ABSTRACT The high Brazilian dependence on potash fertilizers has encouraged the agricultural and forestry use of silicate rock powders. Dozens of rock powders, including glauconitic rocks produced in several states in Brazil are currently registered with the Ministry of Agriculture and Livestock (MAPA) as Soil Remineralizers, being generally known as alternative sources of K. The indication of these materials as potassium fertilizers is based on the high Brazilian dependence on K from abroad, which reached around 96% in the 2021 and 2022 harvests. Glauconitic rocks, such as verdetes, slates, and glauconitic siltstones occur in extensive areas in the State of Minas Gerais (Abaeté, Quartel Geral, Cedro do Abaeté, Sete Lagoas, Matutina, and São Gotardo), predominating in the Serra da Saudade formation as the sedimentary cover of the São Francisco Craton. In these rocks, K-K2O contents generally vary in the range of 5-12% m/m. It is soluble in water (0.1-1.4%) and 2% citric acid (0.7-2.3%). In these rocks, the degree of glauconite crystallinity is variable due to different formation conditions and degree of alteration by weathering, especially in rocky outcrops. The use of natural glauconitic rocks as potassium fertilizers has shown low agronomic efficiency due to their low solubility and reactivity. Physical and thermal treatments in the presence of fluxing, chemical (acid or alkaline attacks), and biological (Acidithiobacillus sp.) agents have shown potential for dissolving glauconites. However, studies showing the financial viability of these materials are necessary for both such treatments and their direct use as fertilizers. powders MAPA (MAPA Remineralizers abroad 96 202 harvests verdetes slates Abaeté (Abaeté Geral Lagoas Matutina Gotardo, Gotardo , Gotardo) Craton KK2O KKO K2O O 512% 512 5 12% 12 5-12 mm m m/m 0.11.4% 0114 0.1 1.4% 0 1 4 (0.1-1.4% 2 0.72.3%. 0723 0.7 2.3% . 7 3 (0.7-2.3%) weathering outcrops reactivity fluxing attacks, attacks attacks) Acidithiobacillus sp. sp glauconites However 9 20 KK KO 51 5-1 11 0.11.4 011 01 0. 14 1.4 (0.1-1.4 72 0.72.3% 072 07 23 2.3 (0.7-2.3% 5- 0.11. 1. (0.1-1. 0.72.3 2. (0.7-2.3 0.11 (0.1-1 0.72. (0.7-2. (0.1- 0.72 (0.7-2 (0.1 (0.7- (0. (0.7 (0 (

ABSTRACT The performance of colorimetric methods for P quantification has been overlooked by researchers for decades. We investigated the performance of two blue colorimetric methods for P quantification, Braga and Defelipo (B&D) and Murphy and Riley (M&R), using two commonly soil P extractants, Mehlich-1 (M1) and Mehlich-3 (M3). Specifically, we evaluated the color development time and its stability in different soil extractant solution proportions (1:1 or 1:4 v/v), the optimum wavelength, limits of detection, and element quantification. Our results indicate that M3 leads to lower limits of detection and quantification for both colorimetric methods, particularly for B&D. For M1, the volumetric ratio (1:1 or 1:4) did not influence color development and both B&D and M&R methods showed a fast color development. However, B&D showed greater color stability (from 5 to 600 min) and an optimum wavelength of 711 nm, while M&R was stable from 27 to 600 min an optimum wavelength of 889 nm. For M3 soil extractant, there are important issues, such as M&R being unstable and B&D presenting slow color development. In addition, the spectral profile obtained from soil extractant was different from the one obtained by the calibration curve without soil for both M&R and B&D. Therefore, the adoption of original methods on P quantification in M3 extracting solution represents a potential source of error, leading to wrong P fertilizer recommendations. Thus, the best option for P quantification in M3 extracts seems to be the use of Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). decades BD B D (B&D M&R, MR , M R (M&R) extractants Mehlich1 Mehlich 1 Mehlich- M1 (M1 Mehlich3 3 M3. . (M3) Specifically 11 (1: 14 4 1: v/v, vv v/v v v/v) However 60 71 nm 2 88 issues addition Therefore error recommendations Thus ICPAES. ICPAES ICP AES (ICP-AES) (M&R (M (M3 (1 6 7 8 (ICP-AES (

ABSTRACT: There are several globally accepted methods to chemically characterize P-fertilizers, but not all are suitable to predict the agronomic efficiency of the P sources in terms of plant nutrition. Our aim was to investigate the performance of P extractors for fertilizers, investigating the consistency of different methods for P sources of varying properties and the related plant responses. The experiment was carried out in a greenhouse, using corn as a model plant. Phosphorus values extractable in water, 2 % citric acid, 2 % formic acid, ammonium neutral citrate + water, and acid ammonium citrate were evaluated for eight P fertilizers of varied solubility and correlated with P uptake by corn. The extractors citric acid and formic acid recovered no predictive amounts of P from crystalline apatite sources (Araxá and Patos phosphate rocks, PRs). However, they showed a satisfactory performance for Bayóvar PR and partially acidulated PRs but extracted low amounts of P from soluble P sources such as superphosphates. Neutral ammonium citrate + water extractors could accurately predict the efficiency of soluble P sources but underestimated the performance of Bayóvar (a reactive PR). In contrast, the extractor acid ammonium citrate, AAC, (pH 3) accurately predicted the agronomic efficiency of all P fertilizers. We therefore suggest AAC as an effective predictor of the agronomic effectiveness of any inorganic phosphorus sources.

O K é um nutriente encontrado em baixos teores em solos brasileiros, sendo necessário grande aporte via fertilização para alcançar produtividades satisfatórias das culturas. O Brasil apresenta elevada dependência externa e possui limitadas reservas de minerais solúveis de K, tradicionalmente explorados para a produção de fertilizantes. Por outro lado, é comum a ocorrência no país de minerais silicatados ricos em K não explorados comercialmente. Neste trabalho, objetivou-se caracterizar mineralógica e quimicamente amostras de verdete, separadas em frações granulométricas e avaliar seu potencial de uso com fertilizante potássico.A composição mineral do verdete é à base de glauconita, quartzo e feldspatos. Os teores totais de K2O no verdete variaram de 5,18 a 9,0 dag/kg. O teor de K extraído em água ou em ácido cítrico a 2% foi inferior a 2,4% do K total, indicando baixa reatividade do verdete e limitações para seu uso direto como fonte de K. O fracionamento físico e a sedimentação em água são processos ineficientes para promover a concentração de K nas diferentes frações do verdete. Os teores totais de K em algumas amostras de verdete são consideráveis, podendo viabilizar o uso desta rocha como matéria prima para produção de fertilizantes potássicos mais reativos.

Potassium is a nutrient found at low levels in Brazilian soils, requiring large inputs of fertilizers to achieve satisfactory crop yields. Brazil has high external dependence and limited reserves of soluble K mineral, which is traditionally exploited for the production of fertilizers. On the other hand, it is common the occurrence in the country of potassium-rich silicate minerals which are not commercially exploited. This study aimed to characterize mineralogically and chemically samples of verdete rock separated into size fractions and evaluate its potential as potassium fertilizer. The mineral composition of verdete rock is based on glauconite, quartz and feldspar. The total K2O content in verdete rock ranged from 5.18 to 9.0 dag/kg. The K content extracted in water or 2% citric acid was 2.4% below the total of K, indicating low reactivity of verdete rock and limitations for direct use as K source. The processes of physical fractionation and sedimentation in water are inefficient to promote the concentration of K in the different verdete rock fractions. The total K content in some samples are considerable and may enable the use of this rock as raw material for production of more reactive potassium fertilizers.