Long-Term Research with Semi-Arid Irrigated Corn: What Have We Learned and What Now?.

Long-term agricultural research sites are crucial for developing sustainable agronomic practices that preserve ecosystem services while maximizing crop productivity and economic returns. An irrigated corn production study was initiated in 1999 near Fort Collins, CO.  Over the past 17 years, we have investigated the effects of N fertilizer source and rate, crop rotation, and tillage management effects on crop yields, trace gas fluxes, soil C and N cycling, and economic returns providing an integrated evaluation of best-management practices for semi-arid irrigated corn. N fertilizer requirements are about 180 kg ha^-1 for optimum corn yields and for providing sufficient stover C to maintain soil organic matter stocks. Results from N source experiments showed decreased N₂O fluxes with some enhanced efficiency N fertilizers under reduced tillage, but not conventional tillage. Strip tillage showed yields similar to conventional tillage, increased SOM levels and decreased N₂O similar to no-till, and also maximized economic returns. Residue return to the soil is crucial to maintaining soil organic matter, although no till corn yield is enhanced with stover removal in the short term.  Application of manure can increase soil quality and sequester C, although GHG emissions are increased. These and other results will be presented, along with descriptions of current research investigating the impacts of novel cropping systems (e.g., multi-cropping) on soil C and N dynamics, greenhouse gas emissions, and microbial community structure.