100
legume-based treatments in the topsoil (Table 1). The Lilongwe topsoil pH ranged
from 5.9 (Sole MZ + 92 N) to 6.1 in a number of previous legume-based treatments.
Furthermore, the overall mean total soil N was 0.06 and 0.056 for the topsoil and
subsoil, respectively. Soil organic carbon (C) was also low, with overall means of
1.2 and 1.1 for the topsoil and subsoil, respectively. On the other hand, the available
(Mehlich-3) P was high with overall means of 42.4 and 39.2 mg kg
−1
for the topsoil
and subsoil, respectively (Table 1).
For the Dowa site, Table 1 shows a slightly acidic soil reaction with a pH range
of 6.1–6.3 for the topsoil and a pH of 6.0–6.4 for the subsoil. Total soil N was low
to medium, with overall mean values of 0.14 and 0.10 in the topsoil and subsoil,
respectively. Soil organic C was medium with overall mean values of 2.75 and
1.95 in the topsoil and subsoil, respectively. On the other hand, available (Mehlich-3)
P was medium with overall mean values of 29.7 and 26.9 mg kg
−1
for the topsoil and
subsoil, respectively.
3.3 Stover Quality from Previous Cropping Systems
for Lilongwe and Dowa Sites
Results showed different characteristics of the maize stover, ranging from high
quality (N % > 2.5 and C/N ratios <25) to low quality (N % < 2.5 and C/N ratios
>25). For the Lilongwe site, sole cowpea (CP) stover was of the highest quality,
with N concentration of 2.7% and C/N ratio of 16.4, whilst maize stover from the
maize-cowpea intercrop showed the lowest quality with N concentration of 0.7%
and C/N ratio of 59.4. For the Dowa site, high-quality stover was depicted in Sole
CP and Sole PP, both with N concentration of 2.8 with C/N ratios of 15.9 and 16.4,
respectively. Maize stover in the intercrops with cowpea and pigeon pea showed the
lowest quality characteristics, with N concentrations of 0.8 and 0.7% and C/N ratios
of 63.5 and 58.1, respectively.
3.4 Field Soil Mineral N Patterns as Influenced by
the Previous Season at Lilongwe and Dowa Sites
Figure 2 shows mineral N (NO 3
−
, NH 4
+
) levels in soils sampled from planting week
to week 11 after planting. Results are presented only for the legume-based sub-plots
that did not receive inorganic N fertilizer application to elucidate the clear effect of
the previous cropping systems. The general trend showed decrease in mineral N
levels from the planting week to the later weeks.
There were significant differences (P < 0.05) in nitrate N levels due to the previous cropping systems. Nitrate N levels for previous legume-based systems were
significantly higher (P < 0.05) than that in the previous Sole MZ by a mean of
K. O. W. Njira et al.
legume-based treatments in the topsoil (Table 1). The Lilongwe topsoil pH ranged
from 5.9 (Sole MZ + 92 N) to 6.1 in a number of previous legume-based treatments.
Furthermore, the overall mean total soil N was 0.06 and 0.056 for the topsoil and
subsoil, respectively. Soil organic carbon (C) was also low, with overall means of
1.2 and 1.1 for the topsoil and subsoil, respectively. On the other hand, the available
(Mehlich-3) P was high with overall means of 42.4 and 39.2 mg kg
−1
for the topsoil
and subsoil, respectively (Table 1).
For the Dowa site, Table 1 shows a slightly acidic soil reaction with a pH range
of 6.1–6.3 for the topsoil and a pH of 6.0–6.4 for the subsoil. Total soil N was low
to medium, with overall mean values of 0.14 and 0.10 in the topsoil and subsoil,
respectively. Soil organic C was medium with overall mean values of 2.75 and
1.95 in the topsoil and subsoil, respectively. On the other hand, available (Mehlich-3)
P was medium with overall mean values of 29.7 and 26.9 mg kg
−1
for the topsoil and
subsoil, respectively.
3.3 Stover Quality from Previous Cropping Systems
for Lilongwe and Dowa Sites
Results showed different characteristics of the maize stover, ranging from high
quality (N % > 2.5 and C/N ratios <25) to low quality (N % < 2.5 and C/N ratios
>25). For the Lilongwe site, sole cowpea (CP) stover was of the highest quality,
with N concentration of 2.7% and C/N ratio of 16.4, whilst maize stover from the
maize-cowpea intercrop showed the lowest quality with N concentration of 0.7%
and C/N ratio of 59.4. For the Dowa site, high-quality stover was depicted in Sole
CP and Sole PP, both with N concentration of 2.8 with C/N ratios of 15.9 and 16.4,
respectively. Maize stover in the intercrops with cowpea and pigeon pea showed the
lowest quality characteristics, with N concentrations of 0.8 and 0.7% and C/N ratios
of 63.5 and 58.1, respectively.
3.4 Field Soil Mineral N Patterns as Influenced by
the Previous Season at Lilongwe and Dowa Sites
Figure 2 shows mineral N (NO 3
−
, NH 4
+
) levels in soils sampled from planting week
to week 11 after planting. Results are presented only for the legume-based sub-plots
that did not receive inorganic N fertilizer application to elucidate the clear effect of
the previous cropping systems. The general trend showed decrease in mineral N
levels from the planting week to the later weeks.
There were significant differences (P < 0.05) in nitrate N levels due to the previous cropping systems. Nitrate N levels for previous legume-based systems were
significantly higher (P < 0.05) than that in the previous Sole MZ by a mean of
K. O. W. Njira et al.