University of Waikato

Video: Watching CO2 exchange and maize growth

A short time-lapse video of maize growing and the measured cumulative CO2-C exchange from eddy covariance.

Down is a loss and up is a gain. There are initial C losses before maize growth is established and then gains as the maize grows. The net C balance will also need to take into account removal of C with harvest.

The animation has been provided by University of Waikato's Louis Schipper and created by University of Waikato's Aaron Wall as part of the PhD he is doing alongside his role in the NZAGRC programme. More information on this work can be found at http://www.nzagrc.org.nz/soil-carbon.html

Anne Wecking

The opportunity to work with the Quantum Cascade Laser (QCL) made it an easy decision for German PhD student Anne Wecking to move to the other side of the world.

“It’s a privilege to work with a piece of technology like this—the way it functions is pretty fancy and its implication on future greenhouse gas inventories might mean we can reconsider our current ways of budgeting the emissions of nitrous oxide.”

Anne’s PhD is about the quantification and mitigation of nitrous oxide emissions from grazed pastures, and is supervised by Professor Schipper.

“The QCL provides us with continuous and precise data about the amount of nitrous oxide present in the surface near atmosphere. In combination with wind data, we can integrate emissions over hectares,” she says. “This is a great technological advance forward, and is helping us to further understand what’s happening on the farm scale.”

Read more about the QCL

Laser has bright future in nitrous oxide emissions measurement

A modest-looking metal box sitting in a Waikato paddock may seem unassuming at first glance, but what’s on the inside has the potential to transform the way greenhouse gas emissions are measured.

The box contains state-of-the art technology called a Quantum Cascade Laser, and it’s helping scientists funded by the New Zealand Agricultural Greenhouse Gas Research Centre get a much clearer picture of nitrous oxide emissions produced by farming.

Nitrous oxide (N2O) is an important component of New Zealand’s greenhouse gas emissions profile. It predominantly comes from agriculture, and from livestock urine patches in particular—the nitrogen content in urine is more than plants can use, so the excess is transformed through microbial processes into nitrous oxide.

Professor Louis Schipper from the University of Waikato is co-leading this part of the NZAGRC’s research programme into nitrous oxide emission mitigation. He says because urine patches are so scattered, it can be difficult to measure nitrous oxide at the paddock scale. “In the past we’ve measured nitrous oxide emissions using chambers, which are small enclosures that fit over the soil—they take samples over time to give us a production rate of the gas,” says Professor Schipper.

“But you need a lot of chambers—and a lot of time—to try and measure emissions from all urine patches. It’s an enormous task and the variability is very hard to capture.”

He says while methodologies have been developed to deal with that variability—and chambers continue to have a very useful role in the science of measuring agricultural greenhouse gas emissions—there are still a lot of gaps in the data they provide.

This is why Professor Schipper and his team are now using a Quantum Cascade Laser (QCL), which was purchased recently by the University of Waikato. The QCL has been installed at the Troughton Farm research site in Waikato, which has been used to support a range of research projects to understand soil carbon and nitrous oxide emissions from New Zealand dairy farms.

“The current micro-meteorological technique we use—eddy covariance—allows us to measure the nitrous oxide emissions that are coming from the paddock as a whole, rather from individual urine patches,” says Professor Schipper. “While the technique has been around for a while, it’s been difficult to take measurements with sufficient precision. This is where the QCL is a game changer because it can determine nitrous oxide concentration very quickly, to an extremely high precision. It’s measuring ten times a second, to about 0.2 parts per billion—that’s unprecedented, and when practically applied to the paddock setting it’s a real breakthrough in terms of routine measurement.”

He says the QCL is able to continuously measure emissions of nitrous oxide over six to eight hectares, and integrate its measurements.

“There’s a pipe that draws air into the QCL—ours is mounted on a small tower and is about two metres off the ground,” explains Professor Schipper. “For every metre above the ground that the air is taken from, the QCL integrates measurements from over a 100 metre radius. That means if you place the air pipe two metres up you’re essentially measuring nitrous oxide over a 200 metre radius; if it’s three metres up you’re measuring a 300 metre radius, and so forth. You can choose how much area you want to measure.

“The device allows us to get an average measurement of how much a nitrous oxide a paddock is emitting, rather than what’s happening above just one patch,” he says. “It’s a bit like looking at an impressionist painting—if you zoom in on a single brush stroke you don’t get much of an idea what’s going on, but using the QCL we’re able to step back and see the bigger picture.”

Professor Schipper says the more detailed data from the QCL should also make it easier to develop models that will allow scientists to make predictions about nitrous oxide emissions in other locations.

“This technology is great but there’s still an important role for chambers, which are really useful for making comparisons between multiple treatments within a paddock,” says Professor Schipper. “In the end we want eddy covariance and chambers to be working together—that will give us the best results.”

He says he is very excited to be working with this kind of technology and seeing its potential.

“Yes it’s pretty fancy science, but we’re not losing sight of the long term goal of reducing greenhouse gas emissions—hopefully the QCL will make that easier.”

Read more about Anne Wecking, who is working with the QCL as part of her PhD

Congratulations to Dr Jack Pronger

Jack Pronger has completed his PhD defence to become a fully fledged scientist.

Jack submitted his PhD investigating the water use and water use efficiency of mixed pasture swards at Troughton farm. 

Jack has taken up a position at Landcare Research, Hamilton and is working on soil carbon starting with looking at the effects of irrigation in collaboration with Paul Mudge.

Jack was supported by NZAGRC's Student Scholarship Programme and also received funding from Flower Trust, University of Waikato and DairyNZ and was supervised by Louis Schipper, Dave Campbell and Mike Clearwater.

Do glucosinolate hydrolysis products reduce nitrous oxide emissions from urine affected soil?

S.F. Balvert, J. Luo, L.A. Schipper, Do glucosinolate hydrolysis products reduce nitrous oxide emissions from urine affected soil?, Science of The Total Environment, Volume 603, 2017, Pages 370-380, ISSN 0048-9697, http://dx.doi.org/10.1016/j.scitotenv.2017.06.089.

Highlights

• The effectiveness of glucosinolate hydrolysis products at inhibiting N₂O emissions in a high N environment was tested.
• Laboratory and field trials measuring N₂O production and soil mineral N cycling were conducted.
• Some glucosinolate hydrolysis products reduced nitrification rates.
• Where inhibition occurred it was short lived.
• Glucosinolate hydrolysis products with different R groups did not inhibit soil nitrogen processes to the same degree.

Read more (external link)

Professor Louis Schipper talks about soil carbon

Louis Schipper talks to Bryan Crump on RNZ Nights about soil carbon. He talks about soil organic matter, soil density, nutrients (nitrogen, phosphorus, sulphur), land use and the ways we can store more carbon in soil to reduce the amount of carbon dioxide in the atmostphere without reducing food production.

Louis also talks about the 4 pour mille initiative and its challenge to increase carbon content of soils by 0.4% per year to offset fossil fuel emissions.

Listen (external link)

About Louis

Professor Louis Schipper

Louis Schipper is a Professor at the University of Waikato who investigates soil biogeochemical processes at landscape scales and how they might be manipulated to achieve improved environmental performance while maintaining production. For the last decade, Louis has led teams determining changes in carbon stocks of pasture soils at paddock to national scales. This research demonstrated that while carbon in the majority of pastures on flat land was at steady state, some of our important soils had lost substantial carbon while hill-country soils have gained large amounts. These data have been central to developing a national picture of New Zealand’s carbon budget. They have also used micro-meteorological approaches to evaluate high-resolution fluxes of carbon at farm scales to identify practices that increase carbon stocks, generating in-depth understanding of climatic effects (e.g., drought, rainfall) and management impacts (pasture renewal, cultivation, new pasture species). Louis is an elected fellow of the New Zealand and American soil science societies with multiple awards from the NZ Society. He has published >130 papers (Scopus H-index of 36), supervised ~40 PhD/MSc students, and developed substantial soil and environmental resources for schools.

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.

Highlights

• 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.

Read more (external link)

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.

Abstract
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.

Read more (external link)

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

Highlights

• 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.

Read more (external link)

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.

Abstract
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.

Read more (external link)

Herbicide application during pasture renewal initially increases root turnover and carbon input to soil in perennial ryegrass and white clover pasture

McNally, S. R., Laughlin, D. C., Rutledge, S., Dodd, M. B., Six, J., & Schipper, L. A. (2017). Herbicide application during pasture renewal initially increases root turnover and carbon input to soil in perennial ryegrass and white clover pasture. [Article]. Plant and Soil, 412(1-2), 133-142.

Abstract

Aims
Increasing the input and turnover of root tissue is considered to be one method that may increase carbon (C) inputs and storage in soil. The use of herbicide during pasture renewal (periodic re-sowing of pasture) is expected to increase root inputs and turnover as plants die. The objective of this study was to quantify the short-term impact of pasture renewal on root turnover and C input to soil of ryegrass-clover pastures.

Methods

Pastures were labelled in the field using a 13C isotope pulse labelling method within 1 m2 clear chambers. Five daily labelling events were carried out during one week in paired treatment plots within 3 replicate paddocks. One plot per paddock was sprayed with herbicide and then the pasture was renewed by direct drilling of seed. The 13C of roots and soil (0–100 mm) was measured at regular intervals over an 89-day period.

Results

Herbicide application caused an initial rapid turnover time of 17 days followed by a slower turnover time of 524 days, compared to unsprayed pasture which had a root turnover of 585 days. Faster root turnover following herbicide application resulted in greater cumulative C input to soil over 89 days with approximately double the C input in the sprayed treatment (3238 ± 378 kg C ha−1) compared to the unsprayed treatment (1726 ± 540 kg C ha−1).

Conclusions

The use of glyphosate during pasture renewal increased root turnover and resulted in a greater short term cumulative C input to soil. This study provides the first values of root turnover and C input to soil during a pasture renewal event in New Zealand pasture systems and contributes to the understanding of how pasture roots may influence the soil C input following plant death in grassland systems.

Read more (external website)

Low spatial and inter-annual variability of evaporation from a year-round intensively grazed temperate pasture system

J. Pronger, D.I. Campbell, M.J. Clearwater, S. Rutledge, A.M. Wall, L.A. Schipper, Low spatial and inter-annual variability of evaporation from a year-round intensively grazed temperate pasture system, Agriculture, Ecosystems & Environment, Volume 232, 2016, Pages 46-58, ISSN 0167-8809,

http://dx.doi.org/10.1016/j.agee.2016.07.011

Ecosystem scale measurements of evaporation (E) from intensively managed pasture systems are important for informing water resource decision making and validation of hydrologic models and remote sensing methods. We measured E from a year round intensively grazed temperate pasture system in New Zealand using the eddy covariance method for three years (2012-2014). Evaporation varied by less than 3% both spatially (770⿿783mm) and temporally (759-776mm) at an annual scale. The low spatial and temporal variation largely occurred because E was strongly controlled by net radiation (r2=0.81, p<0.01, daytime, half-hourly), which did not vary much between sites and years. However, E was strongly limited when volumetric moisture content (VMC) declined below permanent wilting point causing a strong reduction in the decoupling coefficient and an increase in the Bowen ratio. Grazing events appeared to have no effect on E during autumn and winter but reduced E by up to 5% during summer and spring while complete removal of vegetation during autumn herbicide application reduced E by ⿼30%. This implied that over the pasture regrowth period soil water evaporation (ES) could provide up to 70% of E relative to a vegetated site (during autumn) and, given that grazing events removed about 60% of leaf area, these findings suggest ES was likely able to compensate for decreased transpiration post-grazing. Agreement between measured E (EEC) and FAO-56 reference crop E (Eo) was good when soil moisture limitation was not occurring. However, during periods of soil moisture limitation Eo exceeded EEC and a correction factor was needed. We trialled the water stress coefficient (Ks) and a simple three bin VMC correction factor (KVMC) and found the KVMC approach worked better at a daily and monthly scale while both approaches worked well at an annual scale.

Estimates of annual leaching losses of dissolved organic carbon from pastures on Allophanic Soils grazed by dairy cattle, Waikato, New Zealand

Sparling, G. P., E. J. Chibnall, et al. (2016). "Estimates of annual leaching losses of dissolved organic carbon from pastures on Allophanic Soils grazed by dairy cattle, Waikato, New Zealand." New Zealand Journal of Agricultural Research 59(1): 32-49.

Abstract

Dissolved organic carbon (DOC) flux on a conventional New Zealand dairy farm was measured for 1 year to assess the contribution from DOC to the total farm C budget. Soil solution was collected using ceramic cups at 60 cm depth. Soil drainage was calculated from a water balance model using rainfall, evaporation and soil water storage data from two eddy covariance systems. Solution was collected approximately every 14 days. The DOC concentration was 5.7±15.6 µg C ml-1 (mean and standard deviation). No significant differences (P<0.05) in DOC concentrations were detected between the four soil types, the two sampling areas, nor date of sampling. The accumulative amount of DOC leached was obtained by combining the soil solution concentrations with the daily estimates of drainage. The mean annual amount of DOC leached was 13?29 kg C ha-1 y-1and the contributed 2?5% to the net farm annual carbon balance.

Read more (external website)

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

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.

Abstract
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.

Read more (external website)

Masters Student: Olivia Jordan

Olivia with NZ PM Rt Hon John Key (Oliva is second from the left)

Olivia is conducting an MSc thesis examining root biomass of different pasture swards in a trial at a New Zealand industry research farm.

This work is aligned to an investigation of above-ground plant traits by Landcare Research.

Olivia is supervised by Professor Louis Schipper at the University of Waikato.

Olivia has a background in farming is very interested in finding a career in the farming industry.

Undergraduate student: Alex Tressler

Alex Tressler is a fourth year undergraduate student at the University of Waikato.  He is currently in his final year of a BMS studying Agribusiness and Strategic Management.

Alex's recent NZAGRC research project was to examine the potential for effective economic policy in regards to soil carbon within pastoral agriculture in New Zealand.

"The research included exploration of foreign policy and initiatives as well as comparisons of our own proposals, whilst assessing the viability of these ideas based on academic literature and theoretical real world applications."

Alex plans to complete his BMS and continue working in agribusiness to "help maintain and improve our country's competitive advantage."