Soil moisture and gaseous N-flux (N2O, N-2) dynamics in Costa Rican coffee plantations were successively simulated using a mechanistic model (PASTIS) and two process-based models (NGAS and NOE). Two fertilized (250 kg N ha(-1) y(-1)) coffee plantations were considered, namely a monoculture and a system shaded by the N-2 fixing legume species Inga densiflora. In situ N2O fluxes were previously measured in these plantations. NGAS and NOE used specific microbial activities for the soils. To parameterize NGAS, we estimated N mineralization via in situ incubations and the contribution of heterotrophic soil respiration to total soil respiration. Potential denitrification rates and the proportion of denitrified N emitted as N2O were measured in the laboratory to define the values of NOE parameters, as well as nitrification rates and related N2O production rates for parameterizing both models. Soil moisture and both NGAS and NOE N2O fluxes were best modelled on an hourly time step. Soil moisture dynamics were satisfactorily simulated by PASTIS. Simulated N2O fluxes by both NGAS and NOE (3.2 and 2.1 kg N ha(-1) y(-1) for NGAS; 7.1 and 3.7 kg N ha(-1) y(-1) for NOE, for the monoculture and shaded plantations respectively) were within a factor of about 2 of the observed annual fluxes (4.3 and 5.8 kg N ha(-1) y(-1), for the monoculture and shaded plantations respectively). Statistical indicators of association and coincidence between simulated and measured values were satisfactory for both models. Nevertheless, the two models differed greatly in describing the nitrification and denitrification processes. Some of the algorithms in the model NGAS were apparently not applicable to these tropical acidic Andosols. Therefore, more detailed information about microbial processes in different agroecosystems would be needed, notably if process-oriented models were to be used for testing strategies for mitigating N2O emissions. (C) 2009 Elsevier Ltd. All rights reserved.
Tag: denitrification
Potential economic benefits of modifications to urea that increase yield through reduction in nitrogen losses
Many modifications to urea such as inhibitors, algicides, soluble salts, and acidifying agents have been proposed to overcome losses of urea-N, but little is known about the potential economic benefits and acceptable farm-level prices for modified urea. The objective of this study was to develop and use a method for estimating the potential economic benefits of modifications to urea that reduce N losses and enhance crop yields. The method is applicable for crops with a response to N that is well represented by a quadratic model, and for modifications to urea that do not alter the maximum attainable yield with added N. The increment in profit of farmers with the use of modified urea is determined by the difference in net benefit between modified urea and conventional urea when these fertilizers are used at rates that maximize profit. The increment in profit with modified urea increased linearly with increasing saving of N from loss, decreased with the increasing cost of modifying urea, and increased as the price of conventional urea-N increased. The increased price of N for modified urea, expressed as a percentage increase over the price of conventional urea-N, must be <20% when N saving = 17% of applied N, <40% when N saving = 29% of applied N, and <80% when N saving = 44% of applied N to obtain a positive increment in profit. The results suggest that modified urea would be most economical in environments with high response of the crop to urea-N, high price of conventional urea, and high losses of urea-N that can be prevented by the urea modification
Arbuscular mycorrhizal fungi potentially regulate N2O emissions from agricultural soils via altered expression of denitrification genes
Agricultural soils are an important source of nitrous oxide (N2O), a potent greenhouse gas involved in the destruction of the protective ozone layer that contributes to global warming. During N2O production, soil microorganisms play important driving and regulating roles. A few recent studies have revealed the potential effects of arbuscular mycorrhizal fungi (AMF), a widely distributed soil fungi, on controlling N2O emissions. However, how AMF regulate N2O production from soils remains poorly understood. To address the knowledge gap, we manipulated two independent soil environments, which were either allowed (AM) or prevented (NM) access by AMF hyphae in a microcosm experiment (n = 5). Soil physicochemical properties, N2O flux, the diversity of bacterial communities, and the abundance of key genes responsible for N2O production were assessed in both treatments over three months. Results showed that the presence of AMF significantly decreased N2O emissions from agricultural soils in the 1st month, and the abundance of key genes responsible for denitrification (nirK and nosZ) significantly decreased in AM treatments, indicating that the regulation of N2O emissions is transmitted by AMF-induced changes in the denitrification process. A structural equation model further revealed that AMF indirectly influenced N2O emissions by altering the abundance of N metabolism-related genes, rather than by altering soil chemical properties or the diversity of bacterial communities. Thus, we proposed a possible mechanism by which AMF can regulate denitrification activities and therefore N2O emissions from agricultural soils.