Principles of Soil Management - Principles of Sustainable Soil Management in Agroecosystems - page 2

1.1 INTRODUCTION
World soil resources are finite, unequally distributed among diverse regions, fragile
and prone to degradation by land misuse and soil mismanagement, and vulnerable to
extreme events related to the abrupt climate change (ACC). The land area prone to
degradation processes is estimated at 3500 Mha affecting livelihood and wellbeing
of a large proportion of underprivileged population living in regions characterized
by a harsh climate and agriculturally marginal lands (Bai et al. 2008). Further, the
resource-poor farmers are unable to invest in soil and water conservation techniques
and in replenishing soil fertility. Thus, a perpetual use of extractive farming prac-
tices by small landholders of the tropics and subtropics and cutting corners for quick
economic returns by large-scale commercial farmers have exacerbated the problem
of a widespread distribution of depleted and degraded soils, often with a truncated
topsoil layer because of the accelerated soil erosion (Lal 2001, 2003). Whereas the
area equipped for supplementary irrigation has expanded to ~287 Mha (FAO 2012),
it has also caused severe problems of groundwater depletion (Lal and Stewart 2012)
and secondary salinization (Oldeman 1994). Yet, the food production must be dras-
tically increased to feed a world population of 10 billion (Borlaug and Dowswell
2005), to meet the food demands of the growing population and changing the dietary
preferences toward more animal-based than plant-based diet. By 2030, global cereal
demand for food and animal feed is expected to be 2.8 billion Mg/year, which is dou-
ble the production in 2005 (Lobell et al. 2009). With a small, if any, scope for bring-
ing new land under cultivation, productivity must be increased from the existing
agricultural land per unit area, time, and use of energy-based input (i.e., fertilizer,
irrigation). In accord with the concept of zero net land degradation (Lal et al. 2012),
any new land degradation must be negated by restoration of prior degraded land.
Therefore, the objective of this chapter is to describe the basic principles of soil man-
agement in the context of the present status of agronomic productivity and the availability
of the soil and water resources to meet the growing demands for global food production.
1.2 AGRONOMIC YIELD TRENDS AND RESOURCE USE
The world cereal grain yield increased 2.63 times from 1353 kg/ha in 1961 to 3564
kg/ha in 2010 ( Table 1.1 ). The highest increase of 3.9 times occurred in East Asia,
from 1414 kg/ha in 1961 to 5497 kg/ha in 2010. The lowest increase of 1.3 times
occurred in Central (middle) Africa from 713 kg/ha in 1961 to 953 kg/ha in 2010
(Table 1.1). The cereal yield in Africa, ranging from 810 kg/ha in 1961 to 1501 kg/ha
in 2010, has lagged behind that of all other continents ( Figure 1.1 ). Indeed, the Green
Revolution of the 1960s and 1970s bypassed the entire continent of Africa. Despite
the adoption of improved varieties, agronomic yields in Sub-Saharan Africa have
stagnated probably because of the widespread problem of soil degradation and nutri-
ent depletion. The adverse effects of degraded/depleted soils have been exacerbated
by the harsh and uncertain climate. For example, the fertilizer use in Africa is the
lowest, at 3.2 × 10 6 Mg of NPK. In comparison, nutrient (NPK) use in Asia is ~90 ×
10 6 Mg or 63.5% of the world consumption ( Table 1.2 ). Indeed, the rate of fertilizer
(NPK nutrients) use in Africa is merely 13 kg/ha, compared with 156 kg/ha in Asia