Agriculture Reference
In-Depth Information
Table 3.8.5.
Crop management system and rotation effects on total nitrogen and assimilable
P
2
O
5
content in the soil. Values followed by the same letter in the same column are not statistically
different at the 0.05 probability level.
Total nitrogen (‰)
Assimilable P
2
O
5
(p.p.m.)
1993
1997
1993
1997
Soil depth (cm)
0-7
7-30 0-30
0-7
7-30 0-30
0-7
7-30 0-30
0-7
7-30 0-30
Mean effects
CS
b
0.74
b
b
0.74
b
b
0.74
b
b
24.2
b
1.12
0.92
0.97
13.0
11.6
11.8
16.1
15.1
LIS
1.19
0.88
0.96
a
1.27
a
a
0.82
a
a
0.93
a
11.6
11.5
11.6
a
29.6
a
11.7
15.9
Rot. 1
1.15
0.93
0.98
1.02
0.77
0.83
13.4
12.0
12.6
24.6
15.6
15.3
Rot. 2
1.17
0.89
0.95
0.98
0.81
0.85
11.5
11.7
11.8
27.1
13.6
15.3
Rot. 3
1.16
0.89
0.95
1.02
0.76
0.82
12.0
11.0
10.9
29.2
12.6
15.9
Interactions
CS
×
Rot. 1
1.13
0.97
1.01
0.78
0.74
0.74
14.8
12.0
12.6
22.4
19.6
20.3
CS
×
Rot. 2
1.20
0.89
0.96
0.77
0.74
0.75
11.6
12.2
12.1
25.5
15.6
17.9
CS
×
Rot. 3
1.04
0.91
0.94
0.69
0.75
0.73
12.7
10.6
11.0
24.8
13.2
15.9
LIS
×
Rot. 1
1.17
0.89
0.96
1.27
0.80
0.91
12.1
12.0
12.0
26.7
11.5
15.1
LIS
×
Rot. 2
1.13
0.88
0.94
1.20
0.89
0.96
11.3
11.2
11.2
28.7
11.6
15.6
LIS
×
Rot. 3
1.29
0.87
0.97
1.35
0.78
0.91
11.4
11.4
11.4
33.5
12.0
17.0
Year
1.16
0.90
0.96
1.01
0.78
0.83
12.3
11.6
11.7
26.9
13.9
15.5
1.8tDMha
−1
year
−1
, respectively). Average crop residues produced under
CS (4.4 t DM ha
−1
year
−1
) did not allow the preservation of the initial soil
organic matter content, presumably because of the higher mineralization
rate associated with the use of deep ploughing in such climatic conditions.
Observed soil organic matter trends in our study are in accordance with
those found by Blevins and Frye (1993) for the effects of tillage systems on
soils having a relatively low initial soil organic matter content. Positive
effects of legume crops on soil characteristics - not yet pronounced in our
study - were also observed by Dalal
et al
. (1995) in a similar environment.
However, these authors noted a sharp decrease in soil fertility soon after
adoption of conventional tillage, which was not observed in our case. It is
worth stressing that a thorough evaluation of the effects of agricultural
management systems on soil fertility can only be made in the long term
(Janzen, 1995).
The preliminary results of our study suggest that in Southern Italy,
where high summer temperatures enhance soil organic matter mineraliza-
tion rates and low rainfall limits biomass production, the adoption of a
low-input system based upon no-tillage seems more appropriate for
preserving the beneficial effects of setaside on soil properties. In this
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