Nitrogen and phosphorus control carbon sequestration in agricultural ecosystems: modelling carbon, nitrogen, and phosphorus balances at the Breton Plots with <i>ecosys</i> under historical and future climates
R. F. Grant, Miles Dyck, Dick Puurveen
Abstract
Perennial legumes in crop rotations increase soil C sequestration from greater productivity with N 2 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, N 2 fixation also drove increases in modelled N 2 O emissions of ca. 0.06 g N m −2 yr −1 , which partially offset gains in SOC. Gains in harvest, SOC, and N 2 O 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 N 2 O 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.