Each of the past several years have proven rainy and problematic about the time many of our rice acres are ready to receive nitrogen fertilizer and go to flood. Our goal is always to apply preflood nitrogen in the most efficient manner to set ourselves up for maximum yield potential achieved with the lowest input costs. Unfortunately, this isn’t always easy.
If we can make our preflood nitrogen applications onto dry soil at the four- to five-leaf stage and establish a timely permanent flood, then we’re in great shape. However, flooding can take time, so we recommend using NBPT-treated urea if flooding will take longer than two to three days on a loam soil or longer than seven days on a clay soil.
That’s easy enough — apply nitrogen to dry soil and flood up. But what about when we can’t get the soil to dry? That’s the area recent research efforts have begun to focus on.
The goal is to make every attempt to get the soil dry before the end of the recommended nitrogen application window based on the DD50 Rice Management Program. If we still cannot get the soil dry by that point, it’s time to make a move or risk lost yield potential as a result of the planting not having sufficient nitrogen as it begins tillering — which is the first yield component.
If we’ve reached the end of the window and soil is muddy with no standing water, apply NBPT-treated urea and attempt to let the soil dry beneath it before flooding. However, if rainfall occurs before the soil dries, go ahead and flood up.
The preferred preflood N management option is always to apply NBPT-treated urea onto dry soil and establish the permanent flood in a timely manner (~ seven days) to incorporate N below the soil surface. If faced with soil conditions that are not dry and before resorting to any other N application option, wait until the final recommended time to apply N based on the DD50 Rice Management Program.
Going with a “spoon feed” approach into standing water carries additional risk and possibly costs but can also be used as a last resort to maximize yield potential. Do not begin these spoon-feed applications until the end of the recommended nitrogen window. When you go this route, apply 100 pounds urea per acre once a week for a minimum of four total applications.
When spoon-feeding into standing water, there is no need to use NBPT-treated urea. Rice fertilized in this way will be taller and more rank compared to rice fertilized with more efficient methods, so there are additional risks of increased lodging and disease pressure. But yield potential remains high.
Do not apply large rates of nitrogen into the floodwater or you risk losing most of the nitrogen before the plant has a chance to take it up. When rice plants are small, their nitrogen uptake is initially slow, and too much nitrogen can be lost before the plants can capture it.
Every field is unique and should be managed that way. Following recommended timings from the DD50 Rice Management program (http://www.DD50.uaex.edu) can help to maximize yields by increasing efficiency. Let’s still hope for dry soil conditions to make things easier.