Long‐term crop rotation diversity, tillage system, and nitrogen fertilizer effects on crop productivity, soil organic carbon, and nitrogen concentration in a temperate humid climate

Abstract No‐tillage and crop rotation diversity effects on soil organic C (SOC) and total N have been well documented in the literature. However, it is not clear how these strategies interact with N fertilizer management to impact soil C and N and crop yield. Therefore, a long‐term experiment (24 years) was used to quantify the effects of crop rotation (continuous corn [CC, Zea mays L.], corn–soybean [ Glycine max L., CS], corn–soybean–wheat [ Triticum aestivum L., CSW], CSW undersown with red clover [CSWrc, Trifolium pratense L.], soybean–winter wheat [SW], SW undersown with red clover [SWrc], and soybean–soybean [SS]), tillage system (conventional tillage [plow] and no‐tillage), and N fertilizer management (−N and +N) on crop productivity and SOC and total N concentration in 0–30 cm depth in 2019 at Ridgetown, Ontario. SOC concentration was significantly different among the tested crop rotations (CC, CS, CSW, and SW) in all the soil depths. For instance, at 0‐ to 5‐cm depth, SW (39.6 ± 1.58 mg g −1 ) had the greatest, while the remaining three crop rotations (average 30.2 ± 1.86 mg g −1 ) had the least SOC concentration. In contrast, tillage treatment effects on SOC were observed in 0‐ to 5‐cm and 20‐ to 30‐cm depths where no‐tillage had 23.2% and 21.3% greater SOC concentration than conventional tillage, respectively. Unlike SOC, tillage and crop rotation did not have significant effect on total N concentration. Among the crop rotations, CSWrc (9.76 ± 0.55 Mg ha −1 ) had the greatest corn yield, while CSW, SWrc, and SW (avg. 4.32 ± 0.11 Mg ha −1 ) had the greatest soybean yield. Neither red clover nor N fertilizer application increased SOC and total N concentration in all crop rotations and tillage treatments even though corn and wheat yield was increased with N fertilizer. Our results suggested that corn and soybean yield variability decreased with an increase in SOC content and addition of winter wheat to crop rotations, suggesting that building SOC storage and including winter wheat have long‐term implications on developing agroecosystem resiliency.