A Bio-dynamic Agriculture Model based on Rock Dust: A Case Study in Alto Alegre, Roraima, Brazil

1.1 Soil remineralization using rock dust:In addition to the benefits outlined in the abstract, rock dust has been shown to increase the cation exchange capacity (Anda et al., 2015) and water-holding capacity of sandy soils (Kahnt et al., 1986). However, many rock dusts are either inefficient or contain potentially toxic elements in harmful levels. As a result, the effectiveness of applying finely ground rocks to tropical soils largely depends on their chemical and mineralogical composition, soil deficiencies, and the specific requirements of the crops being grown (van Straaten, 2017).

This advantage of rock dust over chemical fertilizers is particularly evident in highly weathered soils found in tropical regions, where traditional soluble fertilizers may be expensive or unavailable (Swoboda, Döring, & Hamer, 2022). An analysis by Swoboda, Döring, and Hamer (2022) of 48 crop trials demonstrated the potential of rock dust as an alternative source of potassium (K) and a multi-nutrient soil amendment for tropical soils, while the benefits for temperate soils remain unclear. Positive outcomes were particularly observed with mafic and ultramafic rocks such as basalts and rocks containing nepheline or glauconite. Among various silicate rock powders (PRS), basalt powder stands out. Basalts, being igneous rocks with a mafic composition, are rich in magnesium (Mg) andiron (Fe) silicates and have a basic pH. These rocks also provide essential nutrients for plant nutrition, including phosphorus (P), potassium (K), calcium (Ca), and several micronutrients (Swoboda, Döring, & Hamer, 2022).

Viana, Caetano, and Pontes (2021) describe a technique that combines intermediate doses of basalt powder with larger doses of cattle manure. While various methods are used, the most effective approach was found to be the combination of rock dust with another type of fertilizer. Da Silva et al. (2017) emphasize that integrating rock powders with organic materials that support biological activity can influence the mineral alteration process. However, there is limited knowledge on how materials affect the dissolution of ground rocks, particularly basalt rock powder.

During composting, the nitrogen cycle plays a crucial role in determining compost quality (Hoang et al., 2022). This article will discuss strategies for mitigating nitrogen loss. Some researchers, however, present findings without thorough research, such as lab tests or real-world farm applications. Ramos et al. (2022) suggest that combining organic fertilizers with rock powder can meet the nutritional needs of both macro and micronutrients, with application costs of rock powder being significantly lower (<60%) and having long-term fertility benefits. Specifically, corn and bean plants grown in soils enriched with basalt dust yielded up to five times more than crops without basalt dust (Conceição et al., 2022). Similarly, Bauwhede et al. (2024) report that rock dust helps reduce nutrient leaching by providing a slow, sustained release of nutrients into the soil. However, this depends on the mineralogy of the rock, soil acidity, and the testing methodology. Grecco et al. (2016) highlight that the low processing costs and the need for alternative fertilizers support the practice of using ground rocks on soil. Nevertheless, studies on this subject are limited, and the nutrient release rate remains unclear as different rocks react differently to weathering, influencing nutrient availability.

Dos Santos et al. (2016) explain that nutrient release from rock dust occurs more slowly compared to chemical fertilizers. While this slow release is an advantage in some cases, it can also be a disadvantage, as it extends the process and requires larger quantities of material to be applied to the soil.

Lopes-Assad et al. (2006) found that the fungus Aspergillus niger is effective in solubilizing phosphate rocks through the production of organic acids. In the treatment with Aspergillus niger, pH fluctuated over time, with increased acidity leading to higher potassium (K) solubilization rates. However, when treating alkaline ultramafic rocks with Aspergillus niger, the acidity decreased, resulting in a reduced K solubilization rate.

To counter soil acidity, it is common practice to lime the soil with calcium and/or magnesium carbonates (such as calcite and dolomite). These minerals react with hydrogen ions released by the soil water, as well as carbon dioxide and aluminum in the form of hydroxide, thereby mitigating aluminum toxicity (Goulding, 2016).

The application of rock dust depends significantly on the crop being cultivated. Some crops, such as lettuce, require a high concentration of nutrients in the short term, and therefore, basalt may not be ideal for these situations. Hanish et al. (2024) found that applying up to 100g of basalt filler powder to both tested soils did not result in any significant increase in lettuce yields. The yields observed without soluble fertilizer (averaging 50g per pot of lettuce) were nearly four times smaller than those achieved with fertilizer treatments. Lettuce cultivation requires high doses of soluble inputs to meet the crop'snutritional demands within its short production cycle. As a result, basalt powder, with its low nutrient concentration, was unable to fulfill the crop'sshort-term needs.

Guimarães et al. (2020) found that banana orchards fertilized solely with mineral sources produced higher fruit yields compared to those fertilized with organic-mineral sources. However, the organic-mineral fertilization resulted in lower soil acidity and higher availability of phosphorus (P) and potassium (K). It was also observed that excessive potassium in the soil could cause nutritional imbalances in the plants, potentially reducing their productive potential. Consequently, further studies on banana fertilization strategies are necessary to improve nutritional balance.

It is important to approach the overestimation of rock dust as a fertilizer in Brazil with caution, as noted by Viana, Caetano, and Pontes (2021). They acknowledge that rock dust holds significant potential for Brazilian agriculture but is still underexplored. More research is required, particularly focusing on the agronomic effectiveness of rock dust when combined with animal manure (Viana et al., 2021).

According to Organicospro (2018), a well-known type of ground rock is limestone, which is rich in calcium carbonate (calcite limestone) or calcium magnesium carbonate (dolomitic limestone). In contrast, basalt powder is rich in silicate minerals that provide silicon to the soil—a crucial nutrient for promoting plant health and boosting productivity. These and other examples underscore the role of basalt powder in restoring degraded and leached soils, stimulating soil biology, and enhancing overall production. Some advantages of biomineralization include: • Replenishing nutrients in weak and impoverished soils • Reducing acidity overtime • Improving soil structure by enhancing oxygen content • Lowering chemical fertilizer costs • Increasing seed germination • Enhancing the growth of roots and plant aerial parts • Thicker stems and bark • Creating a protective leaf film against diseases, wind, and frost • Increasing durability post-harvest • Providing a greater quantity of nutrients Batista (2016) applied basalt rock powder in varying quantities, with and without the addition of limestone, to soil samples. In samples with limestone, potassium levels increased compared to those without limestone, and the pH was higher. Soil pH correction was less pronounced when limestone was not included in the treatment. It is important to note that soil re-acidification is a slow process, and superficial reapplication of limestone is sufficient to correct it. The study concludes that while soybean yields showed a modest but positive response to limestone reapplication (an average yield increase of 252 kg ha−1 year−1), corn yields were less affected (Hammerschmitt et al., 2021).

Among the aluminosilicate minerals found in rock dusts (RDs) are orthosilicates (e.g., olivine), inosilicates (e.g., pyroxenes like diopside, amphiboles like hornblende), tectosilicates (e.g., orthoclase, plagioclase, nepheline, leucite), and phyllosilicates (e.g., biotite and muscovite) (Calabrese et al., 2022; Swoboda et al., 2022; van Straaten, 2006). RDs can serve as an alternative to conventional liming, but unlike lime, they have a lower acid-neutralizing capacity (ANC) and release their alkalinity more gradually. Additionally, they provide a range of nutrients, including calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), and sulfur (S) (De Vries et al., 2021; Ramos et al., 2022; Swoboda et al., 2022).

Swoboda, Döring, and Hamer (2020) found that several rock modifications significantly improve the agronomic effectiveness of silicate rock powders (SRPs). Enhanced weathering of SRPs could also sequester substantial amounts of CO2 from the atmosphere, and supplying silicon (Si) could enhance plant resistance to abroad spectrum of biotic and abiotic stresses. More research is needed to fully understand the use of silicate rock powders (SRPs) when combined with limestone, chemical fertilizers, or animal manure. Particularly, studies should focus on the type of rock, the type of soil, the crop being cultivated, and the application quantity, as illustrated in Figure 1 below: FIGURE 1: Factors influencing the use of silicate rock powders-SRPs (Swoboda Döringb & Hamera, 2022) Bergmann and Holanda (2014) explain that when considering the use of a rock as a soil remineralizer, it is essential to investigate these processes through petrography. This method enables the identification of minerals, their texture, crystallization order, grain size, and overall integrity. Additionally, the materials added to the soil must meet strict criteria, including limits on harmful or potentially harmful elements, such as toxic heavy metals, and components that could contribute to soil salinization or introduce inert minerals that may degrade soil structure, such as sodium and quartz compounds. 1.2 Best practices and lessons learned from bio-dynamic agriculture: An excellent alternative to industrial agriculture, which is also in decline due to excessive mechanization, chemical manipulation, herbicide use, and neglect of environmental conservation, is bio-dynamic agriculture.

Bio-dynamic farming goes beyond organic farming by adopting a holistic, ecological, and ethical approach to farming, gardening, food, and nutrition. It is a way of living, working, and relating to nature and our vocations, fostering awareness of the uniqueness of each landscape and the inner development of individuals, as well as the collective growth of the community. Common practices in bio-dynamic agriculture include striving for self-sufficiency in energy, fertilizers, plants, and animals; organizing activities around the natural rhythms of the environment; utilizing a diverse range of plants, fertilizers, and animals in a healthy manner; approaching work with seriousness, precision, order, and attention to detail; and maintaining punctuality in executing tasks (Paull, 2011).

Campbell and Watson (2012) and Raupp (2001) found that soil improvement in bio-dynamic agriculture is achieved through proper humus management. This includes applying well-fermented manure and organic fertilizers, practicing effective crop rotation, ensuring good soil functioning, implementing protective measures such as windbreaks, and using cover crops, green manures, and diversified crops instead of monocultures. Mixed cultivation is also emphasized to allow plants to support each other.

Boicean & Dent (2020) suggest that crops that deplete the soil, such as corn, potatoes, cabbage, and cauliflower, should alternate with crops that replenish the soil, such as legumes (peas, beans, clover, etc.). Additionally, deep-rooted crops should be alternated with shallow-rooted crops, and those requiring fertilizers should be paired with those that can thrive without them. Inline with bio-dynamic practices, FAO (2021) reports that sustainable agricultural practices can reduce damage to ecosystems and ensure food production despite challenges like climate change, extreme weather, droughts, and other disasters. These practices also contribute to the progressive improvement of land and soil quality. 1.3 Study on the Potential for the Use of Rock Dustin Roraima: A noteworthy study on soil balancing in Roraima was conducted by Bergmann and Holanda (2014) as part of the broader project Geodiversity of the State of Roraima: Geology Program of Brazil (2014). The diverse soils, combined with climatic factors, terrain, and management limitations, allowed for the identification of six geographical units based on their potential for soil use and occupation in Roraima.

The most suitable area for soil balancing is the basic rock region (composed of Diabase, Basalt, and Gabro), which is dominated by vertical changes and includes red argisols, red oxisols, vertisols, chenosols, and nitisols. In Roraima, soils with low natural fertility and high acidity prevail, posing significant challenges to agricultural use. However, eutrophic soils, found in limited areas, have higher agricultural suitability and are more intensively used, though they still suffer from low technology adoption, as they are located in remote or rural settlement areas.

The lack of proper infrastructure also restricts productivity in Roraima, as the road network is insufficient for the timely delivery of supplies and efficient production flow. Additionally, labor is often underqualified, and public investments are lacking. Despite these challenges, the state'sequatorial location provides favorable climatic conditions for agriculture, allowing most crops to yield better results compared to other Brazilian regions. Overcoming these challenges is crucial for economic growth, social inclusion of indigenous communities, and sustainable development. Sustainable agricultural practices, including rock balancing, playa key role in addressing these issues.

Agriculture in Roraima is mainly practiced in the La Sabana region, where various soil types, such as canosols (yellow, red-yellow, and red), argisols (red and yellow-red), and neosols (hydromorphic quartarene and organic, fluvic, and surface litholic), dominate. These soils are characterized by low base saturation, low cation exchange capacity, and high acidity. In particular, levels of interchangeable phosphorus are very low, requiring constant pH correction.

The most fertile soils in the state are found in the basic rock regions: the Pedra Preta Sill in the Uiramutã region, the volcanic rocks of the Apoteri formation near Nova Olinda, and the area around Taiano. The best areas within the basic volcanic rock domain are located in Vila do Taiano (northwest Roraima), Sierra de Nova Olinda (central Roraima), and near the indigenous community of Flechal in Uiramutã. These regions feature soils derived from basaltic rocks from the Apoteri formation, including red oxisols, organic slopes, and chernosols, along with nitisols associated with diabases, diorites, and gabbros of the Pedra Preta threshold. These areas exhibit a pronounced relief with strongly wavy topography under forest cover. Figure 2 shows a taian diabase sample, collected in the municipality of Alto Alegre, and with strongly positive phosphomolibdate test.

FIGURE 2: Samples of diabase from Taiano (municipality of Alto Alegre) with strong positive phosphomolybdate test.

In addition to the municipality of Alto Alegre, in the municipality of Iracema, the presence of rare earth minerals, niobio, barium and phosphate are cited.

In Brazilian family agriculture, rock powders are used in consortium with waste of organic origin (animal manure and green fertilizer), and the farmer frequently produces their inputs through the composting process (possible thanks to a series of microorganisms), which allows increasing the efficiency of nutrient extraction.

TheN is generally provided by the practice of green fertilizers, and plants such as Tithoniadiversifolia (honey flower) are also used, capable of adding Kin proportions of up to 4.3% in leaves and ground stems added to the compost (Palm et al., 1997 Apud van Straaten, 2007) For such success it is important to consider the use of rock powders within the soil-plastic system, which includes the entire microbiota of the soil. and particularities of plant roots extraction systems (Mundstock, 2013). According to investigation indicative results, rock dust can be applied to any crop, in particle sizes that range between 0.105 and 4.0 mm, similar to limestone, by casting or use of machines. The amounts vary according to the ground and the cultivation in question, oscillating between 0.5 and 8 tons/hectare. Due to its already established use and performance in agronomic trials, it can be affirmed that in Brazil, the volcanic rocks of basic composition of the Serra Geral formation (basaltos and diabasas of the southern, southeast and central-west regions) have good potential for balancing combined with the fact that they are often available as fine crushers. While these rocks have relatively low silica contents, they have high contents of CA, mg and faith that are associated with mineral structures with lower resistance to solubilization, being able to make them available in the short term, when added to the ground in the correct grain size.

Alkaline rocks, being rich in K,in addition to having volcanic terms with microcrystalline matrix, are very suitable for use in soil remineralization.

In Brazil, a Poços de Caldas phonolite is the only rock to date authorized for commercialization as adequate for use as an alternative to potassium chloride (KCL), a imported soluble fertilizer widely used in Brazilian agriculture (Cortes et al., 2009). It is also important to note that the use of these rocks does not exclude the analysis of oligoements, to quantify micronutrients and potentially harmful elements (Bergmann and Holland, 2014). 1.4 The problem of excessive imports of chemical fertilizers in Brazil: The rock dust brings to the plants a greater collection of elements. In addition to macronutrients P, k, calcium (ca), sulfur (s) and magnesium (mg), depending on the rock used, essential micronutrients can be offered, such as zinc (zn), copper (cu), iron (faith), manganese (mn), molybdenum (mo), boron (b), cobalt (co) and nickel (ni). In high solubility monoements fertilizers, the contribution is mostly limited to nitrogen (N), P and K macronutrients, although there are currently complex fertilizer formulas containing CA, Mg, Sand micronutrients (mainly Band Zn). However, the negative aspect refers to the high solubility of the nutrients present in this type of input for Brazilian climatic conditions.

Thus, soil remineralization techniques are considered alternative routes to fertilize exhausted soils due to the loss of nutrients. Its importance is great in countries such as Brazil, which imports around 65% of the raw materials necessary to manufacture fertilizers and presents a worrying demand projection on production in this sector, which is expected to reach 83% in 2025 (Bergmann and Holland, 2014). ), as shown in Figure