96
2.3 Soil Sampling and Analysis
Soil sampling and analysis were also conducted in the 2014/2015 growing season. Soil
samples were collected from each of the plots in the previous legume-based treatments
in the depth ranges of 0–15 cm and 15–30 cm. This was after harvesting the legumebased treatments of 2013/2014 growing season, in preparation for the 2014/2015 growing season. Soils were analysed for total N, available P, soil organic carbon (SOC) and
pH using the micro-Kjeldahl method, Mehlich-3 extraction procedures, wet oxidation
and potentiometric method, respectively, as outlined by Anderson and Ingram (1989).
Soil analysis results for the 2014/2015 growing season are presented in Table 1. Rainfall
was recorded from each of the sites during the cropping season.
2.4 Treatments and Residue Quality Determination
The 2013/2014 legume-based treatments included sole pigeon pea (PP), sole cowpea (CP), pigeon pea-cowpea (PP + CP) intercrop, pigeon pea-maize (PP + MZ)
intercrop, cowpea-maize CP + MZ) intercrop, sole maize (unfertilized – Sole MZ)
and sole maize fertilized at 92 kg N ha
−1
(Sole MZ + 92 N). The 92 kg N ha
−1
is the
current recommended N rate by Malawi’s Ministry of Agriculture and Food Security
(MoAFS) (2012). The plot size was 15 m × 7 m. The crop residues were incorporated in the soil soon after harvesting. The legume-based cropping systems’ treatments were arranged in randomized complete block design (RCB).
In the 2014/2015 study year, treatments were superimposed on the 2013/2014
legume-based treatments. Each legume-based treatment plot was split into four subplots that received different levels of inorganic N as follows: 0, 45, 90 or
120 kg N ha
−1
(in the 7 m × 3.75 m sub-plots). Therefore, the split plot arrangement
in RCB was obtained. The sources of N applied were the basal NPK fertilizer
(23:21:0 + 4S) and the top-dressing N fertilizer was urea (46% N). One maize seed
was planted per each planting station at a spacing of 25 cm between planting stations along the ridge/row and 75 cm between ridges. The maize variety used was the
DKC 8053. All conventional crop management practices such as land preparation
and weeding were followed. Nitrogen concentration and C/N ratios were determined in the crop residues before incorporation, to assess their quality according to
assess their quality according to Palm et al.(2001) and Brady and Weil (2008).
2.5 Soil Mineral N Assessment During the Growing Season
Soil samples were collected from the 0–20 cm depth by augering a minimum of three
randomly selected points from each sub-plot. Composite samples were made from
soils of each sub-plot. Then, the composite samples were kept in cooler boxes and
K. O. W. Njira et al.
2.3 Soil Sampling and Analysis
Soil sampling and analysis were also conducted in the 2014/2015 growing season. Soil
samples were collected from each of the plots in the previous legume-based treatments
in the depth ranges of 0–15 cm and 15–30 cm. This was after harvesting the legumebased treatments of 2013/2014 growing season, in preparation for the 2014/2015 growing season. Soils were analysed for total N, available P, soil organic carbon (SOC) and
pH using the micro-Kjeldahl method, Mehlich-3 extraction procedures, wet oxidation
and potentiometric method, respectively, as outlined by Anderson and Ingram (1989).
Soil analysis results for the 2014/2015 growing season are presented in Table 1. Rainfall
was recorded from each of the sites during the cropping season.
2.4 Treatments and Residue Quality Determination
The 2013/2014 legume-based treatments included sole pigeon pea (PP), sole cowpea (CP), pigeon pea-cowpea (PP + CP) intercrop, pigeon pea-maize (PP + MZ)
intercrop, cowpea-maize CP + MZ) intercrop, sole maize (unfertilized – Sole MZ)
and sole maize fertilized at 92 kg N ha
−1
(Sole MZ + 92 N). The 92 kg N ha
−1
is the
current recommended N rate by Malawi’s Ministry of Agriculture and Food Security
(MoAFS) (2012). The plot size was 15 m × 7 m. The crop residues were incorporated in the soil soon after harvesting. The legume-based cropping systems’ treatments were arranged in randomized complete block design (RCB).
In the 2014/2015 study year, treatments were superimposed on the 2013/2014
legume-based treatments. Each legume-based treatment plot was split into four subplots that received different levels of inorganic N as follows: 0, 45, 90 or
120 kg N ha
−1
(in the 7 m × 3.75 m sub-plots). Therefore, the split plot arrangement
in RCB was obtained. The sources of N applied were the basal NPK fertilizer
(23:21:0 + 4S) and the top-dressing N fertilizer was urea (46% N). One maize seed
was planted per each planting station at a spacing of 25 cm between planting stations along the ridge/row and 75 cm between ridges. The maize variety used was the
DKC 8053. All conventional crop management practices such as land preparation
and weeding were followed. Nitrogen concentration and C/N ratios were determined in the crop residues before incorporation, to assess their quality according to
assess their quality according to Palm et al.(2001) and Brady and Weil (2008).
2.5 Soil Mineral N Assessment During the Growing Season
Soil samples were collected from the 0–20 cm depth by augering a minimum of three
randomly selected points from each sub-plot. Composite samples were made from
soils of each sub-plot. Then, the composite samples were kept in cooler boxes and
K. O. W. Njira et al.