Massey University

Modelling NH3 volatilisation within a urine patch using NZ-DNDC

Giltrap, D., S. Saggar, et al. (2017). "Modelling NH3 volatilisation within a urine patch using NZ-DNDC." Nutrient Cycling in Agroecosystems 108(3): 267-277.

Abstract

Urea concentrations in urine patches deposited during animal grazing can be over ten times higher than typical fertiliser application rates, potentially leading to large ammonia (NH3) losses. The processbased NZ-DNDC model was modified to better simulate soil pH changes and ammonia (NH3) emissions following urine application using data collected from a New Zealand field trial. After modification, simulated 30-day NH3 emissions decreased from 506 to 117 kg N ha-1 compared to measured emissions of 78 ± 3 kg N ha-1 (mean ± standard error) and the Nash–Sutcliffe Effi- ciency (NSE) for daily NH3 emissions increased from -7.11 to ?0.97 for the parameterisation dataset. However, modified model correctly estimated the cumulative emissions for the first 7 days. Using the same parameterisation on an independent dataset from a nearby site gave cumulative 18-day NH3 emissions of 84 kg N ha-1 compared to the measured 48 ± 2 kg N ha-1 (mean ± standard error). However, the NSE for daily NH3 emissions was -0.71, indicating site specific parameterisation might be needed. The sensitivity of NH3 emissions to ±5 and ±10% errors in 4 model parameters was tested. The sensitivities ranged from -0.36 to ?0.71. The highest sensitivity was to the rate of NH3 transfer from the soil solution to the atmosphere and the lowest sensitivity was to the rate of urea hydrolysis.

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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

Abstract

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

https://doi.org/10.1079/PAVSNNR201611054 

A mechanistic model of hydrogen

Yuancheng Wang, Peter H. Janssen, Tammy A. Lynch, Bruce van Brunt, David Pacheco, A mechanistic model of hydrogen–methanogen dynamics in the rumen, Journal of Theoretical Biology, Volume 393, 21 March 2016, Pages 75-81, ISSN 0022-5193

Abstract
Existing mathematical models to estimate methane production in the rumen are based on calculation of hydrogen balances without considering the presence of methanogens. In this study, a mechanistic model of methane production is proposed that depicts the interaction between hydrogen concentration and methanogens in the rumen. Analytical results show that it meets biological expectations, namely increased fractional passage rate leads to a greater growth rate of methanogens, and a greater steady state hydrogen concentration. This model provides a basis on which to develop a more comprehensive model of methane production in the rumen that includes thermodynamics and feed fermentation pathways.

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Does gibberellin biosynthesis play a critical role in the growth of Lolium perenne? Evidence from a transcriptional analysis of gibberellin and carbohydrate metabolic genes after defoliation

Liu, Q., C. S. Jones, et al. (2015). "Does gibberellin biosynthesis play a critical role in the growth of Lolium perenne? Evidence from a transcriptional analysis of gibberellin and carbohydrate metabolic genes after defoliation." Frontiers in Plant Science 6(NOVEMBER).

Global meat and milk production depends to a large extent on grazed pastures, with Lolium perenne being the major forage grass in temperate regions. Defoliation and subsequent regrowth of leaf blades is a major and essential event with respect to L. perenne growth and productivity. Following defoliation, carbohydrates (mainly fructans and sucrose) have to be mobilized from heterotrophic tissues to provide energy and carbon for regrowth of photosynthetic tissues. This mobilization of reserve carbohydrates requires a substantial change in the expression of genes coding for enzymes involved in carbohydrate metabolism. Here we tested the hypothesis that gibberellins (GA) are at the core of the processes regulating the expression of these genes. Thus, we examined the transcript profiles of genes involved in carbohydrate and GA metabolic pathways across a time course regrowth experiment. Our results show that following defoliation, the immediate reduction of carbohydrate concentrations in growing tissues is associated with a concomitant increase in the expression of genes encoding carbohydrate mobilizing invertases, and was also associated with a strong decrease in the expression of fructan synthesizing fructosyltransferase genes. We also show that the decrease in fructan levels is preceded by increased expression of the GA activating gene GA3-oxidase and decreased expression of the GA inactivating gene GA2-oxidase in sheaths. GA3-oxidase expression was negatively, while GA2-oxidase positively linked to sucrose concentrations. This study provides indicative evidence that gibberellins might play a role in L. perenne regrowth following defoliation and we hypothesize that there is a link between gibberellin regulation and sugar metabolism in L. perenne. © 2015 Liu, Jones, Parsons, Xue and Rasmussen.

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Undergraduate Student: Martina Alvarez Camps

"My name is Martina Alvarez. I am 19 years old and about to start my second year of Chemical and Materials Engineering at the University of Auckland."

Martina spent the summer with Dr Carolyn Hedley and Dr Pierre Roudier at Landcare Research looking at the effect of moisture on soil spectra and the use of the External Parameter Orthogonalisation (EPO) algorithm to predict carbon content of field moist soil using air dry soil spectra models.

Martina's work has given her the opportunity to learn new skills and expertise in this field of soil science.

"I have learned about Visual-Near Infrared (VisNIR) spectroscopy and its benefits to soil science due to its quick soil carbon content predictions. I have also become aware of how samples are handled and scanned, the need for pre-processing of spectra and its application using the computer programming language R and how to accommodate the experiment to unexpected occurrences."

Changes in denitrification rate and N2O/N2 ratio with varying soil moisture conditions in New Zealand pasture soils

Jha, N., Saggar, S., Tillman, R., & Giltrap, D. (2012). Changes in denitrification rate and N2O/N2 ratio with varying soil moisture conditions in New Zealand pasture soils In: Advanced Nutrient Management: Gains from the Past - Goals for the Future. (Eds L.D. Currie and C L. Christensen). 

Abstract

Denitrification is the primary process of N2O production in temperate grassland soils and accounts for 60% of the total N2O emissions globally. There are various soil and environmental factors that regulate denitrification and affect denitrification rate (DR) and N2O/ N2 ratio. Among these, soil moisture is the most important. Generally, DR increases and N2O/N2 ratio decreases with increasing soil water content. However, the effect of changing soil moisture on DR and N2O/N2 ratio may vary with the type of soil, its nutrient status and the management practices followed on the farm. The interrelationships among the various factors affecting DR are not very well quantified.

Therefore, the current study was planned to investigate the effect of soil moisture on DR and N2O/N2 ratio in five different New Zealand pasture soils with varying physical and chemical characteristics such as soil texture, total porosity, pH, NO3- and NH4+ content, total nitrogen (TN), total carbon (TC), microbial biomass carbon (MBC) and denitrification enzyme activity (DEA). The experiment involved incubation of surface (0-10cm) and subsurface (10-20cm) soil samples at field capacity (FC) and complete saturation at constant temperature (25oC). DR and N2O/N2 ratio were estimated using an acetylene inhibition (AI) technique.

Denitrification rates were higher in soils incubated at saturation than in soils incubated at FC. Similarly, the N2O/N2 ratio decreased in soils when incubated at saturation as compared to FC. The extent of these increases in DR and decreases in N2O/N2 ratio with increasing moisture content varied among the soils due to differences in NO3- and NH4+ content, MBC and DEA of the soils.

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