Global Maize Project in the United States: Ames, Iowa

The Ames, Iowa research site is one of several experiments around the world involved in the Global Maize Project. There are several focus areas of the project, including the effect of withholding N application on crop productivity, attempting to increase crop yield while lessening environmental effects, and attempting to improve N use efficiency (NUE). An across-year data analysis (2011-2014) summary shows several key results for the project.

Across both the farmer practice (FP) system and ecological intensification (EI) systems, corn yields increased 72% with N application. Soybean yield is the same in both systems, however, slightly lower yield occured when N was applied to corn. The N in the FP system is all anhydrous ammonia applied pre-plant at 157 to 162 kg N/ha, with the rate determined using the Corn Nitrogen Rate Calculator and current N and corn prices. The N in the EI system is a split pre-plant/sidedress N application of ammonium nitrate/urea-ammonium nitrate solution at a total of 134 to 190 kg N/ha, with the range due to adjustment of rate based on canopy sensing in some years. When N is applied, corn yield in the FP is slightly higher (4.5%) than in the EI. Without N applied, corn yield with in the FP is 28% higher than in the EI. This indicates more N supply from the soil to corn with the FP that includes tillage for both crops compared to the EI that is strip-till corn and no-till soybean. Since the FP has greater yield with no N applied, the N use efficiency (NUE) is higher for NUE measures of agronomic efficiency (AE) and relative efficiency (RE) with the EI system – due to greater delta yield increase with N applied in the EI, as both of those NUE measures use yield increase from N application per unit of N applied. However, the N efficiency is the same for both systems with the NUE measure of partial factor productivity (PFP), because it is based on yield level produced per unit of N applied.

In summary, the FP system has produced higher corn productivity than the EI system, and therefore overall greater crop productivity across the rotation. It is important to realize that good farmer corn and soybean production practices in Iowa are highly productive and near the maximum yield potential. However, NUE and soil N resource utilization due to use of tillage in the FP may be important issues to consider for long-term cropping intensification.