1. Cadmium is a naturally occurring heavy metal in soils. Cadmium is only acutely toxic at very h... more 1. Cadmium is a naturally occurring heavy metal in soils. Cadmium is only acutely toxic at very high levels, but it does accumulate in kidneys and livers which can lead to chronic toxicity problems. Current dietary surveys for New Zealander’s indicate that the daily intake of cadmium is lower than the World Health Organisation (WHO) tolerable daily intake guidelines. It is unlikely that at current food cadmium levels there are any adverse health implications for the New Zealand population. However, there is some potential for the intake guidelines to change in future as new science come to hand, and there is a need for continued vigilance. 2. Phosphate fertiliser is the primary source of cadmium accumulation in agricultural soils, and the industry has imposed a voluntary limit on the levels of cadmium in fertilisers. However, low cadmium sources of phosphate rock are limited in supply and uncertain in their availability. Moreover there are no commercially viable processes for removi...
The New Zealand Agricultural Greenhouse Gas Research Centre was recently established. One of thre... more The New Zealand Agricultural Greenhouse Gas Research Centre was recently established. One of three core science areas will develop management guidelines for the conservation and, where likely, sustainable increase of soil carbon (C) storage associated with land-based food and fibre producing activities. It has been estimated that soils beneath grazed pasture store 85% of New Zealand's soil C to a depth of 0.3 m. Research has improved estimation at a national scale, but pastoral soils data remains fragmented, geographic coverage limited, and most samples obtained from a depth <0.1 m. There has been little research about manipulating and verifying C storage rate in soils beneath grazed pasture. For these soils, C storage is already substantial including some from primal forest vegetation cleared by European settlers around 150 years ago. Modelling will develop better understanding of influential soil C cycling processes in grazed pasture systems. A potential for soil C storage ...
A field trial was conducted on a yellow-grey earth in the Hawke’s Bay (mean annual rainfall 875 m... more A field trial was conducted on a yellow-grey earth in the Hawke’s Bay (mean annual rainfall 875 mm) over a period of 5 years to measure the effects of lime applications (0, 5, 10 t/ha) on soils high (50 kg P/ha applied annually) or low (5 kg P/ha applied annually) in phosphorus (P). The average annual pasture production on this dryland soil in the absence of applied lime or P was 5060 kg DM/ha (range 3861-6024). The botanical composition of the pasture was variable, average annual legume composition (4/o on DM basis) ranging from 3 to 42%. The predominant. legume was subterranean clover (Trifolium subterranean) with white clover (Trifolium repens) making a small contribution in some years. In the first two years after application responses to lime were large (lo-20%), due entirely to liming stimulating the grass component of the pasture, and consistent with liming enhancing the rate of net mineralisation of soil organic nitrogen (N). In years three and-four-the-dominant treatment ef...
In New Zealand, the demand for nitrogen fertiliser has increased markedly since the early 1980s. ... more In New Zealand, the demand for nitrogen fertiliser has increased markedly since the early 1980s. Potentially, this trend has significant environmental and climate change implications. While many factors could contribute to this trend, little work has been done to examine the drivers of increased use of nitrogen fertiliser in New Zealand. In this paper, we review the international literature and
Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted anim... more Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted animal urine. In soil, urea hydrolyses rapidly to ammonium (NH4(+)) and may be lost as ammonia (NH3) gas. Unlike nitrous oxide (N2O), however, NH3 is not a greenhouse gas although it can act as a secondary source of N2O, and hence contribute indirectly to global warming and stratospheric ozone depletion. Various urease inhibitors (UIs) have been used over the last 30 years to reduce NH3 losses. Among these, N-(n-butyl) thiophosphoric triamide (nBTPT), sold under the trade name Agrotain®, is currently the most promising and effective when applied with urea or urine. Here we conduct a critical analysis of the published and non-published data on the effectiveness of nBTPT in reducing NH3 emission, from which adjusted values for FracGASF (fraction of total N fertiliser emitted as NH3) and FracGASM (fraction of total N from, animal manure and urine emitted as NH3) for the national agriculture greenhouse gas (GHG) inventory are recommended in order to provide accurate data for the inventory. We use New Zealand as a case study to assess and quantify the overall reduction in NH3 emission from urea and animal urine with the application of UI nBTPT. The available literature indicates that an application rate of 0.025% w/w (nBTPT per unit of N) is optimum for reducing NH3 emissions from temperate grasslands. UI-treated urine studies gave highly variable reductions (11-93%) with an average of 53% and a 95% confidence interval of 33-73%. New Zealand studies, using UI-treated urea, suggest that nBTPT (0.025% w/w) reduces NH3 emissions by 44.7%, on average, with a confidence interval of 39-50%. On this basis, a New Zealand specific value of 0.055 for FracGASF FNUI (fraction of urease inhibitor treated total fertiliser N emitted as NH3) is recommended for adoption where urea containing UI are applied as nBTPT at a rate of 0.025% w/w. Only a limited number of published data sets are available on the effectiveness of UI for reducing NH3 losses from animal urine-N deposited during grazing in a grazed pasture system. The same can be said about mixing UI with urine, rather than spraying UI before or after urine application. Since it was not possible to accurately measure the efficacy of UI in reducing NH3 emissions from animal urine-N deposited during grazing, we currently cannot recommend the adoption of a FracGASM value adjusted for the inclusion of UI.
New Zealand Journal of Agricultural Research, 2013
ABSTRACT Using data from pastoral soils sampled by horizon at 56 locations across New Zealand, we... more ABSTRACT Using data from pastoral soils sampled by horizon at 56 locations across New Zealand, we conducted a meta-analysis. On average, the total depth sampled was 0.93±0.026 m (± SEM), and on a volumetric basis, the total C storage averaged 26.9±1.8, 13.9±0.6 and 9.2±1.4 kg C m−2 for allophanic (n=12), non-allophanic (n=40) and pumice soils (n=4), respectively. We estimated the total C storage, and quantified the uncertainty, using the data for samples taken from the uppermost A-horizon whose depth averaged 0.1±0.003 m. For A-horizon samples of the allophanic soils, the mean C content was 108±6 g C kg−1 and the bulk density was 772±29 kg m−3, for non-allophanic soils they were 51±4 g C kg−1 and 1055±29 kg m−3, and for pumice soils they were 68±9 g C kg−1 and 715±45 kg m−3. The C density—a product of the C content and bulk density—of the A-horizon samples was proportional to their air-dried water content, a proxy measure for the mineral surface area. By linear regression with C density of the A-horizon, the total C storage could be estimated with a standard error of 3.1 kg C m−2, 19% of the overall mean.
ABSTRACT Urine deposited by grazing animals in patches is the single largest source of N2O emissi... more ABSTRACT Urine deposited by grazing animals in patches is the single largest source of N2O emissions in New Zealand. In recent years, a nitrification inhibitor, dicyandiamide (DCD) has been developed that substantially reduces these emissions. However, uncertainty exists about the sustained effectiveness of repeated use of DCD on reducing N2O emissions from urine patches. The aim of this study was to determine if DCD application for 4 or 5 consecutive yr alters its effectiveness to reduce N2O emissions from cow urine patches (EF3). A second objective was to summarise results of New Zealand studies published in the last decade on effects of DCD to reduce N2O emissions from animal urine. At ‘repeated-DCD-use’ sites and ‘non-DCD’ sites in Canterbury and Southland (New Zealand), N2O emissions were measured for 6mo from three treatments being: Control, Control+DCD, Urine and Urine+DCD. At the Canterbury site, DCD application reduced (P
1. Cadmium is a naturally occurring heavy metal in soils. Cadmium is only acutely toxic at very h... more 1. Cadmium is a naturally occurring heavy metal in soils. Cadmium is only acutely toxic at very high levels, but it does accumulate in kidneys and livers which can lead to chronic toxicity problems. Current dietary surveys for New Zealander’s indicate that the daily intake of cadmium is lower than the World Health Organisation (WHO) tolerable daily intake guidelines. It is unlikely that at current food cadmium levels there are any adverse health implications for the New Zealand population. However, there is some potential for the intake guidelines to change in future as new science come to hand, and there is a need for continued vigilance. 2. Phosphate fertiliser is the primary source of cadmium accumulation in agricultural soils, and the industry has imposed a voluntary limit on the levels of cadmium in fertilisers. However, low cadmium sources of phosphate rock are limited in supply and uncertain in their availability. Moreover there are no commercially viable processes for removi...
The New Zealand Agricultural Greenhouse Gas Research Centre was recently established. One of thre... more The New Zealand Agricultural Greenhouse Gas Research Centre was recently established. One of three core science areas will develop management guidelines for the conservation and, where likely, sustainable increase of soil carbon (C) storage associated with land-based food and fibre producing activities. It has been estimated that soils beneath grazed pasture store 85% of New Zealand's soil C to a depth of 0.3 m. Research has improved estimation at a national scale, but pastoral soils data remains fragmented, geographic coverage limited, and most samples obtained from a depth <0.1 m. There has been little research about manipulating and verifying C storage rate in soils beneath grazed pasture. For these soils, C storage is already substantial including some from primal forest vegetation cleared by European settlers around 150 years ago. Modelling will develop better understanding of influential soil C cycling processes in grazed pasture systems. A potential for soil C storage ...
A field trial was conducted on a yellow-grey earth in the Hawke’s Bay (mean annual rainfall 875 m... more A field trial was conducted on a yellow-grey earth in the Hawke’s Bay (mean annual rainfall 875 mm) over a period of 5 years to measure the effects of lime applications (0, 5, 10 t/ha) on soils high (50 kg P/ha applied annually) or low (5 kg P/ha applied annually) in phosphorus (P). The average annual pasture production on this dryland soil in the absence of applied lime or P was 5060 kg DM/ha (range 3861-6024). The botanical composition of the pasture was variable, average annual legume composition (4/o on DM basis) ranging from 3 to 42%. The predominant. legume was subterranean clover (Trifolium subterranean) with white clover (Trifolium repens) making a small contribution in some years. In the first two years after application responses to lime were large (lo-20%), due entirely to liming stimulating the grass component of the pasture, and consistent with liming enhancing the rate of net mineralisation of soil organic nitrogen (N). In years three and-four-the-dominant treatment ef...
In New Zealand, the demand for nitrogen fertiliser has increased markedly since the early 1980s. ... more In New Zealand, the demand for nitrogen fertiliser has increased markedly since the early 1980s. Potentially, this trend has significant environmental and climate change implications. While many factors could contribute to this trend, little work has been done to examine the drivers of increased use of nitrogen fertiliser in New Zealand. In this paper, we review the international literature and
Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted anim... more Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted animal urine. In soil, urea hydrolyses rapidly to ammonium (NH4(+)) and may be lost as ammonia (NH3) gas. Unlike nitrous oxide (N2O), however, NH3 is not a greenhouse gas although it can act as a secondary source of N2O, and hence contribute indirectly to global warming and stratospheric ozone depletion. Various urease inhibitors (UIs) have been used over the last 30 years to reduce NH3 losses. Among these, N-(n-butyl) thiophosphoric triamide (nBTPT), sold under the trade name Agrotain®, is currently the most promising and effective when applied with urea or urine. Here we conduct a critical analysis of the published and non-published data on the effectiveness of nBTPT in reducing NH3 emission, from which adjusted values for FracGASF (fraction of total N fertiliser emitted as NH3) and FracGASM (fraction of total N from, animal manure and urine emitted as NH3) for the national agriculture greenhouse gas (GHG) inventory are recommended in order to provide accurate data for the inventory. We use New Zealand as a case study to assess and quantify the overall reduction in NH3 emission from urea and animal urine with the application of UI nBTPT. The available literature indicates that an application rate of 0.025% w/w (nBTPT per unit of N) is optimum for reducing NH3 emissions from temperate grasslands. UI-treated urine studies gave highly variable reductions (11-93%) with an average of 53% and a 95% confidence interval of 33-73%. New Zealand studies, using UI-treated urea, suggest that nBTPT (0.025% w/w) reduces NH3 emissions by 44.7%, on average, with a confidence interval of 39-50%. On this basis, a New Zealand specific value of 0.055 for FracGASF FNUI (fraction of urease inhibitor treated total fertiliser N emitted as NH3) is recommended for adoption where urea containing UI are applied as nBTPT at a rate of 0.025% w/w. Only a limited number of published data sets are available on the effectiveness of UI for reducing NH3 losses from animal urine-N deposited during grazing in a grazed pasture system. The same can be said about mixing UI with urine, rather than spraying UI before or after urine application. Since it was not possible to accurately measure the efficacy of UI in reducing NH3 emissions from animal urine-N deposited during grazing, we currently cannot recommend the adoption of a FracGASM value adjusted for the inclusion of UI.
New Zealand Journal of Agricultural Research, 2013
ABSTRACT Using data from pastoral soils sampled by horizon at 56 locations across New Zealand, we... more ABSTRACT Using data from pastoral soils sampled by horizon at 56 locations across New Zealand, we conducted a meta-analysis. On average, the total depth sampled was 0.93±0.026 m (± SEM), and on a volumetric basis, the total C storage averaged 26.9±1.8, 13.9±0.6 and 9.2±1.4 kg C m−2 for allophanic (n=12), non-allophanic (n=40) and pumice soils (n=4), respectively. We estimated the total C storage, and quantified the uncertainty, using the data for samples taken from the uppermost A-horizon whose depth averaged 0.1±0.003 m. For A-horizon samples of the allophanic soils, the mean C content was 108±6 g C kg−1 and the bulk density was 772±29 kg m−3, for non-allophanic soils they were 51±4 g C kg−1 and 1055±29 kg m−3, and for pumice soils they were 68±9 g C kg−1 and 715±45 kg m−3. The C density—a product of the C content and bulk density—of the A-horizon samples was proportional to their air-dried water content, a proxy measure for the mineral surface area. By linear regression with C density of the A-horizon, the total C storage could be estimated with a standard error of 3.1 kg C m−2, 19% of the overall mean.
ABSTRACT Urine deposited by grazing animals in patches is the single largest source of N2O emissi... more ABSTRACT Urine deposited by grazing animals in patches is the single largest source of N2O emissions in New Zealand. In recent years, a nitrification inhibitor, dicyandiamide (DCD) has been developed that substantially reduces these emissions. However, uncertainty exists about the sustained effectiveness of repeated use of DCD on reducing N2O emissions from urine patches. The aim of this study was to determine if DCD application for 4 or 5 consecutive yr alters its effectiveness to reduce N2O emissions from cow urine patches (EF3). A second objective was to summarise results of New Zealand studies published in the last decade on effects of DCD to reduce N2O emissions from animal urine. At ‘repeated-DCD-use’ sites and ‘non-DCD’ sites in Canterbury and Southland (New Zealand), N2O emissions were measured for 6mo from three treatments being: Control, Control+DCD, Urine and Urine+DCD. At the Canterbury site, DCD application reduced (P
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