title: The ability of nitrification inhibitors to decrease denitrification rates in dairy farm soils

authors: Watkins, Natalie Lisa

subjects: Nitrification inhibitors

abstract: Increasing pressure is being placed on the dairy industry to reduce nitrogen losses from soil.  Nitrification inhibitors are a management strategy that could be implemented on dairy farms to help reduce losses of nitrogen.  Nitrification inhibitors work by temporarily inhibiting the microbial conversion of soil ammonium to nitrate.  Past trials have indicated that nitrification inhibitors can increase grass production and decrease nitrate leaching; however, little is known about the long-term effects on other soil nitrogen processes such as denitrification.  Denitrification rates in soils can be limited by the availability of substrate (carbon and nitrate) and by insufficient anaerobic microsites. 

The objective of this thesis was to establish whether the nitrification inhibitor, dicyandiamide (DCD), could decrease denitrification rates in dairy farm soils by limiting nitrate availability.  A field trial was established at Dexcel's research farm near Hamilton, New Zealand on a Typic Orthic Allophanic Soil. Twenty replicated field plots were established in a paddock, ten plots acted as controls and ten plots had DCD applied to the soil once a month at a rate of 30 kg ha-1 yr-1.  Denitrification rates were measured using the acetylene inhibition technique on intact soil cores.  Ammonium and nitrate concentration, soil carbon availability, denitrifying enzyme activity and soil pH were measured from soil samples collected monthly.  

Two further field experiments and one laboratory experiment were undertaken.  The distribution of denitrifying enzyme activity with soil depth was measured to ensure that the depth to which denitrification was sampled (15 cm) in the field experiment was sufficient.  DCD degradation in the field during 20 days was measured to establish how long the effects of DCD might last.  A laboratory study investigated whether DCD would decrease denitrifying enzyme activity in soil, when soil conditions were optimized for denitrification. 

More than 80% of the denitrifying enzyme activity occurred in the top 15 cm of the soil profile, indicating that the depth to which samples were collected was sufficient.  There was no significant decrease in denitrification rates in the field experiment when DCD was added.  Nitrification was partially inhibited as shown by a significant increase in soil ammonium (+14%) and a significant decline in soil nitrate (-17%) in the DCD-amended soils compared to the control soils.  However, the decline in soil nitrate was not great enough for nitrate to limit denitrification.  Nitrate concentrations were consistently greater than 5 mg NO3- kg-1 soil (the proposed threshold for declines in denitrification).  The laboratory study supported the field study with DCD having no effect on denitrifying enzyme activity and nitrate concentrations remaining above 5 mg NO3- kg-1 soil.  So while DCD reduced nitrification rates and the formation of nitrate, denitrification rates were not limited by nitrate availability.  DCD was completely degraded in the soil 19 days after DCD application, with a half-life of 2.9 days, which may be a reason for the minor inhibition of nitrification.  Denitrifying enzyme activity, carbon availability and soil pH were all unaffected by the application of DCD.

text: The ability of nitrification inhibitors to decrease denitrification rates in dairy farm soils Increasing pressure is being placed on the dairy industry to reduce nitrogen losses from soil.  Nitrification inhibitors are a management strategy that could be implemented on dairy farms to help reduce losses of nitrogen.  Nitrification inhibitors work by temporarily inhibiting the microbial conversion of soil ammonium to nitrate.  Past trials have indicated that nitrification inhibitors can increase grass production and decrease nitrate leaching; however, little is known about the long-term effects on other soil nitrogen processes such as denitrification.  Denitrification rates in soils can be limited by the availability of substrate (carbon and nitrate) and by insufficient anaerobic microsites. 

The objective of this thesis was to establish whether the nitrification inhibitor, dicyandiamide (DCD), could decrease denitrification rates in dairy farm soils by limiting nitrate availability.  A field trial was established at Dexcel's research farm near Hamilton, New Zealand on a Typic Orthic Allophanic Soil. Twenty replicated field plots were established in a paddock, ten plots acted as controls and ten plots had DCD applied to the soil once a month at a rate of 30 kg ha-1 yr-1.  Denitrification rates were measured using the acetylene inhibition technique on intact soil cores.  Ammonium and nitrate concentration, soil carbon availability, denitrifying enzyme activity and soil pH were measured from soil samples collected monthly.  

Two further field experiments and one laboratory experiment were undertaken.  The distribution of denitrifying enzyme activity with soil depth was measured to ensure that the depth to which denitrification was sampled (15 cm) in the field experiment was sufficient.  DCD degradation in the field during 20 days was measured to establish how long the effects of DCD might last.  A laboratory study investigated whether DCD would decrease denitrifying enzyme activity in soil, when soil conditions were optimized for denitrification. 

More than 80% of the denitrifying enzyme activity occurred in the top 15 cm of the soil profile, indicating that the depth to which samples were collected was sufficient.  There was no significant decrease in denitrification rates in the field experiment when DCD was added.  Nitrification was partially inhibited as shown by a significant increase in soil ammonium (+14%) and a significant decline in soil nitrate (-17%) in the DCD-amended soils compared to the control soils.  However, the decline in soil nitrate was not great enough for nitrate to limit denitrification.  Nitrate concentrations were consistently greater than 5 mg NO3- kg-1 soil (the proposed threshold for declines in denitrification).  The laboratory study supported the field study with DCD having no effect on denitrifying enzyme activity and nitrate concentrations remaining above 5 mg NO3- kg-1 soil.  So while DCD reduced nitrification rates and the formation of nitrate, denitrification rates were not limited by nitrate availability.  DCD was completely degraded in the soil 19 days after DCD application, with a half-life of 2.9 days, which may be a reason for the minor inhibition of nitrification.  Denitrifying enzyme activity, carbon availability and soil pH were all unaffected by the application of DCD.

year: 2007

title: COP26 local panel: Finance and economics

authors: Oxley, Les

abstract: Local experts discuss some of the key themes from COP26. This panel covers Climate Finance, Responsible Business Conduct and Transformational Economics.

text: COP26 local panel: Finance and economics Local experts discuss some of the key themes from COP26. This panel covers Climate Finance, Responsible Business Conduct and Transformational Economics.

year: 2021-11-04

title: Imaging and Imagining the Waikato: A Spatial History c.1800-c.1914

authors: Dench, Simon Jeffery

subjects: colonisation

abstract: This thesis reframes the history of the Waikato from the late eighteenth to the early twentieth centuries through a spatial history approach using a visual archive. I argue that Pākehā images of the Waikato were both contemporary records and instruments of colonisation in the region, and that the discursive power of these images is undiminished. In this thesis I focus on spatial occasions represented by maps and photographs in order to reframe the history of colonisation in the Waikato.
First, I move visual sources of historical evidence, specifically maps and photographs, from the periphery to the centre of the frame. An exploration of
the historical context of the selected maps and photographs serves as the narrative framework for the thesis in a strategy that replaces the more usual method of choosing images to illustrate a text that has already been written. This theoretical and methodological framework for what I consider to be a richer and more satisfying use of visual evidence in history is a key feature of this thesis. Second, I employ a colonisation lens to emphasise the negative consequences of colonisation for the indigenous people and landscapes, as well as the diverse and far from unproblematic experiences of the colonists themselves. This thesis positions three phases of Pākehā colonisation: Reconnaissance, Invasion and Occupation. These overtly militaristic labels apply to real military actions as well as to less obvious but longer-lasting and wider-spread discursive strategies of incursion and control.
While this thesis emphasises the negative impacts of colonisation, this is a history from the colonisers’ point of view. The images that form the focus of the thesis were created by Pākehā in the service of Pākehā intentions, actions and identities. But, rather than serving to justify or excuse colonisation as an end that justified the means, I undermine the inevitability inherent in the traditional settlement narrative. I do this by highlighting the ambiguities and contradictions of the colonisers’ intentions and experiences through a close and contextualised reading of the images they made to record and represent themselves. In the process, I refute the legitimacy and validity of Pākehā claims to control Waikato spaces.

text: Imaging and Imagining the Waikato: A Spatial History c.1800-c.1914 This thesis reframes the history of the Waikato from the late eighteenth to the early twentieth centuries through a spatial history approach using a visual archive. I argue that Pākehā images of the Waikato were both contemporary records and instruments of colonisation in the region, and that the discursive power of these images is undiminished. In this thesis I focus on spatial occasions represented by maps and photographs in order to reframe the history of colonisation in the Waikato.
First, I move visual sources of historical evidence, specifically maps and photographs, from the periphery to the centre of the frame. An exploration of
the historical context of the selected maps and photographs serves as the narrative framework for the thesis in a strategy that replaces the more usual method of choosing images to illustrate a text that has already been written. This theoretical and methodological framework for what I consider to be a richer and more satisfying use of visual evidence in history is a key feature of this thesis. Second, I employ a colonisation lens to emphasise the negative consequences of colonisation for the indigenous people and landscapes, as well as the diverse and far from unproblematic experiences of the colonists themselves. This thesis positions three phases of Pākehā colonisation: Reconnaissance, Invasion and Occupation. These overtly militaristic labels apply to real military actions as well as to less obvious but longer-lasting and wider-spread discursive strategies of incursion and control.
While this thesis emphasises the negative impacts of colonisation, this is a history from the colonisers’ point of view. The images that form the focus of the thesis were created by Pākehā in the service of Pākehā intentions, actions and identities. But, rather than serving to justify or excuse colonisation as an end that justified the means, I undermine the inevitability inherent in the traditional settlement narrative. I do this by highlighting the ambiguities and contradictions of the colonisers’ intentions and experiences through a close and contextualised reading of the images they made to record and represent themselves. In the process, I refute the legitimacy and validity of Pākehā claims to control Waikato spaces.

year: 2018