Research points to struvite as a national alternative for phosphate fertilizers.

Scientists from Embrapa Agrobiologia (RJ) indicate that the use of struvite as a slow-release fertilizer, produced from swine farming waste, is a viable alternative to reduce the use of imported phosphate fertilizers in soybean and wheat crops. Experiments in soybean crops, for example, showed that the product was able to supply up to 50% of the phosphorus demand, maintaining a productivity of 3.500 kilograms per hectare (kg/ha), similar to that of national soybeans in 2025, which was 3.560 kg/ha with the use of conventional fertilization.

This is yet another initiative from Brazilian agricultural research to reduce Brazil's dependence on imports of these inputs, which currently account for about 75% of national demand.

Caio de Teves Inácio, a researcher at Embrapa Agrobiologia and coordinator of the study, emphasizes that it's not just about replacing a fertilizer. "We are creating a new technological route for Brazilian agriculture, aligned with sustainability, autonomy, and innovation," he stresses.

Struvite is a material formed by magnesium and ammonium phosphate crystals, produced from the chemical precipitation of nutrients present in swine farming waste. "It is a fertilizer that represents the concept of a circular economy applied to agriculture. We transform an environmental liability, which is animal effluent, into a high value-added agricultural input," explains the researcher.

Field experiments also show that the agronomic efficiency of the fertilizer is superior in terms of recovering phosphorus applied to the soil. Brazilian tropical soils, highly depleted by the climate, tend to fix phosphorus quickly, limiting the efficiency of conventional fertilizers. The gradual release of struvite and its alkaline reaction proved to be beneficial in increasing the utilization of the nutrient.

A promising fertilizer

Preliminary recommendations also indicate that struvite can be applied alone or in combination with soluble fertilizers, in doses ranging from 50% to 100% of the agronomic recommendation for phosphorus, depending on the crop and soil.

Because of this, researchers have developed and are testing an organomineral fertilizer that combines mineral nutrients with organic matter. In experiments evaluating phosphorus diffusion in the soil, the formulation obtained 50% higher results in the first 28 days compared to pure granulated struvite.

Environmental and economic benefits

The benefits of adopting struvite are not only agronomic, but also economic and environmental. "We are talking about a national technology that reduces dependence on imported inputs, reuses nutrients from agricultural waste, and improves the efficiency of phosphorus use, a non-renewable natural resource," emphasizes Inácio.

In addition to further contributing to the reduction of the risk of environmental contamination by soluble phosphorus, the mineral fertilizer exhibits high agronomic efficiency in tropical soils, with high phosphorus fixation.

In parallel, the use of struvite represents a solution to the problem of inadequate disposal of animal waste. On farms with intensive pig production, especially in the South and Midwest regions, the precipitation of struvite allows for the removal of excess nutrients before application to the soil, reducing the risk of contamination of surface and groundwater. This characteristic also contributes to the expansion of farm production, which is limited precisely by the amount of nutrients (phosphorus and nitrogen) that can be discharged into the soil.

From an economic standpoint, the fertilizer could become a new source of income for producers, who would then generate a marketable input from the waste. "It is also an economically viable alternative and especially attractive for medium and large pig farmers," points out the researcher. Embrapa estimates indicate that the adoption of the technology on farms with more than 5 pigs could generate approximately 340 tons of struvite per year in the country.

Struvite is still poorly understood in the Brazilian scientific context.

The production of struvite from the recovery of nutrients from effluents (for example, from pig farming wastewater or urban sewage) is seen as one of the most sustainable technologies within the concept of a circular economy. This approach not only avoids pollution from excess nutrients in waterways, but also generates a fertilizer with good availability for plants – a second-generation fertilizer – produced from waste.

Globally, interest in struvite has grown exponentially in the last decade. More than 80 struvite production facilities were already operating in 2019, mainly in developed countries facing phosphorus surpluses stemming from intensive livestock farming or high population density. China, the United States, and Germany lead research and innovation in this field, often through international cooperation. However, Brazilian participation is still in its infancy, leaving a knowledge gap regarding struvite performance under tropical conditions.

"It's a paradox: we have a promising resource, but little is known about its behavior in our soil conditions, which are predominantly acidic and have a high capacity for phosphorus adsorption," Inácio points out. In fact, the widespread occurrence of acidic soils in Brazil, rich in iron and aluminum oxides, favors phosphorus fixation, significantly reducing the available fraction of this nutrient and the efficiency of any phosphate source.

Alignment with public policies

Research on struvite aligns with the guidelines of the National Fertilizer Plan, which aims to expand national production and encourage more efficient and sustainable alternative sources. Large-scale adoption could contribute to food security and the competitiveness of Brazilian agribusiness.

In addition to Embrapa Agrobiology, the following institutions are participating in the research: Embrapa Soils (RJ), Embrapa Swine and Poultry (SC), the Federal University of Santa Catarina (UFSC, Florianópolis campus), the Federal University of Santa Maria (UFSM), the University of Rio Verde (UniRV), and the Farroupilha Federal Institute (Santo Augusto campus, RS). Funded by the National Council for Scientific and Technological Development (CNPq) and Embrapa, the research is advancing in proving the agronomic efficiency, economic viability, and environmental benefits of the fertilizer.

“We believe that struvite has a strategic role for the future of Brazilian agriculture. Our job is to provide the scientific basis so that it can be registered and adopted safely and efficiently in the field,” concludes the researcher from Embrapa Agrobiology.

What is struvite?

Struvite is a white mineral with the chemical formula MgNH4PO4·6H2O, containing approximately 12% phosphorus (P), 5% nitrogen (N), and 10% magnesium (Mg). Its main agronomic characteristic is its low solubility, which allows for the slow and gradual release of nutrients, following the crop cycle. This is especially advantageous in tropical soils, such as those in Brazil, where soluble phosphorus tends to be rapidly fixed, becoming unavailable to plants. Its alkaline reaction in the soil, in contrast to soluble fertilizers, which are acidic, is another important characteristic that promotes its use in tropical soils.

The unique aspect of struvite lies in the fact that it is produced from organic waste. In Brazil, the focus is on precipitation from swine manure. This process, in addition to reducing the pollutant load of these effluents (rich in nitrogen and phosphorus), results in an input with added agronomic value. It's the principle of the circular economy in action: transforming an environmental liability into a high-value product for agriculture.

The urgent need for a national solution for phosphorus.

Phosphorus is the second most important nutrient in agriculture, after nitrogen. A lack of available phosphorus in the soil can directly affect plant growth, flowering, grain filling, and fruiting, resulting in decreased productivity.

Unlike nitrogen, which is abundant in the atmosphere, mineral sources of phosphorus are finite and non-renewable. Although fears of an imminent depletion of phosphate rocks have diminished in recent decades – with estimates of global reserves for centuries to come – dependence on a few producing countries and price shocks are a reality.

Brazil, with limited domestic reserves, is particularly vulnerable, which has motivated the government to create incentive programs to reduce this external dependence. "Our high dependence on imported fertilizers is a strategic weakness for Brazil's food security," notes the expert.

For him, research with struvite is not just a search for an alternative fertilizer, but a path to food sovereignty and a more autonomous and sustainable agricultural development model. "We need technologies that allow for the efficient use of phosphorus and the recovery of nutrients present in our own waste," concludes Inácio.