There have been a few questions about the yield potential of late-planted rice over the past few days. The general rule of thumb for rice planted in May in south Louisiana is that you should only expect 65% of your yield potential if you are planting a variety in May and 75% of your yield potential if you were planting a rice hybrid.
I thought that I would put this rule to the test and see if it holds true with recent rice varieties from Dr. Linscombe’s date of planting studies. I pooled together the data from 2010 to 2014. Our general recommendation window for planting rice in south Louisiana is March 10 to April 15.
So, I took the data and separated planting dates inside the recommended planting window and those outside the recommended planting window. I used regression analysis to determine the relationship between the planting date and the relative (percent of maximum) yield across the dates of planting.
The results can be seen below.
The first thing that you will notice is that the relative grain yield is highly variable across years. This is to be expected since the weather patterns can vary considerably from year to year.
The regression for the data within or slightly before the recommended window indicate that 100% to 80% of the relative grain yield can typically be expected within the recommended window. The linear regression line for the rice planted outside the planting window shows that approximately 0.5% of the remaining 80% yield potential is lost for rice varieties for every day past April 15.
This excludes RiceTec hybrids, which were not included in the trials during these years. Therefore, rice planted on May 15 (30 days past April 15) would have a yield potential of 65%. Looks to me like the old yield potential rule of rice planted in May still fits pretty well!