Can Bioslurry Replace Some Synthetic Pesticides? (AFNNET)
by Alan Anderson
December 14, 2015
Cliffson Zakaria Maro is a RISE-AFNNET MSc student at Sokoine University of Agriculture in Tanzania. His year of coursework, completed in November 2015, included an astounding range of topics: research methodology, statistics and data management, pharmacognosy (the study of medicinal drugs derived from plants or other natural sources), public health, microbiology, biopesticides, entrepreneurship, project management, analytical chemistry, and the biological interaction of drugs in the body.
The subjects that most strongly caught his interest, he said, were pharmacognosy, followed by entrepreneurship and project management. Entrepreneurship interests him partly because it emphasizes small and medium-sized enterprises, especially those in which farmers and others make or sell traditional medicines, expanding their horizons beyond common low-margin crops such as sorghum and maize.
“When I came to SUA,” he said, “I wrote in my proposal that I wanted to find a natural product to study. I was prepared to start my studies on ants, because they are very destructive to farmers. But my professor found some difficulties I might have in my project. He advised me to look into another question, which he had discovered in southern Tanzania, in the Njombe region. There he had heard that farmers were applying a bioslurry to vegetables as fertilizer. This is an area with many insect pests, and the farmers told him that the inserts were no longer eating the vegetables that were fertilized by the bioslurry. Naturally he wanted to know why, and I agreed that it sounded very interesting as a project.”
The term “slurry” refers to a fluid mixture of small particles—usually containing water—that offers a convenient way of handling large amounts of solids, such as dirt, clay, pulverized coal, cement, or manure. In the region Cliffson chose to explore, bioslurry is the principal byproduct of biogas digesters, which are used to extract methane from cow manure. Many users simply discard the bioslurry after the methane is removed, which both pollutes the environment and wastes useful organic material. Cliffson planned to investigate whether or not bioslurry is a more effective fertilizer than raw manure, and also whether it has the ability to reduce crop damage caused by pests.
In preparing for his master’s fieldwork, Cliffson drew up a proposal with four objectives. He has already completed some sections of it, though important parts are still awaiting answers.
Cliffson intends to administer a questionnaire to farmers who are using bioslurry. He wants to ask them exactly which pests it has reduced, how the farmers make and use the slurry, how long they store it before use, and whether it actually kills pests or simply repels them. He also wants to understand the farmers’ attitudes about bioslurry and its value.
He also plans to hold a field trial to demonstrate what the farmers are doing. He has already tested spinach, a vegetable that is commonly grown in the region, as his experimental crop. He tested it both in the field and in a greenhouse. On one portion of the crop he applied no pesticide, and found that caterpillars ate about a third of the leaves. On a second portion, he applied only bioslurry, and on the third portion he applied the synthetic Farmguard pesticide. The best outcome was seen in the bioslurry portion, second best in the pesticide portion, and the worst in the portion without protection.
Using techniques of microbiology with the help of a lab technician, he has examined the bacterial content of the bioslurry. He has found references in the literature to the presence of Bacillus thuringiensis, a common bacterium used as an alternative to synthetic pesticides, but has not yet found it.
He has explored the biochemistry of the bioslurry using thin-layer chromatography to identify the constituents. Using samples from the biogas plants of five farmers, he found, first, 1,2-dicholoromethane; then hexane; then methanol; then a combination of methane and hexane. “I came to realize,” he said, “that the chromatographic profile was the same in all five. Now I want to compare this profile with profiles published in the literature.”
With these results, Cliffson is partway through his four goals, with some important answers still to come: how much the farmers really know about bioslurry, its specific effect on pests, and its microbial contents. Depending on the answers to these and related questions, he may have an opportunity to exploit the power of both the entrepreneurship and pharmacognosy he enjoyed most during his coursework.
“These are important questions to answer,” he said, “because there is a big market for organic products here in Tanzania. The market is growing fast. People don’t want to use synthetics anymore because they are aware of the harm chemicals can do. People have been spraying so much to get rid of pests, and they have found that the vegetables are full of pesticides. Whether the slurry is killing the pests, or whether it is more of a repellant, it seems to be working, and this can be part of a new solution.”
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