|
What Is This Indicator, and Why Is It Important?
This indicator reports the yield of corn, soybeans, wheat,
hay, and cotton, as an index with 1975 as the base year. Values
above 1.0 indicate higher yields, typically measured as tons
or bushels per acre, than in 1975; values below 1.0 indicate
lower yields than in 1975. These five crops account for about
90% of harvested acreage in the United States and more than
half the monetary value of all crops (see
Monetary Value of Agricultural Production).
Increasing the amount of food grown per acre has allowed
U.S. agriculture to produce more food and fiber without corresponding
increases in farm acreage. The total acreage used for agricultural
production has declined slightly over the past half-century
(see Total Cropland), and a significant
increase in the acreage devoted to agriculture is generally
considered unlikely.
What Do the Data Show? Per-acre yields of
the major crops grown in the United States have increased
dramatically over the past 50 years. Yields for three of the
five major crops (corn, wheat, and cotton) more than doubled
over this period, with corn yields increasing almost fourfold.
Of these five major crops, soybean yields increased the least,
but even they nearly doubled over the period.
Discussion Increases in crop yields are
believed to result from a combination of factors. These include
improvements in breeding, changes in cultivation practices,
and increased use of a variety of inputs, including pesticides
and fertilizers. More intensive use of farmland is thought
to play an important role in improving yields, but it may
also have negative effects, such as increased concentrations
of nitrogen, phosphorus, or pesticides in streams, lakes,
and coastal waters (see the Farmland nitrogen
and phosphorus indicators,
the Farmland pesticide indicator,
and the Core National nitrogen
indicator).
|
