Impact of Management Practices on Carbon and Water Fluxes in Corn–Soybean Rotations

Abstract

Core Ideas Soil management affects carbon and water dynamics. Net ecosystem production was higher in reduced till systems. Ecosystem respiration was higher in tillage systems. Residue management most likely to affect net ecosystem production and ecosystem respiration. Corn [Zea mays L.] and soybean [Glycine max (L.) Merr.] are important US crops, and soil management typically comprises tillage activities, yet improvements in management practices may have substantial impact on C and water dynamics. This study's aim was to determine management impact on C and water fluxes. Four eddy covariance stations monitored evapotranspiration (ET) and net ecosystem production (NEP) in 2016–2017 in two corn–soybean–rotation systems—a conventional and a transitional system to reduced till with cover crop (i.e., aspirational). Net biome production (NBP), gross primary production (GPP), ecosystem respiration (RE), and inherent water use efficiency (IWUE*) were calculated. Aspirational site NEP was higher than the conventional site with 565 vs. 421 g C m−2 in corn, and 108 vs. −64 g C m−2 in soybean. The aspirational RE was lower than under conventional management for both corn and soybean. Aspirational corn GPP was lower than conventional with 1285 and 1405 g C m−2, and no difference in soybean with 750 and 742 g C m−2. Linear regression (p < 0.05) showed higher NEP regression slopes in spring in the conventional compared with the aspirational system, with −0.016 and −0.004 in soybean, and −0.012 and −0.005 in corn. The soybean‐years were a C source in both management systems. Although annual ET was similar among crops and management with 589 to 610 mm, the growing season IWUE* was higher under conventional management. Reduced tillage substantially improved C dynamics in corn and soybean, whereas ET was less affected.