Agronomic potential of four rock powders, pure or mixed, as soil remineralizers

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.

Effects of Rock Powder Additions to Cattle Slurry on Ammonia and Greenhouse Gas Emissions

For several decades, farmers have been mixing rock powders with livestock slurry to reduce its NH3 emissions and increase its nutrient content. However, mixing rock powders with slurry is controversial, and there is currently no scientific evidence for its effects on NH3 and greenhouse gas (GHG) emissions or on changes in its nutrient content due to element release from rock powders. The major aim of this study was therefore to analyse the effects of mixing two commercially established rock powders with cattle slurry on NH3, CO2, N2O and CH4 emissions, and on nutrient release over a course of 46 days. We found that rock powders did not significantly affect CO2 emission rates. NH3 and N2O emission rates did not differ significantly up until the end of the trial, when the emission rates of the rock powder treatments significantly increased for NH3 and significantly decreased for N2O, respectively, which coincided with a reduction of the slurry crust. Cumulative NH3 emissions did not, however, differ significantly between treatments. Unexpected and significant increases in CH4 emission rates occurred for the rock powder treatments. Rock powders increased the macro- and micronutrient content of the slurry. The conflicting results are discussed and future research directions are proposed.

High Efficiency Stabilization of Lead in Contaminated Soil by Thermal-organic Acid Activated Phosphate Rock

Phosphate rock powder (PR) has been shown to possess the potential to stabilize lead (Pb) in soil. Most of the phosphorus (P) minerals in the world are low-grade ores, which makes it difficult to achieve the expected stabilization effect on heavy metals. This study compared the changes in the phase composition and structure of PR and three kinds of activated phosphate rock powder (APR) (organic acid activated PR, thermal activated PR, and thermal-acid activated PR), and used APR for the stabilization of Pb-contaminated soil. PR/APR was characterized by different methods. The stabilization effectiveness of APR on Pb-contaminated soil was evaluated by toxicity leaching procedure, the Pb products adsorbed on APR and stabilization mechanism of APR on Pb were analyzed. The results showed that the crystallinity of fluorapatite phase decreased after all the activation treatments. The APR showed decreased crystallinity and 3.4-fold increase in specific surface area, and a 53.07% and 49.32% increase in soluble P content in oxalic acid activated PR and citric acid activated PR, respectively, when compared with those of PR. These changes improved the stabilization effect of APR on Pb-contaminated soil, and the stabilization effectiveness was as follows: thermal-acid activated PR > organic acid activated PR > thermal activated PR. In particular, oxalic acid-600℃ activated PR showed the best effect, presenting 94.0%-99.8% reduction in Pb leaching concentration following addition of 2%-10% modifier. Product characterization after Pb adsorption on APR showed that Pb was adsorbed onto APR by forming pyromorphite precipitation with APR.

Byrsonima crassifolia seedlings growth on ground basalt rock

Ground basalt rock may represent a labile reservoir of nutrients, providing a low-cost, nutrient-rich substrate for seedling formation and plant growth. The study aimed to evaluate the development of a native plant murici [Byrsonima crassifolia (L.) H.B.K.] seedlings using two different application rates of ground basalt rock with two particles sizes. The experiment was performed in a greenhouse, in which treatments were arranged in a random block design with five replications in a factorial scheme (2 x 5 + 1), with five doses of finely ground basaltic rock (0.42; 1.04; 2.08; 4.17 and 8.33 g kg-1), two grain sizes (G1 Ø < 0.05 and G2 Ø < 0.10 mm mesh), and a treatment with soil without rock powder addition (the control 0.0 g kg-1 of rock powder). The seedlings were cultivated in substrate incubated for 120 days with the ground basaltic rock. Six months after the seedlings were planted variables involving growth and nutrient content variables were evaluated. Grain size affected nutrient availability from finely ground rock (Ca, Mg, Fe, and Zn). The growth of murici seedlings linear increase with ground basaltic rock application rates, with better results when a 0.05 mm grain size was used.