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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.
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.
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.