Influence of two management practices in the Canadian Prairies on radiative forcing.

Surface albedo and soil carbon sequestration are influenced by agricultural management practices which impact the Earth's radiation budget and climate change. In this study we investigate the impact of reduced summer fallowing and reduced tillage in the Canadian Prairies on climate change by estimating the change in radiative forcing due to albedo and soil carbon sequestration. Seasonal variations of albedo, which are dependent on agricultural management practices and soil colour in three soil zones, were derived from 10-day composite 250-m Moderate Resolution Imaging Spectroradiometer (MODIS) data. Using this information, we found an overall increase of surface albedo due to the conversion from summer fallowing to continuous cropping and from conventional tillage (CT) to either no-tillage (NT) or reduced tillage (RT). The increase was dependent on soil brightness, type of vegetation and snow cover. Using data from the Census of Agriculture and taking into consideration both albedo and soil carbon changes, we estimated that from 1981 to 2016, the total radiative forcing for the cropland area in the Canadian Prairies was -405 μW m due to the conversion of CT to either NT or RT and about 70% was due to the change in albedo. During the same period, the total radiative forcing was -410 μW m due to a reduction in the area under summer fallow and about 62% was due to the change in albedo. The equivalent atmospheric CO drawdown from these two management changes from albedo change was about 7.8 and 8.7 Tg CO yr, respectively. These results demonstrate that it is important to consider both the changes of soil carbon and surface albedo in evaluating climate change impacts due to agricultural management practices.