Evaluation of nitrogen sources and application methods for nitrogen-rich reference plot establishment in corn
Five different N sources were compared with null N treatment to evaluate their performance for N-rich reference plot establishment in corn (Zea mays L.). The sources, including calcium ammonium nitrate (CAN), urea ammonium nitrate (UAN), polymer-coated urea (PCU) and environmentally smart nitrogen (ESN) in 2007 and 2008, and urea (URE), were broadcast or in-soil banded at the rate of 225 kg N ha–1. A greenhouse trial was also conducted with N applied as CAN, URE, and ESN. Net photosynthesis rate (PN) and chlorophyll fluorescence parameters (Fv/Fm or Fv'/Fm') were measured to assess N sources effects on corn photosynthesis. Relative photosynthetic capacity (RPC) and relative chlorophyll fluorescence capacity (RCFC) were calculated to evaluate the performance of N sources in N-rich reference plot establishment. There were no differences in the release pattern of N from different sources that could lead to differences in RPC and RCFC during the period when N status diagnosis is normally performed. Hence, all sources were equally effective to establish N-rich reference plots in our experimental conditions. It was also found that growers have the flexibility to either broadcast N at sowing or to band N along the rows at a later time after corn emergence.