106
percentage was similar to that of the Lilongwe site. Increasing amount of N led to
significant increase in grain protein content (Fig. 5) with the lowest amount of
10.2% at 0 kg N ha
−1
and highest amount of 13.1% at 120 kg N ha
−1
inorganic fertilizer application.
3.8 Nitrogen Use Efficiency as Influenced by the Previous
Cropping System at Lilongwe and Dowa Sites
The nitrogen use efficiency as demonstrated by the PFP N showed significant differences (P < 0.05) as influenced by cropping systems and amount of fertilizer N
applied (Table 2). Treatments that were previously legume-based systems were significantly higher in terms of their N use efficiency in both applied and indigenous N
(PFP N ) than those that were previously Sole MZ and Sole MZ + 92 N. The overall
mean values for treatments that were previously Sole MZ and Sole MZ + 92 N were
not significantly different. The highest efficiency for PFP N was at 45 kg N ha
−1
in all
the treatments, and the treatment that was previously Sole CP showed a slightly
higher value than the rest.
For the Dowa site, the PFP N was significantly (P < 0.05) influenced by the cropping systems and fertilizer N amount applied (Table 2). Similar to the Lilongwe site,
the highest NUE was at 45 kg N ha
−1
fertilizer application rate in all legume-based
treatments. All the former legume-based treatments showed mean PFP N values that
were higher than the common ranges of 40–70 and were all significantly higher
(P < 0.05) than that under the Sole MZ. The treatment that was previously PP + CP
intercrop showed a slightly higher value than the rest.
4 Discussion
In this study an integrated nutrient management approach was implemented; crop
residues were retained to the system and different levels of inorganic fertilizer were
added. Levels of N concentrations and C/N ratios of the different crop residues used
under the present study were similar to those of other past studies (Palm et al. 2001;
Mtambanengwe et al. 2007; Abera et al. 2013). For both sites, sole cropped legume
residues showed the highest quality (high N and lower C/N ratios) which can be
attributed to the nutrient accumulations achieved during the growth of those crops.
On the other hand, legume crop residues from intercropped species (Table 3) still
satisfied the high-quality (i.e. high N concentration and low C/N ratios) criteria
according to Palm et al. (2001) and Brady and Weil (2008).
For the Lilongwe and Dowa sites, soil mineral N (NO 3
−
and NH 4
+
) patterns
showed ranges (Fig. 2) similar to those that have been reported by a number of
authors in similar environments (Mhango 2011; Matusso et al. 2014). The signifiK. O. W. Njira et al.
percentage was similar to that of the Lilongwe site. Increasing amount of N led to
significant increase in grain protein content (Fig. 5) with the lowest amount of
10.2% at 0 kg N ha
−1
and highest amount of 13.1% at 120 kg N ha
−1
inorganic fertilizer application.
3.8 Nitrogen Use Efficiency as Influenced by the Previous
Cropping System at Lilongwe and Dowa Sites
The nitrogen use efficiency as demonstrated by the PFP N showed significant differences (P < 0.05) as influenced by cropping systems and amount of fertilizer N
applied (Table 2). Treatments that were previously legume-based systems were significantly higher in terms of their N use efficiency in both applied and indigenous N
(PFP N ) than those that were previously Sole MZ and Sole MZ + 92 N. The overall
mean values for treatments that were previously Sole MZ and Sole MZ + 92 N were
not significantly different. The highest efficiency for PFP N was at 45 kg N ha
−1
in all
the treatments, and the treatment that was previously Sole CP showed a slightly
higher value than the rest.
For the Dowa site, the PFP N was significantly (P < 0.05) influenced by the cropping systems and fertilizer N amount applied (Table 2). Similar to the Lilongwe site,
the highest NUE was at 45 kg N ha
−1
fertilizer application rate in all legume-based
treatments. All the former legume-based treatments showed mean PFP N values that
were higher than the common ranges of 40–70 and were all significantly higher
(P < 0.05) than that under the Sole MZ. The treatment that was previously PP + CP
intercrop showed a slightly higher value than the rest.
4 Discussion
In this study an integrated nutrient management approach was implemented; crop
residues were retained to the system and different levels of inorganic fertilizer were
added. Levels of N concentrations and C/N ratios of the different crop residues used
under the present study were similar to those of other past studies (Palm et al. 2001;
Mtambanengwe et al. 2007; Abera et al. 2013). For both sites, sole cropped legume
residues showed the highest quality (high N and lower C/N ratios) which can be
attributed to the nutrient accumulations achieved during the growth of those crops.
On the other hand, legume crop residues from intercropped species (Table 3) still
satisfied the high-quality (i.e. high N concentration and low C/N ratios) criteria
according to Palm et al. (2001) and Brady and Weil (2008).
For the Lilongwe and Dowa sites, soil mineral N (NO 3
−
and NH 4
+
) patterns
showed ranges (Fig. 2) similar to those that have been reported by a number of
authors in similar environments (Mhango 2011; Matusso et al. 2014). The signifiK. O. W. Njira et al.