Therefore, we conducted the hitherto most comprehensive review of SRPs. Despite the inherent complexity and thus inconsistency of SRP findings, our review of 48 silicate rock powder studies concluded these major findings on their effectiveness as fertilizer:

1.     Results on soils in temperate regions remain inconclusive and benefits will depend on a careful selection of sufficiently soluble rocks with nutrients that match the crop demand.

2.    The highest potential was confirmed for strongly weathered soils in the humid and sub-humid tropics, as dissolution rates reach a maximum in these environments. Importantly, neither conventional fertilizers nor liming can fill the escalating gap for affordable and accessible K sources and micro-nutrient fertilizers, so SRPs must be seriously considered as a major future soil amendment in these regions. Additionally, SRPs can ameliorate two other major constraints in tropical soils: low pH and low cation exchange capacity (CEC).

3.     Many tropical soils are deficient in Si, an often overlooked yet crucial nutrient, for which the demand is expected to substantially increase in the future, since 7 out of the 10 globally most produced crops are Si accumulators. 

4.     SRPs can induce plant biotic and abiotic stress resistance, thereby reducing the dependence on pesticides and strengthening plants in the face of climate change.

5.     Ample potential exists to improve SRPs effectiveness by modifications like acid treatments or mixtures with compost and biochar.

6.     From an agronomic perspective, the most suitable rocks are fast weathering feldspathoids and mafic/ultramafic rocks like basalts.

7. Future SRP studies should first consider the factorial framework presented in our review to avoid a poor selection of factors. Eventually, a common SRP methodology with a minimum set of factorial information needs to be developed to allow for a better and statistically rigorous comparability of studies. 

At Inplanet, we exclusively focus on remineralizing tropical soils with mafic/ultramafic rocks in the humid and sub humid tropics. Furthermore, we directly tackle the issue of lacking study-comparability by creating solid methodologies that will be applied to all our future projects.

The effectiveness of fertilizing with silicate rock powders in Brazil

An interview with Antonio from Agrobizão

Antonio Alexandre Bizão has 23 years of experience in rock powder research. He started his first comparative experiments in the late 90s already. Initially he conducted the remineralizer (nota that certified rock powders are called “remineralizers” in Brazil) research as a secondary activity while working as a rural producer and agronomist sales representative. For about 10 years now he has been exclusively dedicated to soil remineralizers after he got his master’s degree in the field of soil fertility.

Antonio, what motivates you to work with rock powder fertilization?

What motivates us to do this work is knowing that in Brazil there are many people committed to qualitative and result based agriculture. Wherever farmers start to use remineralizers and see the advantages, they become a fan of this technique and then often start innovating by themselves. It is as if the remineralization process acts as a seed that awakens people to seek new alternatives for a more sustainable, more emancipated, and especially more profitable agriculture. A recurring fact is that after we introduce rock powders, the rural producer is generally inclined to make use of other bio based inputs in the following years, studying regenerative agriculture and other possibilities of organic planting.

What are the main benefits of the use of rock dust from your point of view? 

Throughout the many projects at Agrobizão we observed, inter alia,……increase of biological activity in the soil.

…increased CEC of the soil.
…continuously and gradually nutrient provision.
…rationalizes the use of potassium.
…neutralization of aluminum (Al) and release of phosphorus (P)
…chemical, physical and biological improvements in the soil as…
…increases of pH of the soil in the medium/long term.
…improved plant health and resistance.
…improved nutrient cycling and soil regeneration.
…increases fertilizer use efficiency.
…stimulated soil biological activity and plant investment in root growth.

Regarding the reduction of synthetic agricultural chemicals, what is the potential of rock dust in general? 

With the use of soil remineralizers the farmers can use chemical fertilizer more rationally. The soil remineralizer generates a layer of new, healthier soil with an increased CEC. A major differential compared to synthetic chemicals is the permanence of the product in the soil, its release of nutrients is gradual, so the reapplication does not need to be done every year while the positive effects on soil and crops persists for several years.

What are the yield improvements that you observe after the application of rock powder? What reduction of other inputs do your farmers usually achieve? 

Today we observe several types of benefits related to yields after the application of remineralizers. Currently, we have around 34 products registered in the MAPA (Ministry of Agriculture of Brazil) and another 50 in the process of registration. It is important to remember that, even if all remineralizers have to fulfill a minimum quality standard (e.g. soma de bases >9%, see technical norm), the products are naturally very heterogeneous and each rock powder has its own set of strengths.

Generally speaking, what we can say is that we often manage to reduce the amount of chemical fertilizers by about 30% in annual crops such as soybeans, corn, and sorghum. In perennial crops such as coffee, we have achieved reductions of 20%, and in high value-added crops such as tomatoes, potatoes, and onions, we have achieved around 15% reduction in fertilizer use. 

It is important to remember that when it comes to reducing the consumption of fertilizers, we are talking about a complex management that uses both silicic products with potassium content and natural phosphates, in addition to cover cropping prior to commercial cultivation. 

Do you think that rock powder will be a conventional input in the future?
What is missing for the mass adoption of rock powder in Brazil?

First of all, it is important to make clear that soil remineralization should not be treated as an isolated product or input but as a process. Soil remineralization is one of the tools that should be used in conjunction with other practices to create healthy soil. We treat the soil, and it is the soil that will take care of the plants.

I believe the remineralizer will get the space of an “indispensable basic input” when there is a change in the farmer’s mentality. Afterall, the soil is a space for interaction between inorganic materials, like minerals, and biology. If one wants to produce well there must be a balance and proportionality between these means. We see healthier, more productive plants with higher resistance to drought and pests. These are the consequences of a balanced soil environment which can be achieved through rock powders. It is necessary to holistically think about the soil, and not only in the placement of a product to solve a problem, that’s one of the key messages we try to convey to the farmers we are working with.

In case this blog post made you curious about the potential of rock powder fertilization and you are interested in our exclusive case studies about the reduction of conventional farming inputs after rock powder use in Brazil, get in touch!