Influence of rainfall amount and livestock grazing on soil respiration in a moist Kenyan savannah

Abstract

The influence of livestock grazing and changing rainfall patterns on soil respiration (Rs) in the tropical savannah in Lambwe is unclear. Measurements of Rs using chambers were conducted between June and November 2012 in a humid savannah in Western Kenya to determine how simulated rainfall amounts and cattle grazing affected soil respiration. The experimental layout was split plot comprising rainfall simulations which were laid on grazed and fenced blocks, respectively. The rainfall simulations split plots each measured 6 m × 3 m and were covered with rainout gutters above the canopy of the herbaceous layer to either increase or reduce ambient rainfall by 50%. Grazing increased soil bulk density and significantly ( p <0.05) lowered soil respiration rates and soil water content irrespective of the rainfall treatment. The positive correlation between Rs and root biomass in both grazed and fenced plots revealed a significant contribution of root growth activities to Rs. Increased soil water content (SWC) by rainfall addition improved water penetration into deeper soil layers and therefore stimulated root and microbial activities which in turn built up soil respiration. Reduction in SWC by rainfall exclusion lowered microbial contact with the organic substrate and likely caused death and / or inactivity of roots.