Climate change is projected to expand agriculture into regions previously unsuitable for crop production. However, the effects on soil health, crop performance, and carbon dynamics remain uncertain across diverse local contexts. To address this knowledge gap, I conducted a short-term study of a semi-arid rangeland near Kamloops, British Columbia, where contiguous forested and grassland areas were converted to corn for cattle grazing with inputs of compost, chemical fertilizer and herbicide. I quantified total ecosystem carbon (TEC), 13 biochemical and physical soil variables, and corn yield and quality metrics. Soil variables were synthesized into a Soil Quality Index (SQI) and a Soil Multifunctionality Index (SMF), based on enzyme activities representing carbon, nitrogen, and phosphorus cycling capacities.
Forest conversion reduced total ecosystem carbon (TEC) by 41%, whereas grassland conversion had no significant effect on TEC. Although forest-converted soils showed an 86% increase in soil organic carbon (SOC) stocks, and grassland-converted soils showed no significant SOC stock change despite identical compost and corn residue amendments. These gains masked active microbial utilization and rapid carbon turnover: soil respiration rose by 80% in forest plots and enzymatic activities increased under both conversions. Compared to the forest conversion, the grassland conversion achieved higher Soil Quality Index (SQI) and Soil Multifunctionality Index (SMF) scores and produced 21% more corn (14.95 versus 12.39 Mg ha⁻¹) with greater crude protein in stalks (11.16% versus 7.59%) and cobs (4.57% versus 3.74%). However, the accelerated SOC mineralization in both conversion scenarios undermines the potential for long-term carbon sequestration under these agricultural practices.
These results demonstrate that, despite short-term SOC gains in forest converted soils and enhanced soil function in the grassland conversion, annual corn with grazing at the studied site was a suboptimal management strategy for maintaining stable soil carbon pools. Future work should assess long-term, post-conversion carbon dynamics and alternative cropping systems to inform sustainable, context-specific land-use decisions.
