324 It is important to highlight that no actinolite with fibrous (asbestiform) habit was detected in any of the samples examined. Figure 4 – Backscattered electron (BSE) image of actinolite (arrow) observed in sample SN4FD00096, and its respective ED spectrum. 4.3 Agronomic Efficiency Tests in Greenhouse Conditions The application of fresh mafic rock, following the laboratory-based acidity adjustment methodology, led to significant improvements in the chemical properties of the soils after the incubation period. In both the Red Oxisol (LV) and the Quartzarenic Neosol (NQ), the reaction of the rock promoted an increase in soil pH proportional to the applied doses (Figure 5A). As a result, the levels of exchangeable aluminum decreased with increasing doses of the mafic rock, thereby reducing soil acidity (Figure 6B). The application also enhanced calcium and magnesium contents, increased the sum of bases, and improved base saturation in both soils (Figures 6C–F). These results demonstrate that fresh mafic rock is a promising alternative for soil acidity correction and for supplying Ca and Mg to crops. Improved soil chemical conditions further resulted in greater accumulation of potassium, calcium, and magnesium in plant tissues, indicating additional agronomic benefits beyond acidity correction. After soybean and corn cultivation, the accumulation of K, Ca, and Mg in plant tissues was calculated based on nutrient concentrations and drymatter production (Figure 6). Even with uniform potassium fertilization applied to all treatments, all doses of fresh mafic rock resulted in greater K accumulation in plant tissues in the LV compared with the control (D0). In the NQ, K accumulation increased progressively up to dose D3. In contrast to the soil K content observed after corn cultivation, the average K accumulation in plant tissues was 623% higher in LV and 692% higher in NQ compared with soybean, demonstrating the superior physiological efficiency of corn in absorbing this nutrient. Calcium accumulation in corn also increased with higher doses of fresh mafic rock in both soils. For soybean grown in LV, no significant differences in Ca accumulation were observed among treatments. In the NQ, however, all doses resulted in higher accumulation of Ca than the control, with D4 and the limestone treatment showing the highest values. Despite soil Mg levels being lower than those observed in the limestone treatment, corn displayed Mg accumulation comparable to D3, D4, and CAL in the clay soil, and from D2
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