Global application of an unoccupied aerial vehicle photogrammetry protocol for predicting aboveground biomass in non-forest ecosystems.

Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, and are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely sensed biomass products and are undersampled by in situ monitoring. Current global change threats emphasize the need for new tools to capture biomass change in non-forest ecosystems at appropriate scales. Here we developed and deployed a new protocol for photogrammetric height using unoccupied aerial vehicle (UAV) images to test its capability for delivering standardized measurements of biomass across a globally distributed field experiment. We assessed whether canopy height inferred from UAV photogrammetry allows the prediction of aboveground biomass (AGB) across low-stature plant species by conducting 38 photogrammetric surveys over 741 harvested plots to sample 50 species. We found mean canopy height was strongly predictive of AGB across species, with a median adjusted R 2 of 0.87 (ranging from 0.46 to 0.99) and median prediction error from leave-one-out cross-validation of 3.9%. Biomass per-unit-of-height was similar within but different among, plant functional types. We found that photogrammetric reconstructions of canopy height were sensitive to wind speed but not sun elevation during surveys. We demonstrated that our photogrammetric approach produced generalizable measurements across growth forms and environmental settings and yielded accuracies as good as those obtained from in situ approaches. We demonstrate that using a standardized approach for UAV photogrammetry can deliver accurate AGB estimates across a wide range of dynamic and heterogeneous ecosystems. Many academic and land management institutions have the technical capacity to deploy these approaches over extents of 1-10 ha-1. Photogrammetric approaches could provide much-needed information required to calibrate and validate the vegetation models and satellite-derived biomass products that are essential to understand vulnerable and understudied non-forested ecosystems around the globe.

Comparison of Spaceborne and UAV-Borne Remote Sensing Spectral Data for Estimating Monsoon Crop Vegetation Parameters.

Various remote sensing data have been successfully applied to monitor crop vegetation parameters for different crop types. Those successful applications mostly focused on one sensor system or a single crop type. This study compares how two different sensor data (spaceborne multispectral vs unmanned aerial vehicle borne hyperspectral) can estimate crop vegetation parameters from three monsoon crops in tropical regions: finger millet, maize, and lablab. The study was conducted in two experimental field layouts (irrigated and rainfed) in Bengaluru, India, over the primary agricultural season in 2018. Each experiment contained n = 4 replicates of three crops with three different nitrogen fertiliser treatments. Two regression algorithms were employed to estimate three crop vegetation parameters: leaf area index, leaf chlorophyll concentration, and canopy water content. Overall, no clear pattern emerged of whether multispectral or hyperspectral data is superior for crop vegetation parameter estimation: hyperspectral data showed better estimation accuracy for finger millet vegetation parameters, while multispectral data indicated better results for maize and lablab vegetation parameter estimation. This study's outcome revealed the potential of two remote sensing platforms and spectral data for monitoring monsoon crops also provide insight for future studies in selecting the optimal remote sensing spectral data for monsoon crop parameter estimation.

Life Cycle Assessment of bioenergy production from mountainous grasslands invaded by lupine (Lupinus polyphyllus Lindl.).

Mountainous grasslands are typically important habitats both for fauna and flora but increasingly suffer from invasions by neophytes (i.e. Lupinus polyphyllus Lindl.) in most German low mountain areas, which eventually threatens species richness. Regular defoliation is required to eliminate the invasion, however, at present options to handle the harvested biomass are limited. Integrated generation of solid fuel and biogas from biomass (IFBB) and anaerobic digestion (AD) are two possible options to utilise the biomass and convert it into energy. There is substantial environmental impact associated with the energy and resource usage during conversion of the biomass into fuel and during usage of fuels and co-products obtained. This study examines IFBB and AD to identify the best option in terms of environmental impacts and primary energy usage, also looking at alternatives for process parameters along the life cycle that would reduce environmental impacts. It was found that IFBB was a better option compared to AD, as it had higher environmental and primary energy savings across all grassland sites. Higher energy conversion efficiency of IFBB resulted in higher greenhouse gas (GHG) and energy savings, even though the energy usage for the processing steps were higher compared to AD. Biomass yield was positively related to the savings, providing better GHG and energy savings for grasslands containing invasive species. There were no savings in terms of acidification (AP) and eutrophication potential (EP) for both IFBB and AD, however AP and EP was lower using IFBB compared to AD. Hence, biomass originating from mountainous grasslands with lupine invasion could be effectively utilised with IFBB, as this option had lower environmental impacts and higher energy savings compared to AD. Biomass from non-invaded grasslands could also be converted effectively using IFBB, hence IFBB could be used to utilise the harvested biomass in the situation where the invasion is eliminated.

The potential of UAV-borne spectral and textural information for predicting aboveground biomass and N fixation in legume-grass mixtures.

Organic farmers, who rely on legumes as an external nitrogen (N) source, need a fast and easy on-the-go measurement technique to determine harvestable biomass and the amount of fixed N (NFix) for numerous farm management decisions. Especially clover- and lucerne-grass mixtures play an important role in the organic crop rotation under temperate European climate conditions. Multispectral sensors mounted on unmanned aerial vehicles (UAVs) are new promising tools for a non-destructive assessment of crop and grassland traits on large and remote areas. One disadvantage of multispectral information and derived vegetations indices is, that both ignore spatial relationships of pixels to each other in the image. This gap can be filled by texture features from a grey level co-occurrence matrix. The aim of this multi-temporal field study was to provide aboveground biomass and NFix estimation models for two legume-grass mixtures through a whole vegetation period based on UAV multispectral information. The prediction models covered different proportions of legumes (0-100% legumes) to represent the variable conditions in practical farming. Furthermore, the study compared prediction models with and without the inclusion of texture features. As multispectral data usually suffers from multicollinearity, two machine learning algorithms, Partial Least Square and Random Forest (RF) regression, were used. The results showed, that biomass prediction accuracy for the whole dataset as well as for crop-specific models were substantially improved by the inclusion of texture features. The best model was generated for the whole dataset by RF with an rRMSE of 10%. For NFix prediction accuracy of the best model was based on RF including texture (rRMSEP = 18%), which was not consistent with crop specific models.

Prediction of Biomass and N Fixation of Legume-Grass Mixtures Using Sensor Fusion.

European farmers and especially organic farmers rely on legume-grass mixtures in their crop rotation as an organic nitrogen (N) source, as legumes can fix atmospheric N, which is the most important element for plant growth. Furthermore, legume-grass serves as valuable fodder for livestock and biogas plants. Therefore, information about aboveground biomass and N fixation (NFix) is crucial for efficient farm management decisions on the field level. Remote sensing, as a non-destructive and fast technique, provides different methods to quantify plant trait parameters. In our study, high-density point clouds, derived from terrestrial laser scanning (TLS), in combination with unmanned aerial vehicle-based multispectral (MS) data, were collected to receive information about three plant trait parameters (fresh and dry matter, nitrogen fixation) in two legume-grass mixtures. Several crop surface height metrics based on TLS and vegetation indices based on the four MS bands (green, red, red edge, and near-infrared) were calculated. Furthermore, eight texture features based on mean crop surface height and the four MS bands were generated to measure horizontal spatial heterogeneity. The aim of this multi-temporal study over two vegetation periods was to create estimation models based on biomass and N fixation for two legume-grass mixtures by sensor fusion, a combination of both sensors. To represent conditions in practical farming, e.g., the varying proportion of legumes, the experiment included pure stands of legume and grass of the mixtures. Sensor fusion of TLS and MS data was found to provide better estimates of biomass and N Fix than separate data analysis. The study shows the important role of texture based on MS and point cloud data, which contributed greatly to the estimation model generation. The applied approach offers an interesting method for improvements in precision agriculture.

Element concentrations in urban grass cuttings from roadside verges in the face of energy recovery.

Grass from municipal roadside verges is a potential yet largely unused resource for bioenergy recovery, which is mainly due to its unknown elemental composition. Therefore, we measured the concentration of 16 elements (Ca, K, Mg, N, Na, P, S, Al, Cd, Cl, Cr, Cu, Mn, Pb, Si and Zn) in a material from the city of Kassel harvested in different management intensities. The element concentrations were mainly close to reference values of agricultural or nature conservation grassland and usually within the range of literature data. Concentrations of most elements, including heavy metals, were below limiting values. Only N and Cl concentrations in the raw material exceeded the limiting values for combustion, but washing and dewatering of the biomass with the "integrated generation of solid fuel and biogas from biomass" technique resulted in concentrations in the press cake well below the limiting values. Considering the element concentrations of grass from urban roadside verges, utilisation for energy recovery may be possible, provided an appropriate technology is applied.

Comparative life cycle assessment of biogas plant configurations for a demand oriented biogas supply for flexible power generation.

The environmental performance of biogas plant configurations for a demand - oriented biogas supply for flexible power generation is comparatively assessed in this study. Those configurations indicate an increased energy demand to operate the operational enhancements compared to conventional biogas plants supplying biogas for baseload power generation. However, findings show that in contrast to an alternative supply of power generators with natural gas, biogas supplied on demand by adapted biogas plant configurations saves greenhouse gas emissions by 54-65 g CO(2-eq) MJ(-1) and primary energy by about 1.17 MJ MJ(-1). In this regard, configurations with flexible biogas production profit from reduced biogas storage requirements and achieve higher savings compared to configurations with continuous biogas production. Using thicker biogas storage sheeting material reduces the methane permeability of up to 6m(3) d(-1) which equals a reduction of 8% of the configuration's total methane emissions.

Cost analysis of concepts for a demand oriented biogas supply for flexible power generation.

With the share of intermittent renewable energies within the electricity system rising, balancing services from dispatchable power plants are of increasing importance. Highlighting the importance of the need to keeping fuel costs for flexible power generation to a minimum, the study aims to identify favourable biogas plant configurations, supplying biogas on demand. A cost analysis of five configurations based on biogas storing and flexible biogas production concepts has been carried out. Results show that additional flexibility costs for a biogas supply of 8h per day range between 2€ and 11€MWh(-1) and for a 72h period without biogas demand from 9€ to 19€MWh(-1). While biogas storage concepts were identified as favourable short term supply configurations, flexible biogas production concepts profit from reduced storage requirements at plants with large biogas production capacities or for periods of several hours without biogas demand.

Energetic conversion of European semi-natural grassland silages through the integrated generation of solid fuel and biogas from biomass: energy yields and the fate of organic compounds.

Twelve European habitat types were investigated to determine the influence of the IFBB technique (integrated generation of biogas and solid fuel from biomass) on the fate of organic compounds and energy yields of semi-natural grassland biomass. Concentration of organic compounds in silage and IFBB press cake (PC), mass flows within that system and methane yields of IFBB press fluids (PF) were determined. The gross energy yield of the IFBB technique was calculated in comparison to hay combustion (HC) and whole crop digestion (WCD). The IFBB treatment increased fibre and organic matter (OM) concentrations and lowered non-fibre carbohydrates and crude protein concentrations. The PF was highly digestible irrespective of habitat types, showing mean methane yields between 312.1 and 405.0 LN CH4 kg(-1) VS. Gross energy yields for the IFBB system (9.75-30.19MWh ha(-1)) were in the range of HC, outperformed WCD and were influenced by the habitat type.

Bioenergy as a biodiversity management tool and the potential of a mixed species feedstock for bioenergy production in Wales.

A cutting management regime maintains high levels of biodiversity in semi-natural habitats across Europe. We utilise three years of annual yield data from Welsh semi-natural areas to calculate the mean feedstock production from cutting management to be 1.05×10(6) t DM annum(-1). Using formulae based upon Fischer Tropsch (FT) fuel process models, we predict that 2.12×10(5) t of FT fuel annum(-1) could be produced. That represents 38% of the Welsh transport sector's green house gas (GHG) reduction target for 2020. Alternatively, predictive formulae reveal that methane yields from anaerobic digestion of the feedstock could reduce GHG emissions by 11% of the domestic sector's reduction target for 2020. Electricity generation from methane is also explored. The results presented encourage further investigation into the contribution of this resource to sustainable domestic energy supply. Furthermore, the proposed system would potentially protect a broad range of ecosystem services and maintain biodiversity.

Economic assessment of the integrated generation of solid fuel and biogas from biomass (IFBB) in comparison to different energy recovery, animal-based and non-refining management systems.

The study aimed at the identification of favourable land use options for semi-natural grassland management and preservation. Economic assessments of energy recovery by the integrated generation of solid fuel and biogas from biomass (IFBB) in comparison with dry fermentation (DF) and hay combustion systems (HC), beef cattle production (BC) and non-refining landscape preservation measures, such as mulching (MU) and composting (CO), were carried out in this study. Energy recovery systems made profitable use of semi-natural grasslands with the highest economic returns attained by IFBB-AO (Return On Investment, ROI: 22.75%) and HC (ROI: 22.00%) systems, followed by the IFBB-SA (ROI: 7.71%) and the DF system (ROI: 6.22%). Animal husbandry (BC) and non-refining management systems (MU, CO) were not profitable considering the current framework conditions. Input parameters critical for profitability were modified in order to identify influences of changing framework conditions.

Mineral concentrations in solid fuels from European semi-natural grasslands after hydrothermal conditioning and subsequent mechanical dehydration.

The integrated generation of solid fuel and biogas from biomass (IFBB) is particularly designed for the conversion of semi-natural and high biodiversity grassland biomass into energy. This biomass is problematic in common energy conversion techniques, e.g. biogas conversion or combustion, because of its chemical composition. The IFFB process separates the material into a fibre rich solid fuel and a fluid, which is rich in minerals and highly digestible constituents and is used for anaerobic digestion. Biomasses from 18 European semi-natural grassland sites have been processed in an IFBB prototype. The impact of different chemical and botanical parameters on mass flow of mineral plant compounds and their concentrations in the fuel has been investigated. Fuel quality was significantly influenced by chemical and botanical parameters and the quality could be significantly improved during processing. Biomass with a high grass proportion and fibre content showed the best fuel qualities after IFBB treatment.

Life cycle assessment of the integrated generation of solid fuel and biogas from biomass (IFBB) in comparison to different energy recovery, animal-based and non-refining management systems.

The study compares energy production from semi-natural grasslands by the integrated generation of solid fuel and biogas from biomass (IFBB) through mechanical separation of the biomass with the dry fermentation (DF) and hay combustion system (HC). In addition, traditional use for beef cattle production and non-refining systems of landscape conservation, i.e. mulching and composting, are considered. Highest conversion efficiency (45-54% of the gross yield), net savings of fossil fuels (44-54 GJ ha(-1)) and net savings of greenhouse gases (2.9-3.7 t CO(2-eq)ha(-1)) are obtained by HC and IFBB. Potentials of DF are limited due to low digestibility of the mature biomass.