Long-term research trials provide unique insights into nutrient management at different states, transitional and equilibrium. Nitrogen (N) and phosphorus (P) management recommendations are often based on experimentation that is less than a decade in duration. Yet cropping system response and nutrient availability is expected to change over time as feed-forward mechanisms are influenced by tillage and residue inputs that alter soil C, N and P pools.  The Long Term Ecological Research Row Crop (LTER-Row Crop) 20 year trial underway at the W.K. Kellogg Biological Station in Michigan provides insights into the interaction of tillage, winter cover management and fertilizer input levels on nutrient availability, soil characteristics and performance of a corn-soybean-wheat rotation. Monitoring of soil carbon, N, P, water status and plant productivity has elucidated differences in performance during transition years of the first decade and the second decade of performance for conventional, reduced tillage, low input and organic management systems. A reduced requirement for soluble N inputs was observed over time in treatments with winter cover crops, as the potentially mineralizable N pool increased and substitutes currently for 60 to 100% of fertilizer N. Cereal yield in the initial 5 years of the trial was substantially reduced (11% to 48%), whereas in that last five years yield reduction has become modest (0 to 17%), compared to conventionally managed systems. Nitrogen efficiency for low-input managed corn compared to conventionally managed corn is 2-fold higher. Interestingly, P availability in cover crop managed, low-input soybean has also been increased as measured by Bray extract and a P-bioassay. Taken together, the results from this long-term trial are consistent with feedback mechanisms that alter nutrient availability and productivity profoundly, compared to minimal impacts from recent inputs of soluble nutrients. This has implications for agronomic management of row crops in the Upper Midwest.