Showing papers by "Arvin R. Mosier published in 2008"

N 2 O release from agro-biofuel production negates global warming reduction by replacing fossil fuels

Abstract: The relationship, on a global basis, between the amount of N fixed by chemical, biological or atmospheric processes entering the terrestrial biosphere, and the total emission of nitrous oxide (N2O), has been re-examined, us- ing known global atmospheric removal rates and concentra- tion growth of N2O as a proxy for overall emissions. For both the pre-industrial period and in recent times, after taking into account the large-scale changes in synthetic N fertiliser pro- duction, we find an overall conversion factor of 3-5% from newly fixed N to N 2O-N. We assume the same factor to be valid for biofuel production systems. It is covered only in part by the default conversion factor for "direct" emissions from agricultural crop lands (1%) estimated by IPCC (2006), and the default factors for the "indirect" emissions (follow- ing volatilization/deposition and leaching/runoff of N: 0.35- 0.45%) cited therein. However, as we show in the paper, when additional emissions included in the IPCC methodol- ogy, e.g. those from livestock production, are included, the total may not be inconsistent with that given by our "top- down" method. When the extra N2O emission from biofuel production is calculated in "CO2-equivalent" global warm- ing terms, and compared with the quasi-cooling effect of "saving" emissions of fossil fuel derived CO2, the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), depending on N fertilizer uptake efficiency by the plants, can contribute as much or more to global warming by N2O emis- sions than cooling by fossil fuel savings. Crops with less N demand, such as grasses and woody coppice species, have more favourable climate impacts. This analysis only consid- ers the conversion of biomass to biofuel. It does not take into account the use of fossil fuel on the farms and for fertil- izer and pesticide production, but it also neglects the produc- tion of useful co-products. Both factors partially compensate each other. This needs to be analyzed in a full life cycle as- sessment.

N2O emissions from agricultural lands: a synthesis of simulation approaches

Abstract: Nitrous oxide (N2O) is primarily produced by the microbially-mediated nitrification and denitrification processes in soils. It is influenced by a suite of climate (i.e. temperature and rainfall) and soil (physical and chemical) variables, interacting soil and plant nitrogen (N) transformations (either competing or supplying substrates) as well as land management practices. It is not surprising that N2O emissions are highly variable both spatially and temporally. Computer simulation models, which can integrate all of these variables, are required for the complex task of providing quantitative determinations of N2O emissions. Numerous simulation models have been developed to predict N2O production. Each model has its own philosophy in constructing simulation components as well as performance strengths. The models range from those that attempt to comprehensively simulate all soil processes to more empirical approaches requiring minimal input data. These N2O simulation models can be classified into three categories: laboratory, field and regional/global levels. Process-based field-scale N2O simulation models, which simulate whole agroecosystems and can be used to develop N2O mitigation measures, are the most widely used. The current challenge is how to scale up the relatively more robust field-scale model to catchment, regional and national scales. This paper reviews the development history, main construction components, strengths, limitations and applications of N2O emissions models, which have been published in the literature. The three scale levels are considered and the current knowledge gaps and challenges in modelling N2O emissions from soils are discussed.

Moisture pulses, trace gas emissions and soil C and N in cheatgrass and native grass-dominated sagebrush-steppe in Wyoming, USA

Abstract: Effects of large-scale weed invasion on the nature and magnitude of moisture-pulse-driven soil processes in semiarid ecosystems are not clearly understood. The objective of this study was to monitor carbon dioxide (CO2) and nitrous oxide (N2O) emissions and changes in soil carbon (C) and nitrogen (N) following the application of a water pulse in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) communities dominated by the exotic annual grass cheatgrass (Bromus tectorum) and by the native perennial grass western wheatgrass (Pascopyrum smithii). Sampling locations were established in shrub interspaces dominated by B. tectorum and P. smithi and beneath shrub canopies adjacent to interspaces dominated by B. tectorum and P. smithi, where no grass was present. Soils were classified as fine-loamy, mixed, Borollic Haplargids. Soil samples (0–10 cm) and air samples were collected at 0, 4, 8, 24, 49, 72, and 216 h following additions of 25.4 mm of water. Soil samples were analyzed for dissolved organic carbon (DOC), microbial biomass carbon (MBC), extractable ammonia (NH4+), extractable nitrate (NO3−), and dissolved organic nitrogen (DON). Grass species induced differences in soil nitrification, N2O and CO2 emissions, and the quantity and timing of labile C available to microbial populations responding to increased moisture availability. In the first 8-h phase after wetting P. smithii soils had the greatest CO2 emissions compared to other soils but B. tectorum soils had the greatest N2O emissions and the greatest increases in CO2 emissions relative to before wetting. Microbial biomass C in B. tectorum interspace soils increased rapidly but the response was short-lived despite sufficient water availability. After the first 8 h of soil response to wetting, the observed MBC declines in B. tectorum interspace coincided with disproportional DOC and DON concentration increases. Similar DOC and DON increases were also observed in B. tectorum soils beneath shrub canopy. In contrast, DOC and DON concentrations in P. smithii soils remained unaffected by soil wetting and small MBC increases observed during the first 8-h phase did not decline as rapidly as in B. tectorum interspace soils. In conclusion, summer drying-wetting cycles that occur frequently in areas invaded by B. tectorum can accelerate rates of nitrification and C mineralization, and contribute significantly to trace gas emissions from sagebrush-steppe grasslands. With frequent summer rainfall events, the negative consequences B. tectorum presence in the ecosystem can be significant.

Long-term enhancement of N availability and plant growth under elevated CO2 in a semi-arid grassland

Abstract: Summary 1While rising atmospheric CO2 has the potential to enhance plant growth and biomass accumulation, rates of these processes may be constrained by soil nitrogen (N) availability. Despite much effort, it is still uncertain how elevated CO2 affects long-term soil N dynamics. 2We used open-top chambers to examine the effect of 5 years of elevated atmospheric CO2 concentration (720 vs. 368 p.p.m.) on N dynamics in a semi-arid grassland ecosystem in north-eastern Colorado, USA. In the first year 0·5 g m−2 of ammonium nitrate-N, 99·9 atom%15N, was added to each plot. We examined the effect of elevated CO2 on N mineralization and plant N uptake by tracking the labelled and total N in plant and soil over the following 5 years. 3Plant growth and plant N uptake remained significantly higher under elevated than under ambient CO2. The fraction of labelled N (expressed per unit of total N) in above-ground biomass declined over time, and this decline was greater under elevated CO2. The amount and fraction of labelled N in the soil did not change with time and was unaffected by elevated CO2. These results suggest that with time, N released from mineralization in the soil diluted the labelled N in above-ground biomass and that this dilution effect caused by N mineralization was greater under elevated CO2. More of the mineralized N ended up in the above-ground biomass of Stipa comata and forbs (C3) than in Bouteloua gracilis (C4) under elevated CO2. 4Increased soil moisture under elevated CO2 likely supported higher rates of N mineralization, thereby reducing N constraints on plant growth. Therefore, in semi-arid systems, plant growth and species composition responses to elevated CO2 may be more persistent than in mesic systems where N mineralization is less constrained by soil moisture.

Transient elevation of carbon dioxide modifies the microbial community composition in a semi-arid grassland

Abstract: Using open-top chambers (OTC) on the shortgrass steppe in northern Colorado, changes of microbial community composition were followed over the latter 3 years of a 5-year study of elevated atmospheric CO2 as well as during 12 months after CO2 amendment ended The experiment was composed of nine experimental plots: three chambered plots maintained at ambient CO2 levels of 360±20 μmol mol−1 (ambient treatment), three chambered plots maintained at 720±20 μmol mol−1 CO2 (elevated treatment) and three unchambered plots The abundance of fungal phospholipid fatty acids (PLFAs) shifted in the shortgrass steppe under the influence of elevation of CO2 over the period of 3 years Whereas the content of the fungal signature molecule (18:2ω6) was similar in soils of the ambient and elevated treatments in the third year of the experiment, CO2 treatment increased the content of 18:2ω6 by around 60% during the two subsequent years The shift of microbial community composition towards a more fungal dominated community was likely due to slowly changing substrate quality; plant community forage quality declined under elevated CO2 because of a decline of N in all tested species as well as shift in species composition towards greater abundance of the low forage quality species (Stipa comata) In the year after which CO2 enrichment had ceased, abundances of fungal and bacterial PLFAs in the post-CO2 treatment plots shifted slowly back towards the control plots Therefore, quantity and quality of available substrates had not changed sufficiently to shift the microbial community permanently to a fungal dominated community We conclude from PLFA composition of soil microorganisms during the CO2 elevation experiment and during the subsequent year after cessation of CO2 treatment that a shift towards a fungal dominated system under higher CO2 concentrations may slow down C cycling in soils and therefore enhance C sequestration in the shortgrass steppe in future CO2-enriched atmospheres

Impacts of population growth, changing food preferences and agricultural practices on the nitrogen cycle in East Asia

Abstract: 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.

Evaluation of a polyolefin coated urea (Meister) as a fertilizer for irrigated cotton

Abstract: The effectiveness of two polyolefin coated products, ‘Meister 70’ and ‘Meister 270’, as slow-release sources of nitrogen (N) for irrigated cotton, and uncoated calcium carbide as a source of acetylene to inhibit nitrification of urea-N and reduce losses by denitrification were studied. The crop was grown on a grey clay in the Namoi Valley of north western New South Wales. The fertilisers were applied at 50 and 150 kg N/ha, combined factorialy with two application times, either pre- or post-sowing. Meister 270 did not release N fast enough to supply the plant’s requirements, and is not recommended as a source of N for cotton. Meister 70 was worthy of further study as a pre-sowing source of N because it maintained a higher concentration of ammonium in the soil for longer than urea, resulted in lower soil nitrate concentrations at all times, and increased the apparent recovery efficiency of fertilizer N. The uncoated calcium carbide was not as effective as the wax-coated material tested in previous studies.

Chapter 18. DAYCENT Simulated Effects of Land Use and Climate on County Level N Loss Vectors in the USA

Abstract: Publisher Summary This chapter provides an overview of the DAYCENT ecosystem model and describes the nitrogen gas sub-model of DAYCENT. The model was used to explore how land use, precipitation, and soil texture impact total nitrogen losses and nitrogen gas emissions at the national scale using county level resolution simulations of cropped lands, grazed land, and native vegetation. Total nitrogen losses and the proportion of total losses due to NO3 leaching both tended to increase with nitrogen inputs. At the national scale, NO3 leaching was the major loss vector for both native and cropped/grazed systems because both nitrogen inputs and leaching are positively correlated with water inputs. However, leaching was responsible for less than half of total nitrogen losses for ∼50% of the counties under native vegetation and ∼15% of the counties for cropped/grazed systems.