Building soil fertility in the humid tropics is a difficult project. Not only because the soil itself is thin, but due to the fact that below the fertile surface of leaf litter, rotting trees and decaying organic matter is a mineral and nutrient deficient zone of usually acidic clays called oxisols or, less commonly, utisols. With up to 90% of tropical forest biomass living within the plants and organic matter and only a paltry 10% occurring in the actual soil, protection and cultivation of soil is extremely important in sustaining fertility.
For many of our farm partners, like Federico, we’re rehabilitating slashed-and-burned lands that have been heavily leached of nutrients or are lacking the balance of minerals needed to allow plants access to important nutrients like phosphorous. One technique used extensively in tropical climates to take advantage of oxisols is the heavy application of lime or calcium carbonate to raise the soil pH and begin improving the soil structure and mineral availability for plants.
We would love to pump multiple metric tons of lime or calcium into the soil, but our distant location from traditional sources and concerns about mineral extraction practices makes large-scale delivery undesirable. But, our plants need their calcium. What to do?
… Enter the mighty eggshell.
Composed of 98% calcium carbonate, eggshells are an untapped source of calcium, but in their solid form they are very slow to decompose into a form ready for plant uptake. To change the eggshell into a soluble form, we need to use vinegar (acetic acid) to breakdown the calcium carbonate and transform it to water-soluble calcium acetate. From there we can use the diluted solution as a foliar spray on the plants for fast absorption, usually in 24-56 hours.
Calcium is an essential nutrient for cell wall reinforcement as well as protein synthesis, water transfer and carbohydrate translocation. The challenge is that calcium is mostly immobile in plants and won’t be sent to areas in need. By applying a bi-weekly treatment of calcium acetate mixed with other nutrients, we’re able to counteract the calcium-deficient soils and provide needed nourishment for the plants.
Two-months ago we started collecting eggshells from various restaurants in Iquitos, especially Dawn of the Amazon Cafe, and food vendors in the Eco Ola Permaculture Capital of the Amazon, Mazán. Instead of letting more organic waste be trashed in the local dumps, we’re able to recycle these essential minerals for improving plant health and robustness.
The process goes like this:
- Eggshells are picked up daily in Mazán or delivered weekly to the farm from Iquitos
- The shells are sun-dried to evaporate any moisture, limit pests and reduce toasting time
- Shells are then crushed to increase surface area to further reduce toasting time
- We toast the shells over a wood fire until the majority have a nice black char to them (we’ve noticed over multiple solutions that the shells seem to dissolve faster with longer toastings
- A volume mix of 1:1 of table vinegar and toasted eggshells is prepped and shaken in a bottle
- Every day we shake the bottle and add more vinegar as space is created in the production of carbon dioxide gas
- In roughly four-weeks the eggshells have mostly dissolved and we use a 15-21 tablespoon dilution in 15-liters of water for foliar spraying
Toasting the eggshells is a bit unpleasant, especially at first when we were toasting them wet and filled with maggots. At least the maggots added some additional nutrients, but introducing the sun-drying before toasting has made the process much more pleasant. But, do be warned, as you will reek of toasted eggshells, especially if doing multiple batches.
We look forward to documenting the process and sharing photos of our test plots of the solution with you all!