Stability of soil organic matter and soil loss dynamics under short-term soil moisture change regimes

Abstract

Soil properties are known to be influenced Soil Organic Matter (SOM) resident time. However, there is limited information on the interactive effects of SOM quality and soil moisture on SOC and Microbial Biomass Carbon (MBC) hence on soil losses. Therefore, this study investigated the effects of different organic matter and soil moisture in soils with low (<2%) initial SOC content on the SOC, MBC and soil loss with time of organic matter incorporation. Six soils were incubated for 34 weeks at 25°C after adding high quality (C/N=23) Vachellia karroo leaf litter and low quality (C/N=41) Zea mays stover. The effect of SOM quality and soil moisture on the SOC content, MBC and soil loss was significantly (P<0.05) the same within but varied across soils. Soils that were continuously wet lost more SOC than under alternating wet-dry moisture conditions. Microbial biomass carbon was controlled by the availability of organic matter and moist soil conditions. Low MBC values corresponded to high SOC and soil loss. Continuously wet soils with high sand particles promoted rapid loss of SOC compared to alternating wet-dry soils. Therefore, continuously wet sandy soils are likely to contribute more to the climate warming than alternating wet-dry soil moisture. In the wake of the climatic change, addition of OM in continuously wet soils need to be regulated but to reduce soil loss re-application of fresh OM has to be more frequent under continuously wet sandy soils than in alternating wet-dry moisture regimes.