Abstract: Soil nitrate-N dynamics during the dry-to-wet transition (DWT) season and its management are
key determinants of soil productivity in low-input systems of the dry savanna zone of West
Africa. Two field experiments were conducted in 2013 and 2014 with the aim to determine the
effect of soil tillage and rainfall intensity on native NO3-N dynamics during DWT. The study on
the effects of soil disturbances on N mineralization compared mechanical tillage with a no-till
treatment. The effect of rainfall intensity on nitrate dynamics was assessed by comparing natural
rainfall with a simulated 30% increase and a 30% reduction. Mechanical soil tillage increased N
mineralization in 2013 and during the initial phase of DWT in 2014. Towards the end of DWT,
most nitrate from wetland soils adjacent to a tilled upland had disappeared, while N
mineralization continued in the lowland below the reduced tillage treatment. Reduced rainfall
increased the nitrate accumulation in the soil profile with little apparent nitrate losses. With
increased rainfall, on the other hand, most nitrate had disappeared once the volumetric soil
moisture exceeded 25%. We conclude that tillage and rainfall differentially affect soil-N dynamics
during DWT and, there is a need for site-specifically adapted soil-N-conserving management
strategies. |