Agriculture Reference
In-Depth Information
Table 9.2
Mean Legume Biomass and Total N Input
1
for 2002 and 2003
2002
2003
Legume biomass
(kg/ha)
Total N input
(kg/ha)
Legume biomass
(kg/ha)
Total N input
(kg/ha)
Cropping system
MZ+F
NA
45
a
NA
45
a
MZ-F
NA
0
b
NA
0
b
SS+1/2F
360
31
c
208
27
c
TV+1/2F
628
38
c
197
27
c
PP+1/2F
409
34
c
208
28
c
1
Total N input combines organic and inorganic N sources. NA, not applicable. Lowercase letters indicate statisti-
cal differences based on nonparametric median tests (
P
< 0.05). Absence of letters indicates the factor was not
significant.
Table 9.3
D2 Simple Regressions of Foliar Nutrient Content, Legume Biomass, and N Input
with Maize Yields from 2003 and 2004
2003
2004
Variable
Beta
R
2
P
value
N
Beta
R
2
P
value
N
Foliar %N
0.489
0.239
0.000***
103
0.507
0.257
0.000***
60
Foliar %S
0.509
0.259
0.000***
103
0.513
0.263
0.000***
55
Foliar %P
NA
NA
NA
NA
0.233
0.054
NA
45
Legume biomass
1
0.442
0.190
0.003**
45
0.531
0.282
0.003**
30
Total N input
2
0.544
0.296
0.000***
79
0.662
0.438
0.000***
50
Note:
Beta, slope of the regression line when predictor and independent variables are standardized (indicates the
direction of the relationship);
R
2
, proportion of variability in the dependent variable attributable to the
regression equation;
P
value, significance level, with *
P
< 0.05, **
P
< 0.01, and ***
P
< 0.001. N, total number
of cases; NS, not significant; WS, whole soil; LF, light fraction.
1
Legume biomass does not include MZ+F or MZ-F treatments.
2
Total N includes both organic and inorganic fertilizer sources; also includes all five treatments.
recycled from
Sesbania
and pigeon pea fallows (Ndufa et al., 2009) or to the total amount of
inorganic and organic N sources applied (Mtambanengwe and Mapfumo, 2006). Kamanga,
Waddington, et al. (2010) suggested that to have a positive impact on maize yields, legume
dry matter biomass should be at least 2,000 kg ha
-1
, but here we found that much smaller
quantities of legume biomass combined with modest amounts (22.5 kg N ha
-1
) of inor-
ganic N provided benefits for farmers with access to limited quantities of fertilizer. It is
also possible that there are cumulative benefits from annual legume relay cropping since
1996 on overall soil quality that contribute to enhanced maize yields, even though we
were unable to demonstrate changes over time in major soil nutrients with legume use
(see Section 9.7.1). Others have suggested that long-term soil quality benefits accrue from
repeated legume use (Kamanga, Waddington, et al., 2010a; Franzel and Scherr, 2002).
A focus on improving legume biomass production in combination with the use of
moderate amounts of fertilizer clearly has the potential to greatly improve maize yields
in this region. Efforts are needed both to improve agronomic management of the legumes
and to better understand the mechanisms by which legumes improve maize yields.
Legume density and planting arrangement can have major effects on intercrop perfor-
mance (Mucheru-Muna et al., 2010; Snapp and Silim, 2002), and timing of incorporation
will affect residue quality, which will in turn affect N release dynamics. If residue quality
Search WWH ::
Custom Search