Response of Two Rice Varieties to Midseason Nitrogen Fertilizer Application Timing.

A study was initiated in 2010 to examine the influence of midseason nitrogen (N) application timing on the grain yield of two conventional rice (Oriza sativa L.) varieties currently grown in the southern United States. The rice varieties chosen for the study were the long-grain, semidwarf ‘Cheniere’ and the long-grain, short stature ‘Taggart’. During each study year, individual plots received either 50 or 100 kg N ha^-1 applied at the 4- to 5-leaf growth stage just prior to establishment of the permanent flood followed by a midseason application of 50 kg N ha^-1. In 2010, midseason N was applied at 12.7-mm internode elongation (IE), 12.7-mm IE + 7 days, or 12.7-mm IE +14 days. In 2011, midseason N was applied earlier in reproductive growth at beginning internode elongation (BIE), 12.7-mm IE, and 12.7-mm IE + 7 days. In 2012, midseason N was applied at BIE, 12.7-mm IE, 12.7-mm IE + 7 days, and 12.7-mm IE + 14 days. The first year results showed rice grain yield increased for both varieties as midseason N application was delayed from 12.7-mm IE to 12.7-mm IE + 7 or 14 days.  There was no difference in grain yield between the 12.7-mm + 7 and 12.7-mm + 14 day application timings. In the second year rice grain yield significantly increased when midseason N was applied at all application times, but only at the lower preflood N rate of 50 kg N ha^-1. In 2012, rice grain yield response was similar among application times, but each timing significantly increased grain yield compared to plots receiving no midseason N. These initial results indicate that currently grown rice varieties do not always respond to midseason N and that when they do the midseason N application window may be wider than previously grown varieties.