Dairy Manure Application Method and Timing Influence N Availability to Corn.

Manure N credits will vary with application method and time until incorporation, however minimal information exists regarding N availability from in-season manure application. The objectives of this study were to understand how corn yield and manure N credits are impacted by 1) spring preplant or sidedress applications of dairy slurry and 2) manure application method and time until incorporation. This study was conducted from 2009 to 2012 on a somewhat poorly drained Withee silt loam. Pre-plant dairy manure treatments  (mid- to late-May) were either injected or incorporated with a tandem disk immediately after manure application (< 1 hour), 1 day later, or 3 days later. Injection was with an S-tine injector with 15-inch spacing at a 4- to 6-inch depth. All plots were chisel plowed 3 to 5 days after application. Sidedress manure applications (5- to 6-leaf stage) were either injected with an S-tine injector (30-inch spacing) or surface applied. Urea was applied pre-plant at 0, 45, 90, 134, 179, and 224 kg N ha^-1 and incorporated with a disk. Each treatment was replicated four times in a randomized complete block design. Dairy slurry was applied at ~63.1 kL ha^-1 with on average 14% solids, 177 kg total N ha^-1 and 69 NH₄-N kg ha^-1. Injecting manure resulted in 51 and 53 % of total N applied being available from the preplant and sidedress treatments, respectively. Preplant broadcasting with incorporation within 1 hour or 1 day of application resulted in 36 and 37 %, respectively, of total N being available. Thirty-four percent of manure N was available when broadcast prior to planting and incorporated after 3 days; while 32% was available when surface banded (no incorporation) at sidedressing. In general, N availability decreased as time to incorporation increased and sidedress injected manure is as available as preplant injected manure.