Effect of tillage and nitrogen rate on corn yield and nitrogen and phosphorus uptake in a corn-soybean rotation

Understanding tillage, N, and P interactions can contribute to improved N and P utilization and crop response. This study examined the interaction effects of tillage and N rate of two N sources on N and P uptake by corn (Zea mays L.). The study was conducted on Kenyon loam (fine loamy, mixed, mesic Typic Hapludolls) soil at the Iowa State University Northeast Research and Demonstration Farm near Nashua, IA. A randomized complete block design with a split-plot arrangement in three replications was used for the two separate N source experiments. The tillage systems consist of no-tillage (NT), strip-tillage (ST), and chisel plow (CP) as main plots. Within each tillage four N rates (0, 85, 170, and 250 kg N ha(-1)) were assigned as subplots for each N source of manure (total N) and fertilizer (anhydrous ammonia) in a corn-soybean [Glycine max (L.) Merr.] rotation. Tillage and increase in N rate beyond 85 kg ha(-1) had no effect on corn grain yield with both N sources. Tillage x N rate had a significant effect on plant N and P uptake, especially at early growth stages with both N sources. Recovery percentage of applied N across all tillage systems and N rates was 40% and 27% for manure and fertilizer sources, respectively, at the 12th-leaf growth stage of corn (V12). Plant N and P uptake at V12 growth stage was 44% and 37%, respectively, across tillage systems, N sources, and N rates. The findings indicate that the N rate and seasonal variability have more influence on plant N and P uptake than does the tillage system.