Peanuts are one of the most widely grown legumes in the world, and for many smallholder farmers, they provide a reliable source of lean protein as well as a type of savings account. Capitalizing on the nutrition and income in the peanut crop can make the entire household more resilient, but depends largely on simple post-harvest interventions, Peanut Innovation Lab research finds. 

A paper in an upcoming issue of Peanut Science shows that using a tarp to dry peanuts and hermetically sealed bags to store them can increase the crop yield available for a farmer to consume or sell, even without changing any preharvest practices.

Research done under the Peanut Innovation Lab’s precursor, the Peanut & Mycotoxin Innovation Lab, tested a series of interventions in the field and at postharvest in Ghana to see how different combinations of improved practices impact yield and the quality of the crop. 

Not surprisingly, the research found that adding weeding and inputs during the growing season increases yield. 

But, the research also showed that simply drying nuts on a tarp would make a significant difference in the size and quality of the final crop, providing higher yield, healthier nuts for consumption and the potential for new markets due to lower aflatoxin contamination. Drying on a tarp and storing in hermetically sealed bags offered the largest increase in yield, allowing the farmer to preserve the quality of the crop for four months to sell when prices would be higher. 

In two years of trials, researchers found that farmers in Central Ghana who followed strictly traditional pre- and postharvest practices would have just 59 percent of their original crop in good condition to sell four months after harvest. Drying nuts on a tarp would increase the rate of good kernels to 80 percent, while storing in bags would increase the rate to 89 percent. 

Preserving the size and quality of the crop through postharvest interventions increases farmers’ ability to use groundnuts as a form of savings and draw down on that stored asset as needed. As prices increase over time, farmers also see a greater return on their investment, positioning them to invest in the next season. 

The findings come from experiments conducted near Drobonso in the Sekyere Afram Plains District and near Ejura in Ejura-Sekyedumasi district, both in the Ashanti Region of Ghana. Researchers evaluated different combinations of traditional farmer practices and improved practices in the field, drying and storage, measuring yield and aflatoxin contamination at harvest, after drying peanut pods to 10 percent moisture, and after storing peanut for four months. 

In the field, researchers tested improved practices such as hand weeding six weeks after planting, applying soap to reduce insect pests, and applying ground oyster shells as a source of calcium. Post-harvest, they tested drying peanut pods on a polyethylene tarp rather than the bare ground and storing in hermetically-sealed plastic bags rather than traditional poly bags.

The experiments showed that using improved practices during the growing season reduced aflatoxin, but also that drying on a tarp (even if the nuts were grown under traditional practices) would reduce aflatoxin. After four months in storage, the nuts dried on tarps continued to have lower aflatoxin than the nuts dried on the ground. 

The researchers suspected that drying peanut on tarps minimizes movement of spores from the soil surface onto pods, especially if it rains during the drying. Farmers might also cover nuts more easily when they are drying on a tarp, by pulling a portion of the tarp over the crop or moving it indoors. A study of PICS bags in Niger found that, after 6.7 months of storage, unshelled groundnuts stored in a woven bag would lose 8.2 percent of weight to pests, while shelled groundnuts would lose 28.7 percent. Groundnuts stored in PICS bags would retain their original weight and germination rate at the end of the six months.

While farmers struggle to acquire credit to invest in improved practices, results showed that increased revenue from greater yields and higher quality in the form of non-damaged kernels more than pay for the costs of improved practices during the growing cycle, as well as for drying tarps and hermetically-sealed storage bags.

Aflatoxin also is a particular concern in Ghana, where hot, dry conditions promote the fungus that leads to aflatoxin accumulation. Farmers lose millions in formal trade, while growers’ families face increased health risks because families are more likely to consume the damaged kernels that are less valuable in the market.

As growers look to the potential of international trade, they see the potential for more income, but also strict limits on aflatoxin, which can be managed by the same post-harvest interventions. 

“With the nation's projection to increase its export above 20 percent, having the ability to reduce aflatoxin opens and give continuous secure access to potential industrial market opportunities by developing new sustainable supply chains,” said William Ofori Appaw, the Technical Head for Food Science and Technology labs at KNUST and lead author of a paper summarizing the results of research in central Ghana. The paper, which detailed research done in central Ghana, is scheduled to be published next month in Peanut Science, the leading academic journal on peanut research. A sister paper with similar findings in northern Ghana is also under review. 

“Better understanding how to control aflatoxin helps to ensure good quality groundnuts for local industry and consumption,” said Appaw.

While aflatoxin itself is tasteless, the fungus may lead to shriveled or misshapen kernels that are consumed by the farmers’ families. Studies show that prolonged exposure to aflatoxin can cause life-threatening health problems and irreversible stunting in children.

Finding simple, cost-effective ways to minimize aflatoxin accumulation postharvest may improve a farmer’s income, but also can protect the family from contaminated food. 

“Groundnut is a nutrition dense product and forms a staple food in Ghana,” Appaw said. “Reducing aflatoxin contamination is key to improving nutrition in children, enhancing cognitive development and reduce the severity of opportunistic diseases such as malaria, kwashiorkor etc. in children due to compromised immune system caused by aflatoxin. Reduction of aflatoxin helps to lower the incidence of cancers and its complications as aflatoxin are also carcinogenic in addition to being an immuno-suppressant.

“Overall reducing aflatoxin contamination helps to improve the DALYs (Disability Adjusted Life Year) and enhance improving the quality of life of the populace,” he said.