New rice fertilizer recommendations designed to make decisions easier for producers have been released for the current crop. For the 2003 rice crop, the University of Arkansas Cooperative Extension Service is recommending that nitrogen fertilizer be applied to rice in a two-way split.
The first application should be made onto dry soil at the four- to five-leaf growth stage and then the field should be flooded as quickly as possible. The second application should be made at midseason between green ring, beginning internode elongation, and 0.5-inch internode elongation.
We in the Arkansas Extension Service are discontinuing support for the rice plant area board or rice gauge. We can provide thresholds for plant area board measurements for new varieties for those producers who wish to continue using the board, but we will not be recommending this procedure in the future for various reasons.
We have encountered several problems that apparently cannot be overcome. In response to these calls, I would like to explain our course of action to address the needs of the Arkansas rice farmers.
The first reason for discontinuing the program is due to lack of manufacturing interest. The low sales volume coupled with the initial investment make it undesirable for most people to want to invest the time and money required to produce the rice plant area board.
Since I can't find someone willing to produce them, I can't sell a product that the users cannot obtain.
Secondly, we have more than 10 years of research and verification field work that proves the single or optimum pre-flood nitrogen method is equal to or better than the split application method and usually requires less total nitrogen.
However, we need the rice plant area board to be able to adjust at midseason if we do run short following the optimum preflood nitrogen method. Thus, without the rice plant area board we cannot recommend the optimum preflood nitrogen method.
With that said, remember: the preflood nitrogen application still sets the yield potential in these new varieties but the split application method is a very consistent method of applying nitrogen to rice. Although we will not be using the rice plant area board, producers need to apply more nitrogen preflood and less at midseason than what has historically been recommended.
The third reason for the change in recommendations results from the vegetative growth patterns of some of the new varieties. Newer varieties, such as Cocodrie and CL 121, have a very short vegetative growth stage and effectively no vegetative lag stage.
In order for a nitrogen monitoring method (any method, e.g., plant area board, tissue nitrogen concentration, etc.) to be effective, the plant needs to “pause” growing just prior to midseason. If the plant reaches reproductive growth while it is still using preflood nitrogen, there is no way to tell if the plant is going to have enough to sustain it.
To measure the plant after the preflood nitrogen has been used, we must wait until 0.5-inch internode elongation for varieties such as Cocodrie. While it still can be done, the predictions are not as accurate.
The split application method recommendations are slightly different for 2003, compared to previous years. For instance, the recommendations for Drew, LaGrue, CL 121, and CL 161 (135 pounds of nitrogen per acre total or 300 pounds of urea per acre) will be 90 pounds of nitrogen per acre preflood followed by 45 pounds of nitrogen per acre between green ring and 0.5-inch internode elongation.
The recommendation is 105 pounds of nitrogen per acre preflood followed by 45 pounds of nitrogen per acre between green ring and 0.5-inch internode elongation for varieties such as Ahrent, Bengal, Cocodrie, Francis, and Wells (150 pounds of nitrogen per acre total or 333 pounds of urea per acre).
We are still convinced that we need more nitrogen preflood and are less dependent upon midseason nitrogen.
We will be evaluating this further in our research program and will be discussing the topic throughout this year. We think these changes will make allow producers and agents to feel more comfortable about our fertilizer recommendations.
Charles E. Wilson Jr. is the Extension rice agronomist at the University of Arkansas Rice Research and Extension Center in Stuttgart. e-mail [email protected].