Soil Renewal and Sustainability - Principles of Sustainable Soil Management in Agroecosystems - page 495

20

YA = 1.727 ln (X) - 4.355
R 2 = 0.982

15

YB = 2.2576 e 0.0191X
R 2 = 0.979

10

5

0 000 0
ickness of topsoil (cm)

80 100 120

FIGURE 17.5 Relationship between crop yield and thickness of topsoil. (From Zhu, B. et al.
J Mountain Sci , 27, 735-739, 2009.)

different thicknesses. Root weight of winter wheat and corn gradually increased as a
function of topsoil depth. For both crops, 20 cm of topsoil resulted in the lightest root
weight when compared to the other topsoil thicknesses. In normal rainfall years, the
study concluded that the critical thickness of topsoil for both crops was 40 to 60 cm.

17.10 SOIL SUSTAINABILITY
Sustainability is defined as “managing soil and crop cultural practices so as not
to degrade or impair environmental quality on- or off-site, and without eventually
reducing yield potential as a result of the chosen practice though exhaustion of either
on-site resources or nonrenewable inputs” (Soil Science Society of America 2008).
The 1990 Farm Bill has a more expansive definition and states: “the term sustainable
agriculture means an integrated system of plant and animal production practices
having a site-specific application that will, over the long term (i) satisfy human food
and fiber needs, (ii) enhance environmental quality and the natural resource base
upon which the agricultural economy depends, (iii) make the most efficient use of
nonrenewable resources and on-farm resources and integrate, where appropriate,
natural biological cycles and controls, (iv) sustain the economic viability of farm
operations, and (v) enhance the quality of life for farmers and society as a whole.”
Questions have been raised regarding the consideration of soil as a renewable
resource. Friend (1992) states, “The leading edge of academic thinking now is that
a majority of world soils, apart from the deepest and most rapidly forming, are non-
renewable within a human lifetime.” Thus, time becomes an important factor in any
discussion of both sustainability and renewability. Kummerer et al. (2010) proposed
several general rules in order to use soils in a sustainable manner. They called one
of these the Rule of Transition: resources that are not renewable within human time
scales should be used only within the time needed for the transition from an unsus-
tainable to a sustainable economy. All their rules involve varying time scales and
vary in importance at different points in time and in their interconnectedness in soil
formation and soil development. They conclude that an interdisciplinary temporal