Kiril Manevski

Discrimination of common Mediterranean plant species using field spectroradiometry

Field spectroradiometry of land surface objects supports remote sensing analysis, facilitates the discrimination of vegetation species, and enhances the mapping efficiency. Especially in the Mediterranean, spectral discrimination of common vegetation types, such as phrygana and maquis species, remains a challenge. Both phrygana and maquis may be used as a direct indicator for grazing management, fire history and severity, and the state of the wider ecosystem equilibrium. This study aims to investigate the capability of field spectroradiometry supporting remote sensing analysis of the land cover of a characteristic Mediterranean area. Five common Mediterranean maquis and phrygana species were examined. Spectra acquisition was performed during an intensive field campaign deployed in spring 2010, supported by a novel platform MUFSPEM@MED (Mobile Unit for Field SPEctral Measurements at the MEDiterranean) for high canopy measurements. Parametric and non-parametric statistical tests have been applied to the continuum-removed reflectance of the species in the visible to shortwave infrared spectral range. Interpretation of the results indicated distinct discrimination between the studied species at specific spectral regions. Statistically significant wavelengths were principally found in both the visible and the near infrared regions of the electromagnetic spectrum. Spectral bands in the shortwave infrared demonstrated significant discrimination features for the examined species adapted to Mediterranean drought. All in all, results confirmed the prospect for a more accurate mapping of the species spatial distribution using remote sensing imagery coupled with in situ spectral information.

Integrated modelling of crop production and nitrate leaching with the Daisy model.

Graphical abstract

Spectral Discrimination of Mediterranean Maquis and Phrygana Vegetation: Results From a Case Study in Greece

Mapping the spatial distribution of Mediterranean vegetation is crucial for understanding current ecosystem equilibrium and combating present phenomena, such as desertification and wildfires. Conclusive evidence on the spectral discrimination of such plants is thus necessary. To this end, this study focuses on the discrimination among three trees and three shrubs based on their spectral reflectance measured in a typical Mediterranean environment. Spectra from the plants were acquired by field spectroradiometry in the range between 350 and 2500 nm during an intensive field campaign that took place in Crete island in the spring 2010. Discrimination analysis was performed by applying non-parametric statistical tests on the unaltered spectral reflectance. The multivariate classificatory technique, employed for quantifying the shape similarity between the reflectance spectra, indicated that the majority of the plants possess distinct signatures from one another. The univariate tests implemented pointed out the existence of wavelengths where the plants can be discriminated. The use of unaltered reflectance narrows the statistical difference between the plants to bands in the visible and the shortwave infrared spectrum, but weakens the difference in the near-infrared spectrum, compared to continuum-removed reflectance analysis of the plants already published. The use of unaltered reflectance emphasizes detectable differences induced by the optical properties of the plants, as well as by variation of internal water of the plants related to drought adaptations. All in all, this work highlights the prospect of hyperspectral remote sensing in discriminating those plant species using field spectral libraries coinciding with high-quality radiometrically calibrated imagery.

Denitrification Rates and Controlling Factors for Accumulated Nitrate in the 0-12 m Intensive Farmlands: a Case Study in the North China Plain

Abstract Denitrification in subsoil (to a depth of 12 m) is an important mechanism to reduce nitrate ( NO 3 − ) leaching into groundwater. However, regulating mechanisms of subsoil denitrification, especially those in the deep subsoil beneath the crop root zone, have not been well documented. In this study, soil columns of 0–12 m depth were collected from intensively farmed fields in the North China Plain. The fields had received long-term nitrogen (N) fertilizer inputs at 0 (N0), 200 (N200) and 600 (N600) kg N ha−1 year−1. Main soil properties related to denitrification, i.e., soil water content, NO 3 − , dissolved organic carbon (DOC), soil organic carbon (SOC), pH, denitrifying enzyme activity (DEA), and anaerobic denitrification rate (ADR), were determined. Statistical comparisons among the treatments were performed. The results showed that NO 3 − was more heavily accumulated in the entire soil profile of the N600 treatment, compared to the N0 and N200 treatments. The SOC, DOC, and ADR decreased with increasing soil depth in all treatments, whereas considerable DEA was observed throughout the subsoil. The long-term fertilizer rates affected ADR only in the upper 4 m soil layers. The ADRs in the N200 and N600 treatments were significantly correlated with DOC. Multiple regression analysis indicated that DOC rather than DEA was the key factor regulating denitrification beneath the root zone. Additional research is required to determine if carbon addition into subsoil can be a promising approach to enhance NO 3 − denitrification in the subsoil and consequently to mitigate groundwater NO 3 − contamination in the intensive farmlands.

Nitrogen balances of innovative cropping systems for feedstock production to future biorefineries

Abstract Future biorefineries will prefer crops with high biomass yields, thus may precipitate fundamental changes to the agricultural landscape and the biomass production systems. Understanding the fate of nitrogen (N) in novel agricultural land uses is vital for product optimisation and environmental protection. This work reports and investigates the first multi-annual N balances for novel cropping systems optimised for high biomass production compared to traditional systems under North European climate and soil conditions. In a three-year study, two types of novel systems, i) a rotation of annual crops optimised for maximum biomass production (maize, beet, hemp/oat, triticale as main crops, and winter rye and winter oilseed rape as “second” - cover crops), and ii) perennial grasses (intensively fertilised (festulolium, reed canary grass, tall fescue and cocksfoot), low-fertilised (miscanthus) and unfertilised (grass-legume mixtures)), were compared with iii) traditional systems (continuous maize or triticale, and a cereal crop rotation) at two sites in Denmark varying in temperature, rainfall and soil type (sandy loam and coarse sand). Harvested biomass N and soil nitrate dynamics, as well as model-supported nitrate leaching and field surface N balance (input minus output) of the systems were compared. At each study site, the fertilised perennial grasses outperformed all other systems by doubling biomass N and reducing nitrate leaching by 70–80% compared to the traditional systems. Compared to continuous maize monoculture, the optimised rotation supplied 70% more biomass N and 40% less nitrate leaching on coarse sandy soil, whereas on sandy loam soil it yielded about 10% less biomass N with 50% less nitrate leaching. Field surface N balances were overall neutral/positive, except for festulolium and continuous maize monoculture that slightly mined the soil for N. When N losses by leaching, denitrification and volatilisation were included, soil total N stocks were estimated to decline for the majority of the systems at both sites.

Estimation of land-surface evaporation at four forest sites across Japan with the new nonlinear complementary method

Evaporation from land surfaces is a critical component of the Earth water cycle and of water management strategies. The complementary method originally proposed by Bouchet, which describes a linear relation between actual evaporation (E), potential evaporation (Epo) and apparent potential evaporation (Epa) based on routinely measured weather data, is one of the various methods for evaporation calculation. This study evaluated the reformulated version of the original method, as proposed by Brutsaert, for forest land cover in Japan. The new complementary method is nonlinear and based on boundary conditions with strictly physical considerations. The only unknown parameter (αe) was for the first time determined for various forest covers located from north to south across Japan. The values of αe ranged from 0.94 to 1.10, with a mean value of 1.01. Furthermore, the calculated evaporation with the new method showed a good fit with the eddy-covariance measured values, with a determination coefficient of 0.78 and a mean bias of 4%. Evaluation results revealed that the new nonlinear complementary relation performs better than the original linear relation in describing the relationship between E/Epa and Epo/Epa, and also in depicting the asymmetry variation between Epa/Epo and E/Epo.

Effect of poplar trees on nitrogen and water balance in outdoor pig production – A case study in Denmark

Nitrate leaching from outdoor pig production is a long-standing environmental problem for surface and groundwater pollution. In this study, the effects of inclusion of poplar trees in paddocks for lactating sows on nitrogen (N) balances were studied for an organic pig farm in Denmark. Vegetation conditions, soil water and nitrate dynamics were measured in poplar and grass zones of paddocks belonging to main treatments: access to trees (AT), no access to trees (NAT) and a control without trees (NT), during the hydrological year April 2015 to April 2016. Soil water drainage for each zone, simulated by two simulation models (CoupModel and Daisy), was used to estimate nitrate leaching from the zones in each paddock. N balances (input minus output) for the treatments were computed and compared. The results showed that, in terms of annual water balance and regardless of treatment, simulated evapotranspiration of poplar was 560-569 and 489-498 mm for CoupModel and Daisy, respectively, and corresponding evapotranspiration of grass-clover was 250 and 400 mm, against precipitation of 1076 mm. Simulated drainage below the root zone varied as 620-723 mm for Daisy and 568-958 mm for CoupModel, the higher end of the latter being probably overestimated. Annual nitrate leaching ranged from 32 kg N ha-1 in the poplar zone of NAT up to 289 kg N ha-1 in the control grass zone of NT. The poplar zone showed significantly lower nitrate leaching, by 75-80%, compared to the grass zone. For the control NT treatment, nitrate leaching was approximately 50% higher in the grass zone closest to the hut compared to the grass zone further away. NT treatment also had the largest surface N balance of 468 kg N ha-1 compared to 436 and 397 kg N ha-1 for AT and NAT, respectively. When N losses by leaching and volatilisation were included, soil N balances were 118, 157 and 113 kg N ha-1 for AT, NAT and NT, respectively. Overall, the two simulation models were found useful tools for analyses of water balance for complex agroforestry systems. The findings collectively suggest that it is possible to decrease nitrate leaching from outdoor pig production on sandy soils by inclusion of poplar trees. Additional measures are nevertheless needed to reduce N losses on a mean area basis in paddocks with 20% tree cover.

Modelling agro-environmental variables under data availability limitations and scenario managements in an alluvial region of the North China Plain

Abstract Single or multiple weather station data were combined with soil textural data ranging from low to high detail, i.e., point data from a field station, the FAO Digital Soil Map of the World and a comprehensive data from national soil survey, as input to the Daisy model to simulate and upscale crop yields, drainage and nitrogen leaching for an agroecosystem in the North China Plain. Increasing the detail of the weather data increased the spatial variation of all simulated variables and decreased their regional median. Regional crop yields were simulated well with high-detail input data, though at a weak response to data detail. Simulated regional drainage and nitrogen leaching, and their spatial variability, however, responded well and increased two-to threefold, but their regional medians were similar for medium- and high-detail soil data. This work demonstrates the importance of explicit consideration of weather and soil variability for agro-environmental simulation studies at regional scale.