Agriculture Reference
In-Depth Information
TABLE 12.14
Comparison of Soil Chemical Characteristics with CA and Non-CA Fields in
West Usambara Mountains, Tanzania
CA vs.
No CA
Site
TN
OC
Olsen. P
CEC
Ca
Mg
K
Na
1
Terraces
0.34
4.39
bc
9.18
17.87
6.54
2.27
cd
0.62
0.25
Miraba
0.36
4.24
bc
7.87
22.47
10.79
4.18
a
0.44
0.25
No CA
0.24
2.93
de
5.38
14.27
7.31
2.86
bcd
0.38
0.21
2
Terraces
0.43
5.93
a
4.43
20.06
7.71
1.85
d
0.26
0.24
Miraba
0.35
4.30
bc
5.09
21.86
7.82
3.87
ab
0.15
0.23
No CA
0.34
4.02
cd
3.34
18.26
11.05
2.47
cd
0.24
0.22
3
Terraces
0.48
a
5.50
a
9.18
22.3
a
6.21
c
3.73
ab
0.57
0.22
Miraba
0.26
cd
3.99
cd
6.36
11.06
d
11.28
a
1.19
d
0.26
0.23
No CA
0.17
d
2.39
e
4.55
12.70
cd
8.53
abc
2.09
d
0.24
0.24
Mean
0.36
4.44
8.68
18.82
9.19
3.05
0.37
0.26
CV (%)
21.64
15.76
88.40
18.99
31.38
22.05
63.46
0.10
F
(0.05)
**
***
ns
**
ns
**
ns
ns
Source:
Kimaro, D., own field data.
Note:
Ca, calcium; CEC, cation exchange capacity; K, potassium; Mg, magnesium; Na, sodium; OC, organic
carbon; Olsen P, available phosphorus; TN, total nitrogen; Means with the same superscript letters are
not significantly different (
P
< .05); **,
P
< .01; ***,
P
< .001; ns, not significant.
observed compared with non-CA fields, and could be attributed to reduced soil ero-
sion and supportive soil fertility management practiced by farmers on CA fields, which
involve application of manure, crop residues, and crop rotation (Aziz et al. 2011). On the
other hand, the mean available phosphorus from terraced fields was relatively better fol-
lowed by
miraba
and non-CA fields. This could be due to comparatively better organic
matter content of the terrace and
miraba
fields than non-CA fields that might be, in turn,
attributed to the application of manure and crop residues. Glendinning (2000) asserted
that in most soils, the amount of organic phosphorus is highly correlated with the
amount of organic carbon. The rate of mineralization of organic phosphorus increases
as the organic phosphorus content of the soil increases (Kabba and Aulakh 2004).
12.3.2 e
FFect
oF
c
onservation
a
griculture
on
c
roP
P
roductivity
In a case study conducted in Karatu District, Tanzania, on CA using farmer field
school (FFS), several CA options (Owenya et al. 2011) were tested, including
(i) ripped plot, planted with maize intercropped with lablab; (ii) ripped plot, planted
with maize intercropped with pigeon pea; (iii) nonripped plot, planted with maize
intercropped with lablab, nonripped plot, planted with maize intercropped with
pigeon pea; and (iv) farmers' normal practice of ploughing twice and then planting
maize intercropped with pigeon pea, beans (
P. vulgaris
), and pumpkin (
Cucurbita
maxima
) (Table 12.15). In this case study, farmers realized that crop yield under
CA increased with time (Table 12.16), i.e., from 1.2 Mg/ha of maize in 2004 when
