Agronomic production on coarse soils requires close attention to soil carbon and nitrogen assimilation and mineralization dynamics to manage nitrogen efficiently. Long-term trials underway provide insights into the impact of organic amendments (cover crops and manure) on soluble nitrogen fertilizer requirements in corn-soybean rotation systems at three Michigan State University research stations, including the NSF Long Term Ecological Research site and Living Field Laboratory at the W.K. Kellogg Biological Station, and a potato-corn rotation system at other Michigan experiment stations. Soil and plant response data allows us to examine the short and long-term impacts of enriched versus low quality organic amendments, as well as the integrated use of organic and variable nitrogen fertilization strategies. Yield and nitrogen efficiency are key indicators of system performance and resilience over time, with implications for agronomic and economic sustainability. A reduced requirement for soluble nitrogen additions is apparent in corn and potato production systems in the presence of enhanced soil nitrogen supply. This was not apparent for 3 to 8 years in trials located on Alfisols, and we predict will take longer to be observed in finer-textured soils. Recent and long-term additions of organic amendments have complex consequences for soil aggregation, water infiltration, carbon and nitrogen assimilation mechanisms as indicated by nitrogen mineralization potential dynamics and crop nitrogen response. The cascading and long-term effects of organic amendments require thorough elucidation and integration into crop nitrogen recommendations.