Functions of Biochar/Activated carbon

General information about biochar/activated carbon. Presents biochar as a potential for GHG mitigation and explains the uses and the benefits of adding biochar/activated carbon to soil

Inventory: nitrous oxide (N2O)

The greenhouse gas (GHG) inventory is an annual reporting requirement under the UN Framework Convention on Climate Change. It: -- Underpins domestic climate change policy -- Is calculated using a framework dictated by the Intergovernmental Panel on Climate Change (IPCC) –i.e. N2O = N source x EF -- Gives accurate inventory numbers specific to NZ -- Enables precise assessments of the effects of GHG mitigation strategie

Dietary manipulation as a tool for mitigating nitrous oxide emissions

Currently, for every 100 units of nitrogen (N) used in agriculture, only about 15 are consumed as crop, dairy or meat products (Steinfeld et al., 2006; Robertson and Vitousek 2009). This points to very low N use efficiency in most agricultural systems. In the dairy industry for example, despite improved genetic potential of cows with high nutrient utilisation, the increased external input of feed concentrates and use of fertiliser N have decreased N use efficiency in these systems (Huhtanen et al., 2008). Increasing N use efficiency is a key strategy by which the increasing food demand might be met without a corresponding increase in N losses and nitrous oxide (N2O) emissions. This chapter focuses on the use of dietary intervention or manipulation by incorporating diverse forages or crops into animal based agriculture as an approach for increasing N use efficiency. Dietary intervention is primarily aimed at either reducing the concentration and amount of N in animal excreta, or changing the partitioning of N in urine and dung, while preferably having no detrimental effect on productivity. This may include, but is not limited to, using low N feed supplements to reduce the amount of N consumed and hence lower the amount of surplus N being excreted, or specific dietary supplementation to encourage the partitioning of N toward dung rather than urine. Additionally, forages may be selected for their potential to inhibit soil N transformations by either the root exudation or urine-excretion of plant secondary metabolites. Dietary intervention may not be feasible in many low input, pasture based agricultural systems, however, in more intensive systems such as the New Zealand dairy industry, particularly with the increasing use of animal feed pads and housing practices, supplements are commonly imported and so dietary intervention is more practical

The effects of different cow urinary nitrogen rates on gaseous nitrogen fluxes from pasture soil

Cattle grazing pasture deposit urine at high nitrogen (N) rates that can impact the environment. Among the loss pathways, denitrification, which produces nitrous oxide (N2O) and dinitrogen (N2), is a major way that N can be lost to the atmosphere. There is limited information about N2 losses from grazed-pasture systems after urine deposition due to the method limitations with high ambient N2 concentrations. In this study, the 15N flux method and a high sampling frequency were used to explore N2 and N2O fluxes over time after urine application at two rates (400 and 800 kg N ha-1) on a New Zealand grazed pasture soil. N2O fluxes were significantly higher from the higher N application rate compared with the lower rate but there was no significant difference in N2 fluxes. Dinitrogen was the predominant gaseous N form lost from the applied urinary-N, contributing 32.1 ± 4.1% and 14.4 ± 1.7% of the total deposited N from 400 kg N ha-1 and 800 kg N ha-1, respectively, over the 95 measurement days. Denitrification and codenitrification both occurred in the pasture system, with denitrification being the predominant N2 production pathway, contributing 97.9 – 98.5% of the total N2 production. The similar N2 losses between the two urine-N rates is speculated to be due to enhanced ammonia volatilisation and transfer of N as nitrate, to deeper soil layers at the higher N rate. Soil relative gas diffusivity indicated that high N2 fluxes may have resulted from entrapped N2 diffusing from the draining soil

New Zealand dairy farm systems and key environmental effects

This paper provides an overview of the range of dairy pasture grazing systems used in New Zealand (NZ), the changes with increased inputs over time and associated key environmental effects including nitrogen (N) leaching and greenhouse gas (GHG) emissions. NZ dairy farming systems are based on year-round grazing and seasonal milk production on perennial ryegrass/clover pasture where cows are rotationally grazed in paddocks. There was an increase in stocking rate on NZ dairy farms from 2.62 cows ha−1 in 2000/2001 to 2.84 cows ha−1 in 2015/2016. During the same period annual milk solids production increased from 315 to 378 kg·yr−1 per cow. This performance has coincided with an increase in N fertilizer use (by ~ 30%) and a twofold increase in externally-sourced feeds. Externally-sourced feeds with a low protein concentration (e.g., maize silage) can increase the efficiency of N utilization and potentially reduce N losses per unit of production. Off-paddock facilities (such as standoff or feed pads) are often used to restrict grazing during very wet winter conditions. A systems analysis of contrasting dairy farms in Waikato (largest NZ dairying region) indicates that the increased input would result in an increase in per-cow milk production but little change in efficiency of milk production from a total land use perspective. This analysis also shows that the increased inputs caused an 11% decrease in N footprint (i.e., N emissions per unit of milk production) and a 2% increase in C footprint (i.e., greenhouse gas (GHG) emissions per unit of milk production)

Naturally occurring compounds in animal urine that may inhibit nitrous oxide emissions from soils

Objective: To test the impact of glucosinolate hydrolysis products on N2O emission

Can incorporating brassica tissues into soil reduce nitrification rates and nitrous oxide emissions?

New Zealand agriculture is composed predominantly of pastoral grazing systems; however, forage crops have been increasingly used to supplement the diet of grazing animals. Excreta from grazing animals has been identified as a main contributor of N2O emissions. Some forage crops, such as brassicas (Brassica spp.), contain secondary metabolites that have been identified to inhibit soil N cycling processes, and nitrification in particular. Our objective was to determine if secondary metabolites released from brassica tissues inhibited nitrification and reduced N2O emissions when incorporated into soil, which was amended with a large amount of urea N (such as derived from urine patches deposited during grazing). Three brassica tissues (kale [Brassica oleracea L.], turnip [Brassica rapa L.] bulb, and turnip leaf and stem) and ryegrass (Lolium perenne L.) tissue were incorporated into soil with and without urea solution, and N2O, NO3−, and NH4+ were measured during a 52-d incubation. All brassica tissues reduced urea-derived N2O emissions relative to ryegrass tissues when incorporated into soil. According to the mineral N and microbial community data, this reduction, however, could not be attributed to inhibition of nitrification. Although there was less N2O from urea in the brassica treatments, total N2O emissions increased after incorporation of all tissue residues into soil, so this tradeoff must be explored if brassica tissues are to be considered as a tool for N2O reduction

Nitrous oxide emissions from animal excreta deposited on hill country slopes

The objective of this study was to conduct field measurements of nitrous oxide (N2O) emissions caused by deposition of sheep and beef cattle dung and urine on hill country pasture. This work was carried out on a free-draining volcanic soil at the Whatawhata Research Farm in the Waikato region as part of a series of field trials nationwide conducted in 2015. This research provides field data to determine background N2O emissions and emission factors (EF3, % of the applied excreta N emitted as N2O) for animal excreta deposited in the autumn-winter on steep (>25o) and moderate(12-25o) slopes . N2O flux measurements were made using a closed chamber technique. N2O fluxes from controls on both medium and steep slopes were less than 0.55 mg N2O-N m2 hr-1 through the four month (winter/early spring) measurement period. Greater variability in background emissions was exhibited on the steep slopes than on the medium slopes. There was a slight trend for higher total background N2O emissions from medium (average 0.035 kg N2O ha-1) compared to steep slope areas (average 0.021 kg N2O ha-1), but the difference was not significant (P>0.05). EF3 for all excreta types were generally very low and highly variable. There was a trend for higher EF3 values on the medium slope than on the steep slope, with beef cattle dung on the medium slope having the highest EF3 value and sheep dung on the steep slope having the lowest EF3 value. There was no relationship between EF3 and soil properties, including soil Olsen P, moisture and mineral nitrogen levels

Managing dairy effluents in New Zealand: regulatory policy, best management practice.

Covers New Zealand policy, New Zealand best management through science and research, New Zealand nutrient budgets

Nitrous oxide emissions during forage brassica cropping and grazing

The objectives of this study were to conduct field measurements of nitrous oxide (N2O) emissions caused by deposition of sheep and beef cattle dung and urine on hill country pasture. This work was carried out on a free-draining volcanic soil at the Whatawhata Research Farm in the Waikato region as part of a series of field trials nationwide conducted in 2014 and 2015. This research provides field data to determine background N2O emissions and emission factors (EF3, % of the applied excreta N emitted as N2O) for animal excreta deposited in the autumn-winter on steep (>25o) and moderate(12-25o) slopes . N2O flux measurements were made using a closed chamber technique. N2O fluxes from controls on both medium and steep slopes were less than 0.55 mg N2O-N m2 hr-1 through the four month (winter/early spring) measurement period. Greater variability in background emissions was exhibited on the steep slopes than on the medium slopes. There was a slight trend for higher total background N2O emissions from medium (0.035 kg N2O ha-1) compared to steep slope areas (0.021 kg N2O ha-1), but the difference was not significant (P>0.05). Application of either animal urine or dung increased N2O fluxes, but the patterns and magnitudes of the increases were not consistent between excreta types and slope classes. Changes in the fluxes were not significantly correlated to changes in soil moisture levels, mineral nitrogen (N) concentrations or temperature. EF3 for all excreta types were generally very low, with the averages being less than 0.3% for urine and dung sources, and highly variable. There was a trend for higher EF3 values on the medium slope than on the steep slope, with beef cattle dung on the medium slope having the highest EF3 value and sheep dung on the steep slope having the lowest EF3 value. There was no relationship between EF3 and soil properties, including soil Olsen P, moisture and mineral nitrogen levels. The EF3 values in the hill country appear to be affected by a complex range of physical and biological factors