110
both study sites, and this can be attributed to interactive effects of the high-quality
residues and the applied inorganic N. For maize residues with low quality, NUE can
be reduced by the longer periods of N immobilization and, in turn, not meeting the
synchrony with plant growth stages when the N is greatly needed. This implies that
in the maize monoculture systems, much of the plant growth will only be dependent
of the applied N, which is more susceptible to losses through leaching. According
to Dobermann (2005), common ranges of NUE are 40–70 kg grain kg
−1
N applied.
The PP + CP intercrop and Sole CP NUE values were the highest, but the rest of the
legume-based systems treatments in this study resulted in far much higher NUE
values than the stated ranges. According to Dobermann (2005), NUE values above
the stated ranges are obtained when there is good crop performance at lower rates of
N and in well-managed systems. Therefore, the pigeon pea- and cowpea-based systems planted either in sole cropping, legume-legume intercrops or legume-cereal
intercrops can all be considered good systems for increased NUE and increased
yields for maize in rotation.
5 Summary and Conclusions
Integrated soil fertility management (ISFM) aims at achieving sustainable yields
whilst minimizing costs on the part of a farmer. From this study it can be noted that
integration of pigeon pea and cowpea either as sole crops, legume-legume intercrops or legume-cereal intercrops led to similarly higher N uptake, grain and TDM
yields and harvest indices in the rotational maize than the maize-maize monoculture, with or without inorganic fertilizer. The interactive effect of the legume residues and inorganic fertilizer led to higher maize grain yields, with increases ranging
from 30% under treatment that was previously CP + MZ intercrop (1689 kg ha
−1
) to
59% under treatment that was previously Sole CP (2864 kg ha
−1
) at 0 kg N ha
−1
fertilizer application, than that under treatment that was previously Sole MZ
(1178 kg ha
−1
). Similarly, at the highest rate of N application, 120 kg N ha
−1
, the
previous legume-based treatments produced higher maize grain yields than the
treatment that was previously Sole MZ (3277 kg ha
−1
), by increases ranging from
28% under treatment that was previously CP + MZ intercrop (4525 kg ha
−1
) to 42%
under treatment that was previously Sole CP (5665 kg N ha
−1
), in the Lilongwe site.
For the Dowa site, at 0 kg N ha
−1
, maize grain yield increase over the treatment
that was previously Sole MZ (1454 kg ha
−1
) ranged from 24% under the previously
CP + MZ intercrop (1908 kg ha
−1
) to 48% under treatment that was previously Sole
PP (2792 kg ha
−1
), whereas at 120 kg N ha
−1
, increase over the treatment that was
previously Sole MZ (3204 kg N ha
−1
) ranged from 35% under treatment that was
previously PP + MZ intercrop (4945 kg ha
−1
) to 45% under treatment that was previously PP + CP intercrop (5836 kg ha
−1
).
From this study it is noted that both legume sole cropping and legume-cereal
intercrops, as well as legume-legume intercropping systems involving pigeon pea
and cowpea with residues retained increased N mineralization rates, N uptake and
K. O. W. Njira et al.
both study sites, and this can be attributed to interactive effects of the high-quality
residues and the applied inorganic N. For maize residues with low quality, NUE can
be reduced by the longer periods of N immobilization and, in turn, not meeting the
synchrony with plant growth stages when the N is greatly needed. This implies that
in the maize monoculture systems, much of the plant growth will only be dependent
of the applied N, which is more susceptible to losses through leaching. According
to Dobermann (2005), common ranges of NUE are 40–70 kg grain kg
−1
N applied.
The PP + CP intercrop and Sole CP NUE values were the highest, but the rest of the
legume-based systems treatments in this study resulted in far much higher NUE
values than the stated ranges. According to Dobermann (2005), NUE values above
the stated ranges are obtained when there is good crop performance at lower rates of
N and in well-managed systems. Therefore, the pigeon pea- and cowpea-based systems planted either in sole cropping, legume-legume intercrops or legume-cereal
intercrops can all be considered good systems for increased NUE and increased
yields for maize in rotation.
5 Summary and Conclusions
Integrated soil fertility management (ISFM) aims at achieving sustainable yields
whilst minimizing costs on the part of a farmer. From this study it can be noted that
integration of pigeon pea and cowpea either as sole crops, legume-legume intercrops or legume-cereal intercrops led to similarly higher N uptake, grain and TDM
yields and harvest indices in the rotational maize than the maize-maize monoculture, with or without inorganic fertilizer. The interactive effect of the legume residues and inorganic fertilizer led to higher maize grain yields, with increases ranging
from 30% under treatment that was previously CP + MZ intercrop (1689 kg ha
−1
) to
59% under treatment that was previously Sole CP (2864 kg ha
−1
) at 0 kg N ha
−1
fertilizer application, than that under treatment that was previously Sole MZ
(1178 kg ha
−1
). Similarly, at the highest rate of N application, 120 kg N ha
−1
, the
previous legume-based treatments produced higher maize grain yields than the
treatment that was previously Sole MZ (3277 kg ha
−1
), by increases ranging from
28% under treatment that was previously CP + MZ intercrop (4525 kg ha
−1
) to 42%
under treatment that was previously Sole CP (5665 kg N ha
−1
), in the Lilongwe site.
For the Dowa site, at 0 kg N ha
−1
, maize grain yield increase over the treatment
that was previously Sole MZ (1454 kg ha
−1
) ranged from 24% under the previously
CP + MZ intercrop (1908 kg ha
−1
) to 48% under treatment that was previously Sole
PP (2792 kg ha
−1
), whereas at 120 kg N ha
−1
, increase over the treatment that was
previously Sole MZ (3204 kg N ha
−1
) ranged from 35% under treatment that was
previously PP + MZ intercrop (4945 kg ha
−1
) to 45% under treatment that was previously PP + CP intercrop (5836 kg ha
−1
).
From this study it is noted that both legume sole cropping and legume-cereal
intercrops, as well as legume-legume intercropping systems involving pigeon pea
and cowpea with residues retained increased N mineralization rates, N uptake and
K. O. W. Njira et al.