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Landcare Research is New Zealand's leading provider of solutions and advice for sustainable development and the management of land-based natural resources.
Landcare includes teams of researchers with skills relevant to the Centre in agricultural greenhouse gas emission measurement, carbon exchange and inventory development, soil science, lifecycle assessment and social science.
Modelling NH3 volatilisation within a urine patch using NZ-DNDC
Giltrap, D., S. Saggar, et al. (2017). "Modelling NH3 volatilisation within a urine patch using NZ-DNDC." Nutrient Cycling in Agroecosystems 108(3): 267-277.
Urea concentrations in urine patches deposited during animal grazing can be over ten times higher than typical fertiliser application rates, potentially leading to large ammonia (NH3) losses. The processbased NZ-DNDC model was modified to better simulate soil pH changes and ammonia (NH3) emissions following urine application using data collected from a New Zealand field trial. After modification, simulated 30-day NH3 emissions decreased from 506 to 117 kg N ha-1 compared to measured emissions of 78 ± 3 kg N ha-1 (mean ± standard error) and the Nash–Sutcliffe Effi- ciency (NSE) for daily NH3 emissions increased from -7.11 to ?0.97 for the parameterisation dataset. However, modified model correctly estimated the cumulative emissions for the first 7 days. Using the same parameterisation on an independent dataset from a nearby site gave cumulative 18-day NH3 emissions of 84 kg N ha-1 compared to the measured 48 ± 2 kg N ha-1 (mean ± standard error). However, the NSE for daily NH3 emissions was -0.71, indicating site specific parameterisation might be needed. The sensitivity of NH3 emissions to ±5 and ±10% errors in 4 model parameters was tested. The sensitivities ranged from -0.36 to ?0.71. The highest sensitivity was to the rate of NH3 transfer from the soil solution to the atmosphere and the lowest sensitivity was to the rate of urea hydrolysis.
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The carbon balance of temperate grasslands part I: The impact of increased species diversity
S. Rutledge, A.M. Wall, P.L. Mudge, B. Troughton, D.I. Campbell, J. Pronger, C. Joshi, L.A. Schipper, The carbon balance of temperate grasslands part I: The impact of increased species diversity, Agriculture, Ecosystems & Environment, Volume 239, 2017, Pages 310-323, ISSN 0167-8809, http://dx.doi.org/10.1016/j.agee.2017.01.039.
- Annual C balances were measured for four years over three pastoral blocks on a New Zealand dairy farm.
- Two blocks were renewed to low and high diversity swards, and one block left as an unmodified control.
- Pasture renewal to either sward increased dry matter production relative to unmodified control.
- Renewal to high diversity sward resulted in reduced C loss compared to renewal to low diversity.
- Renewal to neither high nor low diversity sward had benefits for C sequestration over the unmodified control.
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A review of soil carbon change in New Zealand
Schipper, L. A., P. L. Mudge, et al. (2017). "A review of soil carbon change in New Zealand’s grazed grasslands." New Zealand Journal of Agricultural Research 60(2): 93-118.
Soil organic matter is a potential sink of atmospheric carbon (C) and critical for maintaining soil quality. We reviewed New Zealand studies of soil C changes after conversion from woody vegetation to pasture, and under long-term pasture. Soil C increased by about 13.7 t C ha−1 to a new steady state when forests were initially converted to pasture. In the last 3–4 decades, resampling of soil profiles demonstrated that under long-term pasture on flat land, soil C had subsequently declined for allophanic, gley and organic soils by 0.54, 0.32 and 2.9 t C ha−1 y−1, respectively, and soil C had not changed in the remainder of sampled soil orders. For the same time period, pasture soils on stable midslopes of hill country gained 0.6 t C ha−1 y−1. Whether these changes are ongoing is not known, except for the organic soils where losses will continue so long as they are drained. Phosphorus fertiliser application did not change C stocks. Irrigation decreased carbon by 7 t C ha−1. Carbon losses during pasture renewal ranged between 0.8 and 4.1 t C ha−1. Some evidence suggests tussock grasslands can gain C when fertilised and not overgrazed. When combined to the national scale, different data sets suggest either no change or a gain of C, but with large uncertainties. We highlight key land-use practices and soil orders that require further information of soil C stock changes and advocate for a better understanding of underpinning reasons for changes in soil C.
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The carbon balance of temperate grasslands part II: The impact of pasture renewal via direct drilling
S. Rutledge, A.M. Wall, P.L. Mudge, B. Troughton, D.I. Campbell, J. Pronger, C. Joshi, L.A. Schipper, The carbon balance of temperate grasslands part II: The impact of pasture renewal via direct drilling, Agriculture, Ecosystems & Environment, Volume 239, 2017, Pages 132-142, ISSN 0167-8809, http://dx.doi.org/10.1016/j.agee.2017.01.013
- Two blocks had pastures renewed (PR) by direct drill. A third block was a control.
- The PR blocks had smaller positive NEPs than the control block during the PR year.
- Duration of fallow is important in determining total CO2 losses due to PR
- Pasture renewal led to a negative carbon balance (soil C loss) for the PR year
- Addition of C (e.g. manure, effluent, feed) helps to mitigate soil C loss due to PR.
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The trade-offs between milk production and soil organic carbon storage in dairy systems under different management and environmental factors
Kirschbaum, M. U. F., L. A. Schipper, et al. (2017). "The trade-offs between milk production and soil organic carbon storage in dairy systems under different management and environmental factors." Science of the Total Environment 577: 61-72.
A possible agricultural climate change mitigation option is to increase the amount of soil organic carbon (SOC). Conversely, some factors might lead to inadvertent losses of SOC. Here, we explore the effect of various management options and environmental changes on SOC storage and milk production of dairy pastures in New Zealand. We used CenW 4.1, a process-based ecophysiological model, to run a range of scenarios to assess the effects of changes in management options, plant properties and environmental factors on SOC and milk production. We tested the model by using 2 years of observations of the exchanges of water and CO2 measured with an eddy covariance system on a dairy farm in New Zealand's Waikato region. We obtained excellent agreement between the model and observations, especially for evapotranspiration and net photosynthesis.
For the scenario analysis, we found that SOC could be increased through supplying supplemental feed, increasing fertiliser application, or increasing water availability through irrigation on very dry sites, but SOC decreased again for larger increases in water availability. Soil warming strongly reduced SOC. For other changes in key properties, such as changes in soil water-holding capacity and plant root:shoot ratios, SOC changes were often negatively correlated with changes in milk production.
The work showed that changes in SOC were determined by the complex interplay between (1) changes in net primary production; (2) the carbon fraction taken off-site through grazing; (3) carbon allocation within the system between labile and stabilised SOC; and (4) changes in SOC decomposition rates. There is a particularly important trade-off between carbon either being removed by grazing or remaining on site and available for SOC formation. Changes in SOC cannot be fully understood unless all four factors are considered together in an overall assessment.
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Can pH amendments in grazed pastures help reduce N2O emissions from denitrification? - The effects of liming and urine addition on the completion of denitrification in fluvial and volcanic soils
McMillan, A. M. S., P. Pal, et al. (2016). "Can pH amendments in grazed pastures help reduce N2O emissions from denitrification? - The effects of liming and urine addition on the completion of denitrification in fluvial and volcanic soils." Soil Biology and Biochemistry 93: 90-104.
Soil pH plays a critical role in determining the overall rate of several important processes in the agricultural nitrogen cycle. During denitrification, the activity of nitrous oxide reductase (N2O-R) is reduced at low pH. This effect has led to suggestions that soil pH adjustment via liming to enhance the activity of this enzyme might be a viable agricultural greenhouse gas mitigation strategy by enhancing the reduction of N2O in the soil to climatically inert N2. We assessed the effect of liming on the apparent activity of N2O-R by measuring the denitrification end products, N2O and N2, in a series of short-term anaerobic incubations. We compared a weakly-buffered fluvial soil and a well-buffered, volcanic soil under different incubation temperatures and in the presence or absence of a ~600 kg ha-1 cow urine-N amendment. Our results indicated that the liming effect was heavily modulated by soil type, temperature, and urine amendment. Liming (at rates of 1.5 and 3.0 t ha-1 for the volcanic soil and at rates of 5 and 10 t ha-1 for the fluvial soil) caused pH increases of between 0.43 and 1.25 pH units. The highest reductions in N2O in the fluvial soil occurred when the 1.5 t ha-1 rate was used in the fluvial soils under urine addition and at the higher temperature. The combined flux of N2O + N2 did not change with liming. However, an interaction of soil type and urine amendment caused large differences in the partitioning of the denitrification end-products between N2O and N2 - an effect that overwhelmed the relatively modest effects of liming. When the soils were amended with urine-N, the resulting denitrification gases from the volcanic soil were mostly in the form of N2O (60-77%), whereas in the fluvial soil the denitrification products were mostly in the form of N2 and a much smaller portion were in the form of N2O (11-45%). Nevertheless, we found liming-induced enhancements of N2O-R of 15-20% (P < 0.05) in urine-amended, fluvial soil. We suggest some possible mechanisms that would explain such large differences in the N2O/(N2O + N2) product ratio.
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Application of gibberellins to increase productivity and reduce nitrous oxide emissions in grazed grassland: a review of the evidence
David Whitehead, Grant R. Edwards, Assessment of the application of gibberellins to increase productivity and reduce nitrous oxide emissions in grazed grassland, Agriculture, Ecosystems & Environment, Volume 207, 1 September 2015, Pages 40-50, ISSN 0167-8809, https://doi.org/10.1016/j.agee.2015.03.019.
Emissions of nitrous oxide from grassland systems are attributable largely to the use of nitrogen fertilisers and the excreta deposited by grazing animals. There is increasing interest in using gibberellins as a naturally-occurring growth promotant of herbage that could be used to reduce the use of nitrogen fertilisers while leading to similar or greater increases in dry matter. This may provide practical opportunities to reduce nitrogen intake by ruminants and extend the seasonality of herbage growth in spring and autumn while reducing nitrogen losses, resulting in lower rates of nitrogen excretion by grazing animals and reduced nitrous oxide emissions. Our findings from a review of previous studies confirm that gibberellins promote dry matter production, especially when applied in early spring or late summer/early autumn. When gibberellins are applied alone without nitrogen fertiliser, the nitrogen concentration of herbage is reduced and the impacts on forage quality are small and often not significantly different from those for untreated controls. We calculated the consequences of enhanced herbage production on nitrogen excreta returned to the soil as urine by a grazing dairy cow and estimated that one application of gibberellins will result in a relative reduction in nitrous oxide emission per urination event of 18% when compared with emissions from using nitrogen fertiliser. We used the OVERSEER® model and nitrous oxide emissions factors to estimate the impacts of changing herbage dry matter production, foliage nitrogen concentration and timing of one application of gibberellins on annual nitrous oxide emissions for a dairy farm. For one application of gibberellins in late summer and early spring, we estimate reductions in nitrous oxide emissions of 1.6% and 1.3%, respectively, relative to the response for an untreated control. Incorporating the effects of reduced use of nitrogen fertiliser by substituting one split application of fertiliser in late summer or autumn with gibberellins, we estimate reductions on nitrous oxide emissions of between 5 and 6% relative to the response for the untreated control. We conclude that the use of gibberellins with reduced addition of nitrogen fertiliser has the potential to reduce nitrous emissions from grazed grassland. However, acceptance of widespread use of gibberellins will be dependent on cost benefit analysis for farmers.
Keywords: Forage quality; Gibberellins; Grassland production; Grazed grassland; Greenhouse gas mitigation; Nitrous oxide
Assessment of the application of gibberellins to increase productivity and reduce nitrous oxide emissions in grazed grassland
Emissions of nitrous oxide from grassland systems are attributable largely to the use of nitrogen fertilisers and the excreta deposited by grazing animals.
There is increasing interest in using gibberellins as a naturally-occurring growth promotant of herbage to reduce the use of nitrogen fertilisers while leading to similar or greater increases in dry matter.
In a study commissioned by the NZAGRC and carried out by Landcare Research, the conslusion reached is that the use of gibberellins with reduced addition of nitrogen fertiliser has the potential to reduce nitrous emissions from grazed grassland. However, acceptance of widespread use of gibberellins will be dependent on cost benefit analysis for farmers.
Carbon balance of an intensively grazed temperate dairy pasture over four years
S. Rutledge, P.L. Mudge, D.I. Campbell, S.L. Woodward, J.P. Goodrich, A.M. Wall, M.U.F. Kirschbaum, L.A. Schipper, Carbon balance of an intensively grazed temperate dairy pasture over four years, Agriculture, Ecosystems & Environment, Volume 206, 1 August 2015, Pages 10-20, ISSN 0167-8809, https://doi.org/10.1016/j.agee.2015.03.011.
We estimated the net ecosystem carbon (C) balance (NECB) of a temperate pasture in the North Island of New Zealand for four years (2008–2011). The pasture was intensively managed with addition of fertiliser and year-round rotational grazing by dairy cows. Climatic conditions and management practices had a large impact on CO2 exchange, with a severe drought in one year and cultivation in another both causing large short-term (∼3 months) net losses of CO2–C (100–200 g C m−2). However, CO2 was regained later in both of these years so that on annual timescales, the site was a CO2 sink or CO2 neutral. Management practices such as effluent application and harvesting silage also influenced non-CO2–C fluxes, and had a large impact on annual NECB. Despite these major environmental or management perturbations, both NEP and NECB were relatively constant on annual timescales. It is likely that this apparent resilience of the CO2 and C balance to perturbations was at least partly attributable to the relatively warm temperatures, also in winter, providing good growing conditions year-round (in the absence of major perturbations such as moisture stress). In several instances, the farmer’s decisions aimed at maintaining a constant milk yield between years also appeared to contribute to a relatively stable C balance.
Averaged over the full four-year study period, the site was a net sink for both CO2 (NEP = 165 ± 51 g C m−2 y−1), and total C (NECB = 61 ± 53 g C m−2 y−1) after non-CO2–C fluxes were accounted for. Annual NEP and NECB values were similar to results collated from other managed temperate grasslands on mineral soils globally, for which average NEP and NECB were 188 ± 44 g C m−2 y−1 and 44 ± 33 g C m−2 y−1, respectively. In the global dataset, we noted a general trend for increased C sequestration with increasing NEP, suggesting that it may be possible to meet the dual goal of increased pasture production (thus milk, meat and fiber production) and increasing soil C storage in managed temperate grasslands. Identification of management practices that increase C storage while maintaining or enhancing pasture production requires more standardised reporting between NECB studies, and experiments involving side-by-side comparison of treatment and control plots.
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Introducing Dr Jha
The NZAGRC would like to take this opportunity to congratulate Dr Neha Jha on recently completing her PhD and thank her for her contribution to date to the NZAGRC's nitrous oxide research programme.
Neha's PhD study involved steep learning curves on a number of different levels. Originally from Bihar in India, before her arrival in NZ she had never seen such big pastures, let alone cows and sheep grazing outside all day and night. Neha has a Master's degree in soil science and microbiology and these studies focused on Indian agriculture, which is much more diverse than the NZ pastoral system. "Dairying is also big in India", states Neha," but it is very different and the key issues that farmers face are not the same".
After completing her Master's degree, Neha was interested in developing her soil and microbiology skills further and sent through a proposal relating to nitrous oxide emissions from soil to Professor Surinder Saggar (LCR/Massey) and Dr Donna Giltrap (LCR). This proposal resulted in the offer of a PhD position at Massey University and involvement in the NZAGRC-funded denitrification research programme.
Neha's PhD focussed on understanding denitrification processes in different types of soils. During her PhD study, Neha spent a significant amount of time out in those rolling NZ pastures collecting soil samples of differing types from different geographical locations, then investigating their chemical and physical properties and the microbial communities present back in the lab. Key findings were that different soils have differing denitrification potentials, primarily due to the microbes present and soil management history. The end goal of this research is to recognise the soil and environmental factors that have potential to enhance the activity of denitrifiers in reducing nitrous oxide to nitrogen gas. This is vital for the development of novel and effective nitrous oxide mitigation technologies.
Dr Jha is currently completing a one-year postdoctoral position at Landcare Research, still working alongside Surinder Saggar. Her interests in soil, microbiology and greenhouse gases remain high and she is keen to continue publishing and working towards becoming a renowned and respected scientist. Her PhD has led to a number of presentations and she currently has two journal articles submitted for publication. Neha has enjoyed her time in NZ so far and, now that she feels she has conquered the kiwi accent and understands the culture, she is keen to remain here for the foreseeable future.
Biogeography and biophysicochemical traits link N2O emissions, N2O emission potential and microbial communities across New Zealand pasture soils
Sergio E. Morales, Neha Jha, Surinder Saggar, Biogeography and biophysicochemical traits link NO emissions, NO emission potential and microbial communities across New Zealand pasture soils, Soil Biology and Biochemistry, Volume 82, 2015, Pages 87-98, ISSN 0038-0717, http://dx.doi.org/10.1016/j.soilbio.2014.12.018.
The process of denitrification has been studied for decades, with current evidence suggesting that an ecosystem's ability to produce and emit N2O is controlled both by transient ‘proximal’ regulators (e.g. temperature, moisture, N availability) as well as distal regulators (e.g. soil type, microbial functional diversity, geography). In this study we use New Zealand soils as a model system to test the impact of distal regulators (i.e. geography) on microbial communities and their N2O emission potential. Using gas chromatography, soil chemical analyses, 16S amplicon sequencing, terminal restriction fragment length polymorphism (T-RFLP) and quantitative PCR (qPCR) on three denitrifier functional genes (nirS, nirK and nosZ), we assessed the factors linked to N2O emissions across a latitudinal gradient. Results show that soil drainage class, soil texture class, and latitude were powerful regulators of both emissions and emission end products (N2 vs. N2O). Mixed models demonstrate that a few variables (including latitude, texture class, drainage class and denitrifier community data [abundance and diversity] amongst others) were enough to predict both the amount and type of gas emitted. In addition we show that microbial community composition (based on 16S rRNA gene sequencing) can also be used to predict both the gas species and quantity emitted.
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Changes in denitrification rate and N2O/N2 ratio with varying soil moisture conditions in New Zealand pasture soils
Jha, N., Saggar, S., Tillman, R., & Giltrap, D. (2012). Changes in denitrification rate and N2O/N2 ratio with varying soil moisture conditions in New Zealand pasture soils In: Advanced Nutrient Management: Gains from the Past - Goals for the Future. (Eds L.D. Currie and C L. Christensen).
Denitrification is the primary process of N2O production in temperate grassland soils and accounts for 60% of the total N2O emissions globally. There are various soil and environmental factors that regulate denitrification and affect denitrification rate (DR) and N2O/ N2 ratio. Among these, soil moisture is the most important. Generally, DR increases and N2O/N2 ratio decreases with increasing soil water content. However, the effect of changing soil moisture on DR and N2O/N2 ratio may vary with the type of soil, its nutrient status and the management practices followed on the farm. The interrelationships among the various factors affecting DR are not very well quantified.
Therefore, the current study was planned to investigate the effect of soil moisture on DR and N2O/N2 ratio in five different New Zealand pasture soils with varying physical and chemical characteristics such as soil texture, total porosity, pH, NO3- and NH4+ content, total nitrogen (TN), total carbon (TC), microbial biomass carbon (MBC) and denitrification enzyme activity (DEA). The experiment involved incubation of surface (0-10cm) and subsurface (10-20cm) soil samples at field capacity (FC) and complete saturation at constant temperature (25oC). DR and N2O/N2 ratio were estimated using an acetylene inhibition (AI) technique.
Denitrification rates were higher in soils incubated at saturation than in soils incubated at FC. Similarly, the N2O/N2 ratio decreased in soils when incubated at saturation as compared to FC. The extent of these increases in DR and decreases in N2O/N2 ratio with increasing moisture content varied among the soils due to differences in NO3- and NH4+ content, MBC and DEA of the soils.
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