Abstract
Detailed knowledge of chemical, petrographic and mineralogical compositions as well as the effects of applying rock powder on soil chemical properties and plant production are required for classifying these materials as soil remineralizers (SR), as according to Brazilian legislation in force. This study aimed to evaluate the potential of rock powders siltstone, tephrite and olivine melilitite, pure or mixed, on improving the fertility of a Cambisol and a Nitisol as well as the yield of soybean and barley crops grown in succession inside a greenhouse. For that purpose, these products were characterized as their granulometry, chemical, mineralogical and petrographic compositions. Based on the results, it was verified which products met the requirements for registration as SR established by the Normative Instruction Number 5 (NI5) from MAPA. Elemental chemical and grain size analyses indicated that all tested products met the NI5 requirements for their registration as SR. The mineral composition identified through petrographic analyses was confirmed by analyses performed via X-ray diffractometry techniques. Olivine melilitite rock, pure or mixed with siltstone, had the highest agronomic potential when compared to other powders, thus acknowledged as a SR. Although tephrite had little agronomic response on evaluated soils and crops, it also meets the SR requirements. Siltstone fulfilled most of NI5 criteria, except for exceeding the maximum content of free silica (quartz); therefore, it likely does not meet the requirements for its admittance as a SR.
Highlights
Today, the use of rock powder in agriculture has been significantly increasing in Brazil, mainly on organic, alternative, or non-conventional agriculture procedures (Manning & Theodoro, 2020; Ramos et al, 2020)
Mineralogical and petrographic analyses performed on rock powders from pure olivine melilitite and tephrite and on the siltstone + olivine melilitite mixing met the requirements for their classification as soil remineralizers (SR)
In the olivine melilitite and tephrite rocks, petrographic analyses indicated an expressive presence of minerals relatively less resistant to weathering composed by, respectively: olivine, phlogopite, melilitite, cebolite, monticellite, perovskite, aegirine and traces of apatite in the former; and sanidine, aegerine-augite, titanite, nepheline and apatite in the latter
Summary
The use of rock powder in agriculture has been significantly increasing in Brazil, mainly on organic, alternative, or non-conventional agriculture procedures (Manning & Theodoro, 2020; Ramos et al, 2020) These mentioned production systems have restrictions on using soluble fertilizers yet allow using rock powders as nutrient sources, silicates included. Most silicate rocks may contain some essential nutrients in concentrations that are either very low or insufficient in meeting plant demand, as the case of potassium in some rocks (Martins et al, 2015; Basak et al, 2017; Nogueira et al, 2021) When facing these situations, an alternative is mixing two or more rock powders, increasing concentrations of the nutrient of interest in the final mixed composition. Despite the great diversity of these rocks, many of them have been little studied, lacking studies on their elemental, mineralogical and petrographic chemical composition, as well as their agronomic potential in providing improved soil fertility and plant yield, with the purpose of classifying them as soil remineralizers (SR) and to later use them as raw material for producing agrominerals employed in agriculture
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