Nitrogen and phosphorus control carbon sequestration in agricultural ecosystems: modelling carbon, nitrogen, and phosphorus balances at the Breton Plots with ecosys under historical and future climates

摘要

Perennial legumes in crop rotations increase soil C sequestration from greater productivity with N2 fixation. Here, we corroborated increases in soil organic carbon (SOC) and harvests modelled in 5 yr wheat-oats-barley-alfalfa/brome-alfalfa/brome (5Y) vs. 2 yr wheat-fallow (WF) rotations with those measured from 1929 to 2018. Harvest and SOC gains of 100-150 g C M-2 yr(-1) and 15-25 g C M-2 yr(-1) were modelled and measured in 5Y vs. WF rotations with different fertilizer and manure amendments. Modelled gains were closely related to annualized rates of N-2 fixation by alfalfa of 8-10 g N M-2 yr(-1). However, N2 fixation also drove increases in modelled N2O emissions of ca. 0.06 g N M-2 yr1, which partially offset gains in SOC. Gains in harvest, SOC, and N2O emissions of 60-90 g C m(-2) yr(-1), 15 g C m(-2) yr(-1), and 0.05 g N m(-2) yr(-1) were modelled and measured in both rotations with amendments of N+ P relative to unamended treatments. Harvest and SOC gains were smaller, and leaching and N2O losses larger, with amendments of N without P. After 100 yr of RCP 8.5 climate change, harvests in WF changed little from those in baseline runs, whereas those in 5Y rose with N+ P because of increased N-2 fixation. SOC declined in WF with all amendments and could only be raised in 5Y with N + P amendments. These model findings indicated the importance of N-2 fixation and P amendments in determining responses of agroecosystem productivity and C sequestration to climate change.