Abstract—Global food production has grown
faster than population in recent decades, due largely to improved
seeds and increased use of fertilizer and irrigation. Soil degradation which
has slowed yield growth in some areas, depends on farmers'
incentives to adopt conservation practices, but does not threaten
food security at the global level.
Introduction
Increased resource use and improvements in technology and
efficiency have increased global food production more rapidly than
population in recent decades, but 800 million people remain food
insecure (fig. 3.5.1).
Meanwhile, growth in global agricultural productivity appears
to be slowing, and land degradation has been blamed as a contributing
factor. The interactions between biophysical processes and economic
choices are complex, and data necessary to measure these processes
are scarce, so estimates of land degradation's impact on productivity
vary widely—as high as 8 percent per year due to soil erosion
alone in the United States and as low as 0.1 percent per year due
to all forms of soil degradation on a global scale. These differences
make it difficult to assess potential impacts on food security or
the environment, and thus the appropriate nature and magnitude of
policy response.
Improvements in economic analysis of geographic data offer new
insights. ERS recently studied how agricultural productivity varies
with differences and changes in land quality, and how degradation-induced
changes in productivity affect food security. Results indicate that
land degradation does not threaten productivity growth and food
security at the global level. But problems do exist in some areas,
especially where resources are fragile and markets function poorly.
World Food Supplies Have Increased Faster Than Demand…
So Far
Global demand for food has increased rapidly since the
mid-20th century as a result of growth in population, income, and
other factors. The world's population has doubled over the
past four decades, to 6.4 billion in 2004. World population growth
has slowed in recent years, but is still projected to reach 9 billion
by about 2050. Per capita income is projected to grow by an average
of about 2 percent per year over the next decade, continuing recent
trends. Based on these factors, the Food and Agriculture Organization of the United Nations
(FAO) and the International Food Policy Research Institute (IFPRI)
project that global demand for cereals will increase by 1.2-1.3
percent per year over the next several decades, while demand for
meat will increase slightly faster. Most of the increased demand
is projected to come from developing countries, especially from
Asia.
Between 1961 and 1999, the FAO's aggregate crop production
index grew at an average annual rate of 2.3 percent. Crop production
per capita has increased for the world as a whole (at an average
rate of 0.6 percent per year), and in all regions except Africa.
Global cereal production per capita (fig. 3.5.2) has fallen since
1984, with steady increases in Asia offset by long-term declines
in sub-Saharan Africa and more recent declines in North America,
Europe, Oceania, and the former Soviet Union.
But these more recent declines were due not to binding resource
and technology constraints but rather to the combined effects of
weak grain prices, policy reforms, and institutional change. (See
box for definitions)
Definitions
Land quality—The ability
of land to produce goods and services that are valued by humans.
This ability derives from inherent/natural attributes of soils
(e.g., depth and fertility), water, climate, topography, vegetation,
and hydrology, as well as "produced" attributes
such as infrastructure (e.g., irrigation) and proximity to population
centers.
Land degradation—Changes
in the quality of soil, water, and other characteristics that
reduce the ability of land to produce goods and services that
are valued by humans. Some forms of land degradation, such as
nutrient depletion, can be halted and even reversed relatively
easily—for example, by balancing nutrient application
with that taken up in harvested crops. Other forms of land degradation,
such as erosion or salinization, can be slowed or halted through
appropriate management practices, but are generally very costly
to reverse.
Agricultural productivity—A
measure of the amount of agricultural output that can be produced
with a given level of inputs. Agricultural productivity can
be defined and measured in a variety of ways, including the
amount of a single output per unit of a single input (e.g.,
tons of wheat per acre or per worker), or in terms of an index
of multiple outputs relative to an index of multiple inputs
(e.g., the value of all farm outputs divided by the value of
all farm inputs). (See AREI Chapter 3.4)
IFPRI projects that world cereal production will increase by
about 1.3 percent per year through 2020, enough to raise per capita
cereal
production by about 0.2 percent annually. Such increases have the
potential to satisfy projected food demands (and nutritional requirements)
for the foreseeable future, but actual patterns will depend on
the availability and quality of productive resources, as well
as market
incentives, policy measures, and research investments.
Area Growth Is Slowing, So Yields Will Become More Important
FAO reports that the total area devoted to crops worldwide
has increased by about 0.3 percent per year since 1961, to 3.8 billion
acres in 2002. Growth has slowed markedly in the past decade, to
about 0.1 percent per year, as a result of weak grain prices, deliberate
policy reforms (in North America and Europe), and institutional
change (in the former Soviet Union). FAO estimates that an additional
6.7 billion acres currently in other uses are suitable for crop
production, but this land is unevenly distributed, and includes
land with relatively low yield potential and significant environmental
value.
Given economic and environmental constraints on cropland expansion,
the bulk of increased crop production will need to come from increased
yields on existing cropland. FAO data indicate that world cereal
yields rose by about 2.5 percent per year from 1961 to 1990, but
growth slowed to 1.1 percent per year in the 1990s (fig. 3.5.3).
As a result of reduced input use (reflecting low cereal prices),
market and infrastructure constraints, and low levels of investment
in agricultural research and technology, IFPRI and FAO project that
yield growth will slow further to about 0.8 percent per year over
the next several decades (see AREI Chapter
3.4).
Genetic improvements have contributed greatly to gains in yields
and production of major crops, beginning with wheat, rice, and maize
in the 1960s. About half of all recent gains in crop yields are
attributable to genetic improvements. By the 1990s, 90 percent of
wheat acreage in developing countries was in scientifically bred
varieties, as was 74 percent of land in rice and 62 percent of land
in maize. In developed countries, 100 percent of land in wheat,
maize, and rice was in scientifically bred varieties by the 1990s
(and probably even earlier). Gains from genetic improvements will
continue, but likely at slower rates and increasing costs, as gains
in input responsiveness have already been largely exploited (see
AREI Chapter 3.1).
FAO data indicate that increased fertilizer consumption accounted
for one-third of the growth in world cereal production in the 1970s
and 1980s. Growth in fertilizer consumption per hectare of cropland
has been slowing, however, from a global average annual increase
of about 9 percent in the 1960s to an average annual decline of
about 0.1 percent in the 1990s. Among developing regions, per-hectare
fertilizer consumption increased most rapidly in land-scarce Asia
and most slowly in Africa. Growth in fertilizer consumption also
slowed (and even declined) in developed regions, but remains at
relatively high levels. Future fertilizer use will need to balance
its potential to mitigate onsite land degradation (soil fertility
depletion) with the risk of increased offsite degradation (impacts
on water quality, for example) (see AREI
Chapter 4.4).
Water will be a critical factor limiting crop production in the
21st century. Agriculture accounts for more than 70 percent of water
withdrawals worldwide, and over 90 percent of withdrawals in low-income
developing countries. The total extent of irrigated cropland worldwide
has grown at an average annual rate of 1.9 percent since 1961, although
this rate has been declining. About 18 percent of total cropland
area is now irrigated, most of it in Asia. Population growth and
the increasing cost of developing new sources of water will place
increasing pressure on world water supplies in the coming decades.
Even as demand for irrigation water increases, farmers face growing
competition for water from urban and industrial users, and to protect
ecological functions. In addition, waterlogging and salinization
of irrigated land threaten future crop yields in some areas (see
AREI Chapters 2.1 and
4.6).
The Intergovernmental Panel on Climate Change (IPCC), representing
a broad scientific consensus, projects that the earth's climate
will change significantly over the course of the 21st century because
of increasing concentrations of carbon dioxide and other "greenhouse"
gases in the atmosphere. Global crop production would be little
affected in aggregate, but potential impacts and adjustment costs
vary widely, and could be quite high in some areas. For example,
changing patterns of precipitation, temperature, and length of growing
season resulting from a doubling of atmospheric concentrations of
carbon dioxide would tend to increase agricultural production in
temperate latitudes and decrease it in the tropics.
ERS recently examined regional differences in cropland quality
using geographic data on land cover, soil, and climate. About 13
percent of global land area has soils and climate that are of high
quality for agricultural production (fig. 3.5.4).
Figure 3.5.4 - Land quality classes Source: USDA Natural Resources Conservation
Service, World Soil Resources Office
Land quality changes over time as a result of natural and human-induced
processes, but data on these changes are extremely limited. Only
one global assessment has been done to date: the Global Land Assessment
of Degradation (GLASOD) in 1991 (Oldeman et al., 1991). Based on
the judgment of over 250 experts around the world, GLASOD estimated
that 38 percent of the world's cropland had been degraded
to some extent as a result of human activity since World War II.
GLASOD identified erosion as the main cause of degradation (affecting
4 billion acres, mostly in Asia and Africa), followed by loss of
soil nutrients (336 million acres, mostly in South America and Africa)
and salinization (190 million acres, mostly in Asia).
Previous studies have sought to measure land quality's role
in explaining differences in agricultural productivity between countries,
but have only considered factors such as climate and irrigation
because of data constraints. ERS researchers incorporated the role
of soil characteristics as well, and found that the quality of labor,
institutions, and infrastructure also affect productivity. Holding
other factors constant, ERS found that the productivity of agricultural
labor is generally 20-30 percent higher in countries with good soils
and climate than it is in countries with poor soils and climate.
Based on climate and inherent soil properties, scientists with
USDA's Natural Resources Conservation Service have estimated water-induced
erosion rates that vary widely by crop production area, soil, and
region, but range in most cases between 5 and 7 tons per acre per
year. Den Biggelaar et al. (2004) recently reviewed over 300 plot-level
experiments on yield losses due to soil erosion from around the
world and found that for most crops, soils, and regions, yields
decline by 0.01-0.04 percent per ton of soil loss. Combining these
erosion rates and yield impacts allows estimates of potential annual
yield losses to erosion in the absence of changes in farming practices.
These estimates vary widely by crop and region. For example, corn
yield losses to soil erosion range from an average of 0.2 percent
per year in North America to 0.9 percent per year in Latin America.
Differences in crop coverage limit comparison of regional totals,
but aggregating across regions and crops generates an estimated
potential erosion-induced loss of 0.3 percent per year in the value
of crop production.
These estimates represent potential impacts of water-induced erosion
for selected crops on soils and in regions for which plot-level
data were available. Estimated impacts would likely be larger if
other degradation processes and crops were considered. On the other
hand, actual impacts may also be smaller for any given crop and
degradation process to the extent that farmers take steps to avoid,
reduce, or reverse land degradation and its impacts.
Farmers Have Incentives To Address Land Degradation
Farmers choose between alternative technologies based on
biophysical characteristics such as soil quality and access to water,
as well as social and economic characteristics that include land
tenure, income and wealth, and access to credit and information
(see AREI Chapter 4.1).
Understanding of farmers' incentives is thus critical. For
example, practices generating high net returns today may not do
so indefinitely if they result in land degradation over time. But
practices that reduce land degradation and offer higher net returns
over time may require initial investments that inhibit adoption
in the short term. ERS researchers explored such tradeoffs in a
dynamic analysis of soils and economic data from the north-central
United States. Results suggest that actual yield losses under practices
that maximize net returns over the long run will typically be lower
than potential losses derived from agronomic studies, and are generally
less than 0.1 percent per year in the north-central United States.
In order to benefit from a conservation practice that requires
an initial investment, a farmer must anticipate farming a particular
plot of land long enough to realize the benefit. A farmer with a
lease that expires after 1 year, for example, receives only a fraction
of the benefit that would be realized by a farmer with a 5-year
lease, and both receive less benefit than would a farmer who owns
his or her land. ERS research confirms that conservation choices
by U.S. corn producers vary significantly with land tenure and the
timing of costs and returns to different practices.
Even with secure tenure and the prospect of long-term gains, a
farmer might still be unable to afford the initial investment needed
to adopt a particular conservation practice, perhaps due to poverty
or constraints on access to credit. A farmer might also lack the
information needed to compare longrun costs and benefits of alternative
practices. Under such market imperfections, optimal choices by farmers
would likely result in yield losses greater than those estimated
under well-functioning markets, but still less than losses with
no farmer response (fig. 3.5.5).
Farmers' responses to economic incentives lend support to
the lower range of previous estimates of yield losses to land degradation.
This does not mean that such losses are unimportant—just
that they have historically been masked by increases in input use
and improvements in technology and efficiency. Problems do exist
in some areas, especially where resources are fragile and markets
function poorly. Given projections that yield growth is slowing,
yield losses to land degradation are likely to become more of a
concern in the future.
Policymakers Play a Critical Role in Shaping Farmers'
Incentives
When markets function well, private incentives to reduce
land degradation will likely suffice to address onfarm productivity
losses. When markets function poorly, private incentives are diminished.
Policymakers play a critical role in establishing and maintaining
the physical and institutional infrastructure necessary to allow
markets to function effectively. This includes transportation and
communication networks that facilitate input and output markets,
as well as stable and transparent legal and political institutions
that encourage longer-term planning horizons. Clear and enforceable
property rights are critical in providing incentives for landowners
to conserve or enhance land quality.
In some circumstances, it may also be necessary to offer direct
payments to enhance farmers' incentives to adopt conservation
practices. Such payments are well-established in conservation programs
in the United States and in many other countries, but require careful
attention to the timing and magnitude of payments in order to sustain
incentives (see AREI Chapter
5.1). While such approaches pose daunting challenges in terms
of implementation, they may also help achieve the broader agricultural,
environmental, and food security objectives of the World Food Summit,
the United Nations Convention to Combat Desertification, and other
multilateral initiatives.
References and further information
den Biggelaar, Christoffel, Rattan Lal, Keith Wiebe, Hari Eswaran,
Vince Breneman, and Paul Reich (2004). "The Global Impact
of Soil Erosion on Productivity," Advances in Agronomy 81:
1–95.
Eswaran, Hari, and Paul Reich (2001). World
Soil Resources Map Index, U.S. Dept. Agr., Natural Resources
Conservation Service.
Oldeman, L.R., R.T.A. Hakkeling, and W.G. Sombroek (1991). "World
Map of the Status of Human-Induced Soil Degradation: A Brief Explanatory
Note." International Soil Reference and Information Centre
and United Nations Environment Programme.
Wiebe, Keith (ed.) (2003). Land Quality, Agricultural Productivity,
and Food Security: Biophysical Processes and Economic Choices
at Local, Regional, and Global Scales. Cheltenham (UK) and Northampton,
MA (U.S.): Edward Elgar Publishing Co.
