This is the VOA Special English Agriculture Report.

Population growth and economic changes put pressure on farmers to make their fields more productive. As a result, the use of mineral fertilizer is expected to continue to increase.

There are many different kinds of fertilizers. Many have been used since the very beginning of agriculture. Farms that raise animals have a ready-to-use fertilizer that comes from their daily operations. Organic fertilizer usually comes from animal waste, plant material or wastewater.

Some crops fertilize the soil by themselves. Beans release nitrogen. Crops like alfalfa can be left to break down. But, these methods supply limited amounts of soil nutrients.

Farmers, trade groups and policy organizations generally recognize that manufactured fertilizers are necessary. They say it is simply not possible to create enough food without them.

Mineral fertilizers are not organic. The kind used most are nitrogen-based. Nitrogen from the air is mixed with hydrogen from natural gas. This process produces ammonia gas. Other nutrient elements are then added to the ammonia. Today, the biggest producer of nitrogen fertilizer by far is China. It produces more than twenty-one million tons a year.

Another group of fertilizers is made from phosphorus. Crushing the mineral apatite produces this nutrient. Morocco, the United States and China are major producers of phosphorus.

Potassium, or potash, provides a third important crop nutrient. Once, it was made by burning wood. But it is also present in mineral forms that can be mined.

These substances are the basic products of the fertilizer industry.

Mineral fertilizer may permit agriculture in places with fairly poor soil. It can also stop soil from becoming infertile.

Fertilizer does not provide all the answers to productive agriculture, however. Experts say soil biology and biotechnology must also be studied. And they say farmers must consider environmental concerns and possible health dangers. Too much fertilizer can pollute groundwater and damage lakes, rivers and wetlands.

But, fertilizer does increase crop productivity. Next week, we will talk more about the issues and the demands of the future.

This VOA Special English Agriculture Report was written by Mario Ritter.