Plantain and Greenhouse Gas Research

The New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC) was set up in early 2010. Principal investigator Professor Louis Schipper from Waikato University is co-leading a research programme ‘Plants and GHGS’ alongside Cecile de Klein (AgResearch), Hong Di (Lincoln University) and David Whitehead (Manaaki Whenua Landcare Research). One of the research aims is to “define the achievable soil carbon stabilisation capacity of New Zealand grassland soils”. This is about determining how much extra carbon soils could capture.

There is a theory that soil has a limited capacity to store carbon, depending on its type (such as clay content). If there was capacity to store more it could bring benefits to both soil health and climate. Work is underway to help scientists understand what type of soils they might target and what management practices could be applied to build their carbon holding capacity. Farmers are eager to obtain this information so they can improve productivity and play their part in reducing impacts of climate change.

Louis Schipper is particularly interested in nitrous oxide and carbon. Cows release nitrogen in their urine and dung, far more than plants and soil can take up. Microbial processes combine this nitrogen with oxygen atoms to form nitrous oxide that is released to the atmosphere. Each molecule of nitrous oxide is around 300 times more powerful than a molecule of CO2 at warming the planet, and it sticks around in the atmosphere for a long time.

Over the last couple of decades, Louis and his colleagues, Dave Campbell and Aaron Wall, have introduced four eddy covariance towers at Ben and Sarah Troughton’s dairy farm in central Waikato. Sarah and Ben have worked alongside scientists on their farm for around 10 years. The family farm produces milk made into ice cream for their business, The Kowhai Creamery.

The Troughtons have a philosophy of ethical and sustainable practice, and an interest in plant diversity. Their Jersey cows are fed a variety of planted grasses and herbs grown on the property or locally sourced. Cows are milked once a day, with the herd split across autumn and spring calving. The farm claims to be one of the most monitored dairy farms in the world, and is likely to be the only farm in the Southern Hemisphere using a Quantum Cascade Laser (QCL) to track its nitrous oxide emissions.

Eddy covariance quantifies gas fluxes (changes) by directly measuring the gas as it moves between soil, vegetation and the atmosphere. The gases include water vapour, carbon dioxide (CO2) and, most recently, nitrous oxide (N2O). The challenge for scientists has been measuring nitrous oxide. N2O gases released in a paddock are in very, very small amounts but still have a powerful impact on the atmosphere. Adding the QCL to their eddy covariance setup means Louis and his team can collect continuous and precise measurements of nitrous oxide concentrations. The devices measure greenhouse gases 10 times a second to concentrations of about 0.2 parts per billion. These data allows continuous measurement of paddock-scale greenhouse gas emissions over years. Louis explains this enormous amount of gathered data enables researchers to see “the bigger picture”.

Initial work has been to determine how robust this approach is for future research, particularly for testing new mitigation strategies. Recent papers analysing their data have been highly supportive. Some results have been surprising, with patterns of nitrous oxide emissions spikier than expected. Over a year it was calculated the paddocks were producing about 7kg of nitrous oxide per hectare, equivalent to two tonnes of CO2. Another notable finding was that nitrous oxide spiked dramatically after rainfall in summer, when soil microbes were rapidly activated.

Louis’ team is now looking at mitigation strategies with plantain. Research at AgResearch and a number of New Zealand universities has shown the herb has potential to reduce nitrous oxide emissions from cow urine patches. Further research is looking at whether the plant can create conditions in the soil that reduces nitrogen loss by affecting soil microbes, decreasing their ability to create nitrous oxide.

Louis’ team values working directly with farmers. He says they have “excellent ideas about what might work or what we should think about for our research programmes”. He adds it is important to work with the philosophy at the Troughton’s, “this is their farm and we need to find practical solutions that work within their farming approach”. For example, Ben was not keen to change a good paddock to plant plantain, concerned at the carbon loss the bare paddock would incur. Working with Ben, the team managed to get the paddock sprayed off and reseeded with plantain within a short time frame.

Louis’ PhD student, Anne Wecking is working to collate data on the establishment phase of a plantain crop. Each stage of the crop needs to be carefully tracked in order to know at each stage that the net benefits outweigh the negatives. For example, if plantain emissions during the establishment phase are high, this could cancel out any benefits in the next stage. And further along, the need to frequently maintain the sward plantain might undermine any reduced emissions. Early results from this research are expected to start coming through next year.

When considering the best methods to mitigate greenhouse gas emissions from agriculture, Louis cautions that each farm is different and it will be small incremental improvements coupled together that will likely provide the answers. He reminds us of the importance of having farmers onboard with these developments.

The background, goals and outcomes of Louis’ research, and that of other NZAGRC-led or funded researchers seeking practical and sustainable agricultural greenhouse gas mitigation solutions, can be found on the recently established ‘AgMatters’. AgMatters is currently undergoing significant redevelopment and will be relaunched in late March/early April with new content focusing, in particular, on nitrous oxide and soil carbon. AgMatters has been developed by the NZAGRC with funding from MPI.

Showdown Productions Ltd - Rural Delivery Series 15 2020