Proximal Mobile Gamma Spectrometry as Tool for Precision Farming and Field Experimentation

Abstract

Soils naturally emit gamma radiation that can be recorded using gamma spectrometry. Spectral features are correlated with soil mineralogy and texture. Recording spectra proximally and in real-time on heterogeneous agricultural fields is an option for precision agriculture. However, the technology has not yet been broadly introduced. This study aims to evaluate the current state-of-the art by (i) elucidating limitations and (ii) giving application examples. Spectra were recorded with a tractor-mounted spectrometer comprising two 4.2 L sodium iodide (NaI) crystals and were evaluated with the regions of interest for total counts, 40Potassium, and 232Thorium. A published site-independent multivariate calibration model was further extended, applied to the data, and compared with site-specific calibrations that relied on linear correlation. In general, site-specific calibration outperformed the site-independent approach. However, in specific cases, different sites could also replace each other in the site-independent model. Transferring site-specific models to neighbouring sites revealed highly variable success. However, even without data, post-processing gamma surveys detected spatial texture patterns. For most sites, mean absolute error of prediction in the test-set validation was below 5% for single texture fractions. On this basis, thematic maps for agricultural management were derived. They showed quantitative information for lime requirement in the range from 1068 to 3560 kg lime ha−1 a−1 (equivalent to 600–2000 kg calcium oxide (CaO) ha−1 a−1 if converted to the legally prescribed unit) and for field capacity (26−44% v/v). In field experimentation, spatially resolved texture data can serve (i) to optimize the experimental design or (ii) as a complementary variable in statistical evaluation. We concluded that broadening the database and developing universally valid prediction models is needed for introduction into agricultural practice. Though, the current state-of-the-art allows valuable application in precision agriculture and field experimentation, at least on the basis of site-specific or regional basis.

Determination of Soil Constituents Using Shifted Excitation Raman Difference Spectroscopy

“…With this goal in mind, the multidisciplinary project consortium, "Intelligence for Soil (I4S)-Integrated System for Site-Specific Soil Fertility Management", funded within the German national program "Bo-naRes: Soil as a Sustainable Resource for the Bioeconomy", is seeking to develop an integrated sensor system for in situ field application by combining a range of complementary measurement techniques with individual benefits. Selected atomic spectroscopic methods include X-ray fluorescence, 10 laser-induced breakdown spectroscopy, [11][12][13] or gamma spectroscopy, 14,15 whereas molecular spectroscopic techniques comprise mid-infrared, 4 near-infrared, 16 and Raman spectroscopy. 17 While atomic spectroscopy can reveal the total mass fractions of elements, their binding form within the soil cannot be determined by such methods.…”

Overview on Spectral Analysis Techniques for Gamma Ray Spectrometry

“…The detector, positioned 30 centimeters above the ground, measures soil gamma rays with a radius of approximately 2 meters and a depth of 0.3 meters. The accuracy of both measurements is almost the same (R 2 = 0.96) [3]. The detectors used for PMGS include a 1 to 2 × 4.2 L NaI detector [3,24,26] and a φ70 × 150 mm CsI detector [45], among others.…”

“…The accuracy of both measurements is almost the same (R 2 = 0.96) [3]. The detectors used for PMGS include a 1 to 2 × 4.2 L NaI detector [3,24,26] and a φ70 × 150 mm CsI detector [45], among others. The running speed for the on-the-go survey is applied at 0.7 to 1.4 meters per second [3], 0.83 meters per second [26], and 2.8 meters per second [45].…”

“…More recently, measurements using unmanned aerial vehicles and drones have been added to AGRS (e.g., [1]). Carborne now includes field tractor measurements (e.g., [2,3]). Additionally, there are the gamma-ray logging method, which involves measurements in a borehole, and the Seaborn method, which involves placing a measuring device on the seabed or towing it along the seabed [4].…”

Ground vegetation covers increase grape yield and must quality in Mediterranean organic vineyards despite variable effects on vine water deficit and nitrogen status

“…Rudolph et al (2016) demonstrated the statistical advantage of using ECa readings as continuous covariates in regression models over the "improved blocking" strategy. Moreover, the authors recommended the use of additional sensors such as gamma ray to improve statistical models (Pätzold et al, 2020). In addition, the comparison of different experimental designs with and without spatial information showed that including spatial covariates reduced Type I error regardless of the design and D.W. Raffa et al randomization (Alesso et al, 2019).…”