Biochar and compost from cocoa pod husk: opportunities for crop fertilization and suppression of black pod disease

PI: Njukeng Nkengafac (jnkengafac@yahoo.com), Institute of Agricultural Research for Development, Cameroon 
U.S. Partner: Bin Gao, University of Florida
Project Dates: September 2014 to October 2016

Soil depletion, pests, and diseases have been identified as some of the main causes of low production in smallholder farms, which depend on agriculture to make a living and feed their families. Cocoa (Theobroma cacao), 80 percent of which is cultivated by smallholders, is an export crop for many countries in Africa, and black pod disease caused by Phytophthora spp. is a major constraint to its production. While cocoa pod husk has been identified as a major source of inoculum of P. megakarya and is often left in farmers' fields as waste, it can be used for crop fertilization in the form of compost or biochar, thus improving soil fertility, promoting plant growth and resistance to biotic stresses, and, in turn, helping mitigate climate change.

This research study focuses on cocoa pod husk conversion into compost and biochar and aims to characterize the converted product, evaluate its effects on soil physicochemical properties and black pod disease suppression, and assess crop growth and yield. Farmers and students will receive training on composting and biochar preparation and application. Cocoa pod husk will be composted, and some of the husks will be dried and burned in limited oxygen in a kiln to produce biochar. Compost and biochar from cocoa pod husk will be incorporated into soils at different rates, and the soil physicochemical properties, as well as the black pod disease suppression, will be evaluated. The mode of action by which compost and biochar suppress cocoa pod disease will be determined by investigating the microbial basis of disease suppression and induced resistance mechanism. The growth of the plants in these amended soils will also be evaluated. At the end of the study, researchers anticipate to obtain information on how to control P. megakarya and how to improve soil properties for enhanced cocoa production.

Biochar and compost can be used as an alternative to control black pod disease and improve cocoa yields in smallholder farms while reducing farmers' spending on chemicals for black pod disease treatment, as well as their time spent to take care of the farms. Enhanced crop yield would thus improve farmers' income, consequently reducing extreme poverty among smallholder farmers. Converting cocoa pod husk into biochar and compost is expected to provide an affordable source of environmentally friendly fertilizer that can be used for enhanced production of crops and vegetables without depleting the soil, thus enhancing food security and reducing hunger and malnutrition.

Project team members create compost for experimentation (photo courtesy of Dr. Nkengafac).	The team installs and calibrates lab equipment (photo courtesy of Dr. Nkengafac).

Final Summary of Project Activities

Cocoa pod husks are often left in farmers` fields as waste. Converting this material to biochar and compost for soil amendment has multiple benefits as they have been evaluated globally as a means to improve soil fertility, promote plant growth and resistance to biotic stresses, and to mitigate climate change. Therefore, biochar and compost are alternatives to control the black pod disease and cocoa yields in small holder farmers. This will result in reduced spending in buying chemicals for the treatment of the disease as well as time spent to take care of the farms and will leave the farmers with more time to indulge in other income generating activities that will improve their standard of living. Converting cocoa pod husk into biochar and compost provides a cheap source of fertilizer to improve food security and reduce hunger and malnutrition and will help the farmers to produce more without depleting their soils. 

The project was based on cost manure and biochar, produced from cocoa pod husks and then the mature compost was dried and preserved for usage. Samples of the compost and biochar were analyzed and found to be very rich in potassium and nitrogen. The team also conducted a study on the microbial communities to determine microbial populations associated with disease suppression in the compost. The results this study showed that fluorescent pseudomonads were not present in the compost, with heterotrophic bacteria and actinomycetes dominating, as well as the presense of fungi were present in lower density. A second study looking into the invitro antagonistic effects of biochar and compost on P. megakarya to evaluate the effect of compost and biochar on mycelial growth of P. megakarya and detect possible suppressive effects (microbes, lethal effect of chemical component). The compost water extract consistently reduced the growth of P. megakarya compared to the control and the water extract from biochar. Autoclaving compost resulted in loss in growth suppressiveness.

Using the compost and biochar, greenhouse studies were also carried out. These greenhouse experiments aimed to determine the influence of compost and biochar on cocoa plantlets growth, induced resistance against P. megakarya using detached leaf assay, and microbial populations and activities associated with disease suppression in the substrates. The results showed that compost and biochar induced some resistance against P. megakarya. The team also germinated traditional African Leafy vegetable seeds as well as to grow the seedlings using varying concentrations of compost. Results showed that mixing the soil media with biochar or compost manure improved seed germination compared to the control. The seedlings were latter transplanted into beds with different levels of biochar, compost and inorganic fertilizer applications which showed some improvement in marketable vegetable production with supplementation.

Beyond experiments, the team sensitized famers to the use of cocoa pod husk for soil fertility and disease suppression. A questionnaire was administered to evaluate the knowledge of cocoa famers on soil nutrient, pests and disease management. Preliminary analysis of the questionnaire data showed that farmers’ knowledge on soil nutrient pest and disease management was very limited, but that many were interested in using biochar and compost manure as it was a cheap source of fertilizer. Training on compost manure preparation from cocoa pod husk was carried out in the four chosen sites. This was followed by several follow up visits to reinforce the trainings as, in most cases, farmers are reluctant to use a technology they haven't mastered. As of the end of the project, farmers were practicing composting and/or biochar production in their farms and more were willing to learn the techniques of producing these organic materials.

Two students, Martha Mounongo and Longue Morela were supported by the project and graduated after defended their theses while Nkenganyi Felix, a student from the higher technical teachers training college, was in the process of preparing his thesis when the project ended. A draft article on the preparation and characterization of compost and biochar was prepared. 


PEER Cycle 3 Grant Recipients