Alley cropping in the moist savanna of West-Africa. III. Soil organic matter fractionation and soil productivity uri icon

abstract

  • In cropping systems with limited amounts of external inputs, the soil organic matter pool (SOM) may contribute significantly to plant nutrition. The impact of organic inputs on total SOM and particulate organic matter (POM) N contents as affected by soil type and the relationships between sources of N and maize N uptake were assessed for a set of alley cropping trials in the West-African moist savanna. The trials were established in Niaouli (Benin Republic), in Glidji, Amoutchou, and Sarakawa (Togo), and in Bouake and Ferkessedougou (Cote d' Ivoire). The total soil N content, averaged over all treatments and years, varied between 324 and 1140 mg N kg(-1) soil. The POM-N content varied between 50 and 160 mg N kg(-1) soil. The average proportion of soil N belonging to the POM pool ranged between 9% and 29%. This was significantly related to the annual N inputs from maize stover and prunings, when averaged over the different alley cropping treatments. The trial 'age' also appeared to be related to the impact of the different treatments on the POM-N content. The Ferkessedougou soil contained a relatively higher proportion of total soil N in the POM pool because of its relatively high silt and clay content, compared to the other sites. The relative change in POM-N content between 1996 and the initial sampling was about twice the relative change in total soil N content. This suggests that N incorporated in the POM is relatively labile, compared to N incorporated in the other SOM fractions. Maize N uptake was related to the amount of add pruning-N (partial r(2) of 27%), the rainfall during the growing season (partial r(2) of 17%), the POM-N content (partial r(2) of 14%), and to a lesser degree to the POM N concentration (partial r(2) of 5%), the fertilizer N addition rate (partial r(2) of 3%), and the silt and clay content of the soil (partial r(2) of 3%). The POM-N content was shown to be influenced by organic matter additions and soil characteristics and to contribute significantly to maize N supply. This pool may be an important indicator for the soil fertility status of savanna soils.

publication date

  • 1998
  • 1998