Sensitivity analysis and field testing of the RISK-N model in the Central Valley of Chile

We present the results from a sensitivity analysis and a preliminary short-term, site-scale performance assessment of the analytical soil and groundwater nitrate transport RISK-N. The study was carried out in the Central Valley of Chile, on a 2.6 ha corn (Zea mays L.) field underlain by a shallow unconfined aquifer during the cropping season 2000–2001. Nitrogen levels in soils as well as NO₃⁻–N irrigation water and groundwater concentrations were monitored through the crop-growing period, the latter by a network of 16 monitoring wells. A sensitivity analysis shows that both the nitrate flux from the vadose zone and NO₃⁻–N groundwater concentration are mainly influenced by the initial soil nitrogen levels, water input, and soil porosity. Also, simulated groundwater NO₃⁻–N levels are sensitive to changes on the saturated zone denitrification constant. An additional analysis further reveals the significance of the latter parameter, in conjunction with the amount of applied nitrogen fertilizer. We obtained a good agreement between observed average and simulated values. While the model performs well when spatially averaged values are used (root mean square error, RMSE = 1.4 mg l⁻¹ of NO₃⁻–N), the prediction error increases (RMSE = 1.9 mg l⁻¹ of NO₃⁻–N) when the concentration in each well is considered. This fact could be explained by the time and space scale of the experiment and the characteristics of the RISK-N model. The model is easy to use and seems appropriate for mid- and long-term studies of nitrogen contamination in groundwater for agricultural conditions in the Central Valley of Chile and under limited field data availability conditions. However, it needs to be tested for longer periods and under different climatic conditions, soil types, and aquifer characteristics, before its range of applicability can be fully established and recognized.     

Study of the genetic variability and similarity among and within Arachis villosulicarpa, A. pietrarellii and A. hypogaea through isoenzyme analysis

Arachis villosulicarpa is a perennial species cultivated for its soft and tasty seeds by indigenous inhabitants of the Mato Grosso State, Brazil. Besides A. hypogaea, this species is considered as the only species of Arachis which represents a valuable food source for human consumption. Due to the lack of knowledge concerning the genetic diversity of A. villosulicarpa, this study was conducted to evaluate the genetic variability of the accessions from the Germplasm Collection of CENARGEN/EMBRAPA (Brasília, DF, Brazil) and Instituto Agrono^mico (IAC, Campinas, SP, Brazil). In addition, the genetic similarity between A. villosulicarpa, the related wild species A. pietrarellii, and the cultivated peanut A. hypogaea cv. Tatu was evaluated. From the entire sample analyzed of A. villosulicarpa, the accession from Instituto Agrono^mico showed the highest indices of diversity for both enzymatic systems analyzed, pointing this accession as a promising source of genetic variabil ity that must be preserved in the Germplasm Bank. A high level of genetic similarity was observed between A. pietrarellii and A. villosulicarpa, supporting previous suggestions that A. pietrarellii could be the ancestral progenitor species of A. villosulicarpa or that both species originated from a common ancestor.     

Using multiscale spatial analysis to assess fire ignition density in Catalonia,Spain

Introduction   

This article explores the possibility of including multiple spatial scales into a mixed model for predicting the density of human-caused fire ignitions in Catalonia (North-East Spain).     

Effects of foliar nutrients and environmental factors on site productivity in <Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait. stands in Asturias (NW Spain)

• Background   

The effects of foliar nutrients and environmental variables on site productivity in Maritime pine (Pinus pinaster Ait.) stands in Asturias (NW Spain) were studied.     

Optimization and simulation of drying processes using diffusion models: application to wood drying using forced air at low temperature

This paper discusses the suitability of four diffusion models to describe the drying of wood. The first model refers to the analytical solution of an infinite slab with boundary condition of the first kind. In the last three models, the boundary condition is of the third kind and the analytical solutions refer to the following geometries: infinite slab, rectangle, and parallelepiped. The analytical solutions were coupled to an optimizer based on inverse method, which enables to calculate process parameters for an experimental data set. Once the process parameters were determined, the drying kinetics of wood was simulated through each model proposed. The obtained results lead to the conclusion that the first model does not represent the drying kinetics properly. The last three models adequately describe the drying kinetics, but statistical indicators enable to affirm that the best of them is the three-dimensional model.     

Assessment of environment,land management,and spatial variables on recent changes in montado land cover in southern Portugal

Montado decline has been reported since the end of the nineteenth century in southern Portugal and increased markedly during the 1980s. Consensual reports in the literature suggest that this decline is due to a number of factors, such as environmental constraints, forest diseases, inappropriate management, and socioeconomic issues. An assessment on the pattern of montado distribution was conducted to reveal how the extent of land management, environmental variables, and spatial factors contributed to montado area loss in southern Portugal from 1990 to 2006. A total of 14 independent variables, presumably related to montado loss, were grouped into three sets: environmental variables, land management variables, and spatial variables. From 1990 to 2006, approximately 90,054 ha disappeared in the montado area, with an estimated annual regression rate of 0.14 % year^?1. Variation partitioning showed that the land management model accounted for the highest percentage of explained variance (51.8 %), followed by spatial factors (44.6 %) and environmental factors (35.5 %). These results indicate that most variance in the large-scale distribution of recent montado loss is due to land management, either alone or in combination with environmental and spatial factors. The full GAM model showed that different livestock grazing is one of the most important variables affecting montado loss. This suggests that optimum carrying capacity should decrease to 0.18–0.60 LU ha^?1 for livestock grazing in montado under current ecological conditions in southern Portugal. This study also showed that land abandonment, wildfire, and agricultural practices (to promote pastures, crops or fallow lands) were three significant variables influencing montado loss.     

Relationships between long-term trends of air temperature,precipitation, nitrogen nutrition and growth of coniferous stands in Central Europe and Finland

Height growth of 19 Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) stands in Germany, Austria and Finland, for which long-term records of foliar nutrient levels were available, was assessed retrospectively by stem analyses and compared with data from regionally applied yield tables as references. Gridded historical time series of monthly temperature and precipitation were used to characterise the meteorologic conditions at the sampling sites. Climate parameters were tested against height growth in period 1950–2000, and needle N content was tested against height growth for the periods where N measurements were available by means of graphical comparison, as well as simple and multiple regression analyses with the aim to get evidence for causes of possible growth acceleration. Trends of referenced height increment of six out of nine Scots pine stands in Germany were positive during the observation period, and improved N nutrition appeared to be the most important driving factor for this growth acceleration. The variation of precipitation—exhibiting no consistent and uniform long-term temporal trend during the observation period—in contrast seems to be mainly responsible for the interannual fluctuation of height growth. We were not able to detect any general statistical influence of temperature parameters on height growth, although they generally increased. The referenced height growth of three Finnish pine stands slightly decreased during the observation period and there was no indication of a significant improvement of their N supply. Among four Norway spruce stands investigated in Germany and Austria, referenced height increment also increased in three cases; there was again some evidence that improved N nutrition was the stimulating factor. At three study sites in Finland, however, referenced height growth of this species decreased at least from 1985 onwards, whereas mostly no significant trends in N nutrition or precipitation were identified. These differences observed between species and regions are discussed in detail.     

Partitioning of applied <Superscript>15</Superscript>N fertilizer in a longleaf pine and native woody ornamental intercropping system

The cultivation of ornamentals to produce woody floral products—the fresh or dried stems that are used for decorative purposes—may be an attractive option for southeastern landowners looking to generate income from small landholdings. Since many shrubs native to the understory of the longleaf pine (Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between-row spacing of young longleaf pine plantations. The objective of this study was to evaluate how interspecific competition affects the fate of ¹⁵N fertilizer when American beautyberry (Callicarpa americana L.), wax myrtle (Morella cerifera (L.) Small) and inkberry (Ilex glabra (L.) A.Gray) are intercropped with longleaf pine. Nitrogen derived from fertilizer (NDF), utilization of fertilizer N (UFN) and recovery of fertilizer N (RFN_soil) were compared between agroforestry and monoculture (treeless) treatments to assess the effects of competition. Results varied by species, with NDF being higher for C. americana foliage and lower for all M. cerifera tissues in the agroforestry treatment. No effect was observed for I. glabra. UFN was lower for all species in the agroforestry treatment. RFN_soil was higher in the agroforestry treatment for I. glabra, but no treatment effects were observed for C. americana or M. cerifera. Overall, while it is clear that interspecific competition was present in the agroforestry treatment, the inefficiency of fertilizer use suggests that nitrogen was not the most limiting resource. Management interventions, particularly those that address competition for water, will likely be critical to the success of this system.