Frogeye leaf spot, caused by Cercospora sojina, is one of the most important leaf diseases of soybean worldwide. Silicon (Si) is known to increase the resistance of several plant species to pathogens. The cultivars Bossier and Conquista, which are susceptible and resistant, respectively, to frogeye leaf spot, supplied and nonsupplied with Si were examined for the activities of defense enzymes and the concentrations of total soluble phenolics (TSP) and lignin-thioglycolic acid (LTGA) derivatives at 8, 14, and 16 days after inoculation (dai) with C. sojina. The importance of cell wall degrading enzymes (CWDE) to the infection process of C. sojina and the effect of Si on their activities were also determined. Soybean plants were grown in hydroponic culture containing either 0 or 2 mM Si (-Si and +Si, respectively) and noninoculated or C. sojina inoculated. Severity of frogeye leaf spot was higher in cultivar Bossier plants than cultivar Conquista and also in the +Si plants compared with their -Si counterparts. Except for the concentrations of TSP and LTGA derivatives, activities of defense enzymes and the CWDE did not change for +Si noninoculated plants regardless of the cultivar. The activities of lipoxygenases, phenylalanine ammonia-lyases, chitinases, and polyphenoloxidases as well as the activities of CWDE decreased for the +Si inoculated plants. The results from this study demonstrated that defense enzyme activities decreased in soybean plants supplied with Si, which compromised resistance to C. sojina infection.

The present study had the objective to evaluate the effect of blends of KCl and K2SO4 fertilizers and their influence on the yield and the nutritional state of coffee plants, as well as on the chemical composition and quality of the coffee beverage. The experimental design was in randomized blocks with four repetitions and six treatments (T1: 100% KCl; T2: 75% KCl + 25% K2SO4; T3: 50% KCl + 50% K2SO4; T4: 25% KCl + 75% K2SO4; T5: 100% K2SO4; and a control, without application of K). The following analyses were performed: K and Cl content in the leaves and the soil, stocks of Cl in soil, yield, removal of K and Cl with the beans, cup quality of the beverage, polyphenol oxidase activity (PPO), electric conductivity (EC), potassium leaching (KL), the content of phenolic compounds, the content of total sugars (TS), and total titratable acidity (TTA). The stocks of Cl in the soil decreased as the proportion of KCl in the fertilizer was reduced. The fertilization with KCl reduces the cup quality and the activity of the polyphenol oxidase, probably due to the ion Cl. The increase in the application of Cl directly relates to the increase in potassium leaching, electric conductivity, and titratable acidity. Indirectly, these variables indicate damages to the cells by the use of Cl in the fertilizer. The activity of the polyphenol oxidase enzyme and the cup quality indicate that the ion Cl- reduces the quality of the coffee beverage. K content in the leaves was not influenced by the application of blends of K fertilizer while Cl content increased linearly with KCl applied. The application of KCl and K2SO4 blends influenced coffee yield and the optimum proportion was 25% of KCl and 75% of K2SO4. The highest score in the cup quality test was observed with 100% K2SO4.

Sulfuric acid digestion analyses (SAD) provide useful information to environmental studies, in terms of the geochemical balance of nutrients, parent material uniformity, nutrient reserves for perennial crops, and mineralogical composition of the soil clay fraction. Yet, these analyses are costly, time consuming, and generate chemical waste. This work aimed at predicting SAD results from portable X-ray fluorescence (pXRF) spectrometry, which is proposed as a "green chemistry" alternative to the current SAD method. Soil samples developed from different parent materials were analyzed for soil texture and SAD, and scanned with pXRF. The SAD results were predicted from pXRF elemental analyses through simple linear regressions, stepwise multiple linear regressions, and random forest algorithm, with and without incorporation of soil texture data. The modeling was developed with 70 % of the data, while the remaining 30 % was used for validation through calculation of R 2 , adjusted R 2 , root mean square error, and mean error. Simple linear regression can accurately predict SAD results of Fe 2 O 3 (R 2 0.89), TiO 2 (R 2 0.96) , and P 2 O 5 (R 2 0.89). Stepwise regressions provided accurate predictions for Al 2 O 3 (R 2 0.87) and Ki-molar weathering index (SiO 2 /Al 2 O 3) (R 2 0.74) by incorporating soil texture data, as well as for SiO 2 (R 2 0.61). Random forest also provided adequate predictions, especially for Fe 2 O 3 (R 2 0.95), and improved results of Kr-molar weathering index (SiO 2 /(Al 2 O 3 + Fe 2 O 3)) (R 2 0.66), by incorporation of soil texture data. Our findings showed that the SAD results could be accurately predicted from pXRF data, decreasing costs, time and the production of laboratory waste.

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Soils of the semi-arid region of Minas Gerais have small depth; hard, very hard or even extremely hard consistency when dry and very plastic and very sticky when moist; columnar or angular blocky structure and significant cracking along the profile in the dry period, however they have not been deeply studied yet. Thus, the aim of this study was to detail the genesis of Luvisols in the Semi-arid Depression of the Jequitinhonha Valley (MG), incompassing morphological, physical, chemical, micromorphological and mineralogical attributes, and their relationships. The lack of illuviation coatings in the micromorphological analysis is in line with the expressionless and unclear clay skins observed in the top of the B horizon in only one out of the four soil profiles during the field work. Considering the occurrence of expandable 2:1 clay minerals, which can easily modify such pedological feature, caution is recommended in relation to soil genesis interpretation. The lateral loss of the clay fraction from the superficial horizons is highlighted as the main formation process of the Luvisols studied. The cation exchange capacity of these soils revealed remarkable lower values for the Luvisols in semi-arid Brazilian regions.