C.A.M. de Klein

Targeted technologies for nitrous oxide abatement from animal agriculture

Nitrous oxide (N2O) emissions account for ~10% of global greenhouse gas (GHG) emissions, with most of these emissions (~90%) deriving from agricultural practices. Animal agriculture potentially contributes up to 50% of total agricultural N2O emissions. In intensive animal agriculture, high N2O emission rates generally coincide with anaerobic soil conditions and high soil NO3–, primarily from animal urine patches. This paper provides an overview of animal, feed-based and soil or management abatement technologies for ruminant animal agriculture targeted at reducing the size of the soil NO3– pool or improving soil aeration. Direct measurements of N2O emissions from potential animal and feed-based intervention technologies are scarce. However, studies have shown that they have the potential to reduce urinary N excretion by 3–60% and thus reduce associated N2O emissions. Research on the effect of soil and water management interventions is generally further advanced and N2O reduction potentials of up to 90% have been measured in some instances. Of the currently available technologies, nitrification inhibitors, managing animal diets and fertiliser management show the best potential for reducing emissions in the short-term. However, strategies should always be evaluated in a whole-system context, to ensure that reductions in one part of the system do not stimulate higher emissions elsewhere. Current technologies reviewed here could deliver up to 50% reduction from an animal housing system, but only up to 15% from a grazing-based system. However, given that enteric methane emissions form the majority of emissions from grazing systems, a 15% abatement of N2O is likely to translate to a 2–4% decrease in total GHG emissions at a farm scale. Clearly, further research is needed to develop technologies for improving N cycling and reducing N2O emissions from grazing-based animal production systems.

Prioritisation of farm scale remediation efforts for reducing losses of nutrients and faecal indicator organisms to waterways: a case study of New Zealand dairy farming.

The international competitiveness of the New Zealand (NZ) dairy industry is built on low cost clover-based systems and a favourable temperate climate that enables cows to graze pastures mostly all year round. Whilst this grazed pasture farming system is very efficient at producing milk, it has also been identified as a significant source of nutrients (N and P) and faecal bacteria which have contributed to water quality degradation in some rivers and lakes. In response to these concerns, a tool-box of mitigation measures that farmers can apply on farm to reduce environmental emissions has been developed. Here we report the potential reduction in nutrient losses and costs to farm businesses arising from the implementation of individual best management practices (BMPs) within this tool-box. Modelling analysis was carried out for a range of BMPs targeting pollutant source reduction on case-study dairy farms, located in four contrasting catchments. Due to the contrasting physical resources and management systems present in the four dairy catchments evaluated, the effectiveness and costs of BMPs varied. Farm managements that optimised soil Olsen P levels or used nitrification inhibitors were observed to result in win-win outcomes whereby nutrient losses were consistently reduced and farm profitability was increased in three of the four case study farming systems. Other BMPs generally reduced nutrient and faecal bacteria losses but at a small cost to the farm business. Our analysis indicates that there are a range of technological measures that can deliver substantial reductions in nutrient losses to waterways from dairy farms, whilst not increasing or even reducing other environmental impacts (e.g. greenhouse gas emissions and energy use). Their implementation will first require clearly defined environmental goals for the catchment/water body that is to be protected. Secondly, given that the major sources of water pollutants often differed between catchments, it is important that BMPs are matched to the physical resources and management systems of the existing farm businesses.

An analysis of environmental and economic implications of nil and restricted grazing systems designed to reduce nitrate leaching from New Zealand dairy farms. I. Nitrogen losses

Abstract Nitrate leaching is perceived to be a serious consequence of dairy farming due to the uneven return of N in small concentrated urine patches. Management systems in which the direct deposition of urine is avoided throughout the year (nil grazing) or during autumn/winter when the risk of nitrate leaching is highest (restricted grazing) could potentially reduce nitrate leaching. However, possible disadvantages of such systems include a reduction in the clover content of pastures, increases in gaseous losses, and increases in capital and/or operating costs. This paper examines some of the effects of nil and restricted grazing management systems for dairy farming on N flows and losses to the environment. The estimates of N losses are based on the results of a long‐term farmlet study under conventional grazing, on data for an average New Zealand farm, and on literature information. The analysis showed that in nil grazing systems nitrate leaching losses may be reduced by 55–65% compared with conventional grazing systems, and by 35–50% in restricted grazing systems. For nil grazing systems, however, total N losses were 10–35% higher than under conventional grazing because of increased gaseous losses. The total N losses from restricted grazing systems were similar (‐10 to +5%) to those from conventional systems. The analysis showed the potential benefit of a restricted grazing system as a management tool to reduce nitrate leaching losses, especially in areas where contamination of ground and surface waters is ol particular concern.

Statistical analysis of nitrous oxide emission factors from pastoral agriculture field trials conducted in New Zealand

Between 11 May 2000 and 31 January 2013, 185 field trials were conducted across New Zealand to measure the direct nitrous oxide (N2O) emission factors (EF) from nitrogen (N) sources applied to pastoral soils. The log(EF) data were analysed statistically using a restricted maximum likelihood (REML) method. To estimate mean EF values for each N source, best linear unbiased predictors (BLUPs) were calculated. For lowland soils, mean EFs for dairy cattle urine and dung, sheep urine and dung and urea fertiliser were 1.16 ± 0.19% and 0.23 ± 0.05%, 0.55 ± 0.19% and 0.08 ± 0.02% and 0.48 ± 0.13%, respectively, each significantly different from one another (p < 0.05), except for sheep urine and urea fertiliser. For soils in terrain with slopes >12°, mean EFs were significantly lower. Thus, urine and dung EFs should be disaggregated for sheep and cattle as well as accounting for terrain.

An analysis of environmental and economic implications of nil and restricted grazing systems designed to reduce nitrate leaching from New Zealand dairy farms. II. Pasture production and cost/benefit analysis

Abstract Nitrate leaching from animal urine is perceived to be a serious consequence of dairy farming. Previous results suggested that nil and restricted grazing systems could reduce nitrate leaching by up to 50%. It is likely that such systems may also increase pasture production. However, potential disadvantages include reduction in the clover content of pastures and increase in capital and/or operating costs. This paper examines the economic implications of nil and restricted grazing systems based on data from an average New Zealand dairy farm and from a long‐term farmlet study. The analyses suggested that pasture production increased by about 20% and 2–8%, respectively, compared with a conventional grazing system. Based on the average New Zealand dairy farm, the costs/benefit analysis of the nil grazing system suggested a negative return on capital of about ‐10%. For the restricted grazing system, the average return on capital was about 9% (range: ‐4 to 25%) and depended largely on the efficiency of animal excreta use. On farms where an effluent application system is already in place, the average return on capital was 17% (range: 2 to 50%). Based on the farmlet study, the cost/benefit analysis of both grazing systems suggested a small negative return on capital, except when the costs of an effluent application system were excluded. It is concluded that a restricted grazing system for the average New Zealand dairy farm is likely to be economically viable, on farms where an effluent application system or a feed pad is already in place.Abstract Nitrate leaching from animal urine is perceived to be a serious consequence of dairy farming. Previous results suggested that nil and restricted grazing systems could reduce nitrate leaching by up to 50%. It is likely that such systems may also increase pasture production. However, potential disadvantages include reduction in the clover content of pastures and increase in capital and/or operating costs. This paper examines the economic implications of nil and restricted grazing systems based on data from an average New Zealand dairy farm and from a long‐term farmlet study. The analyses suggested that pasture production increased by about 20% and 2–8%, respectively, compared with a conventional grazing system. Based on the average New Zealand dairy farm, the costs/benefit analysis of the nil grazing system suggested a negative return on capital of about ‐10%. For the restricted grazing system, the average return on capital was about 9% (range: ‐4 to 25%) and depended largely on the efficiency of a...

The effectiveness of dicyandiamide in reducing nitrous oxide emissions from a cattle-grazed, winter forage crop in Southland, New Zealand

A study was conducted in Southland, New Zealand to: (i) measure nitrous oxide (N2O) emissions and nitrate (NO3–-N) leaching losses from a cattle-grazed, winter forage crop; and (ii) quantify the effect of dicyandiamide (DCD) in reducing these losses. Drainage losses were measured for 12 months (December 2005–November 2006) from a December-sown kale crop using 12 hydrologically isolated drainage plots at the Woodlands Research Station. N2O emissions were measured for 6 months (June–November) following simulated grazing of the crop in mid-June. N2O emissions from the bare ground following grazing of the crop amounted to 3.6 kg nitrogen (N)/ha for the winter–spring period. This figure is higher than that measured for pasture on the same soil type over a similar period. DCD application significantly reduced N2O emissions for the whole crop area by 25% over this period and reduced the N2O emission factor for urine by 54%. DCD application increased the length of time mineral N (0–10 cm soil depth) was maintained in the ammonium form and significantly reduced soil NO3–-N levels for 6 weeks following the simulated grazing. Annual NO3–-N losses in drainage under this winter forage crop were relatively high at 79 kg N/ha.year, with the majority of this (67%) being lost over the wet summer months (December–January rainfall 434 mm or 200% of normal) during crop growth. The application of DCD following the grazing resulted in a 47% decrease in NO3–-N leached over the winter–spring period (26 kg N/ha v. 14 kg N/ha) with this equating to a 29% decrease over the full 12-month measurement period. This study suggested that winter forage crops are major contributors to N losses from livestock farming systems in Southland and that DCD application following the grazing of such crops by cattle can significantly reduce N2O emissions and leaching N losses.

Soil acidification: A provisional model for New Zealand pastoral systems

Abstract Soil acidification is a major problem internationally and occurs in pastoral systems as a result of nitrate leaching, nutrient transfer/removal, and soil organic matter (SOM) accumulation. Existing mechanistic models on soil acidification calculate acidification rates retrospectively, based on quantitative information on these acidifying processes. This paper presents an outline of a predictive soil acidification model that includes sub‐models for estimating the extent of nitrate leaching, nutrient transfer/removal, and soil organic matter accumulation. The model was used to predict acidification rates in a fertiliser trial on sheep‐grazed pastures, receiving superphosphate fertiliser for 35 years. The predicted rates ranged from 1.46 to 3.83 kmolc/ha.year, which was in moderate agreement with acid additions rates of 3.09 to 3.43 kmolc/ha.year as calculated from measured changes in soil pH and the pH buffer capacity (pHBC). Further development of the model is needed to include a SOM accumulation ...

Integration of measures to mitigate reactive nitrogen losses to the environment from grazed pastoral dairy systems

The need for nitrogen (N) efficiency measures for dairy systems is as great as ever if we are to meet the challenge of increasing global production of animal-based protein while reducing N losses to the environment. The present paper provides an overview of current N efficiency and mitigation options for pastoral dairy farm systems and assesses the impact of integrating a range of these options on reactive N loss to the environment from dairy farms located in five regions of New Zealand with contrasting soil, climate and farm management attributes. Specific options evaluated were: (i) eliminating winter applications of fertilizer N, (ii) optimal reuse of farm dairy effluent, (iii) improving animal performance through better feeding and using cows with higher genetic merit, (iv) lowering dietary N concentration, (v) applying the nitrification inhibitor dicyandiamide (DCD) and (vi) restricting the duration of pasture grazing during autumn and winter. The Overseer® Nutrient Budgeting model was used to estimate N losses from representative farms that were characterized based on information obtained from detailed farmer surveys conducted in 2001 and 2009. The analysis suggests that (i) milk production increases of 7–30% were associated with increased N leaching and nitrous oxide (N2O) emission losses of 3–30 and 0–25%, respectively; and (ii) integrating a range of strategic and tactical management and mitigation options could offset these increased N losses. The modelling analysis also suggested that the restricted autumn and winter grazing strategy resulted in some degree of pollution swapping, with reductions in N leaching loss being associated with increases in N loss via ammonia volatilization and N2O emissions from effluents captured and stored in the confinement systems. Future research efforts need to include farm systems level experimentation to validate and assess the impacts of region-specific dairy systems redesign on productivity, profit, environmental losses, practical feasibility and un-intended consequences.

Short-term measurement of N2O emissions from sheep-grazed pasture receiving increasing rates of fertiliser nitrogen in Otago, New Zealand

The purpose of this short-term study was to investigate the effect of increasing fertiliser nitrogen (N) application rates on nitrous oxide (N2O) emissions over the late winter/early spring period from sheep-grazed pasture in Otago rolling hill country. We measured N2O gas emissions from plots on a mottled Fragic Pallic hill soil receiving 0, 100 and 500 kg N/ha.year for 2 years. Plots were sampled weekly for 10 weeks over the 2006 winter/spring period using a static chamber method. Increased N fertiliser rate and the attendant increase in stocking rate significantly increased total N2O emissions (P < 0.05). Total N2O emissions for the measurement period were estimated to be 0.08, 0.13 and 1.36 kg N2O-N/ha (s.e.m, 0.1, 0.18 and 0.45) for the 0, 100 and 500 N treatments, respectively. Our results suggest that high application rates of fertiliser N (i.e. 500 kg N/ha.year) and attendant increased stocking rates may significantly increase emissions of N2O even in dry winter/spring conditions in Otago rolling hill country. These results will assist in the development of best management guidelines for reducing N2O emissions from fertiliser N in hill country.

The impact of potential nitrous oxide mitigation strategies on the environmental and economic performance of dairy systems in four New Zealand catchments

Abstract The expansion of the New Zealand dairy industry has resulted in growing concern about the environmental impacts. As such, efforts are being made to design environmentally and economically sustainable management strategies. In this desktop study, the performance of two management strategies was assessed for dairy systems in four New Zealand catchments. Survey and monitoring information on farm management, farm production, and soils was used to estimate nitrous oxide (N2O) and total greenhouse gas (GHG, i.e. N2O, methane and carbon dioxide) emissions, nitrate leaching and profitability of farms under current management, and of farms using wintering pads and nitrification inhibitors. Under the wintering pad option, it was estimated that N2O emissions decreased by up to 8%, total GHG emissions increased by up to 10%, and nitrate leaching losses decreased by up to 44%. In terms of economic performance, wintering pads slightly decreased farm Earnings Before Interest and Tax (EBIT) on three of the four catchments. On the other hand, the use of a nitrification inhibitor has the potential to reduce N2O emissions, total GHG emissions and nitrate leaching losses from all catchment case study farms while increasing the EBIT. This study suggested that nitrification inhibitors can be a cost-effective mitigation strategy for reducing dairy farm N emissions to air and water. The analysis also illustrated the importance of assessing environmental mitigation strategies at a farm-systems level, including relevant off-farm activities.