ABSTRACT The concept of production environments, which is widely used to classify the yield potential of soils, and magnetic susceptibility (MS), is emerging as an important tool for mapping ultra-detailed areas. Given this background, this paper aims to evaluate the use of MS as a tool for the identification of areas with different potential the enhancing of sugarcane yield and quality, and the allocation of varieties. An area of 445 ha was sampled at 1 point every 7 ha, and 14 points were determined for stratified sampling following the top of the landscape. Particle size and MS of samples at depths of 0.0-0.2 and 0.2-0.4 m were analyzed. The data on yield and quality of raw material were obtained from a nine crop season database and biometry performed in the 2018/19 crop season. The multivariate analysis of historical results showed the formation of three groups with different yield and quality potential, with a difference of up to 17.28 mg of cane per hectare between the group with the highest and lowest potential, based on soil MS. An analysis of the performance of the varieties involved showed that MS is effective in identifying areas with different potential for sugarcane yield and quality, differentiating by up to 34.5 % the performance of the same variety in different MS classes and by up to 38.5 % the performance of different varieties in similar MS classes. Thus, MS is an effective tool for identifying areas with different potential for sugarcane yield and quality, and can be used for allocating varieties in the field.

Resumo: O objetivo deste trabalho foi estimar os teores de óxidos de ferro (hematita e goethita) e caracterizar a cor e as assinaturas espectrais e magnéticas de solos do Cerrado de Goiás. Foram estudados seis Latossolos e um Cambissolo. As assinaturas espectrais e magnéticas foram determinadas por espectroscopia de reflectância difusa (ERD) e suscetibilidade magnética, respectivamente. Posteriormente, as curvas espectrais e os cálculos de derivativos secundários foram utilizados para determinar os conteúdos de hematita e goethita, além da cor dos solos após conversão em valores tristimulus. Os teores de hematita e goethita também foram obtidos por difratometria de raios-x, e a cor dos solos também foi avaliada em campo (carta de Munsell). Também foram determinados os valores de substituição isomórfica do ferro por alumínio e o índice de avermelhamento dos solos. A ERD pode ser utilizada para estimar os conteúdos de hematita e goethita, bem como a cor dos solos do Cerrado de Goiás. A assinatura espectral é capaz de apontar as principais características dos solos relacionadas aos conteúdos de matéria orgânica, óxidos de ferro, caulinita e gibbsita. A assinatura magnética, característica de solos ricos em óxidos de ferro (hematita e goethita), mostra o predomínio de minerais pedogenéticos.

Abstract: The objective of this work was to estimate the iron oxide contents (hematite and goethite) and to characterize the color and the spectral and magnetic signatures of Cerrado soils in the state of Goiás, Brazil. Six Oxisols and one Inceptisol were studied. Spectral and magnetic signatures were determined by diffuse reflectance spectroscopy (DRS) and magnetic susceptibility, respectively. Then, the spectral curves and the second derivative calculations were used to determine hematite and goethite contents, as well as soil color after conversion into tristimulus values. Hematite and goethite contents were also obtained by x-ray diffractometry, and soil color was also defined in the field (Munsell color chart). The values for the isomorphic substitution of iron by aluminum and the degree of redness were also determined. DRS can be used to estimate hematite and goethite contents, as well as the color of Cerrado soils in the state of Goiás. The spectral signature can point out the main soil properties related to the contents of organic matter, iron oxides, kaolinite, and gibbsite. The magnetic signature, characteristic of soils rich in iron oxides (hematite and goethite), shows the predominance of pedogenic minerals.

Resumo O objetivo deste trabalho foi verificar a eficácia da cor do solo na identificação de áreas com diferentes potenciais produtivos e qualidade de café, em Argissolo Vermelho-Amarelo desenvolvido de arenito, no Planalto Ocidental Paulista, no Estado de São Paulo. Coletaram-se 173 amostras em 39 ha, para a determinação de matiz, valor, croma e índice de avermelhamento do solo, com base nos dados da espectroscopia de reflectância difusa (ERD). Avaliaram-se, também, a produtividade e a qualidade do fruto de café, e calculou-se o índice de diagnose foliar (DRIS). A maior correlação espacial observada pelo variograma cruzado ocorreu entre matiz e DRIS, em pontos distantes em até 497 m. A menor correlação espacial foi observada em croma e produção, em pontos distantes em até 207 m. As áreas com o maior potencial de produtividade (20 a 33 sacas por hectare) apresentaram matiz entre 6,99 e 7,06, croma entre 5,00 e 5,08 e valor entre 4,40 e 4,45. As áreas com o menor potencial de produtividade (3 a 7 sacas por hectare) apresentaram matiz entre 7,27 e 7,68, croma entre 5,20 e 5,28 e valor entre 4,51 e 4,67. Nestes locais, o teor de argila foi de 16 g kg-1, os teores de P variaram entre 65 e 75 mg dm-3, e a soma de bases estava entre 56 e 58 mmolc dm-3. O uso da cor determinada por ERD é eficaz para identificar áreas com diferentes potenciais produtivos e qualidade de café, com precisão de 61 a 97%.

Abstract The objective of this work was to verify soil color effectiveness for the identification of areas with different yield potentials and coffee quality, in an Ultisol developed from sandstone, in Planalto Ocidental Paulista, in the state of São Paulo, Brazil. One hundred seventy-three samples were collected from 39 ha, for the determination of hue, value, chroma, and the soil redness index, based on data of diffuse reflectance spectroscopy (DRS). Productivity and quality of coffee fruit were also evaluated, and the leaf diagnosis index (DRIS) was calculated. The highest spatial correlation, observed in the cross variogram, occurred between hue and DRIS in points up to 497 m apart. The lowest spatial correlation was observed for chroma and production, in points spaced by up to 207 m. The areas with the highest yield potential (20 to 33 bags per hectare) showed hue between 6.99 and 7.06, croma between 5.00 and 5.08, and value between 4.40 and 4.45. The areas with the lowest productivity potential (3 to 7 bags per hectare) showed hue between 7.27 and 7.68, chroma between 5.20 and 5.28, and value between 4.51 and 4.67. In these places, clay content was of 16 g kg-1, P levels varied between 65 and 75 mg dm-3, and the sum of bases was between 56 and 58 mmolc dm-3. The use of the color determined by DRS is effective to identify areas with different productive potentials and coffee quality, with 61 to 97% accuracy.

Soil CO2 emission (FCO2) is one of the main sources of carbon release into the atmosphere. Moreover, FCO2 is related to soil attributes governing the transfer of gases from soil to the atmosphere. This study aimed firstly to describe the spatial variability of hematite (Hm), goethite (Gt), iron extracted with sodium dithionite-citrate-bicarbonate (Fed) contents, soil CO2 emission (FCO2) and free-water porosity (FWP) and secondly, to develop statistical models to predict the above mentioned factors in an Oxisol cultivated under manual harvesting of sugarcane (Saccharumspp.) in southeastern Brazil. The study was conducted on an irregular 50 m × 50 m grid containing 89 points, each 0.5-10 m apart. The 0-0.1 m soil layer at each sampling point was used to assess soil FCO2, moisture and total pore volume. The results were subjected to descriptive statistical and geostatistical analyses using auto- and cross-semivariograms. All soil attributes exhibited a spatial dependence structure and the experimental semivariograms fitted spherical and exponential models. The Gt content was the individual attribute that exhibited the highest linear and spatial correlation, especially with FCO2. We were able to use diffuse reflectance spectroscopy to map large areas, which allows for easy identification and estimation of soil attributes such as FCO2 and FWP. Geostatistical techniques faciltate the interpretation of spatial relationships between soil respiration and the examined properties.

Studies analyzing the variability of clay minerals and magnetic susceptibility provide data for the delineation of site-specific management areas since many of their attributes are important to agronomy and the environment. This study aimed to evaluate the spatial variability of clay minerals, magnetic susceptibility, adsorbed phosphorus and physical attributes in Oxisols of sandstones in different geomorphic surfaces. For that purpose, soil samples were collected every 25 m along a transect located within the area where the geomorphic surfaces were identified and mapped. The transect occupied the central portion of 500 ha, where it was also sampled for density purposes with one sample per six hectares. Soil samples were collected at a depth of 0.0-0.2 m. The results of the physical, chemical, mineralogical and magnetic susceptibility analyses were subjected to statistical and geostatistical analyses. The nature of the clay minerals and magnetic susceptibility was dependent on the variation of the soil parent material. High values of magnetic susceptibility were associated with the presence of maghemite and magnetite of coarse size. The spatial variability of crystallinity and the content of Fe oxides, as well as magnetic susceptibility, were dependent on the age of the geomorphic surfaces. The youngest surface had greater spatial variability of these attributes. The iron (goethite and hematite) and aluminum (gibbsite) oxides in the youngest geomorphic surface influenced the low values of soil density and high values of total pore volume, micropores and P adsorption. The characterization of the spatial variability of Fe oxides and susceptibility allowed for the delineation of homogeneous areas.