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Short-term land-use change from grassland to cornfield increases soil organic carbon and reduces total soil respiration

Mukumbuta, Ikabongo, Shimizu, Mariko, Hatano, Ryusuke
Soil & tillage research 2019 v.186 pp. 1-10
carbon dioxide, cropland, emissions, grasslands, land use change, mineral fertilizers, nitrogen, plant litter, plowing, soil organic carbon, soil respiration, temperature
Land-use change between grasslands and croplands has a significant influence on soil organic carbon (SOC) and soil respiration (RS). However, the response of the different components of RS to land-use changes and variations in temperature and moisture regimes is poorly understood. This study investigated the responses of RS, heterotrophic respiration (RH) and root respiration (RR) to changes of soil temperature, moisture and nitrogen (N), and changes in SOC, accompanying with land-use changes for 11 years. The study was conducted in a >30-year old permanent grassland (OG; 2005–2009), that was ploughed and converted to a cornfield (2010–2012) and then converted to a new grassland (NG; 2013–2015). Three treatments, chemical fertilizer and manure, chemical fertilizer only, and unfertilized control, were assessed. Fluxes of RS and RH were measured using the closed chamber method. SOC was monitored at 0–15 and 15–30 cm soil depth.On average, RS decreased by 25–43% after conversion from OG to cornfield and then increased by 21–33% after the change from cornfield to NG. Contrary to RS, RH increased by more than 30% following land-use change from OG to cornfield and declined by at least 20% after converting cornfield to NG. The contribution of RH to RS was significantly higher in cornfield (60–100%) than in OG (38–60%) and NG (47–80%). The different trends of RS and RH following land-use change calls for a clear distinction of the CO2 source when reporting its emissions from soil. The influence of soil temperature, moisture and N on RS and RH differed among the land-uses. The conversion of grassland to cornfield significantly increased SOC, especially in the manure-amended plot. This increase in SOC in the first 1–3 years of conversion indicates that conversion or ploughing of grassland is important to turn plant litter/applied manure into actual soil carbon. These results call for a rethink of the commonly held notion that conversion of grassland to cropland depletes SOC, as the conversion could be beneficial if done for shorter time periods.