Converting irrigated, conventional-till (CT) systems to no-till (NT) production systems can potentially reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions. Nitrogen fertilization effects on irrigated corn (Zea mays L.) and malting barley (Hordeum distichon L.) yields in a corn-barley rotation were evaluated for 6 yr on a clay loam soil to determine the viability of using a NT system and N needs for optimum crop yield. Six N treatments were established with N rates varying from 0 to 224 kg N ha(-1) for corn and 0 to 1.12 kg N ha(-1) for barley. Corn and barley grain yields were significantly increased by N fertilization each of 3 yr in the rotation. Three year average corn grain yields were near maximum with an available N (AN) (soil + fertilizer + irrigation water N) level of 274 kg N ha(-1). Barley yields increased linearly with increasing N rate with grain protein content near 130 kg protein Mg-1 grain at the highest N rate. Nitrogen use efficiency (NUE) by corn and barley, based on grain N removal, decreased with increasing AN level and ranged from 204 to 39 and 68 to 31 kg grain kg(-1) AN for the low and high N treatments for corn and barley, respectively. Total plant N uptake required to produce one Mg grain at near maximum yield in this study averaged 21 kg N for corn and 27 kg N for barley. Corn and barley residue production increased with increasing N rate. Irrigated, NT corn yields obtained in this corn-barley rotation were acceptable (>10 Mg ha(-1)) for northern Colorado; however, barley yields did not meet our expected yield goal of 5.4 Mg ha(-1) with the N rates used in this study, but grain protein was near maximum for malting barley. An irrigated, NT corn-barley production system appears to be feasible in northern Colorado.
