109
the Malawi farmers’ average. The significantly higher maize plant N uptake and
grain and TDM yields for plots that were previously Sole CP, Sole PP and PP + CP
intercrop than those that were previously Sole MZ and Sole MZ + 92 N at all fertilizer levels can be attributed to the combined effect of high-quality residues and
inorganic N fertilizer, which increased N recovery and yields more than the lowquality MZ residues combined with inorganic N fertilizer. Mtambanengwe et al.
(2007), in a similar study involving Crotalaria juncea green manure and Calliandra
calothyrsus and Pinus patula residues as organic amendments in Zimbabwe,
observed improvements in maize yields by between 24% and 104% from combined
mineral fertilizer and leguminous resources over those from sole fertilizer. On the
other hand, Mahama et al. (2016), in a similar study, reported greater benefits in
maize N uptake due to cowpea and pigeon pea previous cropping systems in the
USA than by that in the soybean system. The trends at the Dowa site were similar
to those at Lilongwe, with slight differences. For instance, the amounts of N uptake
in Dowa were above 50 kg N ha
−1
in all the zero fertilizer plots and in all the previous legume-based cropping system plots, compared to Lilongwe levels that were
lower in the treatment that was previously Sole MZ. This can be attributed to the
initial soil total N and soil organic matter levels, which were higher in Dowa than in
Lilongwe.
The significantly higher harvest indices due to the previous legume-based cropping systems can be attributed to increased synchrony in the release of N from the
high-quality residues and the N requirements of the maize crop. This was complemented by the effect of applied N. However, apart from other treatments being significantly higher than the zero N rate, no differences were observed amongst the
higher fertilizer rates. Maobe et al. (2010) noted the increase in HI with N application from both Mucuna pruriens residues and inorganic fertilizer, but at only
medium rates of N from 30 to 60 kg N ha
−1
and no further increase in HI at the fertilizer rates above 100 kg N ha
−1
.
The crude protein percentages of maize grain in the present study are similar to
those reported in other studies (Silva et al. 2005). Results in the present study show
that increasing the rate of N application led to increase in crude protein content of
the maize grain. Blumenthal et al. (2008) in a review of importance and effect of N
on crop quality summarize a number of studies where increasing the N rate leads to
increase in maize grain protein. However, in the present study, grain protein in
maize differed significantly due to applied inorganic N fertilizer, but significant differences were not observed due to previous cropping systems in both study sites.
This can be attributed to the timing of N application in that the protein content might
have been influenced by top dressing N as fertilizer, which was applied closer to the
tasselling stage and is more likely to have been channelled to kernel development
and filling, as opposed to the N from the cropping system residuals which acted
more as a basal fertilizer for vegetative development. In a similar study, increase in
crude protein content of maize was reported to be influenced by late N application
towards silking (Silva et al. 2005).
The previous legume-based systems resulted in significantly higher NUE in
terms of PFP N than by those that were previously Sole MZ or Sole MZ + 92 N in
Integrated Soil Fertility Management Based on Pigeon Pea and Cowpea Cropping…
the Malawi farmers’ average. The significantly higher maize plant N uptake and
grain and TDM yields for plots that were previously Sole CP, Sole PP and PP + CP
intercrop than those that were previously Sole MZ and Sole MZ + 92 N at all fertilizer levels can be attributed to the combined effect of high-quality residues and
inorganic N fertilizer, which increased N recovery and yields more than the lowquality MZ residues combined with inorganic N fertilizer. Mtambanengwe et al.
(2007), in a similar study involving Crotalaria juncea green manure and Calliandra
calothyrsus and Pinus patula residues as organic amendments in Zimbabwe,
observed improvements in maize yields by between 24% and 104% from combined
mineral fertilizer and leguminous resources over those from sole fertilizer. On the
other hand, Mahama et al. (2016), in a similar study, reported greater benefits in
maize N uptake due to cowpea and pigeon pea previous cropping systems in the
USA than by that in the soybean system. The trends at the Dowa site were similar
to those at Lilongwe, with slight differences. For instance, the amounts of N uptake
in Dowa were above 50 kg N ha
−1
in all the zero fertilizer plots and in all the previous legume-based cropping system plots, compared to Lilongwe levels that were
lower in the treatment that was previously Sole MZ. This can be attributed to the
initial soil total N and soil organic matter levels, which were higher in Dowa than in
Lilongwe.
The significantly higher harvest indices due to the previous legume-based cropping systems can be attributed to increased synchrony in the release of N from the
high-quality residues and the N requirements of the maize crop. This was complemented by the effect of applied N. However, apart from other treatments being significantly higher than the zero N rate, no differences were observed amongst the
higher fertilizer rates. Maobe et al. (2010) noted the increase in HI with N application from both Mucuna pruriens residues and inorganic fertilizer, but at only
medium rates of N from 30 to 60 kg N ha
−1
and no further increase in HI at the fertilizer rates above 100 kg N ha
−1
.
The crude protein percentages of maize grain in the present study are similar to
those reported in other studies (Silva et al. 2005). Results in the present study show
that increasing the rate of N application led to increase in crude protein content of
the maize grain. Blumenthal et al. (2008) in a review of importance and effect of N
on crop quality summarize a number of studies where increasing the N rate leads to
increase in maize grain protein. However, in the present study, grain protein in
maize differed significantly due to applied inorganic N fertilizer, but significant differences were not observed due to previous cropping systems in both study sites.
This can be attributed to the timing of N application in that the protein content might
have been influenced by top dressing N as fertilizer, which was applied closer to the
tasselling stage and is more likely to have been channelled to kernel development
and filling, as opposed to the N from the cropping system residuals which acted
more as a basal fertilizer for vegetative development. In a similar study, increase in
crude protein content of maize was reported to be influenced by late N application
towards silking (Silva et al. 2005).
The previous legume-based systems resulted in significantly higher NUE in
terms of PFP N than by those that were previously Sole MZ or Sole MZ + 92 N in
Integrated Soil Fertility Management Based on Pigeon Pea and Cowpea Cropping…