In the coming decades, continued population growth, rising meat and
dairy consumption and expanding biofuel use will dramatically increase
the pressure on global agriculture. Even as we face these future
burdens, there have been scattered reports of yield stagnation in the
world’s major cereal crops, including maize, rice and wheat. Here we
study data from ~2.5 million census observations across the globe
extending over the period 1961–2008. We examined the trends in crop
yields for four key global crops: maize, rice, wheat and soybeans.
Although yields continue to increase in many areas, we find that across
24–39% of maize-, rice-, wheat- and
soybean-growing areas, yields either never improve, stagnate or
collapse. This result underscores the challenge of meeting increasing
global agricultural demands.
The solid filled circles in each panel are the observed crop yields from
various global locations to serve as illustrative examples. Colour
codes indicate the crop. The solid curves are the statistical model fits
to the data and similarly colour coded according to the crop type. (a) Yields never improved. (b) Yields stagnating. (c) Yields collapsed. (d) Yields still increasing.
At each political unit where (a) maize, (b) rice, (c) wheat and (d)
soybean crop yields were tracked globally, we determined the status of
their current yield trend. The trends were divided into the six
categories and colour coded. We show in the maps only those areas in the
political unit where the crop was harvested.
Food security and land required for food production largely depend on
rate of yield gain of major cereal crops. Previous projections of food
security are often more optimistic than what historical yield trends
would support. Many econometric projections of future food production
assume compound rates of yield gain, which are not consistent with
historical yield trends. Here we provide a framework to characterize
past yield trends and show that linear trajectories adequately describe
past yield trends, which means the relative rate of gain decreases over
time. Furthermore, there is evidence of yield plateaus or abrupt
decreases in rate of yield gain, including rice in eastern Asia and
wheat in northwest Europe, which account for 31% of total global rice,
wheat and maize production. Estimating future food production capacity
would benefit from an analysis of past crop yield trends based on a
robust statistical analysis framework that evaluates historical yield
trajectories and plateaus.
Staple crops include cereal, oil, sugar, pulses, fibre, tuber plus root
crops. The three major cereal crops are rice, wheat and maize. Slopes of
the fitted trilinear models are shown when significant (Student’s t-test; P<0 .01="" i="">n
Historical trend (1965–2011, n=47 years of yield data) is
indicated with the solid line and yellow data points, and associated
linear-regression equation, coefficient of determination (r2) and Student’s t-test P-value
are shown. Trajectories reported in publications that evaluated future
food production potential based on these projected yield trajectories
are indicated with the dashed lines. Numbers associated with each
trajectory indicate the reference in which this exponential rate was
used. The trajectory based on extrapolation of the 1965–2011 linear
regression is also shown.
Fitted model for each crop–region case is indicated in parenthesis. L,
linear; QP, quadratic plateau; PW, piecewise with (+) increasing or (−)
decreasing rate after breakpoint year; LUP or LLP, linear with upper or
lower plateau; EXP, compound exponential.
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