Fertility can refer to the ability of soil to sustain plant growth, or it can refer to the number of live births occurring in a population.

Fertile Soil

Agronomists, or people who study the uses of plants, use the term to refer to soil. Plants grow easily in fertile soil because it contains large amounts of nutrients. These nutrients, which help keep plants healthy, come from minerals and decaying plant and animal matter. Minerals may have been deposited in the soil during the last glacial period, or Ice Age.

Fertilizers can be added to soil to increase fertility. Fertilizers contain nutrients such as phosphorous, nitrogen, and potassium. Composted plant matter, called humus, is a natural fertilizer that can improve soil fertility. Manure, or the droppings of some animals such as bats or cows, is also an excellent fertilizer. Many companies manufacture fertilizers for use on specific crops. These fertilizers can be applied directly to the soil or to the plants.

Poor farming techniques, certain grazing practices, and erosion can make the soil less fertile. Planting a single crop, year after year, can drain the soil of nutrients. Overgrazing by too many cows, goats, or sheep can prevent new grasses from growing. Erosion allows the soil to either blow away by wind or drain away by water.

Fertile soil is usually found in river basins or in places where glaciers deposited minerals during the last ice age. Valleys and plains are usually more fertile than mountains. The Pampas, for example, is an extremely fertile plains region in South America. The Pampas includes parts of Argentina, Brazil, and Uruguay. The Pampas supports both farming and ranching.

Human Fertility

For demographers—people who study population statistics—fertility means the number of live births occurring in a population.

The general fertility rate is the number of live births per 1,000 birthing people of childbearing age (usually ages 15 to 44) in a given year. Governments keep track of the general fertility rate to determine if their population will grow, shrink, or stay the same size. This determines such things as how much food needs to be produced, what sort of public transportation is needed, and how healthcare is addressed.

Fertility rates tend to be lower in high-income countries (HICs), such as the United States, than in low- and middle-income countries (LMICs). There are many reasons for this. Mothers and children have greater access to health care in HICs. This means children's mortality rates, or the number of children who die before turning five, are much lower. Women also have greater access to family planning services. The fertility rate in the developed, HIC of South Korea, for instance, is about 1.2. This means that most women have one child. The fertility rate in neighboring North Korea is nearly two, meaning most women have two children. North Korea is an LMIC.

Women in HIC have access to more education and professional development. Many women choose to go to school or get a job instead of having children at a young age. Many choose not to have children at all. This lowers the fertility rate in HICs.

HICs usually have a school system for young children. In LMICs, young children may work to support their families instead of going to school. The fertility rate may rise because more children means more workers.

The tendency for HICs to have lower birth rates is not always true. The United States has the highest birth rate of all HICs, at about two.

In order to maintain a stable population, each woman must bear two children—one to replace each parent. High fertility rates—where most women give birth to more than two healthy babies—can lead to a population boom. Low fertility rates—where most women give birth to one child or no children—can lead to a dwindling population.

Some nations want to increase their fertility rate. Japan has one of the lowest fertility rates in the world. The country's population is declining and its average age is getting older.

Some want to decrease their fertility rate. China's famous "one child policy" was a good example of this. China is the most populous country in the world. The Chinese government believes that lowering the fertility rate would increase the resources, such as education and jobs, available to its citizens. In the late 1970s, China set taxes and economic fines for families with more than one child. (The fines and taxes do not apply to ethnic minorities and other groups, such as rural farm families.) As a result, the fertility rate in China has dropped. China now has a lower fertility rate than the United States. The policy ended in 2016, and now all women are allowed to have two children.

Fourteen countries have fertility rates with at least six children per woman. These countries are Afghanistan, Angola, Burkina Faso, Burundi, Chad, the Democratic Republic of the Congo, Guinea-Bissau, Liberia, Mali, Niger, Sierra Leone, Somalia, Timor Leste, and Uganda.

Fertility does not always correspond to population. Despite their high fertility rates, the countries listed above make up less than five percent of the world's population. Countries with much larger populations, such as India, China, and the United States, have lower fertility rates.