Managing Nitrogen In Rice In Suboptimal Conditions
DR. JARROD HARDKE
LITTLE ROCK, ARKANSAS
First things first – use the DD50 Rice Management Program to know where you stand on preflood nitrogen timing! If you only use the program for one thing, this is the most important. It’s nice when we can start rice in the optimal window, but the most critical timing is the “final recommended time to apply preflood nitrogen.” This is the date we need to focus on, not on general growth stage or height of plants – DD50 unit accumulation really tells us where we are, especially when we’re riding temperature roller coasters and plant growth is seesawing.
So, the goal is to get preflood N out no later than the final recommended time, but earlier if possible so we can get it incorporated where the plant can use it. However, there is some time built into the program after this date to account for flood-up, but not much. Furrow-irrigated rice is easier since we can get water through the field very quickly. The recommendations below refer to flooded rice.
Scenarios:
Field is dry: Minimum expectations – 1) silt loams – shoes leave little to no impression and soils are at “whitecapping”; 2) clays – surface soil is not tacky and starting to crack. Use urea treated with a recommended NBPT product (e.g. Agrotain) to minimize ammonia volatilization losses which occur when urea is left on the soil surface unincorporated by irrigation or rainfall. Potential N shortfalls can be caught and corrected with no yield penalty 6-8 weeks postflood.
Field is muddy: Wait until the field is free of standing water, and use urea treated with NBPT. After application, attempt to let the soil dry beneath the urea, if possible, but if rain occurs on the applied urea, flood the field. Letting the soil dry prior to flooding allows the urea to incorporate into the soil and will perform similar to that if optimal conditions were present at the time of flooding. **Prior to NBPT, we needed to flood immediately if urea went on damp ground but now we can wait.** When urea is applied to mud and flooding commences before the soil dries, the urea does not incorporate well into the soil, but rather dissolves into the water and is lost from the floodwater before the plant can take it up. If muddy conditions are present and unlikely to dry before another rain, increase preflood rate by 10-20 lb N/acre (20-40 lb urea/acre) and begin flooding. Under very poor conditions, consider a 20-30 lb N/acre (40-60 lb urea) rate increase. **Still strongly suggest attempting to let soil dry as much as possible prior to flooding.**
Field is flooded: If conditions have created standing water through the final recommended time to apply N, set the spills and begin applying N in a “spoon-feed” manner – 100 lb urea/acre once a week for 3-4 weeks. For hybrids, a minimum of 3 and possibly 4 applications of 100 lb urea/acre are needed to maximize yield. For varieties, a minimum of 4 and possibly 5 applications of 100 lb urea/acre are needed to maximize yield. Some varieties may have lower N requirements (e.g. DG263L) and may fall somewhere in between the hybrid/variety spoon-feed recommendations. **For urea applications going into standing water, do not treat urea with NBPT, it only has value when urea is going on the soil.**
Levee field with no way to manage flood (levees not up, or no spills or levee butts): Apply 100 lb urea/acre treated with NBPT prior to rain to start a weekly spoon-feeding program as described above and continue weekly if the field stays wet from rainfall events and flood management isn’t possible. BUT, if at any time in the middle of the spoon-feed program you’re able to get the field in shape to flood, then you can apply whatever remaining amount of N is to be applied to the dry soil and flood up. For example, if you’re normal preflood N rate is 260 lb urea and instead you make a first spoon-feed application of 100 lb urea, if the next week you are ready to flood, you can apply the remaining 160 lb urea and flood.
Call if you have questions or want to talk through scenarios. ∆
DR. JARROD HARDKE: University of Arkansas