Long-term effects of crop rotation, tillage, and fertilizer nitrogen on soil health indicators and crop productivity in a temperate climate

Although diversifying crop rotations with perennials and cover crops and implementing no-tillage practices has been promoted as an effective strategy for increasing soil carbon and nitrogen storage in the long-term, uncertainty still remains, particularly regarding the association between crop productivity and soil health. Therefore, using two long-term experiments, we investigated the effects of crop rotation, tillage system, and nitrogen fertilizer application (at Ridgetown only) on surface soil (0-15 cm depth) parameters (soil organic carbon (SOC), total nitrogen (TN), commercial soil health tests (evolved CO2 and NH3 indicating microbial activity)), and crop yield in 2016. We used 5-yr average crop yield variability to test for the relationship of SOC and TN with crop yield stability. Results indicated that diversification of corn and soybean rotations and their monocultures with cover crops, perennials, and small grain cereals enhanced soil health indicators (by 32% at Ridgetown (21 yr) and 49% at Elora (36 yr)) and crop productivity (16% at Ridgetown and 29% at Elora). At Ridgetown, corn yield was 10.4% greater with including red clover to the corn-soybean-winter wheat than monoculture corn. Similarly, corn yield was enhanced by 25% when alfalfa was added to monoculture corn at Elora. Nitrogen fertilizer application did not increase surface SOC storage at Ridgetown. No-tillage system had greater evolved NH3-N (by 7.2%) and evolved CO2-C (by 27.9%) than conventional tillage at Elora only. Consistent with management effects on crop yield, at both sites, evolved NH3-N and CO2-C were greatest from rotations with winter wheat, red clover, and alfalfa. Additionally, a strong positive relationship of SOC and TN with soil health tests confirms the suitability of the commercial tests to detect management effects on soil health indicators in the long-term. At both sites, SOC positively correlated with crop yield indicating a direct association between soil carbon status and agroecosystem resiliency. We conclude that diversifying crop rotations increases soil microbial activity, surface SOC sequestration, and crop productivity in the long-term; thus, is a critical component for developing sustainable agroecosystems.