107
cantly higher levels of mineral N in the plots that had legume residues (CP and PP),
whether sole cropped or intercropped, can be attributed to high quality of the legume
residues. The maize residues showed very low N concentrations and very high C/N
ratios, whereas the legumes, both CP and PP, showed high quality (Table 3). Zeng
et al. (2010) and Abbasi et al. (2015) studied various crop residues, including those
of maize, groundnuts and soybean, and reported a positive correlation between N
mineralization and initial N contents of the residues. This study confirms that addition of high-quality residues to the poor-quality ones improves the rate of nutrient
mineralization. This can be attributed to the activation of microbial activities in the
soil that need reasonable amounts of nitrogen to facilitate the mineralization process
and reduce the period of N immobilization.
Table 2 Nitrogen use efficiency in the form of PFP N as influenced by the previous cropping
system and fertilizer rate on maize at Lilongwe and Dowa sites, Central Malawi
Site
Fertilizer
rate
Previous cropping systems
Sole
MZ
Sole
MZ + 92 N
Sole
CP
CP + MZ
intercrop
Sole
PP
PP + CP
intercrop
PP + MZ
intercrop
Mean
(FR
effect)
PFP N (kg grain/kg N applied)
Lilongwe 0
–
–
–
–
–
–
–
–
45
55.2 69.1
119.5 104.9
102.3 107.3
107.3
95.1a
90
35.6 46.9
62.7 56.1
58.4 60.3
55.4
53.6b
120
27.3 33.6
47.2 37.7
43.8 38.7
45.1
39.1c
Mean
(CS
effect)
39.4b 49.9b
76.5a 66.2a
68.1a 68.8a
69.3a
F.pr (CS) 0.001
F.pr (FR) 0.001
F.pr
(CS∗FR)
0.048
CV (%) 18.4
Dowa
0
–
–
–
–
–
–
–
–
45
56.7 72.8
116.9 108.4
112.1 121.3
112.0
100.0a
90
38.1 41.7
55.1 59.7
57.9 65.3
58.7
53.8b
120
26.7 32.8
46.8 41.3
41.2 48.6
41.2
39.8c
Mean
(CS
effect)
40.5b 49.1b
72.9a 69.8a
70.4a 78.4a
70.6a
F.pr (CS) 0.001
F.pr (FR) 0.001
F.pr
(CS∗FR)
0.01
CV (%) 14.3
Means were separated using the Tukey’s HSD test at 5% significant level, − = not applicable,
means with different letters are significantly different; CS cropping system, FR fertilizer rate,
symbol ∗ = interaction, PFP N > 70 kg grain/kg N applied may imply very efficiently managed
systems (Dobermann 2005), MZ maize, CP cowpea, PP pigeon pea, 92 N = 92 kg N ha
−1
Integrated Soil Fertility Management Based on Pigeon Pea and Cowpea Cropping…
cantly higher levels of mineral N in the plots that had legume residues (CP and PP),
whether sole cropped or intercropped, can be attributed to high quality of the legume
residues. The maize residues showed very low N concentrations and very high C/N
ratios, whereas the legumes, both CP and PP, showed high quality (Table 3). Zeng
et al. (2010) and Abbasi et al. (2015) studied various crop residues, including those
of maize, groundnuts and soybean, and reported a positive correlation between N
mineralization and initial N contents of the residues. This study confirms that addition of high-quality residues to the poor-quality ones improves the rate of nutrient
mineralization. This can be attributed to the activation of microbial activities in the
soil that need reasonable amounts of nitrogen to facilitate the mineralization process
and reduce the period of N immobilization.
Table 2 Nitrogen use efficiency in the form of PFP N as influenced by the previous cropping
system and fertilizer rate on maize at Lilongwe and Dowa sites, Central Malawi
Site
Fertilizer
rate
Previous cropping systems
Sole
MZ
Sole
MZ + 92 N
Sole
CP
CP + MZ
intercrop
Sole
PP
PP + CP
intercrop
PP + MZ
intercrop
Mean
(FR
effect)
PFP N (kg grain/kg N applied)
Lilongwe 0
–
–
–
–
–
–
–
–
45
55.2 69.1
119.5 104.9
102.3 107.3
107.3
95.1a
90
35.6 46.9
62.7 56.1
58.4 60.3
55.4
53.6b
120
27.3 33.6
47.2 37.7
43.8 38.7
45.1
39.1c
Mean
(CS
effect)
39.4b 49.9b
76.5a 66.2a
68.1a 68.8a
69.3a
F.pr (CS) 0.001
F.pr (FR) 0.001
F.pr
(CS∗FR)
0.048
CV (%) 18.4
Dowa
0
–
–
–
–
–
–
–
–
45
56.7 72.8
116.9 108.4
112.1 121.3
112.0
100.0a
90
38.1 41.7
55.1 59.7
57.9 65.3
58.7
53.8b
120
26.7 32.8
46.8 41.3
41.2 48.6
41.2
39.8c
Mean
(CS
effect)
40.5b 49.1b
72.9a 69.8a
70.4a 78.4a
70.6a
F.pr (CS) 0.001
F.pr (FR) 0.001
F.pr
(CS∗FR)
0.01
CV (%) 14.3
Means were separated using the Tukey’s HSD test at 5% significant level, − = not applicable,
means with different letters are significantly different; CS cropping system, FR fertilizer rate,
symbol ∗ = interaction, PFP N > 70 kg grain/kg N applied may imply very efficiently managed
systems (Dobermann 2005), MZ maize, CP cowpea, PP pigeon pea, 92 N = 92 kg N ha
−1
Integrated Soil Fertility Management Based on Pigeon Pea and Cowpea Cropping…