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Increasing the quantity of carbon stored in agricultural soils has the potential to offset emissions of GHGs to the atmosphere.
However, realising this potential is technically challenging when soil carbon stocks are already high as they are in New Zealand, potential changes in soil carbon are small and spatial variability is high.
The current NZAGRC programme has two components:
- Testing specific management practices that may increase the long term soil carbon store in field situations, and identifying factors that influence the stability of current or newly added soil carbon
- Developing and using models to predict how a range of management practices may influence long and short term soil carbon storage
We have also supported international work to map on farm soil carbon.
Professor Frank Kelliher, AgResearch
Dr David Whitehead, Landcare Research
Some clarification of the impacts of grassland intensification on food production, nitrogen release, greenhouse gas emissions and carbon sequestration: using the example of New Zealand
Anthony J. Parsons, John H. M. Thornley, Susanne Rasmussen and Jacqueline S. Rowarth, 2016, Some clarification of the impacts of grassland intensification on food production, nitrogen release, greenhouse gas emissions and carbon sequestration: using the example of New Zealand, CAB Reviews 2016 11, No. 054
We used an established, process-based model of the dynamics of carbon (C) and nitrogen (N) cycling between plants, soils and animals in grazed temperate pastures to clarify expectations of how some major components of intensification affect the outcomes (short-term and long-term) of alternative systems for food production and environmental impact. We use the example of New Zealand, due to its clear recent history of intensification, the level of concern and hence nature of research undertaken there. A transition from low-input drystock, to dairy (lactation) systems with higher N inputs in fertilizer, and/or C and N inputs in supplements, reveals how at the same intermediate N input, food yield (per ha) can be doubled, while environmental N release halved, with minimal impact on C sequestration. We stress the sources of sustained changes in N release (e.g. nitrate/ nitrous oxide) are altered inputs (fertilizer/supplements) and less so animal numbers in response to these. Much of the increased efficiency is due to ‘improved’ N partitioning in lactating (cf. dry) animals. A reversion to dry-stock (or ‘de-stocking’) therefore offers greater environmental challenge, unless N inputs decline accordingly. Responses to supplements (being a source of C) re-inforce how the driving limitation to the grazed ecosystem is C capture per ha, and we highlight the need for a renewed focus on fundamental research on plant C uptake per ha per unit of N input. We offer a graphical method for visualizing the outcomes of options, and their trade-offs, with implications for policy and future research direction.
Keywords: Intensification, Carbon sequestration, Nitrogen use efficiency, Supplements, Dairy production
Producing a farm-scale soil carbon map
The study site is the Massey University Tuapaka hill country farm. This 470-ha farm, 15 km NW of Palmerston North, consists of two distinctive management blocks – the terrace flats and the hill block.
A legacy soil map was digitised and used to produce soil and parent material datalayers for the digital soil mapping exercise. LIDAR survey data were provided to the project, at a resolution of approximately 1 measurement per square metre in open ground, and processed into a 5-m resolution digital elevation model (DEM). This model was then further processed into additional terrain attribute layers, including slope, aspect, relative wetness (displayed as a wetness index), geomorphological features , and global solar irradiation layers (Figure 5).
These environmental datalayers are used twice in the digital soil mapping process. First, they are used to determine where initial soil carbon measurements should be obtained. This initial sampling method ensures that soils are sampled to proportionally represent the full range of topographic features in the target area and cover the full range of likely soil organic carbon stocks. Second, the datalayers are used together with soil carbon spot measurements to predict a soil carbon map.
Soil cores were collected from 50 stratified positions, and soil carbon stocks were determined at these positions. This dataset was then combined in the spatial modelling step to produce the soil carbon map (Figure 5).
Figure 5: The elevation map, derived from the LIDAR survey, is analysed to give, for example, slope, aspect, wetness index, geomorphic units and solar irridiation maps. Digital soil mapping uses these maps with any other relevant data, such as legacy soil maps, climate layers and geology maps, together with soil carbon spot measurements, to develop a prediction model and produce the soil carbon map.
Reducing New Zealand's agricultural emissions: Mapping soil organic carbon stocks
This publication provides an overview of how we can map the amount of carbon stored in New Zealand soils.
NZAGRC welcomes PCE report on agricultural GHG mitigationWednesday, 19 October 2016The Parliamentary Commissioner for the Environment’s report into greenhouse gas emissions from agriculture highlights the need for a suite of mitigation solutions rather than a single silver bullet.
Report: Potential applications of full inversion tillage to increase soil carbon storage during pasture renewal in New ZealandThis report reviews the potential to use full inversion tillage (FIT) during pasture renewal to increase the soil organic carbon (SOC) stocks of New Zealand’s High Producing Grasslands.December 2015Download this report
KuDos to Aaron Wall of Waikato University
University of Waikato technician, and a pivotal player in the NZAGRC-funded soil carbon programme, Aaron Wall was a winner in last month’s 2015 KuDos Hamilton Science Excellence Awards.
The School of Science Technical Officer picked up the top award in the Hill Laboratories Laboratory Technologist Award section.
Aaron spends much of his time expertly managing the Troughton farm site for the NZAGRC programme. Additionally, he also manages the access to the site for related research by AgResearch, Plant and Food Research and Landcare Research. His excellent relationship with the farm owners, and unsung heros of the whole operation, Ben and Sarah, enables everything to run smoothly.
On top of overseeing what goes on and when at the Troughton site, Aaron is a key part of the NZAGRC research team. He has made considerable novel advances in analysis of eddy covariance data, collation of non-CO2 data and pushed the team to collect additional data that are now proving to be crucial. Aaron is able to bring together deeply technical analysis tools with on-farm understanding and his colleagues feel extremely lucky to have him in their team.
Well done Aaron!
See Aaron in action here: https://youtu.be/qFYZ4R1f-RA
Two PhD studentships in New Zealand: Soil carbon stabilisation and resistance to loss
There are two PhD studentships available that will contribute to a wider programme of research funded by the Global Partnership for Livestock Emission Research entitled: MANAGEMENT OPTIONS FOR INCREASING SOIL CARBON UNDER GRASSLANDS. The PhD students will be based at the University of Waikato (Hamilton, North Island) and Lincoln University (near Christchurch, South Island) and will work closely together to deliver the project objectives.
Intensification of pastoral farming is occurring widely throughout New Zealand (NZ) and the effects on soil processes such as soil carbon storage and stabilisation are poorly known. Some evidence suggests that species-diverse pastures and intensification with irrigation can enhance both pasture production and soil carbon storage. But how stable is this stored carbon and what are the factors that affect its resistance to loss? We have assembled an international team with specialist skills to measure and model the impact of these pasture management practices on soil carbon stabilisation and turnover using advanced stable-isotope techniques. Our findings will be used to develop and validate a process-based model (CenW) that will be used to determine management options for increasing soil carbon stabilisation and its resistance to climate change.
Project 1: Belowground partitioning and stabilisation of pasture-fixed carbonThis PhD project will focus on determining how species-diverse pastures and intensification with irrigation practices affect the stabilisation of C in soils. It will deploy stable isotope techniques to quantifying the C fixed by pasture species and its partitioning to aboveground and belowground components under the different management system. It will also apply physical, chemical and biological fractionation techniques to evaluate the stability of the soil organic C fixed by pastures. The appointee for project 1 will be based at Lincoln University and the nearby New Zealand Institute for Plant and Food Research, Lincoln.
Project 2: Resistance of incorporated soil carbon to lossThis PhD will examine the resistance of stored C to loss in the face of variation in temperature and moisture and physical disturbance. Physical disturbance occurs in pastures during grazing and pasture renewal, whereas temperature and moisture vary naturally and as a product of irrigation and climate change. These disturbances will be used to test and rank the resistance of stored C from different pasture management practices to loss. This project will also use stable isotopes to separate the response of different pools of carbon in soil. The appointee for project 2 will be based at the University of Waikato, within the WaiBER research group (www.waiber.com).
The appointees will each receive a PhD stipend of $27,000 (NZD) per year and have their enrolment fees paid. Funding will be for three years, with provision for a further 6 months of support if required. For more information and to apply for a position, please visit www.careers.plantandfood.co.nz (vacancy number 13948). Applications should include a cover letter with a brief statement of research interests and experience, CV, transcripts and contact information for two referees. Please indicate in your cover letter whether you have a preference for one of the PhD topics and why.
For more information contact:
Prof Louis Schipper firstname.lastname@example.org
Prof Tim Clough email@example.com
Dr Mike Beare firstname.lastname@example.org
Applications open 7 October 2015 and close 6 November 2015.
Soil and pasture research that is sweet enough to eat
Scientific knowledge is usually communicated through text, diagrams and graphs, but the Waikato Biogeochemistry and Ecohydrology Research group (WaiBER) offers an alternative means of communication - via the medium of cake.
Once a paper is accepted, group members are encouraged to make a research cake that summarises the paper to enjoy and celebrate with their colleagues.
The NZAGRC is proud to have played a part in the generation of two recent, clever and edible research cakes (and the papers that inspired them).
The first of these cakes was prepared by Sam McNally (PhD candidate supported by NZAGRC) on acceptance of his first research paper in the journal Plant and Soil. Sam is supervised by Professor Louis Schipper at the University of Waikato.
Sam's paper compared root biomass of ryegrass/clover and more diverse pastures (including plantain, chicory, and lucerne) over the seasons of a year. He found greater root biomass in the more diverse pastures, which also had deeper rooting. The hypothesis is then posed that this greater biomass will increase carbon inputs and potentially storage in soil.
On Sam's cake, the diverse pasture is on the left and you can see greater rooting depth and biomass down the side. Lego man is taking cores on either side of the wooden fence.
McNally, S.R.; Laughlin, D.C.; Rutledge, S.; Dodd, M.B.; Six, J.; Schipper, L.A, 2015. Root carbon inputs under moderately diverse sward and conventional ryegrass-clover pasture: implications for soil carbon sequestration. Plant and Soil. http://dx.doi.org/10.1007/s11104-015-2463-z
The second cake was produced by Dr Susanna Rutledge to celebrate the publication of a paper in Agriculture, Ecosystems and Environment that looked at the carbon balance of a dairy grazed pasture at Scott Farm over four years. This project receives funding from the NZAGRC.
Depicted on the colourful cake is the average carbon inputs and outputs in units of jellybeans (jb), where 1 jb = 200 kgC/ha.y. Inputs (left side) include imported feed, effluent and the net of carbon dioxide exchange. Outputs include milk export, silage and methane. The balance (3 jelly beans) is assumed stored in soil.
S. Rutledge, P.L. Mudge, D.I. Campbell, S.L. Woodward, J.P. Goodrich, A. M. Wall, M.U.F. Kirschbaum, L.A. Schipper, 2015. Carbon balance of an intensively grazed temperate dairy pasture over four years. Agriculture, Ecosystems and Environment, 206, 10-20 http://dx.doi.org/10.1016/j.agee.2015.03.011
Research cakes are a novel way to portray - and celebrate - research done within the WaiBER group.
Check out the other mouth-watering and thought-provoking cakes at http://waiber.com/research-cake
If your work under the NZAGRC-PGgRc science programme is celebrated in an interesting way - or if your work has produced some really great results recently - let us know for a future newsletter story
Reducing New Zealand's agricultural emissions: Soil Carbon
This publication provides an overview of what soil carbon is, how we can measure and determine the changes over time and what New Zealand's current soil carbon levels are. this publication was produced in collaboration with the University of Waikato and released at the National Fielddays 2015.
1525 Frank Kelliher, Principal Scientist (AgResearch) & Professor (Lincoln University)
Frank's presentation covered the New Zealand work on soil carbon.
He explained the concept that, like planting trees, increasing soil carbon stocks can “offset” greenhouse gas emissions and that if New Zealand could increase soil carbon stocks by 1 tonne of carbon per hectare over 1 million hectares, this could offset the rise in greenhouse gases since 1990.
Frank also pointed out that, like trees, soil carbon can take decades to accumulate but this gain can be reversed quickly if land-management practices change again. Additionally it is difficult to measure and often “you don’t know what you’ve got until it’s gone”.
Research into the New Zealand soil carbon situation has shown that although soil carbon stocks are high in many areas of New Zealand, there is strong evidence that more soil carbon could be stored.
How can this be achieved?
The team is running a major field trial at Troughton farm that is looking at farm management practices and determining the effects on soil carbon. Preliminary data suggests that pasture renewal depletes soil carbon, but that the lost soil carbon is ‘restored’ within about a year.
Pasture diversity also appears to increase soil carbon levels.
Additionally, modelling indicates that supplementary feeding may increase soil carbon levels as more carbon is being applied to the soil via excreta.
The effects of irrigation on soil carbon stocks are uncertain currently.
1550 Keith Goulding (Rothamsted Research, UK)
Keith provided an international perspective on nitrous oxide and soil carbon research. With respect to N2O, he highlighted work on investigating the genes related to nitrous oxide emissions and noted that there is one clear message for reducing nitrous oxide, avoid excess nitrogen.
The IPCC has recently indicated that biochar may have a part to play in reducing agricultural GHGs and a number of research groups are searching for natural nitrification inhibitors.
Keith indicated that soil carbon needs to be considered carefully. Data were published that could be interpreted to imply that grasslands could continue to sequester carbon indefinitely. However, this has been refuted and there is agreement that for a specific system there is an upper limit for carbon, and he noted the interesting work in New Zealand in this area. t been proven yet, but it appears that the deeper roots also reduce run off significantly and thus could offer multiple benefits.
Keith concluded with a warning that too much emphasis on soil carbon sequestration could risk taking our eyes off more important climate change threats, such as land clearance and wetland drainage. He also stressed that our priorities should be promotion of good land stewardship and integrated solutions that consider the whole system and do not merely “pollution swap”.
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.
Measuring, modelling and managing soil carbon for future farming
Increasing the quantity and stability of carbon stored in agricultural soils has real potential to offset greenhouse gas (GHG) emissions to the atmosphere. However, realising this potential is not as straightforward as it might first appear.
Firstly, soil carbon stocks are notoriously difficult to measure. Agricultural soil carbon stocks vary according to a number of factors including soil type, climate, geographical location and current and previous management practices, there is a lot of spatial variability and changes with time are slow. It just isn't possible to measure the carbon stored in every tiny bit of soil in every hectare of pasture. So measurements of soil carbon are taken at representative point locations, then estimates of soil carbon need to be made for all of the space in between those points. Consider that there are 11 million hectares of grassland in NZ and you can see why understanding of soil carbon crucially relies not only on measurements but also models that help interpolate between measurements and understand changes over time.
Given the challenges in accurately determining current soil carbon stocks, working out the impacts a certain farm management practice has on soil carbon stocks is also incredibly challenging. The complicated dynamics of soil carbon, that is how long the carbon actually stays in the soil is a specific form, adds another layer of complexity.
Taking into account these challenges, previous NZAGRC-funded work has used data mining and modelling to quantify current levels of soil carbon and determine the maximum amount that could be stored. In many places NZ grassland soil carbon levels were shown to be relatively high, due to the short time since forested sites were converted to pasture. Whilst this is good news, it means that the potential to increase stocks may be limited and it is very important to ensure that farming practices do not deplete the stocks that we already have over time.
NZAGRC Principal Investigators Dr David Whitehead (Landcare Research) and Prof Frank Kelliher (AgResearch/Lincoln University) have taken all of this into account whilst planning the NZAGRC soil carbon programme out to 2017. "The focus of the programme to date has been to use experimental measurements and modelling to test the ability of potential management practices to manipulate the rates of input, incorporation and stabilisation of carbon in soils", says David. "We need to continue to develop opportunities that will provide farmers with practices that can minimise soil carbon losses and increase gains".
The team note that strategies need to be both practical and cost effective to be adopted. With this in mind, a key focus of the updated programme in on two experimental farm sites in the Waikato and Canterbury. "We are really excited to bring our expertise to work on these farms", says David. "The sites are set up to be able to continuously measure a wide range of factors. We can carefully manipulate the system by, for example, planting different pasture species or irrigating or adding nitrogen fertiliser and then see how the change affects the whole farm carbon balance." The large amount of data generated can then be used to estimate conversion of carbon inputs into soil carbon stocks. Additionally, modelling can be used to forecast what the combined effects of different management strategies are likely to be on soil carbon. The end goal is to be able to provide farmers with practical, meaningful advice on how to best manage their farms to maximise soil carbon stocks.
"We can't forget the measurement problem though", adds Frank. "In order to really understand how soil properties and management practices affect long-term storage of soil carbon, we need the best tools possible, and this means next-generation computer models. Changing practices can have long lasting impacts on soil. With the best will in the world, it's difficult to take experimental measurements on the same site over decades. Even if we could, understanding the sheer volume of data generated in light of all of changes over that time period would be daunting". The goal of Frank and his team's work on developing new tools is to identify the soil properties and grassland management practices that most affect soil carbon stabilisation and vulnerability to loss over the short and long term. The overall aim of the NZAGRC programme is to increase stabilised soil carbon stocks as our farmers head into the future.