The spectral reflectance of crop canopy is a spectral mixture, which includes soil background as one of the components. However, as soil is characterized by substantial spatial variability and temporal dynamics, its contribution to the spectral reflectance of crops will also vary. The aim of the research was to determine the impact of soil background on spectral reflectance of crop canopy in visible and near-infrared parts of the spectrum at different stages of crop development and how the soil type factor and the dynamics of soil surface affect vegetation indices calculated for crop assessment. The study was conducted on three test plots with winter wheat located in the Tula region of Russia and occupied by three contrasting types of soil. During field trips, information was collected on the spectral reflectance of winter wheat crop canopy, winter wheat leaves, weeds and open soil surface for three phenological phases (tillering, shooting stage, milky ripeness). The assessment of the soil contribution to the spectral reflectance of winter wheat crop canopy was based on a linear spectral mixture model constructed from field data. This showed that the soil background effect is most pronounced in the regions of 350–500 nm and 620–690 nm. In the shooting stage, the contribution of the soil prevails in the 620–690 nm range of the spectrum and the phase of milky ripeness in the region of 350–500 nm. The minimum contribution at all stages of winter wheat development was observed at wavelengths longer than 750 nm. The degree of soil influence varies with soil type. Analysis of variance showed that normalized difference vegetation index (NDVI) was least affected by soil type factor, the influence of which was about 30%–50%, depending on the stage of winter wheat development. The influence of soil type on soil-adjusted vegetation index (SAVI) and enhanced vegetation index (EVI2) was approximately equal and varied from 60% (shooting phase) to 80% (tillering phase). According to the discriminant analysis, the ability of vegetation indices calculated for winter wheat crop canopy to distinguish between winter wheat crops growing on different soil types changed from the classification accuracy of 94.1% (EVI2) in the tillering stage to 75% (EVI2 and SAVI) in the shooting stage to 82.6% in the milky ripeness stage (EVI2, SAVI, NDVI). The range of the sensitivity of the vegetation indices to the soil background depended on soil type. The indices showed the greatest sensitivity on gray forest soil when the wheat was in the phase of milky ripeness, and on leached chernozem when the wheat was in the tillering phase. The observed patterns can be used to develop vegetation indices, invariant to second-type soil variations caused by soil type factor, which can be applied for the remote assessment of the state of winter wheat crops.
The possibilities of using thermal infrared imaging data for detecting the main parameters of arable soil fertility,
Possibility of detecting soil fertility parameters based on the use of thermal survey data was studied on the test area of Yasnogorsky District, Tula region, Russia. The test area has gray forest slightly eroded arable soils located in the flat part of the slope. During the field works, an open soil surface was photographed using a FLIR VUE 512 thermal imager (range 7.5-13.5 mkm), soil samples were also taken from a layer of 0-5 cm and soil moisture was measured in a layer of 15-20 cm. For almost all parameters of soil fertility (pH, humus content, potassium content, exchange cations - Mg++, K+, Na+), a statistically significant correlation was established (r =0.4-0.7) between them and the survey data in the thermal range of the spectrum. For moderate correlations, polynomial regression equations were compiled. Among the studied fertility parameters, the pH of the salt extract, the content of potassium oxide and potassium exchange cations had significant coefficient of determination (R2 0.60) with the thermal range of the spectrum - R2= 0.61, R2 =0.60 and R2 = 0.63, respectively. The obtained results have shown that thermal imaging can be used to map some parameters of soil fertility for the region. Nevertheless, it turned out to be impossible to reliably detect all the main parameters of soil fertility of the test field on the basis of thermal survey data. However, the thermal soil survey data can be used as auxiliary data when shooting in the visible and nearIR ranges, which helps to improve the accuracy of contactless soil monitoring.
<p>Phosphogypsum (PG) is a by-product of phosphoric acid production, a valuable raw material for reclamation of acidic soils, for remediation of soils contaminated with oil products, a source of rare-earth elements (REE). The use of PG has a positive effect on the development of plants, on the value and quality of yield. Most of the PG produced at the present time is stored in phosphogypsum dumps (PGD), which are a source of pollution of the environment, since the dust particles from dumps can be transported over significant distances. To assess the impact of PGD on the environment and agricultural production it is necessary to identify zones of priority distribution of dust particles and their accumulation in the soils of the surrounding areas. In recent years, geoinformation modeling (GM) have been used to analyze dusting of different types of dumps. There are very few studies on the possibility of using such technologies for modeling the dusting of PGD.</p><p>We carried out GM of dust emissions in the impact area of phosphate fertilizer production factory in Balakovo (Russian Federation).</p><p>The chemical composition of PG samples was determined for whole samples and fractions most susceptible to dusting &#8211; <100 &#181;m. The determination of the total REE composition was carried out by ICP-OES method. REEs content in samples of PG is 30-60 times higher than the Clark values for soils. The predominant indicator elements are La, Ce and Nd, the content of which reaches 500-3000 &#181;g/g. The distribution of microparticles in the fine fractions was analyzed using a laser particle size analyzer from ultrasound-stabilized suspensions. In the aqueous suspension PG aggregates disperse to particles <1 &#181;m, forming in turn several size groups. Local maximum contents form particles with sizes 0.03, 0.14 and 0.67 &#181;m.</p><p>The data allowed using the GM to allocate zones of priority distribution of dust particles and their accumulation in the soils surrounding the PGD area. Dusting simulations were performed for particle sizes 8-1, 1-0.1, 0.1-0.05, 0.05-0.03, 0.03-0.01 and <0.01 mm. The results of spatial modeling of the weighted sum of the relative concentration of dust particles indicate that particles up to 0.1 mm predominantly move in northeast, north and southwest directions, particles 0.1-1 mm predominantly fall in northeast direction, particles 1-8 mm - in north direction.</p><p>Correlation analysis showed that the results of dusting modeling are in good agreement with the spatial distribution of REE. The greatest correlation between the weighted sum of the relative concentration of particles of the analyzed size is noted for the content of La and Ce (correlation coefficients 0.74 and 0.68 respectively). Validation of the model was carried out in a field. Joint analysis of the constructed maps and field data showed that the map of the weighted sum of the relative concentrations of analyzed particles well reflects the spatial variability in the soil content of La and Ce.</p><p>The results of modeling can be used to assess the impact of PGD on the surrounding area and its soil cover.</p><p>The reported study was funded by RFBR, project number 19-05-50016.</p>
The simulation of dusting of phosphogypsum dump of Balakovsky branch of JSC "Apatit" of "PhosAgro" Group of Companies was conducted. On the basis of the analysis of the meteorological data for the period 2006–2019, the information on a projective covering by vegetation for the period 2006–2019, a relief and a soil map modeling of relative concentration for the particles the size less than 0,01 mm; 0,01–0,03 mm; 0,03–0,05 mm; 0,05–0,1 mm; 0,1–1 mm and 1–8 mm was done. It was found as a result of the joint analysis of the constructed maps and field data, that the map of the weighted sum of relative concentrations of the analyzed particles well enough reflects spatial variability of the maintenance in soil La and Ce, prevailing components among the analyzed rare-earth elements (correlation coefficient 0.74 and 0.68 accordingly). The modeling results can be used to assess the impact of phosphogypsum dumps on the adjacent territory and its soil cover.
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