Irrigated Corn and Soybean Response to Nitrogen under No‐Till in Northern Colorado

Abstract

Irrigated, no‐till (NT) production systems can potentially reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions compared with conventional till (CT) systems. Including a legume in the rotation may also reduce N fertilizer requirements. Nitrogen fertilization (6 N rates) effects on irrigated, corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields in a corn–soybean rotation were evaluated for 5 yr on a clay loam soil to determine the viability of an irrigated NT system and N needs for optimum crop yield. Corn grain yields were significantly increased by N fertilization each of 3 yr in the rotation, but soybean grain yields (2 yr) did not respond to N fertilization, averaging 2.79 Mg ha−1. Three year average corn grain yields were near maximum with an available N (AN) (soil + fertilizer + irrigation water N) level of 257 kg N ha−1. Nitrogen use efficiency (NUE) by corn and soybean, based on grain N removal, decreased with increasing AN level and ranged from 155 to 46 and 88 to 18 kg grain kg−1. AN for the low and high N treatments for corn and soybean, respectively. Estimated total N required to produce one Mg grain at maximum yield averaged 20 kg N for corn and 54 kg N for soybean. Corn residue increased with increasing N rate, but soybean residue was constant across N rates. Excellent irrigated, NT corn yields were obtained in this corn–soybean rotation for northern Colorado, but soybean yields were only marginally acceptable. Short soybean plant height (30–40 cm) and shattering made combine harvest difficult resulting in significant grain loss. Improved soybean cultivars are needed for this area to make a corn–soybean rotation a viable production system.