Nitrogen and phosphorus uptake by maize as affected by particulate organicmatter quality, soil characteristics, and land-use history for soils from West African moist savanna zone

The impact of land use (unfertilized continuous maize cropping, unfertilize d and fertilized alley cropping with maize, Gliricidia sepium tree fallow, natural fallow) on the soil organic matter (SOM) status and general soil fe rtility characteristics were investigated for a series of soils representat ive for the West African moist savanna zone. Three soils from the humid for est zone were also included. In an associated pot experiment, relationships between maize N and P uptake and SOM and general soil characteristics were developed. Soils under natural fallow contained the highest amount of orga nic C (1.72%), total N (0.158%), and had the highest effective cation excha nge capacity (ECEC) [8.9 mEq 100 g(-1) dry soil], while the Olsen P content was highest in the fertilized alley cropping plots (13.7 mg kg(-1)) and lo west under natural fallow (6.3 mg kg(-1)). The N concentration of the parti culate organic matter (POM) was highest in the unfertilized alley cropping plots (2.4%), while the total POM N content was highest under natural fallo w (370 mg N kg(-1)) and lowest in continuously cropped plots (107 mg N kg(- 1)). After addition of all nutrients except N, a highly significant linear relationship (R-2=0.91) was observed between the total N uptake in the shoo ts and roots of 7-week-old maize and the POM N content for the savanna soil s. POM in the humid forest soils was presumably protected from decompositio n due to its higher silt and clay content. After addition of all nutrients except P, the total maize P uptake was linearly related to the Olsen P cont ent. R-2 increased from 0.56 to 0.67 in a multiple linear regression analys is including the Olsen P content and clay content (which explained 11% of t he variation in P uptake). Both the SOM status and N availability were show n to be improved in land-use systems with organic matter additions, while o nly the addition of P fertilizer could improve P availability.