By Dustin Harrell, LSU AgCenter Rice Specialist
Warm and dry conditions, with a couple of small showers mixed in to help maintain soil moisture, has provided a quick start to the rice crop this year. The USDA-NASS Louisiana Crop Progress Report (click here to see report) for the week ending March 26 has us currently 42% planted for the state and approximately 13% ahead of our 5-year average.
While this estimate is tremendously faster than we have seen for several of the past few and very wet years, I would venture to say that we are even farther along than 42% in the state. In the southwest part of the state, where we grow approximately 75% of our rice, I would predict that we were about 85% completed on Friday night (March 24th) prior to the rainfall that we saw that night.
A few acres have been planted in the northeast however, planting really has not had a chance to kick-off in earnest since they have received more rainfall and the clay soils in that region have not had a good chance to dry out enough for the drills to roll across the fields.
With that in mind, I would predict that we were approximately 65% planted in the state by Monday (March 26) and 36% ahead of our 5-year average. Either way, we have more rice in the ground now than we typically do this time of year.
Not only do we have a lot of rice planted but the rice seems to be jumping out of the ground and growing at breakneck speed. I would estimate that a significant amount of the rice in the southern part of the state is around that 2- to 3-leaf stage of development right now. I have even been told that we have a few fields which have already established the permanent flood and we have not even reached April yet! How can this be possible you ask? Well, it has to do with the warm conditions we have had this year.
Here at the Rice Station we have had 11 days in the month of March where the daytime highs have been 80 F or above. We are accumulating more daily heat units than normal this time of year. The number of heat accumulated each day above 50 F each day, with adequate soil moisture and no other limiting factors, can be used to estimate rice growth and development. These heat units are often referred to DD50 heat units which is the backbone of the DD50 program. DD50 heat units can be calculated by getting the average daily temperature and subtracting 50.
In general, it takes between 75 to 175 heat units for each subsequent leaf to emerge during the seedling stages of rice development. Rice emergence begins with the appearance of the coleoptile (shoot), followed by the primary leaf, first true leaf, the second leaf, and continues until the fifth leaf or first tiller emerges. Of course, the actual number of DD50 units needed for each stage of seedling development can vary depending the variety being grown. However, 150 DD50 units per rice leaf emergence would be a good estimate for most of our semi-dwarf varieties that we are currently growing.
Using this criterion and our currently accumulated DD50 heat units for rice emerging at three different times (March 1, March 7 and March 14), I plotted where we should expect rice development to be at this time. We would expect that rice emerging on March 14 would currently be at the first true leaf stage of development and closely approaching that second leaf. Rice emerging on March 7th would be just be getting that 4th leaf to emerge. The rice planted in mid-February and emerging around March 1 would be at, or approaching, that second tiller. I tested these predictions with Dr. Linscombe’s date of planting trial here at the Station, and DD50 seems to be a pretty accurate predictor of rice development this year.