Visible and near infrared spectroscopy in soil science

This chapter provides a review on the state of soil visible–near infrared (vis–NIR) spectroscopy. Our intention is for the review to serve as a source of up-to date information on the past and current role of vis–NIR spectroscopy in soil science. It should also provide critical discussion on issues surrounding the use of vis–NIR for soil analysis and on future directions. To this end, we describe the fundamentals of visible and infrared diffuse reflectance spectroscopy and spectroscopic multivariate calibrations. A review of the past and current role of vis–NIR spectroscopy in soil analysis is provided, focusing on important soil attributes such as soil organic matter (SOM), minerals, texture, nutrients, water, pH, and heavy metals. We then discuss the performance and generalization capacity of vis–NIR calibrations, with particular attention on sample pre-tratments, co-variations in data sets, and mathematical data preprocessing. Field analyses and strategies for the practical use of vis–NIR are considered. We conclude that the technique is useful to measure soil water and mineral composition and to derive robust calibrations for SOM and clay content. Many studies show that we also can predict properties such as pH and nutrients, although their robustness may be questioned. For future work we recommend that research should focus on: (i) moving forward with more theoretical calibrations, (ii) better understanding of the complexity of soil and the physical basis for soil reflection, and (iii) applications and the use of spectra for soil mapping and monitoring, and for making inferences about soils quality, fertility and function. To do this, research in soil spectroscopy needs to be more collaborative and strategic. The development of the Global Soil Spectral Library might be a step in the right direction

Enhancement of electric and magnetic wave fields at density gradients

We use Freja satellite data to investigate irregular small-scale density variations. The observations are made in the auroral region at about 1000-1700 km. The density variations are a few percent, and the structures are found to be spatial down to a scale length of a few ion gyroradii. Irregular density variations are often found in an environment of whistler mode/lower hybrid waves and we show that at the density gradients both the electric and magnetic wave fields are enhanced

Use of near infrared reflectance spectroscopy to predict nitrogen uptake by winter wheat within fields with high variability in organic matter

In this study, the ability to predict N-uptake in winter wheat crops using NIR-spectroscopy on soil samples was evaluated. Soil samples were taken in unfertilized plots in one winter wheat field during three years (1997-1999) and in another winter wheat field nearby in one year (2000). Soil samples were analyzed for organic C content and their NIR-spectra. N-uptake was measured as total N-content in aboveground plant materials at harvest. Models calibrated to predict N-uptake were internally cross validated and validated across years and across fields. Cross-validated calibrations predicted N-uptake with an average error of 12.1 to 15.4 kg N ha-1. The standard deviation divided by this error (RPD) ranged between 1.9 and 2.5. In comparison, the corresponding calibrations based on organic C alone had an error from 11.7 to 28.2 kg N ha-1 and RPDs from 1.3 to 2.5. In three of four annual calibrations within a field, the NIR-based calibrations worked better than the organic C based calibrations. The prediction of N-uptake across years, but within a field, worked slightly better with an organic C based calibration than with a NIR based one, RPD = 1.9 and 1.7 respectively. Across fields, the corresponding difference was large in favour of the NIR-calibration, RPD = 2.5 for the NIR-calibration and 1.5 for the organic C calibration. It was concluded that NIR-spectroscopy integrates information about organic C with other relevant soil components and therefore has a good potential to predict complex functions of soils such as N-mineralization. A relatively good agreement of spectral relationships to parameters related to the N-mineralization of datasets across the world suggests that more general models can be calibrated

How far away is the next basket of eggs? Spatial memory and perceived cues shape aggregation patterns in a leaf beetle

Gregarious organisms need to handle the trade-off between increasing food competition and the positive effects of group living, and this is particularly important for ovipositing females. We hypothesized that insect females consider how many conspecifics previously visited a host plant. In a no-choice assay, we show that the gregarious blue willow leaf beetle (Phratora vulgatissima) laid the most eggs and the largest clutches on plants where a sequence of few individual females was released, compared to plants where one or many different females were repeatedly released. Therefore, this species is more sensitive to the indirectly perceived number of conspecifics than the directly perceived number of eggs on a plant. We further hypothesized that females adjust their own intra-plant egg clutch distribution to that of conspecifics and discovered a new behavioral component, i.e., the modulation of distances between clutches. Females adjusted these distances in ways indicating the use of spatial memory, because the largest distance increases were observed on plants with their own clutches, compared to plants with clutches from conspecifics. However, adjustment of aggregation level and distance between clutches occurred only on a suitable, and not on an unsuitable, Salix genotype. We conclude that both behaviors should reduce competition between sibling and non-sibling larvae

Biological control of strawberry diseases by Aureobasidium pullulans and sugar beet extract under field conditions

Grey mould (caused by Botrytis cinerea) is the most important pathogen underlying high fungicide dependence in strawberry fields. Reliable biocontrol agents (BCAs) with improved efficiency are needed to replace fungicides. The yeast-like beneficial fungus Aureobasidium pullulans (AP-SLU6) has previously exhibited great potential to combat grey mould in greenhouse environments. Here we report results from a two-year full-factorial field trial in a conventional strawberry field, in which we tested two different concentrations of A. pullulans (10(7) CFU/ml and 10(6) CFU/ml) and sugar beet extract (SBE). The results showed that all the field treatments reduced grey mould severity postharvest and increased shelf life of the harvested fruit in both years. The best effect was achieved using the highest conidial concentration of A. pullulans, which also resulted in 53% higher fruit production compared to the control treatment at the end of the season, indicating a plant-growth promoting effect of the BCA. These results reveal that spray applications of these novel BCAs contribute to reliable biocontrol of grey mould, leading to improvement of the shelf life of strawberry sales boxes. These findings suggest that A. pullulans and SBE can contribute to a shift from chemical fungicides to sustainable methods without compromising cropping security

Aureobasidium spp.: Diversity, Versatility, and Agricultural Utility

The black yeast-like fungi Aureobasidium spp. are ubiquitous microorganisms found in a wide variety of extreme and benign environments as saprophytes, endophytes, and pathogens. Since this diverse genus includes species with potential uses in agriculture and the food industry, it is important that we explore their evolution and spread in the context of climate change. Aureobasidium spp. are known to be capable of producing a plethora of various metabolites, many of which find applications in the field in the control of plant pathogens. The present review aims to explain how these microorganisms can provide ecological and safe strategies that might be adopted in agricultural production systems and food processing. The versatility and potential of the Aureobasidium genus lie perfectly within the Sustainable Development Goals Agenda 2021-2030 by opening new horizons that are respectful to the environment and human health