I’m Shep O'Neal with the VOA Special English Agriculture Report.

There are many different products that farmers can use to add nutrients to soil.  Organic fertilizers usually come from animal waste, plant material or treated wastewater. 

Farmers who raise animals have a ready-made fertilizer to mix into the soil.  However, animal waste must be treated in order to make good fertilizer. 

Composting is a natural method.  It uses the action of bacteria and other organisms to break down the manure into fertilizer.  The manure must be mixed with a material that provides carbon, such as wood cuttings.  The carbon supports the growth of the organisms.

It is important to mix in enough carbon-supplying material.  If there is too little, nitrogen in the waste will release ammonia gas and smell terrible.

Composting also requires the right amount of water and air.  The compost material should be loose and easy to turn with hand tools.  The compost should be about fifty to sixty percent water.  Too much water will mean that air cannot reach all the material.  This will cool the compost.  It will slow the organic activity and cause a bad smell.  Too little water will also stop the activity.

The process of composting produces heat.  If conditions are good, the compost material should reach about fifty to sixty degrees Celsius.  This heat kills dangerous organisms in the animal waste.  Experts say all of them will be killed if the material stays at fifty-five degrees for fourteen days. 

It takes three to seven months for compost to become ready to use as fertilizer.  After this time, the material will have lost twenty to sixty percent of its mass.

Waste products provide one fertilizer resource.  Some crops supply limited amounts of nutrients to the soil.  Beans release nitrogen.  Crops like alfalfa can be left to break down. 

There are many different kinds of manufactured fertilizers.  The most commonly used mineral fertilizers are nitrogen-based.  Nitrogen from the air is mixed with hydrogen from natural gas.  This process produces ammonia gas.  Other elements are then added to the ammonia. 

Different crops demand different mixtures of nutrients. Many farmers invest in special fertilizers designed just for the kinds of crops they grow. 

This VOA Special English Agriculture Report was written by Mario Ritter.  Our reports are online at voaspecialenglish.com.  We will also have links to more information about composting.  I'm Shep O'Neal.