Short-term nitrous oxide emissions from pasture soil as influenced by urea level and soil nitrate

Nitrogen excreted by cattle during grazing is a significant source of atmospheric nitrous oxide (N2O). The regulation of N2O emissions is not well understood, but may vary with urine composition and soil conditions. This laboratory study was undertaken to describe short-term effects on N2O emissions and soil conditions, including microbial dynamics, of urea amendment at two different rates (22 and 43 g N m-2). The lower urea concentration was also combined with an elevated soil NO3- concentration. Urea solutions labelled with 25 atom% 15N were added to the surface of repacked pasture soil cores and incubated for 1, 3, 6 or 9 days under constant conditions (60% WFPS, 14°C). Soil inorganic N (NH4+, NO2- and NO3-), pH, electrical conductivity and dissolved organic C were quantified. Microbial dynamics were followed by measurements of CO2 evolution, by analyses of membrane lipid (PLFA) composition, and by measurement of potential ammonium oxidation and denitrifying enzyme activity. The total recovery of 15N averaged 84%. Conversion of urea-N to NO3- was evident, but nitrification was delayed at the highest urea concentration and was accompanied by an accumulation of NO2-. Nitrous oxide emissions were also delayed at the highest urea amendment level, but accelerated towards the end of the study. The pH interacted with NH4+ to produce inhibitory concentrations of NH3(aq) at the highest urea concentration, and there was evidence for transient negative effects of urea amendment on both nitrifying and denitrifying bacteria in this treatment. However, PLFA dynamics indicated that initial inhibitory effects were replaced by increased microbial activity and net growth. It is concluded that urea-N level has qualitative, as well as quantitative effects on soil N transformations in urine patches

Nitrous oxide emissions from grazed grassland: effects of cattle management and soil conditions

Traditionally, dairy cattle spend a substantial part of the year on pastures. For organic farming within EU it is specified that ”all mammals must have access to pasturage or an open-air exercise area” which they must be able to use whenever ”weather conditions and the state of the ground permits” (Council Regulation [EEC] No 2092/91 ). Dairy production systems are characterized by a considerable N surplus, and N deposited during grazing represents a significant risk for environmental losses, including N2O emissions. Excess N is excreted mainly in the urine, the composition of which is influenced by factors such as lactation stage, sward quality and intake of supplements. Resulting N concentrations in urine patches can range from 20 to 80 g N m-2, and soil environmental conditions associated with such a range of N inputs could affect the potential for N2O production via nitrification and denitrification. Soil properties and fertilization also influence N2O emissions. This presentation shows results from a work package within the MIDAIR project which aimed to describe known sources of variability within the grazing system, and their impact on N2O emissions. The objective was to evaluate if management changes can be proposed that will reduce the risk for N2O emissions associated with grazing. Field studies have addressed the heterogeneity of soil physical, chemical and microbiological properties, while plot-scale and laboratory experiments have examined the fate of urinary C and N and the microbial response to urine deposition

Soil health as an indicator of sustainable management

Population growth, a widening gap between the rich and poor, environmental degradation, and a re-evaluation of energy use and alternatives will shape life in the 21st century. We will be challenged to increase food supplies for a global population one-and-a-half to two times its current size. But as agricultural systems grow to meet the demands of more people, increased pressure will be placed on our natural resources: competition for land, water and energy resources from both urban and industrial sectors becomes more acute and the available land base remains static or shrinks. Under current practices increased food production will greatly increase inputs into agricultural production systems, thereby vastly increasing opportunity for environmental pollution and degradation and depletion of natural and non-renewable resources (Power, 1996). To sustain agriculture and the world for future generations, we must act now to develop production systems which rely less on non-renewable, petrochemical based resources; rely more on renewable resources from the sun for our food, fiber, and energy needs; and achieve the ecological intensification needed to meet the increased future food demand (Cassman, 1999). However, better coordination with natural processes for meeting our food and energy needs will likely require some life-style change to achieve the multiple goals of economic, ecological, and environmental sustainability. The condition of our soils ultimately determines human health by serving as the major medium for food and fiber production and a primary interface with the environment, influencing the quality of air we breathe and water we drink. Thus, there is a clear linkage between soil quality and human and environmental health. As such, the health of our soil resources is a primary indicator of the sustainability of our land management practices (Acton and Gregorich, 1995). In this special issue, summary findings of an international workshop on “Soil Health as an Indicator of Sustainable Land Management”, held June 24 and 25, 1999 at the GAIA Environmental Research and Education Center in Kifissia, Greece are presented. The objectives of this workshop were to highlight the central role of soil health in sustaining society and assuring future environmental stability and agricultural productivity and to identify critical issues and research and education needs as related to sustainable development. Oral presentations on the first day of this workshop were given by scientists and professionals from the USA, Canada, Germany, Greece, France, Moldova, Poland, Spain, and the UK. On the second day of the workshop, participants worked together in one large group and in three small break-out groups to identify critical issues in sustainable management and to define research and education needs to address these issues. The final product was the identification of high priority research and education needs for the sustainable management of agricultural land and of the management “strategies” needed to achieve sustainability. A major challenge to us as scientists is in finding ways to translate our science into practices that people of the land can embrace to sustain both themselves and the soils and environments on which we all depend

Towards Understanding the Roaming Mechanism in H + MgH → Mg + HH Reaction

The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio three-dimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase space where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. The complex forming trajectories in the HMgH well can either return to the radical channel or “roam” to the MgHH minimum from where the molecule may react

Comparison of passive and active canopy sensors for the estimation of vine biomass production

Recent advances in optical designs and electronic circuits have allowed the transition from passive to active proximal sensors. Instead of relying on the reflectance of natural sunlight, the active sensors measure the reflectance of modulated light from the crop and so they can operate under all lighting conditions. This study compared the potential of active and passive canopy sensors for predicting biomass production in 25–32 randomly selected positions of a Merlot vineyard. Both sensors provided estimates of the normalized difference vegetation index (NDVI) from a nadir view of the canopy at veraison that were good predictors of pruning weight. Although the red NDVI of the passive sensors explained more of the variation in biomass (R2 = 0.82), its relationship to pruning weight was nonlinear and was best described by a quadratic regression (NDVI = 0.55 + 0.50 wt-0.21 wt2). The theoretically greater linearity of the amber NDVI-biomass relationship could not be verified under conditions of high biomass. The linear correlation to stable isotope content in leaves (15N) provided evidence that canopy reflectance detected plant stresses as a result of water shortage and limited fertilizer N uptake. Thus, the canopy reflectance data provided by these mobile sensors can be used to improve site-specific management practices of vineyards

The Evaluation of Hazards to Man and the Environment during the Composting of Sewage Sludge

Composting is considered an effective treatment option to eliminate or substantially reduce potential hazards relating to the recycling of sewage sludge (SS) on land. The variation of four major types of hazards (heavy metals, instability, pathogenic potential and antibiotic resistance) was studied during laboratory-scale composting of two mixtures of sludge and green waste (1:1 and 1:2 v/v). The heavy metal content of the final compost was governed by the initial contamination of SS, with the bulking agent ratio having practically no effect. The composts would meet the heavy metal standards of the United States of America (USA) and the European Union member states, but would fail the most stringent of them. A higher ratio of bulking agent led to a higher stabilisation rate, nitrogen retention and final degree of stability. A good level of sanitisation was achieved for both mixtures, despite the relatively low temperatures attained in the laboratory system. The antibiotic resistance was limited among the E. coli strains examined, but its occurrence was more frequent among the Enterococcus spp. strains. The type of antibiotics against which resistance was mainly detected indicates that this might not be acquired, thus, not posing a serious epidemiological risk through the land application of the SS derived composts

Urea concentration affects short-term N turnover and N2O production in grassland soil

Introduction For Western Europe it is estimated that, on average, 8% of total N excreted by dairy cattle is deposited during grazing (IPCC, 1997). The intake and excretion of N is influenced by factors such as feed composition, lactation stage and pasture quality, and the excretion of excess N as urea in the urine can therefore vary considerably. Urea can lead to high ammonium levels in the soil which may influence N dynamics and gaseous emissions. This laboratory study was conducted to investigate short-term effects of urea concentration on N2O emissions. Methods Solutions containing 0 (CTL), 5 (LU) and 10 g l-1 urea-N (HU) were added to sieved and repacked soil cores of pasture soil at a rate of 4 l m-2. Also, 5 g l-1 urea-N was added to soil amended with 50 μg cm-3 nitrate-N in order to simulate N turnover in overlapping urine spots (LUN). The urea was labelled with 25 atom% 15N. Final soil moisture was 60% WFPS. All treatments were incubated at 14C. Carbon dioxide and N2O evolution rates were determined after c. 0.2, 0.5, 1, 3, 6 and 9 d. At the four last samplings, the replicates used for gas flux measurements were destructively sampled for determination of pH, electrical conductivity (EC), inorganic and total N, as well as dissolved organic C and phospholipid fatty acid composition. On Day 3, soil was also subsampled for determination of potential ammonium oxidation (PAO) and denitrifying enzyme activity (DEA). The amount and isotopic composition of soil N, nitrate, N2O and N2 was determined by IR-MS; labelling of N2 was insignificant. Results and discussion Accumulated CO2 evolution, corrected for CO2 added in urea, was twice as high from HU as from LU, whereas CO2 from LUN was at the level of the CTL treatment after correction. The lower CO2 emission from LUN was associated with a consistent increase in microbial biomass, as reflected in concentrations of PLFA, which suggested that the lower CO2 evolution rate was due to C assimilation rather than growth inhibition. The EC levels in LU, HU and LUN corresponded to osmotic potentials of -0.05 to -0.12 MPa after 1 d, decreasing to between -0.14 and -0.19 MPa after 9 d. These potentials would not normally be stressful, but a negative interaction with high ammonium concentrations has been observed for ammonium oxidation and, particularly, for nitrite oxidation (Harada and Kai, 1968; Stark and Firestone, 1995). PAO measurements after 3d did not indicate any detrimental effects on ammonium oxidisers. Total recovery of urea-N during the experiment was 801.5% (meanS.E.). Soil nitrate accumulated exponentially to concentrations of 90, 60 and 100 mg N kg-1 in LU, HU and LUN after 9 d. Of this, 47, 40 and 58 mg N kg-1 were derived from urea. Nitrification was thus delayed in the HU treatment. Here, a dramatic increase in nitrite concentration to 8 mg N kg-1 was observed between 6 and 9 d, suggesting a selective inhibition of nitrite oxidation. The fact that 33-52% of the nitrate produced was derived from soil N, points to a significant initial turnover of the ammonium pool. Total concentrations of ammonium after 1 d corresponded to 51-61% of urea-N added, and after 3 d to 80-85%. The transient disappearance could be due to microbial assimilation in response to the sudden decrease in osmotic potential. After 6 and 9 d, soil inorganic N corresponded to approximately 100% in LU and LUN, and to 90% in HU. Emissions of N2O during 0-9 d decreased in the order LU>HU>LUN>>CTL and corresponded to 0.1-0.2% of urea-N added. Emission rates for N2O derived from soil were relatively constant in LU, HU and LUN. In HU, the emission of N2O derived from urea increased dramatically between day 6 and 9, parallel to the accumulation of nitrite. Apparently the higher ammonium concentration resulted in accumulation of nitrite which, in turn, led to an accelerated loss of N2O via ammonium oxidation. This implies that management practices which reduce excess N in cattle urine may substantially reduce N2O emissions from grazed pastures

Table of Content

www.enacts.or

AquaCrop Simulation of Winter Wheat under Different N Management Practices

AquaCrop is a well-known water-oriented crop model. The model has been often used to simulate various crops and the water balance in the field under different irrigation treatments, but studies that relate AquaCrop to fertilization are rare. In this study, the ability of this model to simulate yield and the water balance parameters was investigated in a wheat field under different nitrogen management practices. During the 2015–2016 and 2016–2017 growing seasons, meteorological data were provided from a nearby meteorological station, and the evolution of soil water content and final yields were recorded. The model showed a very good performance at simulating the soil water content evolution in the root zone. Notwithstanding its simplicity, AquaCrop based on a semi-quantitative approach for fertility performed well at the field level for the final yield estimation under different nitrogen treatments and field topography variation. Although the correlation coefficient between simulated and measured final yields was high, increased values of variations were observed in the various zones of this experimental field (−50% to +140%). The model appears to be an efficient tool for evaluating and improving the management practices at the field level. The experiments were conducted in Thessaly, which is the largest plain and the main agricultural area of Greece. Thessaly, however, has a strong negative water balance, which has led to a strong decrease in the level of the aquifer and, at the same time, to sea intrusion. There is also a significant risk of contamination of the groundwater aquifer due to increased use of agrochemicals. This analysis is particularly important for Thessaly due to the need for improvement of agricultural practices in this area, to decrease the pressure of agricultural activities on natural resources (soil, water) and reverse the consequences of current management