Soil Renewal and Sustainability - Principles of Sustainable Soil Management in Agroecosystems - page 493

through erosion, creates a surface plant growth medium composed of topsoil essen-
tially diluted with underlying soil materials. One might expect that the “dilution”
process would modify the typical yield loss trends normally observed in soil erosion/
surface soil removal studies. However, this process still seems to result in an expo-
nential yield decrease, at least for soybeans grown on a Mollisol with an average top-
soil layer of 50 to 60 cm (Wang et al. 2009). Fertilizer application seems to modify
the yield values observed for a given topsoil condition but fails to negate the erosion/
crop yield relationship (Figure 17.4). Yields were reduced from 1.68 to 0.61 Mg/ha
when topsoil loss increased from 0 to 70 cm with fertilizer addition (N: 46.4 kg/ha 2 ;
P 2 O 5 : 60.0 kg/ha 2 ; K 2 O: 13.8 kg/ha 2 ) and reduced from 1.35 to 0.36 Mg/ha without
fertilizer addition under corresponding topsoil thicknesses. The average yield reduc-
tions per 10 cm of soil loss when fertilized were 28.8%, 18.9%, 14.5%, 13.2%, 10.6%,
8.8%, and 9.2% at the erosion depths of 10, 20, 30, 40, 50, 60, and 70 cm compared to
the yield at an erosion depth of 0 cm; but when unfertilized, they were 32.6%, 21.1%,
17.7%, 13.5%, 13.2%, 11.6%, and 10.4%, respectively. Inorganic fertilizer additions

2005 2006

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

YA = 0.911e (- H /25.047) + 0.778,
R 2 = 0.735

YA = 1.186e (- H /23.153) + 0.630,
R 2 = 0.858

YB = 0.932e (- H /21.372) + 0.473,
R 2 = 0.9127

YB = 1.140e (- H /27.894) + 0.239,
R 2 = 0.9586

0 020304050
Erosion depth (cm)

60 70 0 0 0 0 0 0

Erosion depth (cm)

60 70

2007 2005-2007 average

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

YA = 0.936e (- H /16.969) + 0.711,
R 2 = 0.676

YA = 0.861e (- H /10.408) + 0.598,
R 2 = 0.859

YB = 0.989e (- H /23.409) + 0.326,
R 2 = 0.764

YB = 0.740e (- H /22.804) + 0.282,
R 2 = 0.790

0 020304050
Erosion depth (cm)

60 70 0 0 0 0 0 0

Erosion depth (cm)

60 70

FIGURE 17.4 Soybean yield as a function of thickness of soil loss under fertilized condition
(a, solid points) and unfertilized condition (b, circles). (From Wang, Z. et al. Sci. China D ,
52, 1005-1021, 2009.)