Make your own fertilizers from cow dung

Apr 08, 2015

CAN cow dung cook? Many people still ask this question especially when being encouraged to keep animals due to their various reasons

By Prossy Nandudu

 

CAN cow dung cook? Many people still ask this question especially when being encouraged to keep animals due to their various reasons.

 

This question can be accurately answered by taking such a person to a home that is depending on cow dung as fuel not only for cooking but for lighting their homes at the same time getting fertilizers for the their crops.

 

Whenever someone is going into animal husbandry what comes first into their mind is selling the milk, and the meat.

 

The cow dung at most is dropped in the banana plantation and yet if processed, it could provide many benefits including gas for cooking, lighting, manure through slurry, hides and the skin, among others.

 

For the cow dung to provide that cheap fertilizer one is required to have a bio digester which is well constructed.

 

A bio digester holds manure in an air-tight tank and heats it to about 100 degrees-just like a cow's stomach. Bacteria in the manure thrive in these conditions and they consume solids in the manure while releasing methane gas.

 

As the heat is tapped at the top, the liquid dung (slurry is pushed out), explains Daniel Mugenga, the business development manager Biogas Solution Uganda.

 

In the digester which normally is air tight, heat of up to 100 degrees Celsius is created and then the methane gas is let out in a tube and collected for cooking and lighting.

 

Slurry is a residue or by product that flows out of the bio digester. It is high in nutrients that are needed for plant growth in addition to providing feeds for fish and pigs.

How to apply slurry 

According to Kalinzi Ibrahim Kiriisa, an agriculture extension worker in sustainable energy, slurry shouldn’t be applied during the flowering season like coffee or other crops that depend on bees for pollination. Slurry in itself is a repellant.

 

It should be applied during the rainy season for the plant to take in the fertilizer quickly because the soils are softer making it easy for the slurry to dissolve.

 

When applying, a farmer should first clear a few meters around the plant, before pouring the liquid and after, the place should be covered with leaves to prevent the fertilizer from escaping into the atmosphere.

 

It is also important for one to take into account the ratios when applying because too much or too little of everything is important.

 

Kiriisa explains that for vegetables, three liters of water should be added onto one liter of slurry and this applies to different crops as these have different intakes meaning that ratios vary.

 

For crops like pineapples, there is need for one to mix both the slurry and urea as slurry alone may not be easily taken in and the more it stays on top of the soil, the more vital nutrients evaporate.

 

To maintain quality, the slurry should be stored only briefly in liquid form in a closed pit or tank and then applied to the fields.

 

Liquid storage involves a certain loss of nitrogen due to the evaporation of ammonia. For that reason, and in order to limit the size of the required storage vessels (a 30-day supply corresponds to about 50% of the biogas plant volume), the storage period should be limited to 2-4 weeks.

 

Benefits of using Slurry to the soil 

It maintains soil fertility especially in tropical areas like Uganda.

 

The process draws carbon, hydrogen and oxygen out of the substrate maintaining essential plant nutrients (N, P, K) in the substance or liquid. For all practical purposes, the volume of the source material remains unchanged, since only some 35 - 50% of the organic substances is converted to gas.

 

Fermentation helps by removing some of the carbon, which has the advantage of increasing the fertilizing effect

 

Organically fixed nitrogen and other plant nutrients become mineralized and, hence, more readily available to the plant growth.

 

Well-digested slurry has no odour, therefore doesn’t attract flies.

 

In the bio digester where the slurry is formed, destructive pathogens and worm ova are killed meaning that plants remain more or less affected by some of those pathogens.

 

Compared to the source material, digested slurry has a finer, more homogeneous structure, which makes it easier to spread

 

Apart from slurry, one could save costs by using biogas for lighting and cooking, according Mugenga.

 

Costs saved on a biogas as fuel 

According to Daniel Mugenga from Biogas Solutions Uganda, a company that is promoting biogas usage in Uganda, a 6 cubic meter biogas digester can save a family of five close to 550,000 shillings which they spend on buying firewood and lighting in rural areas.

 

The analysis was made by Bio Gas Solutions taking into account the fact that people in rural areas are using more firewood and not charcoal that is why the financial analysis was made.

 

For a family in rural areas to have a bio digester the basic requirement is to have a cow which if well fed should be able to give off one and half basins of cow dung.

 

In this case one requires 2.5 basin of cow dung every day from two cows, to be able to provide energy for cooking for four houses, and four hours of lighting using one lamp.

 

For smaller families 

For one to have a four cubic digester, he is required to have one cow, which gives off one basin of cow dung, this should be able to cook for 2 hours and lighting of four hours .This can only power one cooking stove and one lamp.

 

A bigger family or school or institution interested in supplementing on their energy needs with biogas, requires a 13 cubic meter bio digesters, which is fed with 5.5 basins of cow dung, coming from four or more cows.

 

This can provide lighting for five hours using three lamps, and seven hours for cooking.

 

The advantage of using biogas is that it provides a cheaper source of energy for cooking and lighting in rural homes compared to firewood, charcoal and kerosene.

 

Provides clean and smoke free cooking with less health risks like cancer, respiratory complications, and eye problems related to use of firewood and charcoal.

 

Protects the environment through reduced tree cutting and emission of harmful gases.

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