John Waller

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.

Effect of different Neotyphodium endophytes on root distribution of a perennial ryegrass (Lolium perenne L.) cultivar

Abstract Plants of perennial ryegrass either endophyte‐free or infected with Neotyphodium lolii endophyte strain AR1, AR37 or wild‐type, were grown in 105‐mm‐diameter tubes of sand in a glasshouse. Root angles were determined by counting root intercepts on semi‐circular stainless steel mesh transects running from near the edge of the tube at the sand surface to directly under the plant. The average number of root intercepts did not vary between endophyte strains or between their average and the endophyte‐free treatment. However, the linear decline of root intercept frequency with depth varied according to the endophyte status of the ryegrass. Endophyte‐infected plants had fewer roots close to the surface. This effect of shoot endophytes on root distribution patterns in ryegrass may improve the plants tolerance of moisture stress.

Base growth temperatures, germination rates and growth response of contemporary spring wheat (Triticum aestivum L.) cultivars from the US Pacific Northwest

In eastern Washington, spring wheat cultivars that germinate and grow fast at low temperatures will provide the crop with a competitive advantage over spring emerging weeds in commercial production fields compared to cultivars that germinate and grow more slowly. The objective of this research was to develop a protocol to identify spring wheat cultivars that would germinate and grow more quickly at low temperatures. A novel data analysis method was used to separate the germination process into three components: (1) base temperature, (2) time to initiation of germination, and (3) germination rate. Spring wheat cultivars Edwall, Vanna, Wawawai, Wampum, Express, and Spillman were assessed through a series of controlled temperature gradient plate experiments. Base temperatures were not different (P=0.1) across cultivars, and once germination was initiated, germination rates among varieties were uniform (P=0.5). However, significant (P<0.001) differences were detected among varieties for time to germination. A subsequent growth chamber experiment confirmed differences in emergence and growth rate among spring wheat cultivars.

Collagen in two muscles of sheep selected for weight as yearlings

Abstract Collagen concentration and solubility were examined in the semimembranosus and biceps femoris muscles of Romney lambs from the Hight line, a line selected for nine generations on the basis of high body weight at 1 year old. Lambs from the Control (CON) and high body weight (HBW) lines were slaughtered at five ages (0, 42, 70, 274, 365 days). In the semimembranosus muscle, there was no evidence of concentration or solubility differences between the lines at any age, but there was a subtle sex by age interaction, possibly because of increased collagen synthesis in males at puberty. In the biceps femoris muscle, collagen concentration was 14% higher in the HBW line, but there was no difference in solubility. The semimembranosus muscle was shear-tested after cooking to give an objective measure of tenderness. Selection line did not affect shear force. With the semimembranosus muscle, collagen solubility was a better predictor of shear force than collagen concentration, confirming previous work on thi...

Pre-rigor temperature and the relationship between lamb tenderisation, free water production, bound water and dry matter

The M. longissimus from lambs electrically stimulated at 15 min post-mortem were removed after grading, wrapped in polythene film and held at 4 (n=6), 7 (n=6), 15 (n=6, n=8) and 35°C (n=6), until rigor mortis then aged at 15°C for 0, 4, 24 and 72 h post-rigor. Centrifuged free water increased exponentially, and bound water, dry matter and shear force decreased exponentially over time. Decreases in shear force and increases in free water were closely related (r(2)=0.52) and were unaffected by pre-rigor temperatures.

The diagnosis and correction of potassium deficiency in New Zealand pastoral soils: a review

Abstract Field-trial data from a database comprising records of 804 potassium (K) fertiliser trials were used to define the production functions relating exchangeable soil K (quick test K (QTK) 0–75 mm) to the relative response to fertiliser K applications, for the major soil groups in New Zealand. For all soil groups for which there were sufficient data, the production functions were generally flat in the range QTK 5–10, and thus the estimated relative pasture production at QTK 5 and QTK 10 were similar. The critical QTK levels to achieve 97% maximum production were relatively well defined, being 6 (5–8) for sedimentary soils (brown and pallic) and brown soils, and 7 (5–10) for pumice soils. The data for the allophanic soils were unstable and the best estimate was 6 (5–10). For the remaining soils groups (podzols and raw soils, organic, recent and gley soils) for which there was much less data, the relationships were essentially flat over the range QTK 2–10. The probability of pasture responses to applied K increased as soil QTK decreased from 10. For the sedimentary and volcanic soils (including both allophanic and pumice) the probability was about 70–80% at soil QTK < 2. The comparable probabilities were 50–60% for the recent and gley soils, and 30–43% for the podzols and raw soils. A feature of the response functions was that some trials were not responsive to fertiliser K despite having low soil QTK. In most cases this could not be attributed to soil K reserves as measured by the soil TBK test (sodium tetra-phenol-boron extractable which measures exchangeable K plus plant-available but non-exchangeable K). Other possible reasons for this feature in the data are discussed, including uptake of K from below the soil sampling depth and the temporal effects of clover responses to applied K. Soil K buffer capacities—the amount of fertiliser K over and above maintenance required to increase soil QTK by 1 unit (ΔK)—ranged from 50 to > 150 kg K ha−1 (average 124) for sedimentary soils. For some soils (developed organic soils, gleyed soils and podzols), fertiliser K had very little effect on QTK (0–75 mm). It is not clear whether these differences are due to differences in leaching of K from the sampling depth, differences between soils in their ability to absorb and retain applied K or indeed the result of errors in the measurement of this parameter. Estimated maintenance K requirements (i.e. the amount of applied K required to maintain soil QTK levels) increased with increasing soil QTK from 4 to 10, from 0–150 kg K ha−1 yr−1 to 100–300 kg K ha−1 yr−1 in situations where losses of K were extreme due to the removal of all harvested clippings. Given the uncertainties in predicting K responses and the amount of fertiliser K required to correct K deficiency, practical suggestions are offered as to how best to diagnose and manage soil K deficiency. Areas for future research to improve the prediction of pasture responses to fertiliser K are also included.

Effects of dairy factory effluent application on nutrient transformation in soil

Abstract Dairy factory effluent (DFE) contains significant amounts of nutrients such as nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) which are beneficial to plant growth. It also contains high amounts of carbon (C). Lately, there has been some concern that DFE application to pastoral land is adversely affecting plant growth in some regions of New Zealand. In this study, we determined the mineralisation and immobilisation of nutrients particularly C, N, S, and cations, in a DFE‐treated Omeheu sandy loam soil. We report findings from laboratory‐based open incubation studies carried out at 10, 20, and 30°C, with four rates of DFE application (0, 150 000, 300 000, and 450 000 litres ha–1) alone and with added NO3 – (100 kg N ha–1). The DFE was applied at two‐weekly intervals into packed soil columns which were leached with 0.01 MCaCl2 solution. Leachates were analysed for total C, total N, SO4 2–, NO3 ‐, NH4 +, K+, Na+, and Mg2+. Effects of DFE application on soil microbial bio‐mass‐C, hot‐water extractable‐C, and anaerobically mineralisable‐N were also determined. Addition of DFE increased the size of the microbial biomass pool and thereby enhanced immobilisation of nutrients, mainly N and S. The immobilisation was greater at higher temperature. At 10°C, microbes were unable to utilise all of the added C, even at the lowest rate of DFE application, and 40–50% of the C was leached from soil columns. However, at 30°C soil microbes either immobilised or respired between 95–97% of the C added from DFE, and only small amounts of C were measured in the leachates. Addition of NO3 –‐N had no significant influence on the C immobilisation or respiration. Most of the added N (92–97%) from DFE remained immobilised in the soils throughout the study. A high proportion of the NO3 –‐N added with DFE was immobilised in soils at 10 and 20°C, showing the dominating influence of soluble C, added through the two‐weekly application of DFE, in stimulating microbial activity and causing a prolonged immobilisation of N. There was a net mineralisation of about 100 μg NO3 –‐N g–1 soil at 30°C, indicating faster metabolic use of soluble C from DFE by microbes at this temperature. Between 15–35% of the SO4 2–‐S applied from DFE was either immobilised by soil microbes or was adsorbed on soil organic matter. The presence of significant amounts of NH4 + in DFE‐treated soils suggests that parts of the soil columns may have become anaerobic during incubation, causing mineralisation of N from the death of aerobic microbes or decomposition of soil organic matter. A high proportion of the cations (K+, Na+, and Mg2+) that were added with DFE leached out, indicating that DFE application would have very little effect on the availability of these cations for plant uptake. This study, in part, explains that the poor performance of DFE application on pastoral soils predominantly arises through its effects on the availability of N for plant growth.

Bacterial survival and dispersal in spray irrigation aerosols

Abstract New Zealand environmental authorities favour land‐based treatment for wastewaters of faecal origin. However, microbial aerosols from spray irrigation could be a health risk. This study investigated bacterial survival in irrigation aerosols in 105 field trials in spring and summer. Serratia entomophila and tracer spores of Bacillus subtilis var. niger were added to well water at about 105 ml−1 and sprayed onto a flat paddock through either a high‐pressure horticultural sprayer (1400 kPa) to maximise aerosol production or a low‐pressure hammer‐head rotary sprayer (300 kPa), commonly used for irrigation. Aerosol particles were collected in six‐stage Andersen air samplers. Recovery of viable B. subtilis spores decreased with increasing distance from the sprayers, due to dispersion. There was a greater decrease for S. entomophila. Assuming similar dispersion of both micro‐organisms, the relative decrease in S. entomophila was due to inactivation and this inactivation correlated with decreasing relative humidity. Under the prevailing meteorological conditions, viable S. entomophila were dispersed to at least 100 m from the low‐pressure sprayer and 200 m from the high‐pressure sprayer. Irrespective of sprayer type, sampling distance or micro‐organism, the majority of viable organisms were collected on those Andersen sampler stages corresponding to the respirable fraction of inhaled air.

A short-term phosphate fertiliser advice model for grazed pasture as applied to soils in northern North Island, New Zealand

Abstract A short-term (3–4 years) phosphate (P) fertiliser advice model for permanent pasture was developed and applied to field data obtained on highly P-sorbing soils and some low — medium P-sorbing soils in the northern North Island, New Zealand. The model demands that only results from those trials that estimate herbage yield responses to rates of P fertiliser under good rotational grazing management can be used. On highly P-sorbing soils, P status as measured by the Olsen test (to 75 mm depth) correlates positively with the Mitscherlich slope parameter, suggesting that residual P increases the availability of newly applied P. On two soil categories, it was possible to provide P requirement/ Olsen regressions that could be used to give advice on individual fields. On a very large proportion of land, however, there was insufficient field evidence to do so.