No-till Corn Response to Shallow Placement of Anhydrous Ammonia.

Anhydrous ammonia (AA) is used extensively in the Midwest USA as a source of nitrogen (N) for corn (Zea mays L.) production. As farm size increases there is a need to enhance speed of N application without sacrificing efficiency. The objective of this study was to compare a traditional AA knife injection system (TRAD) and a prototype high-speed, low-draft AA opener system (HSLD). This study was conducted in no-till fields following soybean (Glycine max. L. Merr.) during 2007- 2009 in Illinois, Iowa, and Kansas. A factorial arrangement of the two AA systems (TRAD and HSLD), three application times [fall (FA) only in 2008-09, spring pre-plant (SP), and sidedress (SD)], and five N rates (0, 90, 135, 180, and 225 kg N ha^-1) was replicated four times in a split-plot arrangement with time of application as the main plot in a randomized complete block design. FA and SP applications were in-row (future corn row), while SD was between every other row. The TRAD application was at 18-cm depth and 10 km hr^-1 and the HSLD at 10-cm depth and 13 to 16 km hr^-1. Corn yield increased with increasing N rate. Yield with the FA application was 11.1 Mg ha^-1, 3.7 and 3.5% lower than SD and SP applications, respectively.  Across N rates, yield with the TRAD was 3.4% higher compared to the HSLD with SP application (5.5% higher, 665 kg ha^-1, with the highest N rate), but no difference with other application times. This reduction was likely caused by N loss and/or seedling injury with the shallow AA positioned spring preplant in-row. In-season plant measurements produced similar results to those with grain yield. The HSLD is a viable alternative to TRAD when soil conditions are adequate for proper operation of the HSLD and application is not near the seed-row.