High School Project with Aji Peppers Show Increased Growth with Rock Dust and Compost

In our previous article “Students Gain Hands-On Experience with Remineralization at Paulo Freire Social Justice Charter School,” RTE reported on a remineralization experiment carried out in part by high school students. Aji peppers were planted to test the effect of rock dust on plant growth. Now, the results of the experiment are in.



Putting in stakes for plots at Nuestras Raices. (Click to enlarge)

In 2014, Remineralize the Earth (RTE) received a grant of $5000 from the Judith Haskell Brewer Fund of the Community Foundation Serving Richmond and Central Virginia to coordinate several local projects and create a resilient remineralization network in the Pioneer Valley. These initiatives have served as community demonstration projects. These local projects were conducted at the same time that remineralization trials were taking place, under the supervision of Professor Stephen Herbert, at the UMass Deerfield research site and the Agricultural Learning Center.

Measuring out the rock dust carefully (Click to enlarge)

RTE’s last project with this grant was undertaken in the spring, summer, and fall of 2016. The research project was conducted in partnership with Paulo Freire Social Justice Charter School (PFSJCS), a high school located in Holyoke, Massachusetts. In addition, RTE partnered with Nuestras Raices, a grassroots urban agriculture organization promoting community gardens in Holyoke, and Rock Dust Local, a company that specializes in local and regional sourcing of rock dust for remineralization. This project provided students hands-on experience with remineralization and soil management.

The project involved eight science classes made up of about 100 students. Because PFSJCS and Nuestras Raices both serve the Puerto Rican community in Holyoke, RTE chose to focus on a crop that is important to the Puerto Rican community: aji peppers. The peppers were planted in April 2016 and harvested by Dr. Tom Goreau and his team in the fall of the same year.


Testing aji peppers

Harvesting the fruits, roots and shoots (Click to enlarge)

The project was conducted at a Nuestras Raices community garden and allowed high school students to play an integral role in the design and implementation of a research project. Each class had their own set of three plots to monitor: (a) a control plot, (b) a plot treated with rock dust, and (c) a pot treated with rock dust and compost. Rock dust was obtained from Rock Dust Local, while Nuestras Raices provided compost for the project.

The soil at Nuestras Raices was already very fertile, which possibly affected the significance of the experimental results when compared to adding rock dust on poor soils. In less fertile soils, the differences can be dramatic with rock dust producing as much as 2-4 times increased growth. Nevertheless, RTE anticipated there would still be observable differences in plant growth and nutrient density.


Experimental results

Weighing aji peppers, shoots and roots with a kitchen scale (Click to enlarge)

The aji peppers were harvested and measured in September 2016 by Dr. Tom Goreau from RTE’s Board of Directors, his research assistant Thomas Sarkisian, and PFSJCS gardening teacher Julian Hartmann Russell, along with RTE Executive Director Joanna Campe.

During the harvest, the plants were weighed for comparison. The three major parameters compared among the three experimental groups were roots, shoots, and fruits. As shown in Fig. 1, the weight of the roots and the weight of the aji peppers revealed a strong correlation with the amount of rock dust applied to the soil. This indicates that the higher concentration of minerals in the soil where plants grew led to an increase in the weight of plant roots and fruits.

The control plots produced a higher weight for shoots compared to the other plots. This finding was unique to shoots, as the roots and fruits had higher yields with the rock dust and compost. This comparison suggests the possibility that remineralized soils help plants gain more nutrients to develop roots and produce fruits, while reducing the energy spent on growing shoots.

The mixture of rock dust and compost particularly demonstrated the emphasis on growing fruits, with a significant growth in fruit production (aji peppers), about twice the amount of production than in the control group. Rock dust alone increased fruit production by 20% over control.

Figure 1. Bar chart showing the experimental result of roots, shoots, and fruits of aji peppers at the PFSJCS. Note – Multiple plants were planted in each group, and results were averaged for the comparison. (Click to enlarge)

The harvested aji peppers were sent to Logan Labs, LLC in Lakeview, Ohio for fruit analysis. The lab reported that aji peppers grown in soil with added rock dust and compost contained a higher concentration of iron and magnesium, and a lower concentration of potassium and nitrogen, as shown in Fig. 2 above. One can see that the mixture of rock dust and compost increased iron content by 53% and Magnesium by 18%, while it decreased Potassium by 6% and Nitrogen by 26%. Using only rock dust produced a similar, though smaller, effect. Other major nutrient elements remained the same level.

The interpretation of these results is complicated by the fact that the untreated soil was healthy, fertile soil. This was likely to lead to less dramatic results with the addition of rock dust, compared to many studies that have been undertaken on poor soils.

Figure 2. Bar chart showing the percentage differences of Aji pepper fruit nutrient level in groups of control rock dust and rock dust and compost. (Click to enlarge)


Conclusion and future objective

Abundant aji peppers from a single plant (Click to enlarge)

The project at PFSJCS was a hands-on experience for teachers and students to learn about soil remineralization and its effect on agriculture. RTE is developing an online educational resource area for teachers and students, with lesson plans for K-12. In addition to learning, students will have the opportunity to contribute to ongoing research. There will be a GIS map where students around the world can post their results with photos, videos, and information about the local source of rock dust in their region. The current project is an example of the kind of project RTE would like to encourage worldwide.

The results of this project showed a positive influence of rock dust application on plant root and fruit growth. With further funding RTE would like to initiate projects in other regions, providing support for local communities to participate in remineralizing their soils. For examples of scientific studies on remineralization, please see the RTE Online Research Database.

RTE would like to thank the students and faculty of Paulo Freire Social Justice Charter School for their participation in the project. Thanks to Tom Vanacore of Rock Dust Local for donating the rock dust used in the trials. Thanks to Dr. Tom Goreau and his team for harvesting the peppers and collecting the data.


Junning Zhu graduated from Carnegie Mellon University in 2017 with a B.S. in Mathematical Sciences. She has an interest in applying data analytics and math modeling to solving environmental problems. Her work at RTE involves coordinating the research database, analyzing research result data, and managing the social media account on Weibo. She hopes to use her analytical skills to make remineralization and its value more accessible to people of different backgrounds.

Wentao Cao obtained his Ph.D. degree in Geoscience from the University of Iowa.  Specialized in metamorphic petrology and tectonics, he examined high-grade metamorphic rocks from North-East Greenland for his dissertation.  Specifically, he studied retrograde textures, such as melting textures and symplectites in these rocks.  He has been involved with RTE for research data analysis, grant writing, and managing the China social media account (i.e. Weibo).  He is currently teaching geology courses at State University of New York.

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