Agriculture and Environment: Corn (Maize)

Environmental Impacts of Production: Use of Agrochemical Inputs

A range of pesticides is used widely on corn in the United States and elsewhere.

Between 1964 (when Rachel Carson wrote Silent Spring) and 1991, herbicide use on corn in the United States grew from just under 12 kilograms to just less than 100 kilograms of active ingredients per hectare (Runge and Stuart 1998).

In 1992 nearly 70% of the area planted to corn in the United States was treated with the herbicide atrazine (Ribaudo 1993). Cornfield herbicides (like atrazine) as a class of farm chemicals accounted for 47% of total agricultural pesticide use in the nation in the early 1990s. Weed suppressants were applied to about 95% of all corn acres (USDA 1991,1992).

Atrazine persists in the soil, however, and moves in surface and ground water. Atrazine and nitrogen are thought to be one of the main contributors to the "dead zone" in the Gulf of Mexico and a major polluter of underground water supplies throughout the corn belt of the United States.

During the same period the rates of application of insecticides more than doubled from less than 1.5 kilograms per hectare to slightly less than 3.5 kilograms per hectare (Runge and Stuart 1998). The important point here, however, is that the composition of the insecticides changed dramatically away from some of the most hazardous chemicals.

Fertilizers are used more commonly in the production of corn than they were 50 years ago. About 95% of all corn planted in the United States receives supplemental nitrogen. Fertilizers containing phosphate and potash are used on 75-80% of all corn. In all, corn accounts for almost half of the total fertilizer use in the United States (by comparison, wheat has 14% and soybeans 6%).

Fertilizer use is one of the main causes of water pollution and eutrophication in the United States. By 1990 the U.S. Environmental Protection Agency estimated that roughly 650 different active ingredients were for sale as pesticides, down from 1,400 previously. However, about 15-20 new materials are added each year in the United States (Runge and Stuart 1998).

Worst-case estimates of the impacts of eliminating the use of all agrochemicals suggest yield declines on the order of 53% for crops such as corn and 37% for soybeans (Knutson et al. 1990). However, according to Ayer and Conklin (1990) it is likely that these estimates "tend to underestimate the ability of producers to substitute other methods of pest and disease control, such as crop rotations, and to more carefully time and apply new and existing chemicals based on when and where they are most needed."

Integrated pest management (IPM), cropping management, and precision agriculture are important new approaches, but current technology continues to rely on existing pesticides. Analysis also shows that reduction in the use of pesticides will affect the profits of farms of different sizes in different ways. There is good evidence that pesticides used on medium and especially larger farms are being substituted for other inputs such as labour and mechanical weeding (Runge and Stuart 1998).

A bigger issue, however, is pest resistance. By 2000, producers in the U.S. were using 20 times more pesticides and losing twice as much of their crop to pests as they were in 1950. This was one of the main attractions of Bt corn. It produced its own insecticides. However, by as early as 1997, 8 insect pests in the U.S. had become resistant to Bt (Conway 1997, as cited in Hawken et al. 1999).