SimDen – A simple empirical model for quantification of N2O emission and denitrification

The denitrification process, including emission of nitrous oxide (N2O), is an important process both from an agricultural and environmental point of view. However, the process is, due to its high spatial and temporal variability, very difficult and resource demanding to quantify, and the only alternative is often to use simulation models. However, simulation models often need more input information than what is available. Therefore, a simple empirical model - SimDen - for quantifying the denitrification is presented, where only information about soil type and fertilisation are needed as input variables. Basically, the denitrification in SimDen is calculated as (N2O-emission) x (N2/N2O-ratio): - The N2O-emission is derived from input of N and emission factors, as used in the IPCC-methodology. SimDen use emission factors of 0.8% of applied N for inorganic fertiliser and 2.5% for animal manure/slurry and N2 fixation. Only N2 fixation below harvest or grazing height, i.e., fixation in stubble and roots, is considered as N-input. - N2/N2O-ratios are based on literature values. Soil moisture and content of organic matter affect both the N2O-emission and the N2/N2O-ratio, which made it possible to relate the denitrification to the Danish soil types, which differs in hydraulic properties and soil texture. SimDen is verified against a number of field measurements from Danish soils and has been compared to simulations with the soil-plant-atmosphere model Daisy. SimDen can be downloaded from: www.agrsci.dk/simde

Effects of cutting frequency on plant production, N-uptake and N2 fixation in harvested and below-harvest plant biomass of grass clover

Nitrogen (N) accumulating in stubble, stolons and roots is an important component in N balances in perennial ryegrass-white clover swards, and the effects of cutting frequency on the biomass of above- and below-harvest height were studied during two consecutive years. Total dry matter (DM) and total N production, and N2 fixation, were measured at two cutting frequencies imposed in the summers of two years either by cutting infrequently at monthly intervals to simulate mowing or by frequent cutting at weekly intervals to simulate grazing. Total DM production harvested was in the range 3000 - 7000 kg DM ha-1 with lower DM production associated with the frequent cutting treatment, and it was significantly affected by the different weather conditions in the two years. The higher cutting frequency also reduced the biomass below harvest height, but the different weather conditions between years had less effect on stubble and, in particular, root biomass. The biomass of white clover roots was significantly lower than that of perennial ryegrass roots, and remained at a relatively constant level (200-500 kg DM ha-1) throughout the experiment, whereas the biomass of perennial ryegrass roots increased from 2 400 kg DM ha-1 in the year of establishment to 10 200 kg DM ha-1 in the infrequent cutting treatment and 6 650 kg DM ha-1 in the frequent cutting treatment by the end of the experiment, giving shoot: root ratios of 4.7 – 16.6 and 0.5 – 1.6 for white clover and perennial ryegrass, respectively. Annual N2 fixation was in the range 28 – 214 kg N ha-1, and the proportion of N fixed in stolons and roots was on average 0.28. However, since the weather conditions affect the harvested DM production and the shoot: root ratio, care must be taken when estimating total N2 fixation based on an assumed or fixed shoot: root rati

Effect of age and cutting frequency on below-ground biomass in grass-clover

Significant amounts of plant biomass and fixed N are incorporated into soil as roots, nodules and root exudates during the growth of grass-clover, which consequently is exposed to soil microbial degradation when the field is ploughed. This has major implications for our understanding of the potential contributions of legumes in the N economics and losses in grass-clover cropping systems. We have studied the effects of grass-clover pasture age and cutting frequency (simulated grazing) on the development of the above ground as well as the below ground plant biomass, with emphasis on below-harvest contribution to the total N2 fixation

Permporometry: the determination of the size distribution of active pores in UF membranes

Permporometry is a method by which the characteristics of the interconnecting 'active' pores of an ultrafiltration membrane can be measured. It is these active' pores that are responsible for the actual membrane performence. Application of permporometry on different membrane types, including ceramic as well as polymeric membranes, shows that the method can provide objective information on the `active¿ pore size present

Critical points in the analysis of membrane pore structures by thermoporometry

Several ultrafiltration membranes of the anisotropic and isotropic type were characterized by means of the thermoporometry. Successive cooling and heating runs were performed in order to investigate the effects of the water-ice and ice-water phase transitions on the structure of the membranes. The results found for membranes having different casting thicknesses indicate that, in some cases, pores in the sublayer of anisotropic UF membranes frustrate the measurement of the, for the separation, relevant porse present in the top layer

Nitrate leaching in grazed grasslands of different composition and age

In a field experiment at Research Centre Foulum a suction cup technique was used to investigate nitrate leaching from grassland depending on composition (grass-clover or perennial ryegrass), management (grazing or cutting) and age of the swards. In 1997-2001 was investigated the successive nitrate leaching from 4-7 year old grazed grass-clover and ryegrass with cut plots of similar age and spring barley as reference. In 2000-2001 the simultaneous nitrate leaching from newly established swards, swards grazed for 1 and 7 years and swards cut for 7 years was investigated. In the newly established swards nitrate leaching from grass-clover and ryegrass were similar but at increasing sward age nitrate leaching from the fertilized ryegrass increased dramatically compared to a constant low level from the unfertilized grass-clover. Apparently, the clover component of grass-clover was able to equalize differences in soil nitrogen availability in swards of different age. The results of N2 fixation studies in swards of different age in 2001 will be used in the interpretation of the nitrate leaching data

Stress-Induced Leakage Current in p+ Poly MOS Capacitors with Poly-Si and Poly-Si0.7Ge0.3 Gate Material

The gate bias polarity dependence of stress-induced leakage current (SILC) of PMOS capacitors with a p+ polycrystalline silicon (poly-Si) and polycrystalline Silicon-Germanium (poly-Si0.7 Ge0.3) gate on 5.6-nm thick gate oxides has been investigated. It is shown that the SILC characteristics are highly asymmetric with gate bias polarity. This asymmetric behavior is explained by the occurrence of a different injection mechanism for negative bias, compared to positive bias where Fowler-Nordheim (FN) tunneling is the main conduction mechanism. For gate injection, a larger oxide field is required to obtain the same tunneling current, which leads to reduced SILC at low fields. Moreover, at negative gate bias, the higher valence band position of poly-SiGe compared to poly-Si reduces the barrier height for tunneling to traps and hence leads to increased SILC. At positive gate bias, reduced SILC is observed for poly-SiGe gates compared to poly-Si gates. This is most likely due to a lower concentration of Boron in the dielectric in the case of poly-SiGe compared to poly-Si. This makes Boron-doped poly-SiGe a very interesting gate material for nonvolatile memory device

A fast vibro-acoustic response analysis method for double wall structures including a viscothermal air layer

The damping behaviour of a thin air layer between two flexible panels can be used to reduce sound radiation of structural excited panels. The numerical model of the double wall panels takes into account full acousto-elastic interaction and viscothermal wave propagation in the air layer. This means that the resulting system matrices are complex and frequency dependent which makes it difficult to perform response calculations. In this paper a very efficient calculation method is presented which is based on the superposition of uncoupled structural and acoustic eigenmodes. The frequency dependent behaviour is implemented by updating the reduced acoustic submatrices for each frequency step. The method is successfully implemented in the B2000 processor B2FRF

Measuring poverty dynammics and inequality in transition economies - disentangling real events from noisy data

The author uses instrumental variable methods, and the decomposition of income into transitory and persistent components to distinguish underlying income inequality and changes in poverty from the effects attributable to measurement error or transitory shocks. He applies this methodology to household-level panel data for Russia and Poland in the mid-1990s. The author finds that: 1) Accounting for noise in the data reduces inequality (as measured by the Gini coefficient) by 10-45 percent. 2) Individuals in both countries face much economic insecurity. The median absolute annual change in income or spending is about fifty percent in Russia, and about 20 percent in Poland. But roughly half of these fluctuations reflect measurement error or transitory shocks, so underlying levels of income, and spending are much more stable than the data suggest. 3) The apparent high levels of economic mobility are driven largely by transitory events and noisy data. After transitory shocks are accounted for, about eighty percent of the poor in both Russia and Poland remain in poverty for at least one year. So there is a real risk of an entrenched underclass emerging in these transition economies.Inequality,Governance Indicators,Economic Theory&Research,Poverty Diagnostics,Environmental Economics&Policies