Potenziale der teilflächenspezifischen Kalkversorgung von Grünland

Gegenstand war der Erhalt einer optimalen Boden-Acidität im Grünland. Ziele des Vorhabens waren: (i) Entwicklung, Tests und Bewertungen von pH-Sensorsystemen, (ii) Entwicklung von Auswertungsmethoden für die sensorgestützte Bodenkartierung sowie von sen-sorgestützen Entscheidungsunterstützungsalgorithmen zur adaptiven Kalkung, (iii) Ermittlungen der Bodenvariabilität durch Bodensensoren und ihr Zusammenhang mit wesentlichen Eigenschaften des Grünlands. Im Projektverlauf gab es Schwierigkeiten: Budgetkürzungen, Fachkräftemangel, technische Probleme und Schäden, Trockenphasen sowie ein Arbeitsunfall beeinflussten Projektziele und Zeitplanung. Eine Verlängerung und Aufstockung des Projektes kam nicht zustande. Die Ergebnisse wurden nicht voll-ständig erreicht. Erster Untersuchungsgegenstand war die Verletzung der Grasnarbe infolge des mechanischen Bodenkontaktes der Sensoren. Sensoranordnungen sowie Lösungen zum Schließen der Furchen wurden untersucht: Radwalzen, ein modifiziertes Pflugschar sowie im Zuge der Entwicklung alternativer Lösungen zur automatisierten Probeentnahme eine durch den Boden gezogene Kettensäge, ein Kern-bohrgerät und ein schmalerer Messschuh. Im Ergebnis wurde entschieden, ein alternatives absätziges Messverfahren mit Kernbohrgerät zu favorisieren. Weiterer Untersuchungsschwerpunkt war die Zuverlässigkeit des Veris MSP Systems. Nach Störungen in der Software, bei der Datenaufzeichnung, einem Kabelbrand sowie Neubau der Stromversorgung wird der Einsatz im Grünland nicht empfohlen. Es wurde notwendig alternative Messverfahren mit handgehaltenen Sensorsystemen entwickelt. Dies ist durch die absehbare Verfügbarkeit autonomer Mobile gerechtfertigt, mit denen eine absätzige Kartierung möglich wird. Ergebnis ist ein pH-Modul auf Basis von Antimon-pH-Elektroden. Mit der Entwicklung eines Spektrometer-Moduls wurde begonnen. Untersuchungen zur Variabilität und zum Kalkbedarf belegen die kleinräumige Variation von Grünlandvegetation und Boden-pH, engmaschige Beprobungen sind notwendig. Der Boden-pH wirkt neben anderen Faktoren ertragslimitierend und beeinflusst die Artenzusammensetzung. Primär besteht daher großer Entwicklungsbedarf für robuste Sensorlösungen zur engräumigen Bodenuntersuchung auf Grünland

Application of Terahertz radiation to soil measurements: Initial results

Developing soil sensors with the possibility of continuous online measurement is a major challenge in soil science. Terahertz (THz) electromagnetic radiation may provide the opportunity for the measurement of organic material density, water content and other soil parameters at different soil depths. Penetration depth and information content is important for a functional soil sensor. Therefore, we present initial research on the analysis of absorption coefficients of four different soil samples by means of THz transmission measurements. An optimized soil sample holder to determine absorption coefficients was used. This setup improves data acquisition because interface reflections can be neglected. Frequencies of 340 GHz to 360 GHz and 1.627 THz to 2.523 THz provided information about an existing frequency dependency. The results demonstrate the potential of this THz approach for both soil analysis and imaging of buried objects. Therefore, the THz approach allows different soil samples to be distinguished according to their different absorption properties so that relations among soil parameters may be established in future

Soil pH mapping with an on-the-go sensor

Soil pH is a key parameter for crop productivity, therefore, its spatial variation should be adequately addressed to improve precision management decisions. Recently, the Veris pH ManagerTM, a sensor for high-resolution mapping of soil pH at the field scale, has been made commercially available in the US. While driving over the field, soil pH is measured on-the-go directly within the soil by ion selective antimony electrodes. The aim of this study was to evaluate the Veris pH ManagerTM under farming conditions in Germany. Sensor readings were compared with data obtained by standard protocols of soil pH assessment. Experiments took place under different scenarios: (a) controlled tests in the lab, (b) semicontrolled test on transects in a stop-and-go mode, and (c) tests under practical conditions in the field with the sensor working in its typical on-the-go mode. Accuracy issues, problems, options, and potential benefits of the Veris pH ManagerTM were addressed. The tests demonstrated a high degree of linearity between standard laboratory values and sensor readings. Under practical conditions in the field (scenario c), the measure of fit (r2) for the regression between the on-the-go measurements and the reference data was 0.71, 0.63, and 0.84, respectively. Field-specific calibration was necessary to reduce systematic errors. Accuracy of the on-the-go maps was considerably higher compared with the pH maps obtained by following the standard protocols, and the error in calculating lime requirements was reduced by about one half. However, the system showed some weaknesses due to blockage by residual straw and weed roots. If these problems were solved, the on-the-go sensor investigated here could be an efficient alternative to standard sampling protocols as a basis for liming in Germany

Evaluating Soil-Borne Causes of Biomass Variability in Grassland by Remote and Proximal Sensing

On a grassland field with sandy soils in Northeast Germany (Brandenburg), vegetation indices from multi-spectral UAV-based remote sensing were used to predict grassland biomass productivity. These data were combined with soil pH value and apparent electrical conductivity (ECa) from on-the-go proximal sensing serving as indicators for soil-borne causes of grassland biomass variation. The field internal magnitude of spatial variability and hidden correlations between the variables of investigation were analyzed by means of geostatistics and boundary-line analysis to elucidate the influence of soil pH and ECa on the spatial distribution of biomass. Biomass and pH showed high spatial variability, which necessitates high resolution data acquisition of soil and plant properties. Moreover, boundary-line analysis showed grassland biomass maxima at pH values between 5.3 and 7.2 and ECa values between 3.5 and 17.5 mS m−1. After calibrating ECa to soil moisture, the ECa optimum was translated to a range of optimum soil moisture from 7% to 13%. This matches well with to the plant-available water content of the predominantly sandy soil as derived from its water retention curve. These results can be used in site-specific management decisions to improve grassland biomass productivity in low-yield regions of the field due to soil acidity or texture-related water scarcity

Hyperspectral Imaging Tera Hertz System for Soil Analysis : Initial Results

Analyzing soils using conventional methods is often time consuming and costly due to their complexity. These methods require soil sampling (e.g., by augering), pretreatment of samples (e.g., sieving, extraction), and wet chemical analysis in the laboratory. Researchers are seeking alternative sensor-based methods that can provide immediate results with little or no excavation and pretreatment of samples. Currently, visible and infrared spectroscopy, electrical resistivity, gamma ray spectroscopy, and X-ray spectroscopy have been investigated extensively for their potential utility in soil sensing. Little research has been conducted on the application of THz (Tera Hertz) spectroscopy in soil science. The Tera Hertz band covers the frequency range between 100 GHz and 10 THz of the electromagnetic spectrum. One important feature of THz radiation is its correspondence with the particle size of the fine fraction of soil minerals (clay < 2 µm to sand < 2 mm). The particle size distribution is a fundamental soil property that governs soil water and nutrient content, among other characteristics. The interaction of THz radiation with soil particles creates detectable Mie scattering, which is the elastic scattering of electromagnetic waves by particles whose diameter corresponds approximately to the wavelength of the radiation. However, single-spot Mie scattering spectra are difficult to analyze and the understanding of interaction between THz radiation and soil material requires basic research. To improve the interpretation of THz spectra, a hyperspectral imaging system was developed. The addition of the spatial dimension to THz spectra helps to detect relevant features. Additionally, multiple samples can be scanned in parallel and measured under identical conditions, and the high number of data points within an image can improve the statistical accuracy. Technical details of the newly designed hyperspectral imaging THz system working from 250 to 370 GHz are provided. Results from measurements of different soil samples and buried objects in soil demonstrated its performance. The system achieved an optical resolution of about 2 mm. The sensitivity of signal damping to the changes in particle size of 100 µm is about 10 dB. Therefore, particle size variations in the µm range should be detectable. In conclusion, automated hyperspectral imaging reduced experimental effort and time consumption, and provided reliable results because of the measurement of hundreds of sample positions in one run. At this stage, the proposed setup cannot replace the current standard laboratory methods, but the present study represents the initial step to develop a new automated method for soil analysis and imaging

Differences in optical properties of males and females pupae of Anastrepha fraterculus (Diptera: Tephritidae)

One alternative to pesticide-based control of important fruit fly (Tephritidae) species is the sterile insect technique (SIT). SIT is based on mass releases of sterile males (subjected to radiation) to control a given pest population. For several important species such as Rhagoletis pomonella, Bractocera oleae and Anastrepha fraterculus, a technical challenge is to differentiate males from females in the pupal stage. Although for some species sterile females are released in the field, it is not desirable to release females from Anastrepha spp. as puncture damage may occur. Therefore, we investigated hyperspectral and RGB imaging to classify the sex in A. fraterculus pupae. We aimed to discriminate, through the description of RGB spectra and hyperespectral profiles, males and females in different stages of pupal development. Images of pupae of different degree-day (DD) development times were obtained. The hyperspectral profiles pupae of 288, 345 and 403 DD showed differences, indicating that pupal hue is altered throughout the development. In the NIR spectrum (800 to 1,700 nm), a higher reflectance between 1,100 and 1,400 nm was observed. In these bands differences in the spatial standard deviation of reflectance between males and females occur. As for the RGB images we observed differences in radiometric variation angle from the top to the basal part of the pupae. For females the radiometric variation angle was greater (26°) than for the males (15°). Thus, it is possible to determine discriminatory characteristics using the spectral profiles, imaging techniques and data analysis to discriminate the sexes

Terahertz spectroscopy for proximal soil sensing: An approach to particle size analysis

Spatially resolved soil parameters are some of the most important pieces of information for precision agriculture. These parameters, especially the particle size distribution (texture), are costly to measure by conventional laboratory methods, and thus, in situ assessment has become the focus of a new discipline called proximal soil sensing. Terahertz (THz) radiation is a promising method for nondestructive in situ measurements. The THz frequency range from 258 gigahertz (GHz) to 350 GHz provides a good compromise between soil penetration and the interaction of the electromagnetic waves with soil compounds. In particular, soil physical parameters influence THz measurements. This paper presents investigations of the spectral transmission signals from samples of different particle size fractions relevant for soil characterization. The sample thickness ranged from 5 to 17 mm. The transmission of THz waves was affected by the main mineral particle fractions, sand, silt and clay. The resulting signal changes systematically according to particle sizes larger than half the wavelength. It can be concluded that THz spectroscopic measurements provide information about soil texture and penetrate samples with thicknesses in the cm range

Optical Spectrometry to Determine Nutrient Concentrations and other Physicochemical Parameters in Liquid Organic Manures: A Review

Nutrient concentrations in livestock manures and biogas digestates show a huge variability due to disparities in animal husbandry systems concerning animal species, feed composition, etc. Therefore, a nutrient estimation based on recommendation tables is not reliable when the exact chemical composition is needed. The alternative, to analyse representative fertilizer samples in a standard laboratory, is too time-and cost-intensive to be an accepted routine method for farmers. However, precise knowledge about the actual nutrient concentrations in liquid organic fertilizers is a prerequisite to ensure optimal nutrient supply for growing crops and on the other hand to avoid environmental problems caused by overfertilization. Therefore, spectrometric methods receive increasing attention as fast and low-cost alternatives. This review summarizes the present state of research based on optical spectrometry used at laboratory and field scale for predicting several parameters of liquid organic manures. It emphasizes three categories: (1) physicochemical parameters, e.g., dry matter, pH, and electrical conductivity; (2) main plant nutrients, i.e., total nitrogen, ammonium nitrogen, phosphorus, potassium, magnesium, calcium, and sulfur; and (3) micronutrients, i.e., manganese, iron, copper, and zinc. Furthermore, the commonly used sample preparation techniques, spectrometer types, measuring modes, and chemometric methods are presented. The primarily promising scientific results of the last 30 years contributed to the fact that near-infrared spectrometry (NIRS) was established in commercial laboratories as an alternative method to wet chemical standard methods. Furthermore, companies developed technical setups using NIRS for on-line applications of liquid organic manures. Thus, NIRS seems to have evolved to a competitive measurement procedure, although parts of this technique still need to be improved to ensure sufficient accuracy, especially in quality management

Soil Nutrient Detection for Precision Agriculture Using Handheld Laser-Induced Breakdown Spectroscopy (LIBS) and Multivariate Regression Methods (PLSR, Lasso and GPR)

Precision agriculture (PA) strongly relies on spatially differentiated sensor information. Handheld instruments based on laser-induced breakdown spectroscopy (LIBS) are a promising sensor technique for the in-field determination of various soil parameters. In this work, the potential of handheld LIBS for the determination of the total mass fractions of the major nutrients Ca, K, Mg, N, P and the trace nutrients Mn, Fe was evaluated. Additionally, other soil parameters, such as humus content, soil pH value and plant available P content, were determined. Since the quantification of nutrients by LIBS depends strongly on the soil matrix, various multivariate regression methods were used for calibration and prediction. These include partial least squares regression (PLSR), least absolute shrinkage and selection operator regression (Lasso), and Gaussian process regression (GPR). The best prediction results were obtained for Ca, K, Mg and Fe. The coefficients of determination obtained for other nutrients were smaller. This is due to much lower concentrations in the case of Mn, while the low number of lines and very weak intensities are the reason for the deviation of N and P. Soil parameters that are not directly related to one element, such as pH, could also be predicted. Lasso and GPR yielded slightly better results than PLSR. Additionally, several methods of data pretreatment were investigated

An Image Processing Based Approach for Detection of Nitrogen Status in Winter Wheat Under Mild Drought Stress

Abstract. Nitrogen is one of the most important agricultural inputs affecting crop growth, yield and quality in rain-fed cereal production. In this study an image processing based approach was used for detection of nitrogen status in winter wheat. Four N fertilization rates (0, 60, 120 and 240 kg N ha -1 , in total) and two water regimes (irrigated and non-irrigated) were applied to winter wheat. Digital images of the plant canopy were acquired using a Canon camera during the growing season 2012. Different indices were extracted by processing of the images. According to the statistical analyses, all the indices were affected by both N and water supplies. However, Rm, RMB, NRMB, Hue and INT were less sensitive to water supply. Among the indices, crop coverage (CC) showed better results for detection of nitrogen status of the plant. We conclude that digital cameras can be used to assess nitrogen status of winter wheat