual applications of triple superphosphate (TSP) at 0.5, 0.75, 1.0, and 2.0 times the calculated maintenance requirement were measured in 12 field trials for 6 years. The trials were on well‐established, permanent pastures which had typical fertiliser histories and represented major pastoral soils of North and South Islands of New Zealand. The DM response to TSP averaged over all rates and sites was 5% in Year 1, increasing to 23% in Year 4 with little change thereafter. At individual sites, average responses in total DM over 6 years ranged from 4 to 24%. Responses increased steadily with time at four sites, but at other sites changes with time were erratic. Mitscherlich curves were fitted to the 6‐year total DM production data for each site. However, the standard errors in the parameters of these fitted curves were very large, making it impossible to predict with any useful degree of accuracy the rate of TSP required for any specified yield. Respons...

Cadmium cycling in sheep‐grazed hill‐country pastures

Abstract Cadmium (Cd) cycling in a sheep‐grazed hill‐country farming system was investigated to determine the important factors influencing accumulation in edible sheep tissues. A farmlet‐scale trial was established consisting of a total of 10 paddocks that had a history of 15 years of 5 different rates of phosphatic (P) fertiliser applications. The trial comprised 2 flocks of Romney ewes managed at 2 different grazing pressures. Each flock was rotationally grazed over 1 block of 5 paddocks, each of which represented a different rate of P (10, 20, 30, 50, and 100 kg P ha‐1). Over a 4‐year period, the trial investigated seasonal variation of soil and herbage Cd; effect of rate of P and paddock stratum (sheep campsites, tracks, easy, or steep slopes) on soil and herbage Cd; and pasture intake or soil ingestion as possible modes of Cd entry into the grazing animal. Annual Cd liver and kidney tissue accumulation rates in ewes between 18 and 66 months of age were estimated at 19 and 43%, respectively, but were unaffected by grazing intensity. Soil ingestion contributed only 3–6% of total Cd ingestion by grazing sheep. The remainder arose from the pasture diet of the sheep and points to the need to reduce further Cd inputs to soils and minimise the uptake by plants of Cd already present.