The use of fertilizers and pesticides is extensive in United States’ (US) agriculture, and crop production has been aided by these inputs for some time. As demand for crops like corn and soybeans grew, so did the land area dedicated for their production. Fertilizer and pesticide use increased alongside it. Nutrients essential for plant growth are supplied by fertilizers, and pesticides kill plants and animals which harm crops, helping boost production.
Fertilizers and pesticides have a long history of use in the US and are considered important components of modern farming. Fertilizers are used to supply crops with essential nutrients for growth and to help replenish the soil of key elements once a crop has extracted them during the growth process. The use of manure for nutrient application was the predominant fertilizer method for quite some time, but chemically-based fertilizers rapidly gained popularity starting in the 1940’s. Nitrogen was used extensively during World War II in the making of explosives, and after the war ended factories started producing fertilizer from the nitrogen supply. Today, fertilizers are available in many forms, and are widely used to aid plant growth and increase crop production.
Pesticides are chemicals which are used to control weeds and insects which pose a threat to crop production. If left unchecked, weeds can quickly outcompete the crop for essential light, water, and nutrients. Many kinds of insects feed on crops, damaging plants and limiting production. Use of chemicals for pest control dates back to the turn of the 20th century, but applications really took off in the mid-1940s after the advent of the insecticide Dichlorodiphenyltrichloroethane, more commonly known as DDT, and weed-killer 2,4-Dichlorophenoxyacetic acid, or 2,4-D. Popular herbicides like Atrazine and Glyphosate came onto the market in the following decades, along with hundreds of other pesticide formulations, with chemical applications increasing threefold between 1960 and 1981.
Corn, soybeans, wheat, and cotton are the top crops in terms of production acreage in the US. Corn and soybeans dominate the other two. This piece will focus on their production trends and the correlations with fertilizer and pesticide use. Sixty five years ago, harvested area of corn sat around 77 million acres, and average US corn yield was just 54 bushels per acre. Presently, corn acreage is at 82.7 million acres, and yield now sits at a median of over 170 bushels per acre.
US soybean yield has also climbed like corn’s, but with much larger jumps in acreage. In the 1940s, soybean harvested area was at just 10.7 million acres. Today, there are around 89.5 million acres harvested, representing an increase of 736 percent. Soybean yield was less than 20 bushels per acre in the 1940s, but now averages 49 bushels per acre. Corn and soybean production has increased largely because of heightened demand, enhancements in farming technology, and developments of genetically engineered (GE) varieties.
In response to demand which resulted in greater plantings, farmers began to apply more fertilizers and spray more pesticides on the growing production area. With more applications also came greater spending on such inputs. Between 1985 and 2016, adjusted for inflation, US farm expenditures on fertilizers increased from $8.6 billion to $23.5 billion, and spending on chemicals swelled from $3.9 to $15.2 billion. However, expenditures have started to level off or slowly drop as farmers employ an integrated basket of control measures and variable-rate nutrient applications.
The three broad categories of fertilizers are nitrogen, phosphorus, and potassium (NPK)-based. Rates of their combined applications grew after 1960, but have started to level off because of better practices. In 1960, total application rate was 46 pounds per acre per year (lb/acre/yr). By 2004, this rate had reached 146 lb/acre/yr, and now sits between 130-140 lb/acre/yr.
Nitrogen has had the highest application rate of the three nutrients and the biggest jump in use—in 1960, nitrogen application averaged 17 lb/acre/yr, reaching a peak rate of 82.5 lb/acre/yr in 2007. The nutrient accounts for approximately 59 percent of total fertilizer weight. Use of phosphorus and potassium (potash) has been pretty stable since 1960, with both nutrients maintaining rates between 25 and 36 lb/acre/yr since then. They account for around 20 and 21 percent of total fertilizer treatments, respectively.
The four aforementioned crops combined receive approximately 60 percent of all NPK fertilizers. Around 40 percent of total commercially applied NPK is put on corn, whose production is largely concentrated in the Midwestern states. Most soybeans are produced in this region as well, but the crop accounts for less than 10 percent of total NPK use. This is mainly because soybeans are legumes and can fix their own nitrogen to use throughout the growing season. Corn needs more fertilization because it can’t sequester it’s own nitrogen, and harvesting the crop usually requires taking most of the plant, which results in more nutrients being removed from the field at the end of the season that must be replenished.
Pesticide use rose rapidly in the US after 1960 as acreage expanded to meet increasing food demand. With the low price of pesticides relative to other pest control measures like tillage, application increased. Usage has fluctuated over the past 30 years and is largely correlated with crop prices, weather, pesticide regulations, and inventions of new pest resistant GE seed varieties. Today, around $15 billion is spent annually on pesticides, representing a five-fold increase since 1960 when adjusting for inflation.
Sixty years ago, herbicides accounted for around 18 percent of pesticide applications by volume on US crops, and insecticides represented 58 percent. These figures are much different now, with herbicide and insecticide use accounting for approximately 76 and 6 percent of total applications, respectively. Adoption of herbicides grew due to low prices and availability of different chemicals, while insecticide use decreased as formulations became more effective and less product was needed to achieve the intended result. Presently, corn, soybeans, wheat, and cotton receive about 80 percent of total pesticide volume. Corn dominates pesticide usage with a share of approximately 39 percent. Soybeans come in second, with 22 percent of total volume being applied to the crop. These large shares of total volume represent the high demand for the crops in livestock feed. Corn’s role in ethanol fuel production has also helped increase the crop’s acreage and therefore chemical applications.
When GE seeds came onto the US agricultural scene in the late 1990s, there were thoughts that the new technology would increase production while decreasing the amount of pesticides applied. Scientists engineered seeds for plants that could withstand the spraying of the herbicide glyphosate, allowing farmers to spray over growing corn while killing weeds. Others were manufactured to produce their own insecticide known as Bacillus thuringiensis (Bt), with the hopes of limiting insecticide spraying because the GE crops could now produce their own chemical defenses.
However, the opposite appears to be happening. At first, GE technology did decrease the amount of pesticide applications, but this didn’t last long. The reliance on fewer types of herbicides and the repeated applications of them has resulted in resistant weeds which are essentially immune to the chemicals. After a herbicide application fails to control certain weeds, they produce seeds that will grow into even more weeds the next season, resulting in increased herbicide applications. The same holds true for Bt crops—some insects are evolving to continue to feed on plants regardless of any GE technology that is present. While GE crops have helped boost production, it has come at the expense of pesticide resistance issues.
Fertilizers and pesticides are commonplace in US agriculture, and production would not be where it is today without these inputs. Usage of and farm expenditures on fertilizers and pesticides increased greatly after the 1960s as production area grew, but has somewhat leveled off because of diminishing returns and better practices. Growing demand for corn and soybeans will likely maintain strong total input requirements, even if usage per acre decreases due to rising costs and adoption of better practices. Crops will always need nutrients, and there will continue to be pests which need to be controlled. While some negative effects come along with fertilizer and pesticide use, agriculture in the US and globally cannot achieve production sufficient for a population forecast to reach 10 billion by 2050 without it.