Agriculture Reference
In-Depth Information
Table 15.4. Soil characteristics and significant differences by treatment in the
Living Field Lab systems.
a
Management/
Diversity
Soil C
Content
(kg m
−2
)
Total N
(mg N kg
−1
)
C/N Ratio
Phosphorus
a
(mg P kg
−1
)
Potassium
a
(mg K kg
−1
)
Calcium
a
(mg Ca
kg
−1
)
Integrated Conventional
One species
2.7
0.85
9.43
29.8
94.4
1288
Two species
2.8
0.88
9.22
21.9
79.9
972
Three species
2.8
0.90
9.27
25.4
64.5
1074
Six species
3.3
0.94
10.22
28.0
68.1
1126
Organic
One species
3.9
1.15
11.09
50.9
94.1
1299
Two species
3.9
1.17
9.91
53.4
125.5
1491
Three species
4.1
1.20
10.96
44.1
101.5
1395
Six species
3.7
1.10
11.07
40.7
117.2
1443
Analysis of Variance (ANOVA)
P
-value
Management (M)
<0.0001
<0.0001
<0.003
<0.0001
<0.001
0.014
Diversity (D)
NS
NS
NS
0.04
NS
NS
M × D
NS
NS
NS
NS
NS
NS
a
Soils sampled 0- to 20-cm depth in April 2008. Phosphorus, potassium, and calcium extracted using the Mehlich III
method. NS = Not significant (α = 0.05).
Source:
Adapted from Snapp et al. (2010b).
production, on the other hand, did not maintain soil phosphorus and had almost no
discernable effect on soil organic C. Cropping system diversity was not associated
with enhanced soil C in the LFL. Processes influencing C sequestration are com-
plex; organic corn rotations have been associated with both declines (Studdert and
Echeverria 2000) and accumulations (Russell et al. 2009) of soil C.
Water Quality
Nitrate leaching, an indicator of water quality, was measured in the LFL by installing
gravimetric water samplers in cover crop plots. Nitrate loss was pronounced under corn
production, primarily in the spring months prior to planting corn (Sánchez et al., 2004;
Snapp et al. 2010a). Farmers manage for high soil N availability at the onset of growth,
particularly for N-demanding crops such as corn. Soil amended with compost or other
N sources that are high in C content (such as cover crop residues) may be an important
means for managing N, using temporary immobilization to reduce the spring inorganic
N pool (McSwiney et al. 2010). Systems receiving fertilizer N—whether synthetic or
organic—require especially careful management during the spring when intense rain-
fall events and limited plant growth lead to high leaching potential.
The Organic system leached 32 kg NO
3
−
-N ha
−1
yr
−1
, which was about half as
much as the Integrated Conventional system (74 kg NO
3
−
-N ha
−1
yr
−1
), as shown
by gravimetric lysimeters monitored from 1994 to 2000 (Snapp et al. 2010a;
