Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 341

According to The Global Assessment of Human-Induced Soil Degradation
(GLASOD), up to half the world's agricultural land is degraded to some degree
(Oldeman et al. 1991). Degradation of cropland is most extensive in Africa, affecting
65% of cropland, compared with 51% in Latin America and 38% in Asia (CA 2007).
Loss of organic matter and physical degradation of soil not only reduce nutrient
availability but also have significant negative impacts on infiltration and porosity,
which consequently impacts local and regional water productivity; the resilience of
agroecosystems; and global carbon cycles. Accelerated on-farm soil erosion leads to
substantial yield losses and contributes to downstream sedimentation and degrada-
tion of water bodies and infrastructure (Vlek et al. 2010). Nutrient depletion and
chemical degradation of soil are a primary cause of decreasing yields and result in
low on-site water productivity and off-site water pollution. Globally, agriculture is
the main contributor to nonpoint-source water pollution. Water quality problems can
often be as severe as those of water availability. Secondary salinization and water
logging in irrigated areas threaten productivity gains. According to the MEA (2005),
some two-thirds of our ecosystems are degraded. According to FAO (2011a), only
some 10% of the global agricultural land is considered to be under improving condi-
tion; the rest has suffered some degree of degradation, with 70% characterized as
being moderately to highly degraded.
Unfortunately, the problem of agricultural soil degradation is often considered
to be unique to tropical and subtropical regions (Greenland and Lal 1977) or in
developing regions, which is now recognized to be not so. Soil mismanagement and
the traditional physical view of soils have led to serious soil degradation in tem-
perate agroecologies in the industrialized countries (Pretty 2002; Montgomery
2007). For example, in 2002, the European Union initiated the so-called “Thematic
Strategy for Soil Protection,” as it recognized that “Soil is a vital and non-renewable
resource and had not been the subject of comprehensive EU action.” At that time, the
Commissioner of Environment even said that “for too long, we have taken soil for
granted. However, soil erosion, the decline in soil quality and the sealing of soil are
major problems across the EU.” The ensuing discussion in the frame of this strategy
identified eight major soil threats: soil erosion; decline in SOM; soil contamination;
soil sealing; soil compaction; decline in soil biodiversity; salinization; and floods
and landslides. Notwithstanding this, the approach to understanding root causes of
soil degradation in any agricultural environment has remained relatively narrow,
lacking the fuller appreciation of the role of soil biology in the maintenance of soil
health, the role of symbiotic relationships between soil microorganisms and crop
performance, and the disruptive effect of mechanical soil disturbance on soil health
and productive capacity, and on production system resilience (Kassam et al. 2009).
14.3 CAUSES OF DEGRADATION OF AGRICULTURAL SOILS
The root cause of soil degradation in agricultural land use and of decreasing produc-
tivity—as seen in terms of loss of soil health—is the low soil-carbon and soil-life
disrupting paradigm of mechanical soil tillage, which, in order to create conditions
for improved crop performance, debilitates many important soil-mediated ecosys-
tem functions. For the most part, agricultural soils are becoming destructured, our