Despite its discovery by farmers all over the world since ancient days in its connection with increased crop production, farmers in Africa especially Sub-Saharan Africa (SSA) do not apply recommended manure management practices in their farming leading to poor yields.
According to May this year research in 13 SSA countries by a team of experts on Manure Management Practices and Policies in Sub-Saharan Africa: Implications on Manure Quality as a Fertilizer, effective use of livestock manure as a fertilizer depends critically on methods of manure handling and storage which most smallholder farmers in the continent may not be aware of.
In Kenya, for instance, the government the government this year proposed a new bill through the Food Crops Regulations 2018 which if passed was to make it illegal for farmers to use animal manure in food production.
The regulation 30 (1) and (2) of the bill which was drafted by the Cabinet Secretary Agriculture, county governments and the Agriculture and Food Authority states that a grower shall not use raw animal manure for the production of food crops. Instead, growers shall only use chemical fertilizers at rates recommended by the respective County Government.
“This was informed by the fact that most of our farmers are not adhering to good agricultural practices especially in handling the manure hence affecting our export market as the fresh produce may fail health test by the GlobalGAP,” said Antony J.N. Nyaga, KALRO – PTC.
Due to public health concerns, the GlobalGAP forbids the application of untreated manure on leafy vegetables once they are planted and restricts manure application to 60 days before harvesting for other crops.
In addition, poorly discharged manure can lead to contamination and eutrophication of surface and groundwater mainly with nitrate.
Some of these basic recommended manure management practices include roofing animal housing, having a water-proof floor or covering manure during storage.
Without the practices farmers risk causing large nutrient losses during manure storage, increasing greenhouse gas emissions, and reducing the quality of the manure as a fertilizer.
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In a survey of manure management practices on small, medium, and large scale farms in Ethiopia and Malawi indicated that farmers lack knowledge on manure management.
However, farmers are able to access agricultural extension services from both government and non-government agencies, although these extension services rarely included information on improved manure management practices.
Manure contains important plant nutrients such as nitrogen (N), phosphorus (P), potassium (K), and other secondary nutrients and trace elements that if well-managed it can be an asset, promoting sustainable agriculture, and increasing crop production and marketability of the produce, particularly for smallholder farmers in sub-Saharan Africa (SSA).
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Collecting a mixture of bedding material, feed waste, flushing water, feathers, and soil among others together with animal excreta affects the nutrient content of the livestock manure.
This is because bedding materials such as straws usually have lower N concentration than the animal excreta.
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Treating or curing manure can be done in several ways such as drying and composting. The latter is advantageous to the manure user because it reduces the bulk, however, it can results into high losses of nutrients especially nitrogen hence indirect drying in sunlight is recommended.
Composting is an attractive option for turning on-farm organic waste materials into a valuable farm resource which is an excellent soil improver and is cheaper than other soil amendments.
By providing organic matter and soil nutrients, compost improves the structure of the soil, allowing for better aeration, improving drainage, nutrient and water retention, and reduced risk of erosion.
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Stored manure should be covered well to preserve the nutrients and help speed up decomposition of the raw manure.
Here a plastic film is recommended. This is because it can only let 20 per cent of nitrogen out as compared to 55 per cent nitrogen loss in manure that is stored in open heaps.
Another study in Western Kenya also has found that manure stored in open pits had lower mass fractions of N and P than manure in heaps under roof and in open heaps.
It is therefore recommended to shade manure storage facilities as much as possible in order to reduce exposure to high temperatures and subsequent N losses, as well as limiting exposure to rainfall, and thus minimizing nutrient losses due to leaching
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Most farmers in SSA apply manure in agricultural fields in holes, in furrows or spread/broadcasted and incorporated.
However, it is recommended that the manure be incorporated into the soil immediately after application, as it will retain more nutrients (in particular N) that will later be available to crops.
For example, 90% of N from liquid manure will be available to plants if it is incorporated within 8 h compared to only 40% N availability if incorporation is done after 5–7 days.