98
taken to the laboratory and kept in a refrigerator to avoid further mineralization. The
soil mineral N, both nitrate (NO 3
−
) and ammonium (NH 4
+
), were then extracted using
2 M KCl and then analysed colourimetrically according to the procedure as outlined by
Anderson and Ingram (1989). The N mineralization assessments were done as a series
of activities from a week of planting (wk 0) to the 11th week after planting (wk 11).
2.6 Harvesting and Determination of Yields, Harvest Indices
and Plant Analysis to Determine Grain Protein Content
Harvesting was done after the maize had reached physiological maturity and dried.
A net plot of 5.5 m x 1.5 m was demarcated from each sub-plot leaving guard rows,
to avoid outside interference. The maize stalks were cut at ground level with cobs
not removed. These were weighed as the total aboveground biomass. Then the cobs
were detached and the grains were threshed. The net plot grain fresh weight was
recorded and a sample of 100 seeds was taken using a quartering procedure and
brought to the laboratory. Grain yield, total dry matter yield and harvest indices
were determined according to Mloza-Banda (1994). Furthermore, grain N content
was determined using the procedure described by Anderson and Ingram (1989).
Maize grain crude protein content was determined by multiplying grain N concentration by a Jones factor of 6.25, according to FAO (2003).
2.7 Determination of N Uptake and Nitrogen Use Efficiency
Maize plant samples were collected at tasselling, and five plants from each sub-plot
were sampled for determination of N concentration in maize plant, using the procedure
described by Anderson and Ingram (1989). Nitrogen uptake by the maize plant was
determined by multiplying the total aboveground dry matter (TDM) with plant N concentration. On the other hand, nitrogen use efficiency was determined for applied nitrogen, using the partial factor productivity of applied N (PFP N ), whereby the amount (kg)
of grain yield produced is divided by amount (kg) of N applied (Dobermann 2005).
2.8 Rainfall Data Collection
Rainfall amounts in millimetres (mm) were collected from both Lilongwe and Dowa
study sites. For the Lilongwe site, the experiment was conducted at a university research
farm, where a rain gauge is installed and rainfall is systematically recorded every year.
On the other hand, the experiment in Dowa district was implemented at a farmer’s field;
and therefore, a rain gauge was installed on the field and data were systematically
recorded by an extension officer who was residing in the same village. Daily rainfall
recordings of both sites were computed to be presented as monthly rainfall totals.
K. O. W. Njira et al.
taken to the laboratory and kept in a refrigerator to avoid further mineralization. The
soil mineral N, both nitrate (NO 3
−
) and ammonium (NH 4
+
), were then extracted using
2 M KCl and then analysed colourimetrically according to the procedure as outlined by
Anderson and Ingram (1989). The N mineralization assessments were done as a series
of activities from a week of planting (wk 0) to the 11th week after planting (wk 11).
2.6 Harvesting and Determination of Yields, Harvest Indices
and Plant Analysis to Determine Grain Protein Content
Harvesting was done after the maize had reached physiological maturity and dried.
A net plot of 5.5 m x 1.5 m was demarcated from each sub-plot leaving guard rows,
to avoid outside interference. The maize stalks were cut at ground level with cobs
not removed. These were weighed as the total aboveground biomass. Then the cobs
were detached and the grains were threshed. The net plot grain fresh weight was
recorded and a sample of 100 seeds was taken using a quartering procedure and
brought to the laboratory. Grain yield, total dry matter yield and harvest indices
were determined according to Mloza-Banda (1994). Furthermore, grain N content
was determined using the procedure described by Anderson and Ingram (1989).
Maize grain crude protein content was determined by multiplying grain N concentration by a Jones factor of 6.25, according to FAO (2003).
2.7 Determination of N Uptake and Nitrogen Use Efficiency
Maize plant samples were collected at tasselling, and five plants from each sub-plot
were sampled for determination of N concentration in maize plant, using the procedure
described by Anderson and Ingram (1989). Nitrogen uptake by the maize plant was
determined by multiplying the total aboveground dry matter (TDM) with plant N concentration. On the other hand, nitrogen use efficiency was determined for applied nitrogen, using the partial factor productivity of applied N (PFP N ), whereby the amount (kg)
of grain yield produced is divided by amount (kg) of N applied (Dobermann 2005).
2.8 Rainfall Data Collection
Rainfall amounts in millimetres (mm) were collected from both Lilongwe and Dowa
study sites. For the Lilongwe site, the experiment was conducted at a university research
farm, where a rain gauge is installed and rainfall is systematically recorded every year.
On the other hand, the experiment in Dowa district was implemented at a farmer’s field;
and therefore, a rain gauge was installed on the field and data were systematically
recorded by an extension officer who was residing in the same village. Daily rainfall
recordings of both sites were computed to be presented as monthly rainfall totals.
K. O. W. Njira et al.