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"Freney, J R"
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Ammonia volatilization from nitrogen fertilizers applied to cereals in two cropping areas of southern Australia
As farmers in southern Australia typically apply nitrogen (N) to cereal crops by top-dressing with ammonia (NH
3
) based fertilizer in late winter or early spring there is the potential for large losses of NH
3
. This paper describes the results of micrometeorological measurements to determine NH
3
loss and emission factors following applications of urea, urea ammonium nitrate (UAN), and ammonium sulfate (AS) at different rates to cereal crops at two locations in southern Australia. The amounts of NH
3
lost are required for farm economics and management, whilst emission factors are needed for inventory purposes. Ammonia loss varied with fertilizer type (urea > UAN > AS) and location, and ranged from 1.8 to 23 % of N applied. This compares with the emission factor of 10 % of applied N advocated by IPCC (
2007
). The variation with location seemed to be due to a combination of factors including soil texture, soil moisture content when fertilizer was applied and rainfall after fertilizer application. Two experiments at one location, 1 week apart, demonstrated how small, temporal differences in weather conditions and initial soil water content affected the magnitude of NH
3
loss. The results of these experiments underline the difficulties farmers face in timing fertilization as the potential for loss, depending on rainfall, can be large.
Journal Article
Managing soil denitrification
Denitrification of nitrate in the soil can be a mechanism of significant loss of fertilizer and soil nitrogen, but it can
also serve to remove excess NO 3 that is leached below the root zone. Inappropriate management of irrigation water and fertilizer N in irrigated corn has
resulted in leaching of excess N from the rooting zone and contamination of groundwater and also has contributed to the increasing
concentration of N 2 O in the atmosphere. Denitrification can be both microbial and chemical, but the microbial process dominates in most soils
through a stepwise reduction of NO 3 to N 2 . Soil atmosphere O 2 concentration, which is regulated by soil water content interactively with soil texture and microbial respiration, is the
main controller of the process. The oxygen consumption rate depends on the amount of easily degradable organic C compounds
and the interplay of water and carbon in developing in the soil reduced oxic conditions, which regulate not only the amount
of total denitrification but also the ratio of N 2 O to N 2 produced. Appropriate management of nutrient input, relative to crop demand and soil water status, can limit nitrogen loss
from denitrification. This paper describes the role of denitrification in the nitrogen economy of crop production and the
environment, describes the process involved, and presents suggestions for limiting N loss caused by denitrification.
Journal Article
Nitrous oxide emissions from agricultural fields: assessment, measurement and mitigation
In this paper we discuss three topics concerning N₂O emissions from agricultural systems. First, we present an appraisal of N₂O emissions from agricultural soils (Assessment). Secondly, we discuss some recent efforts to improve N₂O flux estimates in agricultural fields (Measurement), and finally, we relate recent studies which use nitrification inhibitors to decrease N₂O emissions from N-fertilized fields (Mitigation). To assess the global emission of N₂O from agricultural soils, the total flux should represent N₂O from all possible sources; native soil N, N from recent atmospheric deposition, past years fertilization, N from crop residues, N₂O from subsurface aquifers below the study area, and current N fertilization. Of these N sources only synthetic fertilizer and animal manures and the area of fields cropped with legumes have sufficient global data to estimate their input for N₂O production. The assessment of direct and indirect N₂O emissions we present was made by multiplying the amount of fertilizer N applied to agricultural lands by 2% and the area of land cropped to legumes by 4 kg N₂O-N ha⁻¹. No regard to method of N application, type of N, crop, climate or soil was given in these calculations, because the data are not available to include these variables in large scale assessments. Improved assessments should include these variables and should be used to drive process models for field, area, region and global scales. Several N₂O flux measurement techniques have been used in recent field studies which utilize small and ultralarge chambers and micrometeorological along with new analytical techniques to measure N₂O fluxes. These studies reveal that it is not the measurement technique that is providing much of the uncertainty in N₂O flux values found in the literature but rather the diverse combinations of physical and biological factors which control gas fluxes. A careful comparison of published literature narrows the range of observed fluxes as noted in the section on assessment. An array of careful field studies which compare a series of crops, fertilizer sources, and management techniques in controlled parallel experiments throughout the calendar year are needed to improve flux estimates and decrease uncertainty in prediction capability. There are a variety of management techniques which should conserve N and decrease the amount of N application needed to grow crops and to limit N₂O emissions. Using nitrification inhibitors is an option for decreasing fertilizer N use and additionally directly mitigating N₂O emissions. Case studies are presented which demonstrate the potential for using nitrification inhibitors to limit N₂O emissions from agricultural soils. Inhibitors may be selected for climatic conditions and type of cropping system as well as the type of nitrogen (solid mineral N, mineral N in solution, or organic waste materials) and applied with the fertilizers.
Journal Article
Direct measurements of methane emissions from grazing and feedlot cattle
Methane (CH4) emissions from animals represent a significant contribution to anthropogenically produced radiatively active trace gases. Global and national CH4 budgets currently use predictive models based on emission data from laboratory experiments to estimate the magnitude of the animal source. This paper presents a method for measuring CH4 from animals under undisturbed field conditions and examines the performance of common models used to simulate field conditions. A micrometeorological mass difference technique was developed to measure CH4 production by cattle in pasture and feedlot conditions. Measurements were made continuously under field conditions, semiautomatically for several days, and the technique was virtually nonintrusive. The method permits a relatively large number of cattle to be sampled. Limitations include light winds (less than approximately 2 m/s), rapid wind direction changes, and high-precision CH4 gas concentration measurement. Methane production showed a marked periodicity, with greater emissions during periods of rumination as opposed to grazing. When the cattle were grazed on pasture, they produced .23 kg CH4 x animal(-1) x d(-1), which corresponded to the conversion of 7.7 to 8.4% of gross energy into CH4. When the same cattle were fed a highly digestible, high-grain diet, they produced .07 kg CH4 x animal(-1) x d(-1), corresponding to a conversion of only 1.9 to 2.2% of the feed energy to CH4. These measurements clearly document higher CH4 production (about four times) for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets. The mass difference method provides a useful tool for \"undisturbed\" measurements on the influence of feedstuffs and nutritional management practices on CH4 production from animals and for developing improved management practice for enhanced environmental quality.
Journal Article
Impacts of population growth, changing food preferences and agricultural practices on the nitrogen cycle in East Asia
While increasing population and changing food preferences have changed agriculture in some East Asian countries to high input systems with greater use of fertilizer nitrogen and greater numbers of animals, the changes and the effects on the environment in the different countries have varied considerably. Many areas still do not use sufficient nitrogen to maximize crop yields. In China, fertilizer nitrogen input has increased from 0.54 Tg in 1961 to 28 Tg in 2005, and the animal population increased dramatically, from 27 to 1,013 million. As a result 13 Tg N was lost to the environment in 2005 as nitrous oxide, ammonia or nitrate. In Mongolia, no fertilizer nitrogen was recorded as having been used until 1970, and current use is only ~4 Gg. The animal population has increased from 23 million in 1961 to 28 million in 2005 and adverse effects on the environment are small (96 Gg N lost). However, a combination of over-ploughing and overgrazing has resulted in soil erosion from wind and rain in both countries and loss of soil nitrogen. These and other effects of changing agricultural systems on the nitrogen cycle in East Asian countries and some approaches to reduce the impact of nitrogen on the environment are reported in this paper.
Journal Article
Changes in the human-monsoon system of East Asia in the context of global change
This book is the first in a series of assessments of regional climate change. Irreversible changes to regional biogeochemistry, and terrestrial and marine ecosystem functioning are brought about by increases in population, intensified land use, urbanization, industrialization and economic development.
eBook
Options for reducing the negative effects of nitrogen in agriculture
After addition to farms by fertilizer, crop residues, biological fixation and animal excreta, nitrogen can be lost through gaseous emission, runoff and leaching to contaminate the atmosphere and water bodies, and cause adverse health effects. The efficiency of fertilizer nitrogen can be increased and losses reduced, by matching supply with crop demand, optimizing split application schemes, changing the form to suit the conditions, and use of slow-release fertilizers and inhibitors. In addition, agronomic practices such as higher plant densities, weed and pest control and balanced fertilization with other nutrients can also increase efficiency of nitrogen use. Efficiency of use by animals can be increased by diet manipulation. Feeding dairy cattle low degradable protein and high starch diets, and grazing sheep and cattle on grasses high in water soluble carbohydrate result in less nitrogen excretion in urine and reduced ammonia volatilization.[PUBLICATION ABSTRACT]
Journal Article
Mitigating Agricultural Emissions of Methane
Agricultural crop and animal production systems are important sources and sinks for atmospheric methane (CH4). The major CH4 sources from this sector are ruminant animals, flooded rice fields, animal waste and biomass burning which total about one third of all global emissions.
Journal Article
Ammonia, methane, and nitrous oxide emission from pig slurry applied to a pasture in New Zealand
Much animal manure is being applied to small land areas close to animal confinements, resulting in environmental degradation. This paper reports a study on the emissions of ammonia (NH₃), methane (CH₄), and nitrous oxide (N₂O) from a pasture during a 90-d period after pig slurry application (60 m³ ha⁻¹) to the soil surface. The pig slurry contained 6.1 kg total N m⁻³, 4.2 kg of total ammoniacal nitrogen (TAN = NH₃ + NH₄) m⁻³, and 22.1 kg C m⁻³, and had a pH of 8.14. Ammonia was lost at a fast rate immediately after slurry application (4.7 kg N ha⁻¹ h⁻¹), when the pH and TAN concentration of the surface soil were high, but the loss rate declined quickly thereafter. Total NH₃ losses from the treated pasture were 57 kg N ha⁻¹ (22.5% of the TAN applied). Methane emission was highest (39.6 g C ha⁻¹ h⁻¹) immediately after application, as dissolved CH₄ was released from the slurry. Emissions then continued at a low rate for approximately 7 d, presumably due to metabolism of volatile fatty acids in the anaerobic slurry–treated soil. The net CH₄ emission was 1052 g C ha⁻¹ (0.08% of the carbon applied). Nitrous oxide emission was low for the first 14 d after slurry application, then showed emission peaks of 7.5 g N ha⁻¹ h⁻¹ on Day 25 and 15.8 g N ha⁻¹ h⁻¹ on Day 67, and decline depending on rainfall and nitrate (NO₃) concentrations. Emission finally reached background levels after approximately 90 d. Nitrous oxide emission was 7.6 kg N ha⁻¹ (2.1% of the N applied). It is apparent that of the two major greenhouse gases measured in this study, N₂O is by far the more important tropospheric pollutant.
Journal Article