Diversifying crop rotations with temporary grasslands - Université de ...

A GENERAL INTRODUCTION
A.I THE CHALLENGES OF SUSTAINABLE AGRICULTURE
Food production is one of the most essential human activities. The biggest part of food
production is based on plants grown as crops that are directly eaten or fed to animals.
Moreover, agriculture is the most important land use worldwide covering about 37% of the
earth’s land surface (Benton, 2007). The worldwide demand of crop products is strongly
increasing due to both the growth of the human population and the changing human diets
towards higher consumption of meat and milk products (Pingali, 2007). In 2050, global food
demand is expected to increase by 50% compared to 2000 (Tilman et al., 2001; Green et al.,
2005). In the past decades, agricultural production was able to follow the increasing demands,
at least on the global scale. Global agricultural food production could e.g. be doubled from
1960 to 1995 (Tilman, 1999), leading even to periods of a global overproduction, although the
problem of hunger could not be solved in many poor countries. Some of the increases in the
global agricultural production can be attributed to a 12-18% increase in world cropland area,
but the biggest part resulted from ‘Green Revolution’ technologies, including the use of
chemical fertilizers, pesticides, high-yielding crop cultivars, mechanization and irrigation
(Matson et al., 1997; Tilman et al., 2002; Foley et al., 2005). The doubling of food production
from 1960 to 1995 was associated with an about 7-fold increase in global nitrogen
fertilization, a 3-4-fold increase in phosphorus fertilization, and a 1.7-2-fold increase in the
surface of irrigated land (Tilman, 1999; Green et al., 2005) and an 7-9-fold increase in the
global pesticide use (WHO, 1990, p. 26; Green et al., 2005).
These developments had various environmental and social impacts challenging the
sustainability of modern agriculture. ‘Over the past 50 years, humans have changed
ecosystems more rapidly and extensively than in any comparable period of time in human
history, largely to meet rapidly growing demands for food, fresh water, timber, fibre and fuel.
This has resulted in a substantial and largely irreversible loss in the diversity of life on Earth’
(MEA, 2005).
Agricultural practices may cause soil erosion, nutrients leaching or desertification
deteriorating the soil resources for future farming (long-term profitability) and accelerating the
euthrophication of terrestrial and aquatic ecosystems (Vitousek et al., 1997; Csathó et al.,
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