Assessing Short‐Term Impacts of Management Practices on N2O Emissions From Diverse Mediterranean Agricultural Ecosystems Using a Biogeochemical Model

Croplands are important sources of nitrous oxide (N2O) emissions. The lack of both long‐term field measurements and reliable methods for extrapolating these measurements has resulted in a large uncertainty in quantifying and mitigating N2O emissions from croplands. This is especially relevant in regions where cropping systems and farming management practices (FMPs) are diverse. In this study, a process‐based biogeochemical model, DeNitrification‐DeComposition (DNDC), was tested against N2O measurements from five cropping systems (alfalfa, wheat, lettuce, vineyards, and almond orchards) representing diverse environmental conditions and FMPs. The model tests indicated that DNDC was capable of predicting seasonal and annual total N2O emissions from these cropping systems, and the model\u27s performance was better than the Intergovernmental Panel on Climate Change emission factor approach. DNDC also captured the impacts on N2O emissions of nitrogen fertilization for wheat and lettuce, of stand age for alfalfa, as well as the spatial variability of N2O fluxes in vineyards and orchards. DNDC overestimated N2O fluxes following some heavy rainfall events. To reduce the biases of simulating N2O fluxes following heavy rainfall, studies should focus on clarifying mechanisms controlling impacts of environmental factors on denitrification. DNDC was then applied to assess the impacts on N2O emissions of FMPs, including tillage, fertilization, irrigation, and management of cover crops. The practices that can mitigate N2O emissions include reduced or no tillage, reduced N application rates, low‐volume irrigation, and cultivation of nonleguminous cover crops. This study demonstrates the necessity and potential of utilizing process‐based models to quantify N2O emissions from regions with highly diverse cropping systems

Property Taxes Under "Classificiation:" Why Do Firms pay More?

This paper examines how communities will behave if they are given the option of taxing the property of commercial establishments (factories, shopping centers, office buildings, etc) at different rates from residential housing. In the last 2 decades many states have enacted legislation which allows communities to discriminate in this manner – called “classification”. We build a simple model wherein firms provide tax revenue without using local services and also create a valuable local job base. Towns thus confront a well defined choice: raise commercial taxes and gain revenue but risk loosing jobs. Firms in turn need to choose a community to locate in but do so with a (finite) negative elasticity with respect to the town taxes. The model yields two schedules between commercial tax rates and firm concentration in a community. A “demand” schedule has greater firm concentration leading a town to select higher commercial taxes, while a “supply” schedule has higher taxes leading to less firm concentration. The model comparative statics suggest that smaller and wealthier communities will encourage firms by keeping taxes low and rely less on their tax subsidy. Empirically we create a panel of towns in Massachusetts that covers the years prior to and after the state allowed such tax discrimination. With this data we find that towns with more pre-existing commerce chose to discriminate most, that such higher taxes gradually do discourage firm location, and that smaller and wealthier towns tend not to engage in tax discrimination

The Co-movement of housing sales and housing prices : empirics and theory

March 1, 200

Princess and the Pea at the nanoscale: Wrinkling and delamination of graphene on nanoparticles

Thin membranes exhibit complex responses to external forces or geometrical constraints. A familiar example is the wrinkling, exhibited by human skin, plant leaves, and fabrics, resulting from the relative ease of bending versus stretching. Here, we study the wrinkling of graphene, the thinnest and stiffest known membrane, deposited on a silica substrate decorated with silica nanoparticles. At small nanoparticle density monolayer graphene adheres to the substrate, detached only in small regions around the nanoparticles. With increasing nanoparticle density, we observe the formation of wrinkles which connect nanoparticles. Above a critical nanoparticle density, the wrinkles form a percolating network through the sample. As the graphene membrane is made thicker, global delamination from the substrate is observed. The observations can be well understood within a continuum elastic model and have important implications for strain-engineering the electronic properties of graphene.Comment: 11 pages, 8 figures. Accepted for publication in Physical Review