Fertilizers. Nitrogen Conservation. Commercial Fertilizers

Only natural fertilization was used when primitive agriculture began about ten thousand years ago. After the early farmers planted their crops in newly opened land, they could harvest crops for only about two years until the soil nutrients were depleted. Then the farmers moved their farm plots and cut down the trees and shrubs in an adjacent plot of land, burned these trees and shrubs, and planted their crops for another two years.

At the end of twenty years of fallow, often the farmers could return to the original piece of land. At this time a new crop of trees and shrubs was present, and fertilizer nutrients had accumulated during the twenty-year fallow period.

About five thousand years later farmers had tamed cattle and horses and utilized these animals for transport and plowing. These animals had an asset in addition to transport and plowing: They produced manure. The early farmers observed that plants grew larger and faster where animal and human diong was deposited.

Slowly, as the livestock population increased, more dung was available for use in crop production. The use of manure as fertilizer helped the farmers increase their crop yields and reduce the fallow period that was necessary with slash-and-burn agriculture. Farmers at this early time also kept sheep, goats, and other animals.

As early as 200 BCE the Roman politician Marcus Porcius Cato (234-149 BCE) suggested that to fertilize crops, pigeon dung and other livestock dung could be saved on meadows. Collecting and transporting livestock manure to cropland for food production required significant labor. For com producing only 1,000 kilograms per hectare, the farmers would have had to collect, transport, and apply about 3 metric tons of manure. This was a major task with the equipment available at this early period. One problem with manure is that it contains about 80 percent water, which makes it difficult to handle and transport.

Nitrogen Conservation. One large cow weighing about 800 kilograms will produce about .9 metric tons of manure per year. Collecting and storing this manure for use in crop production are difficult if the nutrients are to be conserved. Nearly 50 percent of the nitrogen in fresh cattle manure is ammonia, and most of this ammonia will volatize and escape within twenty-four hours. To conserve the ammonia, the manure must be immediately placed either underground or in anaerobic conditions in a lagoon.

The liquid manure may be more difficult to handle than stored or composted manure. Composting the manure, however, results in about 75 percent of the nitrogen being lost during storage. The compost is more easily handled than manure in a lagoon.

Livestock manure continues to be a major source of nitrogen, phosphorus, and potassium fertilizers around the world, including in the United States. In the United States, livestock produce about 1.35 billion metric tons of manure. This manure is estimated to contain 6.75 million metric tons of nitrogen fertilizer. If all this manure were effectively applied to agricultural land in the United States, this would be nearly sufficient to provide the 7.2 million metric tons of nitrogen that is required for U.S. crops annually.

U.S. agriculture from 1770 to about 1940 relied primarily on livestock manure and green manures, such as sweet clover and vetch, to provide the nitrogen needed for crop production. Corn yields during this period ranged from 1,000 to 1,500 kilograms per hectare. Farmers during this period would plant one hectare to a legume, such as clover, and one hectare to corn.

The following year, the hectare in the legume was plowed under and planted to com, and the com hectare was planted to clover or a related legume. The legume that was plowed under before planting the corn provided from 50 to 100 kilograms of nitrogen per hectare. In addition, some livestock manure was applied to the corn acreage, depending on the farming system.

Cave dwellings in the town of Goreme in Turkey. Homes are carved out of sandstone that is sculpted into towers by erosion. The inhabitants create pigeon roosts above their homes and harvest the guano for use as fertilizer

During World War IT, when large quantities of explosives were produced, it was discovered that nitrate is one of the ingredients in explosives. Nitrate, like other nitrogen products, such as ammonia, can also be an effective fertilizer.

Commercial Fertilizers. After World War II, commercial nitrogen, phosphorus, and potassium fertilizers began to be applied to U.S. and other croplands. Initially the amounts were extremely small. In 1945, for example, only about 8 kilograms of nitrogen per hectare were applied to U.S. corn acreage. The quantity of nitrogen fertilizer applied to U.S. com increased to about 150 kilograms per hectare by 1985 and continues near this rate as of 2000. (See table 1.) Commercial phosphorus and potassium fertilizer nutrients also increased from 6 to 8 kilograms per hectare to about 60 kilograms per hectare in 2000. (See table 1.).

The use of commercial fertilizers eliminated the need for 2 hectares to produce 1 hectare of com. One hectare of a legume to produce nitrogen nutrients for corn production was no longer needed. Of course, large quantities of fossil energy are necessary to produce fertilizers, especially nitrogen fertilizer. For example, the production of 1 kilogram of nitrogen fertilizer requires about 18,690 kilocalories or slightly more than the energy in 2 liters of gasoline.

To illustrate how rapidly agricultural technology changed after commercial fertilizers were discovered and produced, the energy inputs just for the nitrogen fertilizer today are greater than the total fossil energy inputs in producing corn in 1945. Corn yields have increased dramatically since 1945, when corn yields were about 2,000 kilograms per hectare. Corn yields in the United States as of 2000 were 8,600 kilograms per hectare. (See Table 1.)

Worldwide, about 80 million metric tons of nitrogen are applied to crops. This nitrogen is vital to crop production. Even with all the nitrogen, phosphorus, potassium, and other nutrients applied in world agriculture, the World Health Organization reports that more than 3 billion people are malnourished in the world. In addition, the Food and Agricultural Organization of the United Nations reports that per-capita grain production has been declining for nearly two decades. Grains are estimated to provide 80 percent of the world's food. In addition to shortages of cropland and irrigation water, per-capita fertilizer use during the past decade has declined more than 20 percent.

The food shortage cannot be blamed only on lack of fertilizers. Cropland is suffering from severe erosion and degradation, and there are severe shortages of freshwater, especially freshwater for irrigation.