Agriculture Reference
In-Depth Information
principles. Notable among these is the “law of the minimum” by Sprengel (1832) and
Justus von Liebig (1843). German agronomist Carl Sprengel (1737-1859) disproved
Thaer's humus theory and formulated the law of minimum. It states that the agronomic
yield of a specific field is determined by the nutrient(s) in least supply. When the most
limiting nutrient (or any other factor) is corrected, yields are then determined by the next
important limiting factor. Mitscherlich (1909) proposed the “law of the diminishing
returns.” It states that an incremental increase in crop yield decreases with progressive
increase in the input of the limiting factor [d y /d x = C ( A - Y ), where x is the input, A is the
maximum possible yield, Y is the yield corresponding with the amount of X supplied,
and C is a proportionality constant]. Wallace (1993) proposed the “law of maximum.”
It states that the effect of specific input on agronomic yield progressively increases as
deficiency of other limiting factors is corrected, and the maximum yield (when factors
are corrected) exceeds the sum of the effects of individual inputs. Ramamoorthy and
Velayutham (2011) proposed “the law of optimum.” It is defined as the concept of soil
test based on major plant nutrients' (NPK) application to crops. It is also the basis of
“precision farming” for sustainable and enduring agriculture.
In the context of the severe and global problem of soil degradation, an important
strategy is to enhance soil and ecosystem resilience, particularly in dryland agro-
ecosystems (Enfors and Gordon 2007). It is also argued that an effective approach
to improving soil quality is by using farmers' knowledge for the soil/site-specific
situations (Tesfahunegn et al. 2011) and social/cultural factors (Anley et al.
2007). Agricultural intensification based on enhanced diversification (Tappan and
McGahuey 2007) can improve agronomic yields while also improving the environ-
ment and alleviating poverty (Brown et al. 2011).
1.6 LAWS OF SUSTAINABLE SOIL MANAGEMENT
Lal (2009a,b) proposed 10 tenets of soil management ( Table 1.7 ). These generic laws
emphasize the following.
1.6.1 p olicy M akerS
Establishing a dialogue with policy makers is important to identifying policies that
reverse the degradation trends. Five basic laws of soil management, which are related
to appropriate policies, are the following.
1.6.1.1 Causes of Soil Degradation and Desertification
The biophysical process of soil degradation and desertification is driven by economic,
social, and political forces. The effectiveness of managing biophysical processes in
minimizing degradation risks and enhancing restoration mechanisms depend on
addressing the human dimensions that affect land misuse, soil management, and
prevalence of extractive farming practices.
1.6.1.2 Human Needs and Stewardship of Natural Resources
Because humans are always dependent on agriculture, improving agriculture is
essential to the stewardship of natural resources. In this context, it is important to
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