Impact of residue characteristics on phosphorus availability in West African moist savanna soils
Nwoke, O.C. | Vanlauwe, B. | Diels, J. | Sanginga, N. | Osonubi, O.
The role of residue characteristics in enhancing the availability of P was investigated in a greenhouse study using two soils from the northern Guinea savanna (NGS) and four from the derived savanna (DS) zones of the West African moist savanna. Eight organic residues of varying C-to-P ratio were used and maize (Zea mays) was grown for 7 weeks. The effect of the organic residues on P availability (measured as resin P and maize P accumulation) differed among the soils. On average, the increase in resin P, calculated as ([(soil+residue)-control]/(control)x100), was between 8% (Davie, DS) and 355% (Danayamaka, NGS). Maize P accumulation was increased by ca: 11% in Davie and Niaouli (DS) soils and 600% in Danayamaka soil. The increase in maize total dry matter yield (DMY) ranged from 2% to 649%. Residues with C-to-P ratio >200 produced lower DMY than those with lower ratios. Residue organic P (Po) extractable with 0.2 N H2SO4 (acid-Po) accounted for 92% (P =0.0001) of the variation in DMY in a step-wise regression with residue parameters as independent variables and mean DMY as the dependent variable. The residue Po extractable with 0.5 M NaHCO3 (HCO3-Po) correlated significantly with DMY in Danayamaka and Davie soils, and with P accumulation in Danayamaka soil. The relationships between the residue Po and DMY might imply that Po fractions in decomposing residues contribute to P availability. However, the suitability of using the Po content of organic residues to predict their agronomic value with respect to P nutrition needs further evaluation.
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